June 2009

Simple, sophisticated level

Level measurement in pulp, paper mill

InTech’s

Flow/Level

www.isa.org/intech

Flow/Level featured

products begin

on page 24.

Columns and departments

4 Automation Update Carbon capture, by the numbers,

and more

8 CertificationCCST focus on orifice plates

22 StandardsValve testing committee revises

standard

23 Safety Don’t get caught in dead time

24 Products & Resources Flow/level releases in the

marketplace

26 Automation Basics Focus on level

Focus on flow

Cover story

Nukes go with the flowBy Javier Zornoza, Jean-Melaine Favennec, Sebastien Szaleniec, and Olivier Piedfer

When it comes to early detection, researchers at a French nuclear power plant are one

step ahead with their development of a data reconciliation nuclear power plant model

to monitor and improve power plant performance. See how their research promises

to help nuclear power plant operators monitor their own stability of thermal power

indicators in the future.

10

14 Level measurement is simple, sophisticated, or both

These are the technologies available for measuring solids and their advantages

and limitations, focusing on several older technologies and so on to the newer

technologies like laser techniques, and ultrasonic, capacitance, guided wave

radar.

18 Paper makerBy Brad Carlberg

In a pulp and paper mill, you can find quite a few uses for level measurement.

Find out which processes work best with which level technologies in this step-

by-step process—from raw material receiving and preparation to converting

and finishing.

InTech’s

Flow/Level

InTech provides

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on-the-job success. Published by

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ISA, InTech addresses the most critical

issues facing the rapidly changing

automation industry.

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www.isa.org June 2009 | Vol 1, Issue 1 Setting the Standard for Automation™

InteCH’s FloW & level June 2009 WWW.Isa.orG 3

4 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

move CO2 and the solvent recovered by

applying energy to break apart the chemi-

cal bonds formed between the two.

This means simply boiling the solvent

off, but the chemistry involved allows

this to happen at lower temperatures.

Amino acid salt formulations are also

more stable than MEA and less likely to

react with oxygen and sulphur dioxide in

the exhaust gases; virtually none of the

solvent should escape into the atmo-

A new and more efficient process

for scrubbing carbon dioxide

(CO2) from power-plant exhaust

gases could make carbon capture a more

reasonable pursuit for the energy industry.

The process promises to remove up to

90% of CO2 from flue gases while using

far less energy than existing methods.

Technology Review reported all carbon-

capture methods reduce a plant’s effi-

ciency by about 11%. The new process,

developed by Siemens, could reduce this

efficiency loss to just 9.2%.

This may not seem like much of an im-

provement, “but in a power plant, that’s

a huge benefit,” said Tobias Jockenho-

evel, head of the project at Siemens, in

Erlangen, Germany.

Capturing CO2

will always consume a

certain amount of energy, said Jockenho-

evel, so the aim is to find ways to keep

these losses to a minimum.

In theory, 99.9% of the CO2

emitted

from a power plant could be removed

using the process, but Jockenhoevel said

90% is the economic optimum in terms

of infrastructure costs and how much en-

ergy is required: “The last 10% costs too

much.”

In August, the Siemens process will test

at a pilot facility built by Siemens and the

energy company E.ON: the Staudinger

coal-fired plant, near Frankfurt.

They will set the plant up so part of

its exhaust gases feed into a chimney

containing a 25-meter-high column that

gives off a solvent mist that reacts with

CO2 under pressure.

As the flue gases pass through the mist,

the CO2

is chemically absorbed, leaving

residual gases to pass out of the chimney.

The CO2 then separates from the solvent,

which recycles for reuse.

“It’s basically like washing the gases,”

said Jockenhoevel. It is a standard ap-

proach to scrubbing CO2; the novelty of

this process comes down to the solvent

and the way we recover it, he said.

The Siemens system uses a solvent made

from amino acid salts. The system can re-

Carbon-capture method goes on trial at German coal plant

sphere along with residual gases.

While the supply of other solvents needs

regular topping off because of these loss-

es, this is not the case with the amino acid

salts, said Jockenhoevel. Instead of heating

the solvent in one location to remove the

CO2, the process dictates two streams that

it heats separately in a way that requires

less energy.

The technology will work with any kind

of power plant that runs on fossil fuel.

“It’s basically like washing the gases. It is a standard approach to scrubbing CO2; the novelty of this process comes down to the solvent and the way we recover it.” —Jockenhoevel

automation update | News from the Field

INTECH’S FLOW & LEVEL JUNE 2009 5

Disregarding those meters based on head

loss differential pressure, velocity change is

the key issue of DP-based flowmeters.

The aim of some primary devices for DP

flow rate measurement is establishing a ve-

locity change along the fluid path flow. That

is what happens with venturi, orifice plate,

nozzle, and cones. Those primary devices

work by reducing the flow path cross section

area at some point in relation to another one,

resulting in a velocity increase on that point.

This increase will provoke an unbalance on

Bernoulli’s equation. Being the height differ-

ence between the two points kept constant,

the equilibrium of the equation only works

by establishing a pressure difference. This dif-

ference is eventually reflects the flow rate.

While some primary devices provoke

the desired velocity difference, other de-

vices makes use of existing natural veloc-

ity change. That is the case of elbows,

which utilize a natural velocity difference

that appears when the fluid path flow has

its direction changed.

What is important to understand is it

does not matter how we determine the

velocity change. The important issue is to

have a velocity change in order to obtain

the desired differential pressure.

Therefore, the hidden law of DP-based

flowmeters could be stated by someone as:

“If along a fluid path flow a velocity differ-

ence does exists, then a pressure difference

is established, and the flow is proportional to

the square root of this pressure difference.”

This simple understanding, supported

by strong theoretical basis, is of utmost im-

portance, and it can promote the use of DP

for flow rate measurement in many other

ways. As an example, this principle works

for flow measurement in many hydro

power plants and pumping systems.

The fact is there is a natural velocity

difference along the cross section of a

hydro turbine when the fluid flows along

its existing spiral case. Hence, a pressure

difference exists at that region, and the

flow rate can be determined as a function

of the square root of this differential pres-

sure. The same principle works to mea-

The hidden law behind DP flowmeters

Differential pressure (DP) tech-

niques for flow rate measure-

ment are widely applied in indus-

try, being responsible for about 25% of

the fluid flow rate metering applications.

Orifice plate, venturi, nuzzle, elbow, and

cone are some examples of primary de-

vices for flow rate determination through

differential pressure measurement.

Low cost, easy mounting, reliability, re-

peatability, accuracy over a wide working

range, and no moving parts are some of

the positive characteristics of DP-based

flowmeters that make them suitable for

the bulk industrial applications.

Mass conservation, equation of conti-

nuity, and the Bernoulli equation form the

theoretical basis of DP flowmeters.

Neglecting system losses, Bernoulli es-

tablishes the total energy at point one (P1)

is the same as at point two (P2). The to-

tal energy results from the summation of

static, kinetic, and potential components,

per this the equation:

Where P is the static pressure (N/m²), ρ

is the fluid density (kg/m³), g is the gravi-

tational constant (m/s²), V is the fluid av-

erage velocity (m/s), and z is the height

from a reference level (m), for points 1

and 2, respectively.

Flumes measuring flow in channels and

galleries also work on the same principle. As

long as the water path flow in the flumes is

open air, the pressure is not the key vari-

able, but rather the fluid level instead.

Fluid path flow

sure the flow rate in centrifugal pumps

with great accuracy and repeatability.

Obviously, the great advantage of stan-

dard primary devices is the previous knowl-

edge of the exact relationship between the

flow rate and the square root of the differ-

ential pressure, which is a proportionality

constant commonly known as K. For the

non-conventional DP flowmeters, the val-

ue of K might be determined theoretically

or by calibration. Due to the difficulties of

theoretical models in catching all system

imperfections, such as fluid density, exist-

ing vortex shedding, and produced head

losses, it is hard to obtain a theoretical

proportionality constant that will lead to

high measurement accuracy.

We can overcome this obstacle by in-

stalling a standard flowmeter in line with

the DP device. We get several flow rate

values and several actual measurements

of the flow rate and the differential pres-

sures. Then we can determine the value

of K using the following formula.

In this equation, K is the sought propor-

tionality constant of the DP flowmeter, Q

and ΔP are the flow rate (m³/s) and the re-

lated differential pressure (N/m²) obtained

for the several N measurements.

In short, the obtaining of a velocity differ-

ence is the key issue behind the DP-based

flow rate meters operation. We can create

this velocity change or get it from an existing

structure. Eventually, we get the flow rate as a

function of the resulting differential pressure.

The knowledge of this simple law is of

utmost importance for the understanding

of DP flowmeters principle of operation.

In addition, it can help spread the use of

DP for flow rate measurement using other

devices than the standard ones.

Source: Edson da Costa Bortoni (bortoni@

unifei.edu.br), BS, MS, and DS, is a pro-

fessor of Industrial Instrumentation at

Itajubá Federal University, Brazil. He is a

Senior Member of ISA.

1

1

News from the Field | automation update

6 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Automation by the Numbers

Restriction-type flow instruments

use the principal that flow rate

is proportional to the square

root of the differential pressure

across the restriction. An orifice plate or venturi goes in the line

creating the restriction of flow and then the high-pressure port

goes eight pipe diameters upstream from the restriction and the

low-pressure port

goes five pipe

diameters down-

stream from the

restriction … and

they attach to

the d/p meter.

45Of the installed base of flowmeters worldwide,

approximately 45% are differential pressure (dP)

meters. dP meters work by using the difference

in pressure between two points of a flowing

system.

In a venturi flowmeter, the different pressures come from a

restriction in the flow line itself. Other dP meters use a wedge, a

nozzle, or an orifice to generate the difference.

