User’s Manual For The Large-Scale CO2

Cooling Plant at Building 158

A guide to operating the CO2 Cooling System at building 158

Prepared by:

Viren Bhanot PH-CMX CERN

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TABLE OF CONTENTS

4 General Overview 4 System Overview 5 User Access Modes 6 Points of Contact 6 Organization of the Manual 6 Definitions and Conventions 9 The Plant 14 User Interface 14 Component Symbols 15 Object/Alarm Information Symbols 15 Interlock Symbols 16 Panels 24 System Summary 24 Two Phase Accumulator Controlled

Loop 26 Start-Up Principle 27 System Control 27 Alarms and Interlocks 31 Safety Precautions 33 Getting Started 33 Requirements From The Client 33 Connecting The Experiment

34 Logging In 34 Pre Start-up Checks 36 Start-up Procedure 39 Stopping the System

40 System Operation 40 Running the Small Experiment Line 41 Running the System in Liquid Phase 41 Adjusting Mass Flow Rates 42 Acknowledging Alarms 46 Taking Measurements and Recording

Data 46 Viewing Parameter Trends Quickly

(Single/Dynamic DPE Trends) 48 Creating a New Plot 49 Configuring Plot Variables 51 Viewing a Created Plot 51 Configuring Created Plots 54 Exporting Data 55 Creating a Plot Page 55 Adding Existing Plots To Plot Page 57 Configuring Plot Variables In Plot Page 59 Troubleshooting 61 Appendix A

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GENERAL INFORMATION

System Overview The test setup at building 158 is a closed-loop two-phase cooling system using CO2 as the secondary

refrigerant and R404a as the primary refrigerant. It is based on the 2PACL (Two-Phase Accumulator

Controlled Loop) principle, which has successfully been used on the LHCb experiment and the Alpha

Magnetic Spectrometer (AMS-02). The system delivers stable operating conditions over a wide range

of evaporator temperatures, using CO2 as the evaporating fluid.

The purpose of this test bench is to give users access to a working, debugged cooling system for

testing their detectors and electronics. The users can connect their system to the test bench and

take measurements of the cooling performance. This enables them to gauge the feasibility of using

CO2 as the cooling fluid in their applications, and also allows them to figure out the proper operating

conditions at which optimum performance is obtained (e.g. evaporation temperature and pressure,

mass flow rate etc.).

Operating Range Pressure ratings of the system The system safety valves are rated to open up at 96 bars pressure. As per the CERN regulations, the

system has been tested and certified to withstand a pressure of 1.43 times the safety valve rating,

140 bars.

Temperature ratings of the system The system compressor is rated to a sub-cooling temperature lower limit of -35 degree C. Therefore,

the lowest accumulator set-point achievable is -30 degree C.

Mass Flow Rates The test bench consists of two lines:

Small Experiment: For testing low mass flow rate applications, with mass flow between 0.5 g/s

and 5 g/s.

Large Experiment: For testing higher mass flow rates, up to a maximum of 15 g/s.

System Architecture The system consists of 2 loops. The primary refrigerant is R404a and the secondary (evaporator)

refrigerant is CO2. The secondary circuit consists of 3 branches; the Small Experiment line (low mass

flow rates), the Large Experiment line (high mass flow rates) and the bypass line, which is used either

in the absence of any experiment, or in conjunction with the small experiment line. It uses a dummy

heater for putting enough heat-load on the chiller to keep it running.

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The system is controlled through a Siemens Programmable Logic Controller (PLC). The PLC uses a 24

VDC power supply. There is an independent 24 V supply to power the components and sensors,

thereby preventing simultaneous failure of the entire control system.

The SCADA (Supervisory Control and Data Acquisition) system is a PVSS-software based User

Interface. This User Interface conforms to the UNICOS (UNIfied Industrial Control System) standards

specified by CERN for control systems.

User Access Modes User access is on a rank-based system with lower ranks of users having more restricted freedom for

manipulating the system. This is done to ensure that newer users do not make harmful changes

inadvertently. There are four ranks defined:

Admin – Complete access to the system. Only for the developers of the test bench and control system

Expert – For users completely familiar with the system. User is able to acknowledge and reset full stop interlocks.

Operator – For newer users who only intend to use the system as a means to take measurements. User is allowed to acknowledge temporary alarms and make changes to components like heaters and valves.

Monitor – For completely unfamiliar users. In this mode, the user can keep track of the system, the alarms, and the recorded data, but is not allowed to manipulate the components like heaters, valves etc.

NOTE: Regardless of the level of expertise of the user, it is strongly recommended that the users

restrict themselves to the lowest rank with which their intended operations can be carried out.

