SAES 2013_066_075

Journal of Engineering Science and Technology Special Issue on Applied Engineering and Sciences, October (2014) 66 - 75 School of Engineering, Taylors University

66

LABVIEW BASED FLOW RATE MONITORING AND MEASUREMENT ALGORITHM FOR ROTARY ENCODER

R. GARMABDARI1,*, S. SHAFIE

1,3, A. GARMABDARI

2,

H. JAAFAR1, A. K. ARAM

1

1Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 2Faculty of Engineering, Islamic Azad University of Qazvin, 1655, Barajin, Qazvin, Iran

3Institute of Advanced Technology, Universiti Putra Malaysia, 43300 Serdang, Selangor, Malaysia

*Corresponding Author: [email protected]

Abstract

The water usage is increasing twice of the rate of global population growth

within the last century. According to the statistical studies, the global

population is growing by roughly 80 million people annually, representing

increased freshwater demand of around 64 billion cubic meters in the same

period of time. This amount of water is being consumed in three fields

comprising irrigation 70%, industry 20% and domestic usage 10%.Therefore,

monitoring and controlling of natural water resources are counted as two most

vital issues in water crisis. For the purpose of control and supervision on natural

water sources, the water consumption parameters such as instantaneous

consumption, flow rate, and accumulated consumption should be measured and

monitored. This paper presents a new monitoring algorithm implemented in

Labview to monitor, calculate and plot the mentioned parameters based on the

rotary encoders such as electromagnetic, ultrasonic, capacitive, or even hall-

effect sensors based. The results show that, the algorithm is capable to measure

and display flow rate, instantaneous and cumulative consumption. It is also able

to recognise and present the fluid flow direction and the system fault.

Keywords: Water measurement, Rotary encoder, Flow rate, Monitoring algorithm.

1. Introduction

Although there are various techniques to monitor and measure water flow rate,

instantaneous and cumulative water consumption parameters, but they require

different equipment to measure and register each one of them. For instance, a water

meter and flow meter are needed to measure consumption and flow rate respectively.

Furthermore, the peripheral software may be required to extract the statistical

Labview Based Flow Rate Monitoring and Measurement Algorithm for.....67

Journal of Engineering Science and Technology Special Issue 10/2014

Nomenclatures

Vx Output voltage of hall sensor x, V

Vy Output voltage of hall sensor y, V

Abbreviations

C.P Counted Pulses

CC Cumulative Consumption

CET Constant Elapsed Time Technique

F.R Flow Rate

MFR Mean of Flow Rate

MR Magneto Resistive Sensor

RPM Round per Minute

information [1]. The difficulty and cost of implementation of such these

measurement systems motivated to design and develop a new display algorithm

based on Labview which is able to plot flow rate, the mean of flow rate,

instantaneous and cumulative consumption graphs. The mean of flow rate has a

statistical concept and generally is calculated every hour during a day. All these

values can be recorded in a database according to their date and time. The stored

information can be utilised to achieve more statistical information such as

periodical consumption which needs to be accomplished in a long period of time.

Furthermore, the errors of the system and flow direction of fluid are presented on

the display of the developed Labview based algorithm.

2. Hall Effect Sensor Based Encoder

Generally, rotary encoders recognise the position of rotary shaft connected to the

rotary part of encoder. Basically, rotary encoders comprise revolving part to

install sensors actuators, fixed part wherein the sensors are placed on it, readout circuit and processor to analyze the coded data [2]. Although rotary encoders are

classified based on principle of operation such as electromagnetic, capacitive,

optical, ultrasonic based encoders, they may also be categorised to magnetic and

optical encoders in terms of small dimension, high performance and dependency

to the environment conditions [3]. Since, the structure of optical encoders are

more complicated than electromagnetic types and also the electromagnetic

encoders have less dependency to the environment condition such as mist, mud,

dirt, water, dust and vibration [4], in this paper, it is focused on electromagnetic

rotary encoders and especially hall-effect based due to their low power

consumption. However, the optical encoders are capable to recognise the angular

position of the revolving shaft in high resolution, but in this scheme, it is

supposed to count the number of rotation of the shaft, detect the direction [5] of

rotation, and recognise the source of error occurred in the system as the main

functions of measurement.