10The continuous-level-measurement market

size in the U.S. within the solids industry

is approaching $100 million. Ultrasonic

technology has the highest share at 22%,

followed by load cell/strain gauge with a

share of 18%. Contacting radar and non-

contacting radar both have shares of approximately 12%. How-

ever, non-contacting radar has the greater growth rate, higher

than 10% compounded annual growth rate, and it will probably

rise at this rate for several more years.

Differential pressure

Magnetic

Coriolis

Turbine

Positive displacement

Thermal

Variable area

Ultrasonic

Vortex

Open channel

Sonar

Optical

Target

Other

44.5%

10.5%

9.6%

9.5%

6.7%

5.0%

4.7%

4.2%

3.3%

0.6%

0.6%

0.3%

0.1%

0.3%

Installed Base of Flowmeters by Type

44.5%

0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0% 35.0% 40.0% 45.0% 50.0%l l l l l l l l l l l

8 and 5

Source: Flow Research

447 U.S. and European air-safety regulators are

considering requiring airlines replace certain

airspeed sensors on Airbus jets because they

suspect faulty speed indications were major contributors to the

June crash of Air France flight 447. The sensors are pitot tubes,

which work by translating airflow pressure (lbs/in2)

passing over the fuselage to

velocity (mph).

Downstream tap low pressure

Upstream tap high pressure

automation update | News from the Field

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◗ Outputs on DMT 2000: upstream pressure, downstream or differential pressure, fl uid temperature in fl ow path, volumetric fl ow rate, & inferential mass fl ow rate for gases/vapors

Easy plug-and-play remote data monitoring in hazardous locations

◗ Web and various Industrial Ethernet protocols supported for data monitoring with CIM76™

◗ TCP/IP enabled connection that bridges the gap between Class 1, Division 2 (Zone 2) and Class 1, Division 1 (Zone 0,1) area running a CT76 iCAN™ intrinsically-safe data network

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8 INTECH’s flow & lEvEl juNE 2009 www.IsA.oRG

ISA Certified Control Systems Technician (CCST) program Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that

measure and control level, temperature, pressure, flow, and other process variables.

These questions come from the Level I study guide, Domain 3, Troubleshooting. Level I represents a professional who has a five-

year total of education, training, and/or experience.

CCST question #1

A beveled orifice should form an angle of:

A. Not less than 30 degrees to the axis of the pipe

B. Not more than 30 degrees to the axis of the pipe

C. Not less than 45 degrees to the axis of the pipe

D. Not more than 45 degrees to axis of the pipe

CCST answer

The orifice plate inserted in the line causes an increase in

flow velocity and a corresponding decrease in pressure. The

flow pattern shows an effective decrease in the cross

section beyond the orifice plate, with a maximum ve-

locity and minimum pressure at the vena contracta.

The vena contracta is that area of the flow stream at its minimum size, where fluid velocity is at its highest level and where fluid

pressure is at its lowest level, and it occurs just downstream of the actual physical restriction.

This flow pattern and the sharp leading edge of the orifice plate that produces it are of major importance. The angle of the bevel

should not be less than 45 degrees. The best answer is C.

Reference: Instrument Engineers Handbook: Process Measurement and Analysis, CRC Press and ISA Press, 2003

CCST question #2

which orifice plate is used to eliminate damming of material at the top or bottom of the pipe?

A. Concentric

B. Round-edged

C. Quadrant-edged

D. Segmental

CCST answer

An orifice plate is a flow-path restriction that we use in flow

detection. They are in a straight run of smooth pipe away

from valves and fittings so they do not interfere with the

restrictor and readings.

The pressures on opposite sides of the plate are different,

and the difference in pressures is proportional to the flow

rate.

Segmental and eccentric plates have many similarities as

to function. The segmental portion of the orifice mitigates

the damming of foreign materials on the upstream side of the orifice.

Eccentric orifice plates work to stop damming as well. The best answer to this question is D, segmental.

Nicholas Sheble (nsheble@isa.org) writes and edits Certification Review.

45o

Vena contracta

Flow pattern with orifice plate.

Concentric Eccentric Segmental

certification review | CCST

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brates the primary side real-time thermal power indicator seeing use for plant operation, and the neutron flux detectors.

Data reconciliation is a method that allows taking full advantage of all the information avail-able on the process. It provides consistently high accuracy on estimated parameters, thus allowing early detection and implementation of corrective action. It is a mathematical method, described in the German Standard VDI 2048, that makes use of measurement redundancies all along the pro-cess. The principle is to correct measurements, as little as necessary, in order to match the bal-ances and constraints of the process.

In order to have accurate thermal power moni-toring with data reconciliation, you need enough redundancy on the secondary circuit to perform accurate evaluations of measurement uncertain-ties and to build a reliable process model.

Fouling problems solvedSince 2002, six nuclear power plants have expe-rienced fouling problems caused by magnetite deposition on feedwater line orifice plates orig-

EDF nuclear power plants provide over 80% of electricity generation in France. The company’s research and development

branch is constantly aiming to monitor and improve power plant performance. To that end, the company developed a data reconciliation nuclear power plant model that would monitor and correct a drift on feedwater flow measure-ments and thus on thermal power. The results led to developing a monitoring center that will help nuclear power plant operators monitor their own stability of thermal power indicators.

Safety issues need reconciliationAn accurate thermal power measurement of feedwater flow-rate is a key requirement for meeting safety constraints for nuclear power plant operators. Each of EDF’s 58 pressurized water reactors is equipped with an accurate (0.5% at 95% confidence level) secondary sys-tem thermal power indicator based on a specific measurement system (sensors and data acqui-sition and processing). This thermal power indi-cator is calculated at least every month and cali-

By Javier Zornoza, Jean-Melaine Favennec, Sebastien Szaleniec, and Olivier Piedfer

Researcher helps nuclear plants reconcile with feedwater flow, thermal power

Nukes go with the flow

10 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Fast Forward

l Reconciliation data model corrects drift on feedwater flow measurements.

l New method allows early detection for cor-rective action.

l Feasibility study results in new center for nuclear power plant operators.

reconciliation detect actual water flow mea-surements drifts?

Feasibility study The first stage of the project was to assess if EDF’s nuclear power plants have enough redun-dancies so the use of data reconciliation method will be profitable. A 4-loop 1300 MWe PWR sec-ondary circuit model was developed including: l 220 measurements

(140 KIT sensors and 80 CEF sen-sors). These mea-surements include mass flow, pressure, and temperature sensors

l More than 850 equations including whole secondary circuit mass and energy balances

l Performance equations for turbines and pumps and pressure drop equations for all components

l 123 redundancies are taken into account in the model To calculate the uncertainties of the 220 mea-

surements, we had to identify all the modules of the different measurement channels between the sensors and the data historian. We calcu-lated uncertainties as the quadratic addition of different terms issued from the specification sheets of every component of the measurement channels. This preliminary and necessary task significantly increased operators’ confidence in their nuclear power plant process control measurements.

As the main concern is thermal power drift monitoring, the feasibility study focused on that calculation. Data reconciliation allowed reducing thermal power uncertainty from 0.45% (at 95% confidence level) on the measured value to 0.22% (at 95% confidence level) on the reconciled value, hence a reduction of uncertainty of 50%.

This stage also enabled performing a sensibil-ity analysis of the reconciled thermal power and thus identifying the main measurements used by the model to recalculate thermal power. As the feedwater flow measurements are the main suspects for drifting, we performed the sensitiv-ity analysis with and without taking into account the feedwater flow measurements in the model.

To evaluate the stability of results given by data reconciliation, we processed all the valid CEF datasets of a whole fuel cycle with the mod-el, where we knew of neither measurement nor component problems to occur. If we met all the assumptions of data reconciliation, the error

inating an underestimation of feedwater flow-rate and thermal power. This impacts the safety and performances of the plant.

EDF’s R&D STEP department (simulation et traitement de l’information pour l’exploitation des systèmes de production or simulation and information technologies for power generation systems) has developed and evaluated several methods to monitor and eventually correct the errors caused by the orifice plate fouling. The most advanced method for thermal power monitoring is data reconciliation. This method is already used in some nuclear power plants in Germany, Switzerland, and the Czech Republic.

Redundancies can come from directly redun-dant sensors or from physical relations between measurements. In order to use data reconcili-ation, you need enough redundancies, either physical-based or sensor-based, on the process. You also need a model of the process, taking into account as many equations as possible. You should at least use mass and energy balance, steam pressure drops, and some performance equations (turbine efficiency, Stodola equation, and pump efficiency). You can also use more complex equations such as heater performance equations. Another requirement is uncertainty values for all measurements and parameters used on the model. As data reconciliation takes into account uncertainties to decide which measurements to correct, it is very important to have accurate uncertainty evaluations on all the measurements the model uses.

The outputs of data reconciliation calcula-tions are: l Reconciled values that match all balances and

constraints of the process l Lower uncertainty on reconciled data than on

measured data l Identification of suspected measurements

A way to quantify the data reconciliation im-pact on a given measurement is to compare the measurement uncertainty and the reconciled uncertainty. To assess the potential of this meth-od to monitor and correct thermal power drifts, EDF R&D conducted a three-year program with the following major stages:

Feasibility study: Are there enough redundan-cies on EDF nuclear power plants? Are data rec-onciliation results stable enough to use them to operate a nuclear power plant?

Drift simulation study: Can data reconcilia-tion detect drifts simulated on feedwater flow measurements? Do drifts, simulated on other key measurements, affect thermal power cor-rection? In an on-site experiment, does data

INTECH’S FLOW & LEVEL JUNE 2009 11

Flow/level

Undetected maximal drifts on key measurements, impact on reconciled thermal power

12 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Flow/level

metering testing facility. Results from this experience show a drift very close to the last data reconciliation estimation.