Points of Contact In case the users require additional assistance for specific tasks, or if they would like to book the test

bench for future use, they are requested to use the following persons as points of contact:

S.No. Name Designation Contact Number Email Address

1. Bart Verlaat Chief Cooling Engineer +41-22-7673679 Bart.verlaat@cern.ch

2. Hans Postema Cooling Coordinator +41-22-7671549 Hans.postema@cern.ch

3. Lukasz Zwalisnki Control System Engineer +41-22-7673405 Lukasz.zwalinski@cern.ch

4. Joao Noite Cooling Engineer +41-22-7679095 Joao.noite@cern.ch

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Organization Of The Manual This manual is divided into seven broad sections:

GENERAL OVERVIEW This section gives a brief overview of the system, its intended usage and other information relevant to the system. SYSTEM SUMMARY This section describes the working principles of the system, the system configuration, the user interface and the various interlocks and alarms of the system. SAFETY PRECAUTIONS Describes the various precautions that must be observed when dealing with the high pressure system. GETTING STARTED Describes the procedures for connecting a system to the cooling plant, and for starting/stopping the system SYSTEM OPERATION Describes detailed and more specific operation of the system once it has been started. TAKING MEASUREMENTS Describes the method for measuring and recording data, exporting i t to files, manipulating it etc. TROUBLESHOOTING Describes the common errors encountered while running the plant and provides solutions for them.

Definitions and Conventions The user interface conforms to the internal UNICOS standards for CERN. As per those standards, the

following naming convention is used:

1. Full Convention: The full name of any object in PVSS is as per the following format EquipmentName_EquipmentLocation_ObjectName For example – QSMC_B158_EH1903 where QSMC stands for Cryogenic Station Main Cooling, B158 is the Building 158 and EH1903 is the small experiment pre-heater.

2. Object Names: The objects in the plant have the following convention:

TTxxxx – Temperature Transmitters PTxxxx – Pressure Transmitters EHxxxx – Heaters MEVxxxx – Manual Valves with Electrical Actuators HVxxxx – Vacuum Port Valves CVxxxx – Control Valves

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Terminology Some important definitions associated with the plant:

Object – Also referred to as component. Includes heaters, valves, condensers, heat exchangers and all other parts which are involved in making a cooling system run. In the case of

Interlock – Refers to any internal protection by the PVSS to prevent unwanted operation of system objects. An Interlock is alternatively referred to as an “Alarm”.

Run-Order – This is a user-input command to the PVSS telling it that the system start may be requested in the future. If run order is activated, the PVSS turns on the interlock checks and is ready to run the start-up procedure. When active, the transparent run-order box turns green:

Figure 1. Run order button (Not currently active). Current Option Mode is shown underneath.

Event – Refers to any action performed by the PVSS system, which may or may not have been caused by the operator. The action may be turning an object on/off, an alarm getting triggered etc.

Panel – Refers to any PVSS window. It is also called a Window or a Screen.

Acknowledge – Acknowledging an alarm refers to the user action which tells the PVSS that the user has been made aware of the alarm. In some cases, resetting the alarm may also be required to complete the acknowledgement.

Instrumentation List The list below describes the names of the different instruments and their description.

Sensor / Actuator Description

TT1101 Temperature transmitter – pump oil bath

TT1102 Temperature transmitter – damper

TT1103 Temperature transmitter – supply line, before internal heat exchanger (IHX)

TT1104 Temperature transmitter – supply line, after IHX

TT1105 Temperature transmitter – after EH1904

TT1106 Temperature transmitter – return line, before the IHX

TT1107 Temperature transmitter – return line, after the IHX

TT1108 Temperature transmitter – after small experiment branch

TT1109 Temperature transmitter – dummy load heater wall temperature

TT1110 Temperature transmitter – Pump Inlet (After Condenser)

TT1111 Temperature transmitter – on Accumulator heater

TT1903 Thermocouple on EH1903 (small experiment pre–heater)

TT1904 Thermocouple on EH1904 (dummy bypass load)

TTChiller01 Temperature transmitter – Chiller temperature before main HX

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TTChiller02 Temperature transmitter – Chiller temperature after EH1302

TTChiller03 Temperature transmitter – EH1903 surface temperature

TTChiller04 Temperature transmitter – Chiller temperature after fans

FT1101 Flow Transmitter – Mass Flow Meter

FT1101_TT Flow Transmitter –temperature measurement (of fluid)

FT1101_Dens Flow Transmitter – density measurement

PT1101 Pressure transmitter – pump

PT1102 Pressure transmitter – before branch split (into small, large and bypass)