Basically, magnetic encoders are used as non-contacting encoders in restricted

applications like the speed of rotation [6]. Many different types of magnetic

encoders have been reported based on the applied technique to sense the motion

of revolving shaft such as magneto resistive sensor (MR) based, differential

transformer with a rotary core, induction based using inductor, and hall-effect

68 R. Garmabdari et al.


sensor based. Although, the proposed Labview based measurement system can be

applied for all types of encoders and the functionality of different blocks of

algorithm are similar, but the approach and method of acquisition data and

calculation blocks must be changed according to the data encrypting procedure.

The hall-effect sensor based angular position encoders are normally utilised in

automotive and industrial applications due to their long life, low power

consumption, and also low cost implementation [7]. The operation principle of

hall-effect sensors is based on the induced voltage in two sides of a hall material

when it is located in a magnetic field according to the angle between materials surface axis and the magnetic flux.

The hall-effect encoders can be classified to different types in aspect of

configuration and application. Some encoders are assigned to only detect and

count the number of complete rotations of rotary shaft [8, 9]whereas another

group is developed to calculate the angular position of rotating shaft with respect

to either a reference point or the last position of rotary shaft. The proposed

algorithm can be applied to both groups of encoders but the only blocks that

should be modified is the calculation and acquisition blocks according to the

output of sensors and utilised measurement technique. For instance, the encoder

which is shown in Fig. 1(a) computes the angular position of rotary shaft utilising

two hall-effect sensors which are separated by 90 degree angular distance. In this

encoder, the angular position of rotary shaft is formulated as follows [10]

{ =

= = 1

(1)

On the other hand, rotary encoders may also be designed to only recognise

and count the number of complete rotations, in order to calculate rotational speed

and detect the direction of rotation. In this case, the number of applied sensors

and actuators can be reduced according to the required accuracy. Since digital

sensors are generally used in this type of rotary encoders, one or more digital

signals are provided at the output of readout circuit. The calculation block of

display algorithm is designed based on inspection of the sequential codes which

are generated by the affected sensors. The structure of a three sensor rotary

encoder implemented on a water meter is presented in Fig. 1(b) [9].

(a) Angular Position

Rotary Encoder.

(b) Three Hall-Effect Sensor

Rotary Encoder.

Fig. 1. Structure of Hall-Effect Sensor Based Rotary Encoder.



In this apparatus, since three digital hall-effect sensors have been sequentially

located on the dial plate, the generated code at the output of interface circuit will

also be sequential according to the direction of rotation and arrangement of

sensors position.

3. Flow Rate and Consumption Measurement and Monitoring Technique

For the purposes of analysis of the obtained data from readout circuit to calculate

and display the water flow rate and consumption, a processing and monitoring

algorithm is required to develop on a standalone system.

Basically, the angular speed is considered as one of the most important types

of measurement in rotary based machines in order to monitor and control the

effective factors on rotation. Basically, there are several techniques to measure the

speed of a rotating shaft. The applied speed measurement approach depends on

the sensory system and interface circuit architecture [11].

Although, the angular velocity can be measured by different methods which are

classified into two main categories; timer /counter based and analog-to-digital based

techniques. These two techniques can also be divided to variety types based on the

predetermined parameters of measurement technique and the data acquisition

approach [11, 12]. The most appropriate technique is selected according to the

required range of measurement such as maximum and minimum value of speed, the

required accuracy, and the output signal of interface circuit. In this paper the constant

elapsed time technique (CET) is applied due to increase the accuracy of measurement

at low speed [13]. The principle of this technique is a combination of two simple and

basic methods including pulse counting and period measurement [14]. As illustrated

in Fig. 2, the input velocity pulse is counted within a predetermined time by a pulse

counter, and also a timer simultaneously is assigned to start and stop timing

between two consecutive velocity pulses, therefore, in spite of termination the

predetermined time, the pulse counter still is running until the next velocity pulse

starts. Therefore, pulse counter continues the counting of speed pulses as long as the

velocity pulse is high[11].