Perspectives The experience feedback of actual er-rors on feedwater flow measurement impacting thermal power indicators on units all around the world has led oper-ators to design and test various meth-ods to ensure accuracy and reliability of this key measurement.

Data reconciliation is one such method for which EDF has invested in a comprehensive feasibility study. In order to have an accurate thermal power monitoring with data reconcili-ation, it is necessary to have enough re-dundancy on the secondary circuit, to perform accurate evaluations of mea-surement uncertainties and to build a reliable process model.

The presented feasibility study has shown the actual efficiency of the data reconciliation method to monitor and correct a drift on feedwater flow mea-surements and thus on thermal power.

In the wake of this successful feasibil-ity study, we decided in 2008 that EDF would set up a monitoring center to help nuclear power plant operators with monitoring the stability of thermal pow-er indicator with data reconciliation.

aBoUt tHE aUtHors

By Javier Zornoza, Jean-Melaine Favennec, Sebastien Szaleniec are with research and

development at EDF in France. olivier Pied-fer is with EDF’s nuclear generation branch.

EDF is a research and development group

studying sustainability of nuclear power

plants, the integration of new technolo-

gies, and innovation in the field of renew-

able energies and storage out of France.

out the drifted measurements as sus-pect, the drift reduction reaches 70%, with a remaining drift value of 0.3%.

The goal for this is task was to esti-mate the lowest possible drift on the key measurements used to reconcile thermal power the data reconciliation model was able to detect and then to quantify the impact of these unde-tected drifts on reconciled thermal power. The final goal is to ensure the reconciled thermal power error (when reconciled thermal power is impacted by one of these drifts) is lower than the thermal power uncertainty limit taken into account in the safety analysis.

on-site experiment After assessing drift detection and cor-rection capacities of the 1300 MWe 4-loop PWR model with the simulation studies, our final task was to experi-ment with real plant data from a nu-clear power plant having fouling on its feedwater flow orifice plates. The cho-sen nuclear power plant was Cattenom, and the developed model was adapted to Units 1 and 2. The experimentation began April 2006 on Unit 2 and October 2006 on Unit 1.

In order to evaluate the quality of the results given by data reconciliation, we compared monitoring results of a sim-pler method (∆P/P) in use since 2005 with plants affected by feedwater flow measurement drifts. This method is based on the difference between varia-tions of HP Turbine inlet pressure and feedwater. When fouling occurs, this difference increases.

During the outage, we installed orifice plates, fixed magnetite on the surface, and calibrated the orifice plates on a flow

should be a normal random variable with a mean of zero.

Even if we can identify a slight up-ward trend in the figure, the error is always lower than its 95% confidence level, thus satisfying the basic assump-tions of the data reconciliation method. Regarding the whole of the secondary circuit, this study allowed identifica-tion of minor modifications of some process control sensors affected by representative biases.

Drift simulation study Once we concluded the feasibility study, we went on the next stage—assessing the capacity of data reconciliation to de-tect and correct drifts on feedwater flow measurements. At the same time, this simulation study allowed evaluation of the detection capacity of drifts on the key measurements identified with the sensitivity analysis, and to quantify the impact of the biggest undetectable drift on reconciled thermal power.

Feedwater flow drift detection The study showed the data reconcili-ation model is endowed with a great sensitivity to detect and correct feed-water flowmeters drifts. We simulated two drift scenarios:

KIT (+3%) and CEF (-1%) FWF sensor drifts. This situation is close to a real one because fouling affects differently the venturis (KIT measurements) and the orifice plates (CEF measurements). In this case, as drifts are of different signs, data reconciliation detects and corrects them easily. The remaining drift on rec-onciled FWF values is 0.07%.

CEF (-1%) FWF sensors drifts. Even if data reconciliation is not able to point

RESOURCES

Putting the Squeeze on Power Plants

www.isa.org/link/SqueezePower

Low-energy nuclear power has

‘promise’

www.isa.org/link/nuclearpower

Case study: Memphis Biofuels

goes online

www.isa.org/InTech/20080701

Key Measurement Maximal Undetected Drift Impact on TP

HPT First stage pressure 1.5% 0.27%

HPT Outlet pressure 1.5% 0.27%

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LP Heaters pumps flow 4% 0.44%

FW Tank temperature (oC) 7% 0.40%

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14 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Another technique involved striking the silo with a mallet or throwing rocks at the sides and then determining level through pitch changes. While these rudimentary measuring methods are labor intensive and generally inaccurate, they provide basic level data for the user.

However, when measurement requires more precision, we supplant these methods with level instrumentation using a variety of sophis-ticated technologies offering point level and continuous level readings. Continuous level data is gradually becoming the measurement of choice—with free air radar currently having the highest growth rate in this market.

Point level measurement Level technology accuracy has significantly im-proved for the solids market in the last five de-cades. Point level switches debuted in the 1940s and replaced many of the basic techniques such as ropes. Installed at the top, bottom, and occa-sionally midsection of a silo, they provide switch points activated by material contact.

Top-level switches provide over-fill protec-tion, avoiding costly clean up efforts and en-vironmental damage. Low-level switches and mid-level switches usually serve for inventory management by giving set points that indicate

Knowing the content level of material in containers such as silos and other simi-lar vessels is extremely important in in-

dustry, but accuracy demands vary according to business requirements; some are satisfied with approximations while others require specific and accurate knowledge of a vessel’s contents.

Accuracy challenges also exist depending on the types of containers and the measured con-tent. Solids containers, like silos, hoppers, or bins, can contain a variety of materials such as cement, aggregates, grain, and sugar, all having unique material properties affecting accurate level measurement.

These vessels also differ in size and design—a typical silo can be 10 meters or greater in height—while bins and hoppers are usually smaller and used as an intermediate buffers be-tween inventory and daily production.

The techniques for measuring a container’s contents range from the basic to the high tech, and before instrument-based measurement became widely used, we often determined content levels by mechanical means. One such technique required the lowering of a measur-ing rope attached to a weight from the vessel’s top, showing the distance to the surface by how much rope played out.

In the past decade, radar has gone from being virtually non-existent in the solids marketplace to the “preferred technology” in the cement industry

Level measurement is simple, sophisticated, or both

INTECH’S FLOW & LEVEL JUNE 2009 15

Flow/level

ments as industry implements “just-in-time” material flow for production. Accurate continuous level mea-surement is critical, ensuring raw materi-als are always available and inventory levels stay as low as possible.

Advantages and limitationsLook at the technologies available for measur-ing solids and their advantages and limitations, focusing on several older technologies and then on newer technologies like laser techniques, and ultrasonic, capacitance, guided wave radar. The conclusion offers a detailed discussion of non-contact radar, the fastest growing technology.

Rope: The most widely used technique for measuring the level within a silo, regardless of height, involves a person dropping a measured rope into the silo from top. The operator opens the hatch and lowers a weighted rope until there is a noticeable difference in resistance. The cal-culation is to subtract the measured distance of airspace from the silo’s total height, and the difference provides the material level. The ad-vantages of this method are it is cost effective and direct. The disadvantage is it is potentially unsafe, requiring the user to go to the top of the silo to take a measurement. Furthermore, there is also exposure to the hazards associated with an open silo in intense heat or dust.

Plumb bob: This technology uses an auto-mated mechanical rope and has names, includ-ing a Yo-Yo, plumb bob, and weight and cable. A weight hangs by a cable from a drum operated by a motor, and the motor unwinds the cable until the weight reaches the material surface. The length of the unwound cable is the mea-sured distance to the material, calculated using electrical pulses from an encoder assembly. The advantages of this technology are it is reason-ably accurate and is suitable for very low bulk density materials. Its disadvantages include mechanical wearing on the parts, resulting in maintenance costs and possible damage to the weight and/or cable under extreme load. It also does not work during filling because the weight can become stuck under falling material.

Laser: This technology uses high frequency electromagnetic waves at laser wavelengths, typically around one micrometer, to measure the distance to the material using the time-of-flight principle. Laser technology has worked

usage trends or fill times.Point level switches require little setup, pro-

vide low cost measurement, and are available in several technologies including radio frequency, capacitance, and mechanical rotary paddles and tuning forks.

One common problem with point level switches, however, is they come in contact with the vessel’s contents, and because the contents are sticky, abrasive, or extremely heavy, they damage the hardware. Point level also provides only the level information at a specific target, so production planning and inventory manage-ment can be difficult, even with carefully spaced switches.

By the time the low-level point switch goes off and the order for more material goes out, the silo is empty, and production stops until new ma-terial arrives. Mid-level switches at key points would help prevent this situation, but adding switches drives up the cost, and the usage rates can still vary depending on production rates.

Requirement for higher accuracy has thus created a demand for continuous level mea-surement technologies that provide level infor-mation over the full range of the vessel.

Continuous level measurement Reliable continuous level measurement devices arrived on the market in the 1970s with ultra-sonic measurement systems. Easy installation from the vessel’s top, and low maintenance be-cause of its non-contacting technology, added to the technology’s appeal. Although limited somewhat to shorter ranges and by limited suc-cess in dusty environments, ultrasonic tech-nology is still widely used for continuous level measurement. Other continuous technologies, including capacitance, guided wave radar, laser, and radar have since joined the market, provid-ing accurate and reliable level data.

However, a large segment of the market still measures silos with calibrated weighted ropes. This labor-intensive technique raises safety concerns, especially in inclement weather as personnel has to climb vessels and also expose themselves to potentially hazardous contents.

Employee safety within production facilities has risen to top priority in the past 10 years, and management now sees silo level measurement as one of the potential areas for high risk, creat-ing a sharp demand for level measurement de-vices that do not place personnel at risk while providing accurate inventory data.

Accurate inventory requirements are yet an-other market driver for continuous level instru-

Fast Forward

l Solids level measurement went from manual rope methods to point level to radar.

l Radar will claim a significant portion of the solids market.

l Level tools include laser, ultrasonic, capacitance, and guided wave radar.

16 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Flow/level

struments cannot only mount on the top of the vessel, but can also be at the bot-tom or on the side of a silo. Its disadvan-tage lies in being a contact technology, which can lead to mechanical damage from abrasion or signal problems from material build up. In solids with moisture or property changes, the readings may also change, reflecting the change in di-electric.

Ultrasonic: Ultrasonic technology uses high frequency sound waves di-rected to the material by a transducer and measures the time-of-flight to and

from the mate-rial. Frequen-cies as low as 5 KHz are used on long range solids materi-als, and higher frequencies at 30KHz or high-er are used on shorter ranges, primarily liquid targets. Ranges of up to 60 me-ters are pos-sible. However, this maximum

range quickly deteriorates with intense dust in the silo. Since ultrasonic tech-nology requires a carrier medium (nor-mally air), any change to this medium has an effect on the measurement. Thus if the silo is pneumatically fed, the dusty atmosphere may prevent a return signal to the sensor. High temperature materi-als will also change the speed of trans-mission, leading to accuracy problems. The material echo also presents a chal-lenge; sloped surfaces may cause indi-rect reflection leading to weak and/or split echoes.

The main advantages of ultrasonic technology are it is low cost and non-contacting. The controller technology determines the effectiveness of the sys-tem. The more sophisticated controllers are capable of intelligent echo process-ing of the return echoes, differentiating between false echoes (ladders, material build up, weld seams) and the material echo. Ultrasonic technology continues to be a low cost, highly reliable technol-

tional to the weight in the silo. The ad-vantage of both of these technologies is they are capable of accurately report-ing the mass of the silo contents. Dis-advantages include hysteresis effects from connector pipes or support mem-bers connecting the silo to the building structure and wind effects. Installation can be difficult and expensive because you usually must lift the silo completely off the ground before setting it directly onto the cells.

Capacitance: Capacitance leveling is a well-proven technology and has been in use for over 50 years in a wide variety of industries. The operating principle uses a capacitor, which stores an electrical charge and which has two parallel plates of a conductive material separated by a dielectric material (a non-conductive or insulating material). The amount of en-ergy stored by this dielectric material is the measured capacitance, and the dif-ference in capacitance between the ma-terial and the empty section marks the level. A capacitance system uses an elec-tronics transmitter with an un-insulated probe (or rope) and a ground (earth) reference. The ground reference can be a metallic tank or silo wall that connects to electrical earth and the product, to keep them at the same potential. The measured material makes up the dielec-tric material and the rope and tank wall the two parallel plates. An increase in level of material results in a proportion-al change in the measured capacitance, which the transmitter then converts to an output signal to indicate level.

The advantage of capacitance tech-nology is it can work in a wide range of ap-plications that involve adverse conditions, in-cluding high temperature, high pressure, and corrosive chemical pow-ders. Another advantage of capacitance is its installation flexibility. In-

effectively for scanning the surface of piles of solids and providing accurate volume measurement. Laser technol-ogy applies to industrial level measure-ment applications, but care is neces-sary to ensure the lens remains clean. Two key advantages of this technology are its extremely long range and its very fast update rates. In addition, the laser beam is extremely narrow, making it ideal for narrow applications. The main disadvantage, however, is its perfor-mance in extremely dusty applications where the laser does not penetrate to the surface.

Nuclear: Nuclear radiation level measurement uses a source containing some type of radioactive material like Cesium or Cobalt located on one side of a silo while the other side contains the electronic detector. The gamma radiation has much less transmissibil-ity through the material than air, thus attenuation indicates its presence be-tween the source and the detector. For continuous level measurement, either a long source or a long receiver sec-tion is used, and these must be in line to ensure the complete silo contents are measured. The distinct advantages of this technique are it is non-invasive and mounted outside the silo walls and it is impervious to the conditions within the silo. Disadvantages are it is typically more expensive than others and can be installation prohibitive. In addition, having a nuclear radiation source requires licensing, as well as a knowledgeable nuclear safety officer onsite. Furthermore, the source will de-teriorate over time and eventually need proper disposal and replacement, a very strict, costly, and formal process.

Load Cell/Strain Gauge: Load cells support the silo and its contents and thus directly report the mass within. The load cells provide an output volt-age proportional to the load, where the voltage calibrates to empty and full tank conditions. Strain gauges are simi-lar in that they report a varying voltage output with load; however, they are easier to install directly onto the sup-port legs of the silo. The strain gauge measures the support structure com-pression under load, which is propor-

TransducerElectronics

INTECH’S FLOW & LEVEL JUNE 2009 17

Flow/level

frequency radar, with its smaller an-tenna sizes and ease of installation, offers significant advantages for solids applications.

Choose the right technology Unfortunately, no single technology applies to all solids level measurement applications. There are many variables to consider when choosing a level mea-surement technology. An experienced vendor with variety of technologies can assist with a technology choice. Be pre-pared to answer these questions about the following when considering the level measurement device for your next application:l Silo height, diameter, shapel Material properties - Bulk density - Dielectric properties (radar or guided wave radar) - Color (laser performance) - Build up/sticky? - Temperature - Abrasive?l Internal structural members in the

silo?l Filling method, locationl Accuracy requiredl Mounting location/size options for

the sensorl Device costl Installation and operational/ maintenance costs

As you can see from the following chart, radar has the widest range of applicabil-ity of all the technologies available.

Nicholas Sheble (nsheble@isa.org) writes

and edits level-technology feature arti-

cles. This piece comes from the ISA EXPO

presentation titled Level measurement

trends in the solids industry.

solids applications other technologies cannot handle. When combined with the benefits of being a non-contacting technology, these advantages make radar a very appealing technology for solids level measurement. To be effec-tive, however, a radar instrument needs to function with solids characteristics in mind. The same devices that work on liquid applications often do not per-form on solids because the level mea-surement challenge on solids differs

from measure-ment on liquids.

Although the microwave spec-trum ranges be-tween 1 and 300 GHz, most radar level measure-ment systems operate between 6 and 26 GHz. The first radar devices used 10 GHz FMCW technology, and this frequency

is still widely used today for liquids. For a given output signal amplitude, low frequency radar requires a much larger antenna; for example, a 6 GHz radar device needs a 400 mm (16”) di-ameter horn to obtain the same signal as a 24 GHz radar device using a 100 mm (4” horn). Low frequency, tradi-tional radar devices are well suited for liquid applications. To use them effec-tively on solids applications, however, a large horn up to 250 mm (10”) diam-eter or even a parabolic dish antenna to capture sufficient signal is required. This large antenna is not practical on most vessels. Larger antennas, like the parabolic dish, require a large opening in the silo roof. Many solids applica-tions have roof structures that are 12 to 18 inches thick and drilling a hole 8 to 10 inches wide and that deep to ac-commodate a level device is generally not practical. Higher frequency de-signs use of antenna horns as small as 3 to 4 inches. If a process connection is necessary, it is much easier to create a small hole than a large one, especially if the vessel roof is concrete. Thus high

ogy for solids measurement and unlike most radar devices can be used without restriction in silos or hoppers, which are completely open (not a closed tank).

Guided wave radar: A contacting technology like guided wave radar or Time Domain Reflectometry has the ad-vantage of being relatively low cost and easy to set up. An electromagnetic pulse follows a guided conductor until it hits the contents and then returns. Operat-ing under the time-of-flight measure-ment principle, the level is calculated. This technology is generally limited to shorter ranges of 30 meters or less and materials that are not extremely heavy or abrasive. Shifting material and ten-sile forces make the instruments prone to broken or tangled cables that could interfere with the process and increase maintenance costs. The bottom of the cable sometimes anchors to ensure the cable does not move around dur-ing material draw down or shifting. If the cable touches the side of the silo, it will report false measurements. Cables must also size appropriately for the silo to ensure they can withstand the huge tensile forces present; however, if the cable is too strong, it can damage the silo roof. To install a cable system, you must wait until the vessel is completely empty before fastening the end of the cable to the bottom of the silo. Alterna-tively, we can use weighted cables, but the silo must first be empty to allow the cable to stretch out to its full length.

Radar: Radar (Radio Detection and Ranging) technology has worked suc-cessfully for liquid level measurement since the mid 1970s on large storage vessels, but the costs were high. As cost decreased and the technology devel-oped further, radar devices work in a wider range of applications, including smaller liquid bulk storage as well as agitated process vessels. Traditionally, radar technology was not for solids ap-plications, only for liquids even though radar is now an affective technology for solids. Because it uses electromagnetic waves in the microwave spectrum be-tween 1 and 300 GHz, which travel at the speed of light and which are virtually unaffected by vapor, pressure, temper-ature, or dust, radar works well in many

RESOURCES

Non-Contact: A Story of Radar Level

www.isa.org/link/NC_radar

Ultrasonic is on the level

www.isa.org/link/0305Ultra

Digging up savings:

Go with the flow

www.isa.org/link/Digg_save

18 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

PaPer M

ak

er

By Brad Carlberg

Level measurement lives in inner workings of pulp, paper mill

In a pulp and paper mill, you can find six main islands of automation: raw material re-ceiving and preparation (the woodyard), the

pulp mill, the powerhouse, the paper mill, con-verting and finishing, and effluent treatment.