Fig. 2. Principle of CET Method to Measure the Angular Velocity.

In this paper, a monitoring and velocity measurement algorithm is developed

based on Labview due to its capability to implement the mathematical and logical

functions. Furthermore, it supports different communication protocols of

peripheral devices such as RS232 and USB [15]. The flow chart of the developed

algorithm is shown in Fig. 3. The proposed algorithm is able to measure the flow

rate, the mean of flow rate, instantaneous and accumulative consumption.

Besides, the source of occurred fault and flow direction can be recognised



utilising this algorithm. The input of the algorithm is an encrypted data string

comprising the number of complete rotations and the BCD code of current state.

This data is transmitted from the interface circuit to the computer (P.C) using

RS232 serial protocol. At the first step of algorithm, the encrypted string is

received via a serial port based on predetermined settings.

Fig. 3. Applied Flow Chart of into Labview Program.

Clearly, the algorithm should be infinitely repeated to plot continuous graphs.

Since the Labview is capable to concurrently execute two different infinite loops

without any interactions on operation of the other blocks. Thus, the receiver block

is separated from the main block of algorithm in order to avoid of missing data at

input while the main loop is being processed as depicted in Fig 4.

In the data receiver block a shift register is employed to store consecutively

each character of data and consequently, the data string is reconstructed

automatically when transmission is completed. Since the main loop was separated

from the received loop, each complete string must be stored in an interface

Check validity and Frame of Data

Yes

No

Read Input Data

Current consumption, the BCD code of current state

START

Data separation

Store the current state BCD code

Store the consumption

Data is valid?

Yes

No

Recognise the source of fault

Fault occurred?

Detect flow direction

Extract Instantaneous consumption

Compute flow rate using CET method

END

Compute cumulative consumption

Display graphs of results, indicate the flow direction

Display the source of the occurred fault



register to compensate the none-synchronization between the main and receiver

loops. It should be considered that the interface register should be cleared after

every reading by the main block.

In the next step of the proposed algorithm as shown in Fig. 5, the validity of

data is checked according to the predefined format of data string. The data format

includes the starting, separating, stopping and the length characters. The length

indicates the number of characters in a data string whereas separating character

presents the start of BCD code for current situation [16].

Fig. 4. Implemented Received Data Stage in Labview.

Fig. 5. Implemented Validity Check, Data

Separation and Fault Recognition Stages.

If the received data is recognised as valid information, then the start and

stop characters are removed and subsequently, the consumption value will be

detached from the BCD code of current state; otherwise, the algorithm starts

again from the beginning to receive new data string. After that, the extracted



information is stored in two registers. Now, the current state of sensors is

compared to the predetermined sequential BCD codes and the last stored state

code in order to recognise the source of fault if any happened. Afterward, the

current codes are substituted with the last codes in a register. In case of fault

occurred in the system, the algorithm is transferred directly to the display fault

source stage and then the iteration will be stopped until the fault is resolved and

system is restarted. If no error is detected in the fault inspecting step, the flow

direction is determined by comparison between the extracted current and last

stored consumption values. Obviously, the flow direction is forward if the

current consumption is greater than its last value and it is reverse if the current

consumption is smaller than the last consumption.

The flow rate is calculated based on CET method as the next task of this stage.