Level technologies such as RF admittance, ul-trasonic, radar, differential pressure, displacers, bubblers, and nuclear can see use in the typical pulp and paper mill. Each of these technologies works when applied properly to liquids, granu-lars, slurries, or interfaces. As a general rule, you can measure liquid levels with any of these tech-nologies. One prevalent liquid level measurement technology, in any industrial plant, is differential pressure transmitters for measuring tank levels.

WoodworkingGranulars, especially measuring the wood chip levels in the chip bins, work well with all tech-nologies except differential pressure, displacers, and bubblers.

The woodyard receives the raw material (pulpwood logs or chips), which is prepared for the pulping processes downstream. Pulpwood logs go through debarking drums and chippers and then combine with received wood chips to be classified (sorted) and stored in either the chip pile or chip bins.

INTECH’S FLOW & LEVEL JUNE 2009 19

FloW/level

FAST FORWARD

l Six islands of automation make up pulp, paper production.

l Level sees use throughout paper-making process.

l Certain processes work best with certain level technologies.

at the wet end of the paper machine. The other end of the pa-per machine is the dry end. In between the wet and dry ends, vacuuming the water from the paper, then pressing it, drying it, and converting or finishing occurs, which means cutting it to the right size, and smoothing the surface and applying a coating if necessary.

As with any manufacturing plant, the pulp and paper mill has air and water effluent streams to treat before releasing back to the environment. You can remove the odors from the air by scrub-bing. Remove particulate from the stack gas by the electrostatic precipitators, and remove the excess heat in the cooling water by passing through heat exchangers so the temperature differential does not harm the environment. The water that goes to the effluent treatment plant, including clarifiers and settling tanks or ponds, is not much different from any munici-pal wastewater treatment facility.

The recovery boiler uses steam sootblowers (usually around fifty per boiler) to blow fly ash in the combustion gases off of the boiler tubes. Without the sootblowers, particulate would build up on the tubes, insulating them and preventing heat transfer to the water. This reduces the steam output from the boiler and lowers the boiler effi-ciency. To level the steam usage to the boiler, the individual sootblowers are on a schedule so they operate in a predefined sequence.

Black liquor evaporators concentrate the weak black liquor from the pulp washing process at around 15% solids to around 60% solids that will burn effectively in the recovery boiler. You can either pack the evaporators single-column or multi-effect (up to seven). To decrease the evaporation temperature, the multi-effect units operate in a vacuum. Optimize the process by using pressure and temperature differential to signal tube fouling that would cause a decreased heat transfer rate and a lower vacuum and auto-matically start a boil-out of the evaporators to clean the fouling.

In the causticizing area of the pulp mill, green liquor reacts with lime to form the white liquor used in the wood-chip digesting (cooking) process. Traditionally, conductivity saw use as a variable to measure the reaction complete-ness. With new nuclear instruments, it is easier to determine the exact chemical constitutes in the white liquor to better gauge the reaction

In the pulp mill, the wood chips mix with al-kaline pulping chemicals (white liquor, mostly sodium hydroxide) in either batch or continu-ous digesters and heat under pressure with pro-cess steam from the powerhouse. The product of the digesters is brown stock pulp in weak (15%) black liquor. The white liquor turns into black liquor because of the dark color of the organic compounds and lignin from the wood chips. Lignin is the glue that binds the wood fibers and gives the wood its strength and rigidity.

The basic purpose of the rest of the pulp mill processes downstream of the digesters is first to clean by screening, refining, washing, and bleaching the wood pulp that goes to the pa-per machine stored in the high-density storage chests. Second, recover and concentrate in the evaporators these chemicals in the black liquor. Then send the strong (65%) black liquor to the powerhouse; liquor guns spray into the furnace of the recovery boiler to make steam for the pro-cess and green liquor. This green liquor goes to the causticizer where it reacts with lime, creat-ing the white liquor.

The recovery boiler will probably have more steam soot blowers to remove the fly ash from the boiler tubes than a gas or oil furnace; however, the main boiler auxiliary equipment (feedwater treat-ment, steam blowdown system, forced or induced draft fans, stack gas analyzers, and steam super-heater and makedown systems) will be no differ-ent than traditional power-generating stations.

The strong black liquor comes to fuel the re-covery boiler from the evaporators and mixes with the saltcake from the electrostatic precipi-tator; it then sprays into the furnace through the oscillating liquor guns. The liquor guns will hopefully atomize the black liquor so it at least partially burns before falling to the bottom of the boiler, called the smelt bed. This molten smelt bed is predominantly made up of sodium oxide and leaves the boiler via the smelt spouts into the green liquor dissolving tank. The density of the green liquor in the dissolving tank is controlled for optimum reactivity when it goes to the causti-cizer to react with lime to make the white liquor.

Wet or dryThe best way to measure slurries is with RF admittance, ultrasonic, radar, and/or nuclear technologies—such as in the case of measuring pulp level in the headbox just before the paper machine or measuring pulping liquor levels in the causticizer, recovery boiler, or digester.

The paper mill is where we lay down the pulp stock on the forming wire by the headbox slice

20 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

FloW/level

chemicals can be reused in the digesting process. The brown stock washers usu-ally consist of multiple (three), counter-current stages, which means pulp stock comes one direction and clean wash wa-ter comes from the opposite direction. Fresh make-up wash water adds onto the cleanest pulp at the latter stages to wash the pulp stock, but the recycled weak liquor wash water adds onto the dirtiest pulp at the earlier stages.

For level applications with inter-faces such as in the chlorine dioxide generator, RF admittance or nuclear level technologies work best. Almost 20 years ago, I remember spending hours during startup of a chlorine dioxide generator to tune genera-tor level loop installed as differential pressure transmitter with a generator density analyzer as well. So you could determine the interface of the genera-tor level by calculating a density-com-pensated level measurement. I never could get an adequate level measure-ment to provide good production rate control. Since then, applications have been more prevalent using continu-ous level nuclear source and scintilla-tion detector technology, transmitting a radiation beam through the center of the chlorine dioxide generator with level accuracies of achieving 1 to 2% of range with high repeatability.

Base your decision whether to bleach the pulp on the final product of the pa-per mill. If the product is cardboard or paper sacks, bleaching is probably un-necessary. But if the product is writing paper, you will need to bleach paper towels, tissue, diapers, etc., then the pulp. The bleach plant usually consists of multiple (three to five) stage wash-ers interspersed between bleach tow-ers. Typically, bleaching chemicals are liquid or gaseous chlorine, chlorine di-oxide, sodium hydroxide, sodium hy-pochlorite, hydrogen peroxide, liquid or gaseous oxygen, and liquid or gas-eous ozone. These bleaching towers allow the resident time (usually one to three hours per tower) for the bleach-ing chemicals to brighten and whiten the pulp.

As with the causticizer, the bleaching process is by nature a process with a long

more uniform pulp stock. The screen, which is a piece of equipment with a ro-tating, cylindrical basket with either slots or holes, lets the optimally-sized pulp fibers pass through but centrifugally re-moves knots, uncooked or undercooked fiber bundles that can recycle back to the digester for additional cooking. The re-finer, which is a piece of equipment with two rotating, rough-surfaced plates, cuts or defibrillates the wood fibers, giving more uniform pulp stock.

Cleanup crewThe digested, screened, and perhaps refined pulp stock, although uniform in fiber size, is still dirty with all the by-organic and inorganic byproducts from the digesting process, known as weak black liquor at around 15% solids. The dark color comes primarily from the lignin. Residual cooking inorganic

completeness. Since the causticizing process is by nature a process with a long lag time and not a good candidate for traditional PID control, a new opti-mization technique involving model-based predictive control (MPC) can tune the process more tightly, which would yield a more consistent white li-quor product.

The pulp digesting process uses batch or continuous digesters. Either way, the principle is the same—the wood chips and the cooking chemicals add to the digester. Under pressure and at an el-evated temperature from the steam addition, the wood chips cook (really explode) for 60 to 90 minutes. The pulp stock slurry exits the digester at a con-sistency of 6%, and the resulting pulp fibers are close to the state they need to be to make the paper.

Screening and refining helps to get a

For level applications with interfaces such as in the chlorine dioxide generator, RF admittance or nuclear level technologies work best.

INTECH’S FLOW & LEVEL JUNE 2009 21

FloW/level

lag time and not a good candidate for traditional PID control; a new optimiza-tion technique using MPC can tune the process more tightly, which would yield a more consistently bleached pulp.

The lime kiln is a large (15 ft diam-eter by 200 ft long), rotating cylinder used to calcinate the byproduct of the causticizing process, the lime mud, to convert it back to the lime that can add into the causticizer. As with the causticizer and bleach plant, the lime kiln process is also a process with a long lag time and not a good candidate for traditional PID control. Again, the MPC technique can tune the process more tightly.

Pressing, dryingAfter all the preparation, pulp stores in the machine chest. From there, the fan pump pumps the pulp stock to the headbox from which we lay down the pulp stock slurry on the fourdrinier wire along the entire width (sometimes

and drag) of the paper sheet, mitigat-ing undue stresses that could cause a paper sheet break.

ABOUT THE AUTHOR

Brad S. Carlberg, P.E. is a senior controls and

instrumentation engineer at Bechtel National

Inc., the government services arm of Bechtel

Group that helps the U.S. destroy stockpiles

of chemical weapons and treat contaminat-

ed wastes out of Richland, Wash.

over 300 inches wide) of the machine via the slice out of the headbox.

The primary control variables in pa-permaking are the basis weight, mois-ture, and caliper (or thickness). A typi-cal paper machine can be as long as a football field. As in the pulp mill where the majority of the processes remove the pulping byproducts; the majority of the paper machine removes the water from the paper in first the forming sec-tion, followed by the press section, and finally, the dryer section.

The use of video cameras at strate-gic points along the paper machine has been effective to alert the opera-tors of events that can cause a paper sheet break. With this information, the operator can avoid an actual sheet, significantly decreasing production downtime. Use of cascaded and cou-pled, variable frequency drives control-ling the various rollers in the fourdrin-ier wire, press, and dryer sections can more tightly regulate the tension (rush

RESOURCES

Cleaning up a dirty business

www.isa.org/InTech/20081102

Mind your Ps

www.isa.org/InTech/20060803

Paper industry growth through

biotechnology

www.isa.org/link/Paper_ind06

ISA Certified Control Systems

Technician (CCST) program

www.isa.org/link/CCSTqu0309

22 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Valve testing committee revises standard

When manufacturers and third-

party test labs perform stan-

dardized testing on control

valves, it is important their standard is up-

dated and easily understood. To this end,

the ISA-75.02 committee on control valve

capacity test procedures has been work-

ing to revise its standard. The committee

has now completed voting procedures

on ISA-75.02.01, Control Valve Capacity

Test Procedures, and has put it up for fi-

nal American National Standard Institute

(ANSI) review.

The purpose of the standard is to sup-

port ANSI/ISA-75.01.01-2002 (60534-

2-1 mod), Flow Equations for Sizing

Control Valves, and ANSI/ISA-75.11.01-

1985 (R2002), Inherent Flow Charac-

teristics and Rangeability of Control

Valves, by providing procedures for test-

ing control valve capacity and related

flow coefficients for compressible and

incompressible Newtonian fluids. This

standard also provides a procedure to

evaluate the major data to calculate the

coefficients.

“The standard is not intended for di-

rect end-user implementation, rather, for

those who will be performing standard-

ized testing in a controlled environment,”

said Chairman Erv Skovgaard. “The stan-

dard helps ensure flow coefficients from

various sources are tested under compa-

rable conditions and are calculated con-

sistently. However, end users may benefit

from reading the standard, for example,

by noting sections on piping configura-

tion and accuracy of the calculated coef-

ficients,” he said.

The scope uses mathematical equa-

tions outlined in ANSI/ISA-75.01.01-2002

(60534-2-1 Mod), Flow Equations for Siz-

ing Control Valves, in providing a test pro-

cedure for obtaining the following:

a) Valve flow coefficient, C (C; Kv)

b) Liquid pressure recovery factors, FL and

FLP

c) Reynolds Number factor, FR

d) Liquid critical pressure ratio factor, FF

e) Piping geometry factor, Fp

f) Pressure drop ratio factor, XT and XTP

g) Valve style modifier, Fd.

This standard is intended for indus-

trial process control valves used in flow

control of Newtonian fluids. The testing

procedure covers a wide range of control

valve styles. However, some valves, such

as very low flow valve and wide-open full-

bore ball valves, are not included.

To ensure required accuracies, the stan-

dard addresses pressure, flow, and tem-

perature measurement and valve position

and describes the various test procedures

and how to evaluate the data collected.

Another goal of the revised standard

is to be self-contained, with numerous

annexes (appendices), and tables for re-

quired data to eliminate the need to refer

to other sources for that data. Some of

the sections the committee tackled to en-

sure consistency included test specimen

(valve), test sections (adjacent piping),

pressure tap location and construction,

and test fluid (compressible and incom-

pressible).

“In the revision process, it became ob-

vious there was a better method to record

changes and the reasons behind why the

changes were needed,” Skovgaard said.

The outcome was a change log, akin to

an engineering change document that

details and controls changes to a drawing

or procedure. The details of the format

and location of the log are under review

by the S&P board.

The writing team that worked on the

“In the revision process, it became obvious there was a better method to record changes and the reasons behind why the changes were needed.” —Skovgaard

revision included manufacturers, integra-

tors, and end users. “Although the stan-

dard has been around for many years, the

team aimed to improve the standard’s us-

ability, consistency, and agreement with

ISA-75.01 terminology and nomencla-

ture,” he said.

New change log

Some of the changes in the new change

log include modifying the scope to reiter-

ate relevant constraints or limitations of

equations, and including verbiage to ad-

vise caution when testing specific valve

styles (such as fractional C valves, line-

of-sight valves, and multi-stage valves).

The committee added a style modifier

to the list of coefficients addressed, and

added clarification to purpose. The com-

mittee also updated nomenclature to be

consistent with revised terminology in

ISA-75.01.

In the general description, they ex-

panded the definition of test section to

be consistent with the IEC test section

definition.

Changes to the test specimen section

included a recommendation to validate

physical or computationally based scaling

methods with tests to establish a degree

of certainty.

Changes to the test section provided

additional guidance in assessing the im-

pact of any mismatch in the inside diam-

eters of the test specimen and adjacent

piping.

Changes to the flow measurement sec-

tion included admonition to follow flow

conditioning recommendations (straight

pipe. etc.) specific to the new modeling

device actually employed.

Changes to the pressure taps section

included verbiage about alignment of ro-

tary valves (shaft with respect to pressure

tap). This also included a forward about

gasket alignment that could impact pres-

sure measurement.

Ellen Fussell Policastro (efussellpolicas-

tro@isa.org) writes and edits Standards.

standards | New Benchmarks and Metrics

INTECH’S FLOW & LEVEL JUNE 2009 23

The biggest concern of an operator is to have a stable process control loop. ... The final control element will influence the stability of a loop more than all the other control elements combined.

tuator/valve combination, or, in case you

use a positioner, the dead band of the

valve divided by the open loop gain of the

positioner plus the positioner’s dead band

(dead band keeps the valve from respond-

ing instantly when the signal changes,

which, in turn, causes dead time).

The valve itself should never have a

dead band of more than 5% of signal

span. Ignoring process dynamics a posi-

tioner may, therefore, improve matters by

an order of magnitude.

However, positioners can raise havoc

with the dynamics of a control loop. The

ideal valve is still the one in which the

operating dead band with tight stem

packing is less than 1%. There you have

maximum stability without the extra cost

and complication of having to use a valve

positioner. Unfortunately, the majority of

valves cannot operate without a position-

er. Luckily, modern positioners have elec-

tronic tuning capabilities that can help to

drive the dead band down.

The very first control valves recognized

the value of low dead band. Low seat leak-

If you are looking for good control

valve design, of course you will look

for quality workmanship, correct selec-

tion of materials, noise emission, and the

like. But pay special attention to low dead

band of the actuator/valve combination

(with tight packing) and tight shutoff, in

cases of single-seated globe valves and

some rotary valves.

The biggest concern of an operator

is to have a stable process control loop.

Nothing makes people more nervous

than a lot of red ink and scattered lines on

a strip of paper from a recorder. The final

control element will influence the stability

of a loop more than all the other control

elements combined.

The biggest culprit here is dead time—

the time it takes for the controller to vary

the output signal sufficiently to make the

actuator and the valve move to a new po-

sition. Here the dead time (TDv

) is the time

it takes for the pneumatic actuator to

change the pressure in order to move to

a different travel position. It is most com-

monly related to the dead band of the ac-

Don’t get caught in dead time

age can be beneficial. First, it saves you the

extra expense of a shut-off valve in case

the system closes down. For safety reasons,

never rely on the control valve for abso-

lute tight shutoff. Second, it saves energy.

Third, it is an unqualified requirement in

temperature control application in a batch

process, especially when you are supplying

a heating fluid to a chemical that can un-

dergo an exothermic reaction.

Another feature is good rangeability. Valves

are usually terribly oversized; that is, they op-

erate only at perhaps 30% of their rated Cv

under normal flow conditions. Furthermore,

it is not wise to operate a conventional valve

trim at less than 5% travel. The reason is the

controller might be slightly unstable at the

low flow rates, and the actuator, following

the sinusoidal output of the controller signal,

will push the plug against the seat. When

this happens, the actuator and positioner will

bleed all the air out, and you end up having

a really big dead time (before the valve gets

moving again) upon signal reversal. In short,

you have a big mess and no control.

Using the 5% travel limit, we find the

Cv is only about 7% of the rated C

v with

a linear characteristic and not much less

with most equal percentage characterized

plugs. This gives us a useful range for the

above-normal Cv of 30% divided by 7%,

which is 4.5:1. However, in most loops,

the pressure drop across the valve always

varies inversely with the flow, that is, a

low DP at maximum flow and a high DP

with low flow. We therefore might find

the actual controllable ratio of maximum

to minimum flow is perhaps only 3:1.

Incidentally, this ratio is the so-called in-

stalled rangeability, which is quite differ-

ent from the inherent rangeability shown

in a manufacturer’s catalog for the same

valve. A simple way to remember this is

the inherent valve rangeability is the ratio

of maximum to minimum controllable Cv

while the installed rangeability is the ra-

tio of maximum to minimum controllable

flow rate in your loop.

SOURCE: Control Valve Primer: A User’s Guide, 4th Edition, by Hans D. Baumann, ISA 2009.

Work Environment Assurance | safety

24 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

Vortex shedding flowmeters

CoolPoint vortex shedding flowmeters offer

a temperature transmitter for measuring

and monitoring both flow and temperature

in processing water, water with chemicals

added, water/glycol coolant and corrosive

fluids. CoolPoint flowmeters with an op-

tional temperature transmitter are designed

for cooling applications involving heat re-

moval. CoolPoint efficiently measures the

flow rate of fluids. Meters with the trans-

mitter have the added capability of moni-

toring temperature readings and transmit-

ting them to a process controller. The

flowmeters are available with brass flow

bodies for water and coolant and with

stainless steel flow bodies for corrosive flu-

ids and water with chemicals added.