For this purpose, two timers are applied which first one measures the constant

predetermined time while another one measures the actual time. Once, the first

valid data string is received, both timers and the pulse counter are run. The

number of pulses is counted within the constant time period of the first timer and

when the predetermined time period elapsed, the current state of sensors is

compared with the reference state wherein the encoder had started to rotate. So,

whenever the last rotation is completed another timer also is stopped and the

measured time by the second timer is stored as the actual time. Then, the flow rate

can be computed by dividing the number of counted pulses (. ) overthe actual time () converted to minute. The unit of calculated flow rate (. ) is round per minute (RPM).

. =.

[]

[]= [] (2)

Next, the cumulative consumption (. ) which is defined as the sum of consumption from the start time till the current moment is computed to display as

below equation.

. = .=0

(3)

The mean of flow rate ()during a certain period of time which normally is considered every one hour, can be computed to determine the peak usage hours.

The mean of flow rate can be extracted using an independent timer to measure the

intervals and it also can be calculated as below.

= (.)

=1

=

.

=1

(4)

where the index refers to the number of calculated flow speeds.The . and represent the counted pulse and measured actual time in each speed calculation

respectively, and denotes the total number of calculated speed within the time period of independent time like one hour. The implemented computation stage of

the algorithm base on Labview program is shown in Fig. 6.

As it can be seen timers A and B are utilised to calculate the flow rate as

explained above and timer C is applied to calculate the mean of flow rate during

every hour. In order to make a pulse counter, the current consumption is

compared with the previous stored value, and if it was not repetitive, the pulse



counter is incremented by one, Otherwise; the value of pulse counter will remain

unchanged. The computed results should be plotted on graphs versus absolute

time as the penultimate stage of algorithm. For this purpose three waveform chart

are utilised as shown in Fig. 6.

Fig. 6. Implemented Computing and Plotting Stages in Labview.

4. The Outputs

The proposed algorithm to measure flow rate, instantaneous consumption, the mean

of flow rate and accumulated consumption was implemented in a hall sensor based

rotary encoder [8]. The rotary encoder detects the number of rotations according to

the sequence of happen states during rotation as explained above. The graphs are

plotted versus absolute time as shown below. As it can be seen from Fig. 7(a), the

flow rate is calculated as a positive value even while the direction of flow is

reversed. Figure 7(b) represents the instantaneous consumption which its gradient

slope is proportional to the flow rate whether in forward or reverse direction.

Therefore, the flow rate and direction of flow can be calculated from the

instantaneous consumption.

(a) Flow Rate. (b) Instantaneous Consumption.

Fig. 7. Experimental Result of Flow Rate and Instantaneous Consumption.



The fault in the measurement system can be recognised based on the

comparison between the sequences of predetermined codes and occur codes.

Therefore if any error in the sensory system or interface circuit happens, the

corresponding code and error message are presented in the front panel of Labview

program as shown in Fig. 8. The flow direction is illustrated via a Boolean

indicator in Labview so that it is switched on once the direction of flow is forward

and vice versa. The mean of flow rate is plotted within a period of one minute to

test the performance of system and it is computed every one hour. This curve

shows how the rate of consumption is changed and determines the maximum

demand of water every hour. The accumulated consumption shows he total water

consumption measured by the proposed system.

Fig. 8. The Mean of Flow Rate, Accumulated, Consumption,

Fault Recognition and Flow Direction Indicators.

5. Conclusion

The implemented algorithm was tested using Labview program and its operation

was verified to plot the flow speed, instantaneous consumption. The functionality

to diagnose the fault and direction has also been confirmed. As a result the

employed algorithm can accurately collect the necessary data utilising minimum

number of measurement equipment. Moreover, all data of the system are saved

into separate files in the database to be used for statistical analysis. The

implemented monitoring algorithm can be utilised by water distributor

organisations in order to monitoring and control the consumption based on water

demand and more importantly to conserve water resources.

Acknowledgment

The authors would like to thank to University Putra of Malaysia and Ministry of

Education, Malaysia for supporting this work under the Fundamental Research

Grant Scheme.



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SAES 2013_066_075