Universal Flow Monitors, Inc.www.flowmeters.com

Air/gas flowmeter

Model ST98HT Mass Flow Meter is for ex-

treme process air/gas temperatures up to

850°F (454°C) and provides highly accurate

flow measurement with superior repeat-

ability. The multi-function ST98HT measures

air/gas mass flow rate, totalized flow and

temperature in a single instrument. It sup-

ports a wide range of critical applications in

electric power generation, chemical refin-

ing, steel production and other processes

with high temperature air or gas flows. The

ST98HT is an insertion-style flowmeter suit-

able for pipe sizes from 2.5 inches to 120

inches (63 mm to 3048 mm).

Fluid Components International www.fluidcomponents.com

Lightning protection for transducers

The manufacturer of KPSI Level and Pressure

Transducers now offers lightning protection

for its Series 300 small bore submersible level

transducers for increased reliability. The Se-

ries 300 features protection against fast rising

voltage transients with the use of two surge

protection components, one located in the

0.75 inch OD 316 housing of the transducer

and one located at the surface, grounded via

DIN-rail or ground wire.

The Series 300 is designed for small-bore

applications to meet the rigorous environ-

ments encountered in a variety of water

level measurements. With an option of

welded 316 SS or titanium construction,

this transducer family features a rugged,

waterproof design and is ideal for ground

water and surface water monitoring, down

hole, dewatering, level control, and ship-

board-use applications.

Pressure Systemswww.pressuresystems.com

Industrial thermal mass flowmeter

Sage Prime Indus-

trial Thermal Mass

Flow Meter is de-

signed to monitor

the flow rate and

consumption of

existing natural

gas lines at indus-

try, government,

univer sities, and

com mercial estab-

lishments. With

con venient mounting hardware, the inser-

tion style easily installs into the main line

or branches of any pipe from 1” and up.

Sage Prime is ideal for sub-metering in In-

dustry at the building, or at the boiler or

heater lines, or for determining individual

gas consumption at condominiums or

apartment buildings.

Sage Meteringwww.sagemetering.com

Flow manager

The company un-

veiled a new

highly scalable

technology plat-

form with the

introduction of its

new FloBoss107

flow manager,

the newest ad-

dition to its best-

in-class FloBoss Flow Manager family of

natural gas and liquids flow computers.

Adding to the new platform advantages,

the FloBoss 107 also features new dy-

namic configuration software and an LCD

touchpad to enhance ease of use. The

new technology platform will serve as the

basis for future product introductions and

as an upgrade to current FloBoss legacy

products. This platform uses a modular,

highly-expandable architecture that con-

sists of plug-in modules for the central

processing unit (CPU), input/output (I/O),

and communications. The modules plug

into a four-slot base chassis.

Emerson Process Management www.emersonprocess.com

Laser level, positioning transmitter

The LM80 laser

transmitter for

non-contact

level measure-

ment and posi-

tioning mea-

sures position

over very long

ranges, at distances up to 500 feet (150

meters). The device accurately measures

level at distances up to 100 feet (30 me-

ters). Whether handling plastics, coal,

grain, or aggregates, the LM80 can mea-

sure any solid surface at any angle.

The small wavelength of the laser

means a narrower beam with virtually no

beam divergence and, therefore, no false

echoes. The LM80 can be installed on any

existing silo nozzle, three inches or larger,

regardless of location. An advanced timing

system and self-correcting signal process-

ing functions allow the device to accurate-

ly and reliably make measurements in the

harshest conditions.

K-TEKwww.ktekcorp.com

products & resources | Flow & Level Instruments

Turbine flowmeter

The LoFlo Series precision turbine flow-

meter now incorporates an integrally

mounted COX 4080 flow computer.

This flow measurement system provides

enhanced accuracy and linearity in

blending, batching, chemical injection

and other demanding industrial appli-

cations. The COX LoFlo Series turbine

flowmeter is designed for measuring

flows as low as 0.006 gallons-per-min-

ute (GPM). The meter offers high accu-

racy, fast response to flow rate changes,

and simplicity of construction with few

parts. It is repeatable to +/-0.25% of

reading, allowing for an overall accu-

racy of +/-0.5%.

COX Instrumentswww.cox-instruments.com

Diaphragm seals

The threaded

flush face dia-

phragm seals

are well-suited

to applications

where a con-

tinuous flow of

process across

the diaphragm

is required to

prevent solids

buildup. They

are used in a wide variety of industrial

applications ranging from oil & gas

to wastewater treatment. The seals

are used with a variety of pressure

instrumentation including gauges,

transducers, and switches. The seals

come in process connections ranging

from ½” npt to 1” npt with either a

¼” or ½” npt instrument connection.

The wetted parts are all 316 stainless

steel. In addition, the COX 4080 in-

corporates enhanced digital signal

processing (DSP) technology allowing

exceptional signal characterization

and fast response to output dynamic

data in engineering units. With this

solution, end users can employ one

device for multiple signal outputs; no

external amplifiers or signal condi-

tioners are necessary.

REOTEMP Instruments www.reotemp.com

Coriolis mass flowmeter

The OPTIMASS 2000 is a large diameter

Coriolis mass flowmeter for accurate and

repeatable bulk measurement in the oil in-

dustry. Using the twin straight tube design

of the OPTIMASS 1000, the product range

has been extended with the OPTIMASS

2000 to provide accurate measurement

for the bulk fluids market. Available in

three sizes, 4 inch, 6 inch, and 10 inch, OP-

TIMASS 2000 wetted parts are constructed

of NACE compliant duplex stainless steel

(ANS 31803), and the meter is available

with flange ratings up to 1,500 lbs, and

flange sizes from 4 inch to 12 inch.

KROHNE www.KROHNE.com/northamerica

Calibration laboratory

The company’s primary standard flowme-

ter calibration laboratory has been ac-

credited by the National Voluntary Labo-

ratory Accreditation Program (NVLAP).

The facility is now accredited to provide

ISO/IEC 17025:2005 liquid calibrations—

the “Gold Standard” for absolute accu-

racy and repeatability. NVLAP is in full

conformance with all recognized stan-

dards for the metrology industry, includ-

ing NIST Handbook 150, ISO/IEC 17025

and Guide 58, as well as ANSI/NSCL Z540.

NVLAP accreditation criteria were estab-

lished in accordance with the U.S. Code

of Federal Regulations (CFR, Title 15 Part

285), NVLAP Procedures and General Re-

quirements.

Flow Technology www.ftimeters.com

Flowmeters, controllers

The Max-Trak Model 180 Industrial Mass

Flow Meters and Controllers are now avail-

able with 316 stainless steel (ANSI or DIN)

flange mounting for gas flow rates up to

1000 slpm (pipe sizes up to 1 inch / 25mm).

This design enhancement expands the pro-

cesses and applications where the Max-Trak

can be installed. The Dial-A-Gas technology

makes Max-Trak the industry’s only multi-

gas capable industrial mass flow controller.

Max-Trak has excellent accuracy (+/-1% of

FS) and repeatability (+/-0.2% of FS), cou-

pled with unsurpassed instrument stability

resulting from a patented, inherently-linear

design, advanced platinum sensor technol-

ogy, and a valve that is strong, flexible and

forgiving. Max-Trak can communicate to a

user workstation via RS-232, RS-485 or one

of 4 analog signals.

Sierra Instrumentswww.sierrainstruments.com

Wave radar level transmitters

The Sitrans LG200 is a line of guided wave

radar level transmitters for liquids, slurries,

interface, and bulk solids. Sitrans LG200 is a

two-wire, loop-powered HART level trans-

mitter that can measure materials with a di-

electric range of 1.4 and higher, tempera-

tures up to 427 degrees Celsius (800 degrees

Fahrenheit), and pressures up to 6250 psig

(431 bar). The Sitrans LG200 line offers reli-

able level and interface measurement in liq-

uids with corrosive vapors, foam, steam,

high viscosity, surface agitation, high fill/

empty rates, low level, and varying dielectric

or density.

Siemens Energy & Automation, Inc. www.sea.siemens.com

INTECH’S FLOW & LEVEL JUNE 2009 25

Flow & Level Instruments | products & resources

able to achieve short span measurement ac-

curacies many other technologies cannot. As

an intrusive technology, however, insulating

granular measurements requires special con-

siderations, such as the moisture range and

location of the sensing element to minimize

errors caused by probe movement.

Ultrasonic/sonic

Ultrasonic transmitters send a sound wave

from a piezoelectric transducer to the con-

tents of the vessel. The device measures

the length of time it takes for the reflected

sound wave to return to the transducer.

A successful measurement depends on

reflection from the process material in a

straight line back to the transducer. Ultra-

sonic’s appeal is the transducer does not

come in contact with the process material

and does not contain any moving parts.

Ultrasonic technology was the first indus-

trially accepted non-contact level measure-

ment in the process control market.

Today’s ultrasonic devices typically re-

quired no calibration and can provide

high accuracy level measurements in liq-

uid and solids applications.

However, excessive process temperatures

and pressure can be a limiting factor. And

since ultrasonic technology is based on a

traveling sound pressure wave, a constant

velocity via its media (air) is required to as-

sure a high degree of accuracy. Material such

as dust, heavy vapors, surface turbulence,

foam, and even ambient noise can affect the

returning signal. Because sound travels at a

constant known velocity at a given tempera-

ture, the time between the transmit burst

and detection of the return echo will be pro-

portional to the distance between the sensor

and the reflecting object. The distance be-

tween the two can be calculated from:

Distance = Rate × Time

Radar

Radar technology broadened non-contact

level technology options. Radar’s inherent

accuracy with its ability to have a narrow-

er beam angle avoided quite a few vessel

internal obstructions from reflecting false

the density of the liquid are constant, then

a unit change in level will result in a repro-

ducible unit change in displacer weight.

Displacers also are affected by changes in

product density. They should only be used

for relatively non-viscous, clean fluids and

work best for short spans.

Floats

Level-measuring devices that use a float

resting on the surface of the measured pro-

cess fluid are legion. Quite a few commodes

use a simple, float-driven, on/off switch,

water-leveling apparatus. As the liquid in a

process rises and falls in its vessel, the float

rises and falls as well. Indicators advise the

operator and/or the automation links as to

the liquid’s level. The float may directly and

mechanically trip a switch, push a magnet,

pull a lever, or raise a pointer. Floats are

made of brass, copper, stainless steel, and

plastics, among other materials.

Float technology advantages include

low cost, if remote reading is required,

adaptability to wide variations in fluid

densities, the ability to see use in extreme

process conditions; unlimited tank height,

and high accuracy.

Disadvantages can include high mainte-

nance requirements, vulnerability to partic-

ulate or product deposition, moving parts

exposed to fluids, and limited pressure rat-

ing. They are also not good for use in agi-

tated vessels and for granular products.

RF admittance, capacitance

For application permitting contact with

what is being measured, radio frequency

(RF) is perhaps the most versatile technol-

ogy for continuous level measurement. RF

uses a constant voltage applied to a rod or

cable (sensing element) in the process. The

resulting RF current is monitored to infer

the level of the process material. RF tech-

nologies handle a wide range of process

conditions—from cryogenics to 1,000°F and

from vacuum to 10,000 psi pressure. It can

withstand severe service in harsh corrosive

environments. RF also is the most preferred

technology for point level measurement,

Instrument suppliers offer more than

20 different level measurement tech-

nologies. All work, when properly ap-

plied. However, each has its strengths and

its weaknesses, and some are not suitable

for certain applications.

Differential pressure

Among the most frequently used devices

for measuring level, differential pressure

(DP) transmitters do not measure level by

themselves. Instead, they measure the head

pressure that a diaphragm senses due to

the height of material in a vessel. That pres-

sure measurement is multiplied by a second

variable, the product’s density. That calcula-

tion shows the force being exerted on the

diaphragm, which is then translated into a

level measurement. Errors can occur, how-

ever, due to density variations of a liquid,

caused by temperature or product changes.

These variations must always be compen-

sated for if accurate measurements are to

be made. DPs are primarily used for clean

liquids and should not be used with liquids

that solidify as their concentrations increase,

such as paper pulp stock.

Bubblers

This simple level measurement has a dip

tube installed with the open end close

to the bottom of the process vessel. A

flow of gas (usually air) passes through

the tube. When air bubbles escape from

the open end, the air pressure in the tube

corresponds to the hydraulic head of the

liquid in the vessel. The air pressure in the

bubble pipe varies proportionally with the

change in head pressure. Calibration is di-

rectly affected by change in product den-

sity, however. Because of this, it becomes

a mass measurement.

Displacers

When a body is immersed in a fluid, it loses

weight equal to the liquid weight displaced

(Archimedes Principles). By detecting the

apparent weight of the immersed displac-

er, a level instrument can be devised. If the

cross sectional area of the displacer and

Principles of level measurement

26 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

automation basics | Level

Hydrostatic pressure: This technology’s ba-

sic principle is measuring total head pres-

sure above a pressure-sensing diaphragm.

Measuring water in below-ground wells is

a major application.

Conductance devices: These switches are

used to measure high or low level in liq-

uids such as water, acids, and conductive

chemicals. The conductivity electrodes are

connected to a relay to provide control

and require little or no calibration.

Float switch: Simple to apply and cost effec-

tive. Because floats are a mechanical level

switch, it is important to use them in applica-

tions where coating build up will not occur.

SOURCE: ISA Handbook of Measurement Equations and

Tables, 2nd Edition, Edited by Jim Strothman, ISA 2006.

has a more narrow beam or pulse width,

than radar since it s completely focused on

a flexible wire or rod. The measurement Is

determined by te trnsit time divided in half.

TDR also does not require cliabraiton.

Magnetostrictive: Allows very high-accuracy

level measurements of non-viscous liquids

at ranges up to 50 feet. The technology is

based on a float with embedded magnets

that rides on a tube that contains magne-

tostrictive wire pulsed with a low voltage,

high current electronic signal. When this

signal intersects the magnetic field, gen-

erated by the float, a torsional pulse is re-

flected back to the electronics. This creates

a time-of-flight measurement. Magneto-

strictive devices require no calibration and

no maintenance when properly applied.

level signals. Radar is unaffected by vapors,

steams, and undesired affects of condensa-

tion that can affect ultrasonic devices. Prop-

erly applied, radar is completely capable

of measuring most liquids and solids level

applications. Frequency modulated con-

tinuous wave is fast enough for tank gaug-

ing, but normally too slow to measure the

turbulent surfaces encountered in agitated

process applications. Like ultrasonic, radar

does not require calibration.

Nuclear

Nuclear level controls see use for continu-

ous measurements, typically where most

other technologies are unsuccessful. They

are extremely suitable for applications in-

volving high temperature and pressures,

or corrosive materials within the vessel. No

tank penetration is needed. Radiation

from the source penetrates through the

vessel wall and process fluid. A detector

on the other side of the vessel measures

the radiation field strength and infers

the level in the vessel. The basic unit of

radiation intensity is the curie, defined

as that source intensity which undergoes

3.70 x 1010 disintegrations per second.

For industrial applications, radiation

field intensity is normally measured in

milliroentgens per hour. Radiation field in-

tensity in air can be calculated from:

D = 1000

Where:

D = Radiation intensity in milliroent-

gens per hour (mR/hr)

Mc = Source strength in millicuries

(MCi)

D = Distance to the source in inches

K = Source constant (0.6 for cesium

137; 2.0 for cobalt 60)

Other level technologies include:

Time domain reflectometry (TDR): A pulse

time of flight measurement much like ul-

trasonic and some radar techniques. Like

radar, it transmits an electrmagnetic pulse

that travels at the speed of light to the

surface of the material to be measured. It

INTECH’S FLOW & LEVEL JUNE 2009 27

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Level | automation basics

acting in the plane of rotation.

With the torque acting in the plane

of rotation, measurement of the torque

happens by placing a sensing means,

such as a strain gage, in the drive shaft.

To measure the mass-flow rate, we hold

the angular velocity—the motor rotation-

al speed—constant, leaving the torque as

a direct measure of mass flow.

Coriolis crosses platforms

A device employing the gyroscopic prin-

ciple of operation in the oscillatory mode

is a tube shaped in the form of the letter

“U.” An electromagnetic oscillator drives

the U-shaped tuning-fork-like structure

at the resonant frequency of the system,

thereby producing a Coriolis acceleration

and resultant force.

The force acts alternately—perpendic-

ular to the flow path—in opposite di-

rections, causing an oscillating moment

about axis O-O of the flowmeter.

The resulting moment (m), acting about

the central axis and in a plane perpendic-

ular to the driving moment (W), produces

a twist-type motion, where the deflection

angle between FC1 and FC2 is directly

proportional to the mass-flow rate.

Nicholas Sheble (nsheble@isa.org) writes

and edits Automation Basics. A source for

this article is Fundamentals of Flow Mea-

surement, Joseph DeCarlo, an Indepen-

dent Learning Module, ISA, 1984.

description of the effect, giving his name

to the Coriolis force.

While air begins flowing from high to

low pressure, the Earth rotates under it,

thus making the wind appear to follow a

curved path.

In the Northern Hemisphere, the wind

turns to the right of its direction of mo-

tion. In the Southern Hemisphere, it turns

to the left. The Coriolis force is zero at

the equator.

This force results from acceleration act-

ing on a mass, and anyone who walks

radially outward on a moving merry-go-

round experiences the force. A person

must lean toward or direct

the mass of his or her mov-

ing body against the force

that the Coriolis accelera-

tion produces.

If we know the force (F)

acting on the body, the ve-

locity (V) of the body, an-

gular velocity of the plat-

form (ω), we can calculate

the person’s mass (M).

By applying this phe-

nomenon to mass-flow

measurement, we create a Coriolis mass

flowmeter. Indeed, there are several types

of meters leveraging the Coriolis Effect.

One straight-up mass-flow device has

rotors containing metal vanes that form

several channels.

This gadget operates at a constant angu-

lar velocity per an external power source.

Any particle of fluid traveling through the

radial channel with velocity V will experi-

ence the Coriolis force, resulting in torque

The global flowmeter market tracks

at nearly $5 billion a year in reve-

nue. One of the two fastest grow-

ing segments of this market is Coriolis.

(Ultrasonic is the other.)

Flowmeter growth is strongest in the

oil and gas industry, and with crude oil

trading between $40 and $150 per bar-

rel over the last 18 months, measurement

accuracy, and reliability are most impor-

tant. That is where Coriolis flowmeters

come in. They are very popular for cus-

tody transfer of petroleum liquids.

Technology of the gods

The first commercial meters appeared in

the 1970s. They measure mass flow di-

rectly with high accuracy and rangeability.

A French engineer and mathematician,

Gustave-Gaspard Coriolis, first described

the Coriolis force in the early 1800s. It is

an effect of motion on a rotating body

and is of paramount importance to me-

teorology, ballistics, and oceanography.

Whereas pressure differences tend to

push winds in straight paths, winds fol-

low curved paths across the Earth. In

1835, Coriolis first gave a mathematical

Coriolis meters use flow vibrations

28 INTECH’S FLOW & LEVEL JUNE 2009 WWW.ISA.ORG

V

F

ω

T torquemeasurement

Motor

ω

Flow

Flow

0 0

W

m

FC2

FC1

U-shaped gyroscopic mass flowmeter

Coriolis mass flowmeter

Coriolis force: The effect of motion on a rotating body.

automation basics | Flow