PT1103 Pressure transmitter – the 2–phase accumulator

PT1104 Pressure transmitter – before pump

PT1105 Pressure transmitter – pump manifold

PT1106 Pressure transmitter – return line before the IHX

EH1101 Pump's Oil Bath electrical heater

EH1102 Damper’s electrical heater

EH1104 Accumulator’s electrical heater

EH1301 Chiller compressor oil electrical heater

EH1302 Chiller dummy load heater

EH1903 Electrical heater on the small experiment branch, pre-heater

EH1904 Electrical heater on the by-pass, dummy load heater

MEV2101 Manual valve with Electrical Actuator on by pass

MEV1101 Manual valve with Electrical Actuator on supply line

MEV1102 Manual valve with Electrical Actuator after return line

MEV1103 Manual valve with Electrical Actuator at the 2–phase accumulator

MEV2101 Manual valve with Electrical Actuator on

MEV2102 Manual valve with Electrical Actuator on

MEV2103 Manual valve with Electrical Actuator on

CV1105 Control valve with Electrical Actuator – on accumulator cooling supply line

Pump Membrane pump

Chiller Compressor for Primary R404a Circuit

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THE PLANT

This section describes the general layout of the plant, and indicates the major components within it.

Figure 2. CO2 Cooling Plant at Building 158. The large red box is the accumulator.

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The chiller circuit is shown below:

Figure 3. Chiller Circuit with components indicated

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The CO2 circuit is shown in the pictures below:

Figure 4. CO2 Circuit with the pump visible.

Figure 5. Condenser

Condenser (Heat Exchanger between R404a and CO2) Internal Heat Exchanger

Small Experiment Mass

Flow Meter

Figure 6. Top View of CO2 Circuit

NV2102 with Actuator

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Figure 7 shows the valves mounted on the panel. These valves are either for allowing shut-off of

different lines (MEVxxxx), or to control the vacuum ports (HVxxxx).

Figure 7. Valves mounted on the panel

Figure 8. Experiment connection ports.

MEV2103

MEV2104

Vacuum Port

HV1107

(Vacuum Port)

MEV1102

Large Experiment

Connection.

Small Experiment

Connection (with

Expansion Valve

knob visible)

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Figure 9 shows the control rack with the PLC, the power supplies, conditioners etc. mounted on it.

Figure 10 shows the Conditioners and the Schrack Contactors and Figure 11 shows the PLC on the

electrical rack.

Figure 10. Contactors (blue) and Conditioners (green). Figure 11. Siemens PLC.

Figure 9. Control Rack – front on the left and the rear on the right.

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USER INTERFACE

This section describes the PVSS User Interface used by the cooling system for control and data

acquisition.

The system utilizes a Siemens Programmable Logic Controller (PLC) for controlling its components.

To allow the user to record data, and also to control the system, it uses a SCADA (Supervisory

Control And Data Acquisition) tool called PVSS (Prozessvisualisierungs und Steuerungs System:

Process Visualization and Control System).

Component Symbols The PVSS uses UNICOS-specific symbols for different components. They are listed below:

Symbol Component Comments

Heater

Colour Coding: Red : Interlock triggered Green, empty : Off or <10% Power Green, half : 10% < Power < 90% Green, full : >90% Power

Electrically Controlled Valve

Red : Interlock triggered Green, empty : <10% Open, or off Green, half : 10% < Open < 90% Green, full : >90% Open

Manual Valve

Pump Red : Interlock triggered Green, half : Off Green, full : On

Compressor

Red : Interlock triggered Green, half : Off Green, full : On

Heat Exchanger

Vessel

Liquid Separator in Chiller circuit, and Accumulator in CO2 circuit

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Object/ Alarm Information Symbols Interlocks and Objects in PVSS are sometimes displayed with a small alphabetic character alongside

their symbol. This letter represents some unusual condition associated with the Interlock/Object.

These symbols are listed below:

Symbol Description Symbol Description

Object in Auto Mode

Warning

Object in Manual Mode

Value below Lower Limit

(“U” for Upper Limit)

Object in Forced Mode Object under PVSS

Regulation

Interlock Masked by operator

Object stopped because of

Stop Interlock

Alarm Blocked by operator

Error (I/O error)

Interlock Symbols In the Alarms panel, a circle represents interlocks (so, for example, a circle might represent an alarm

caused by excess pressure), whereas a square symbol represents either a condition or the reset

button. Here, “condition” means any check which the PVSS performs to check whether the

corresponding alarm should be triggered or not.

Symbol Description Symbol Description

Status OK

(“Reset” Column)

Reset button (Stays green regardless

of alarm condition)

Blinking

Alarm triggered but

unacknowledged. Cause of alarm no

longer active.

(“Cause” column)

Status of interlock condition is true

Steady

Alarm triggered and acknowledged

but cause of alarm still active

(“Cause” column)

Status of interlock condition is false

Blinking

Alarm triggered, but not

acknowledged, and cause of alarm

still active.

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Panels The User Interface uses different “Panels” which are different screens showing different aspects of

the interface.

To open a new PVSS panel: Start-up Windows and log in to the computer (For log-in password, contact an expert). Once

Windows is running, double click on the “CO2_hmi.bat” icon on the desktop. This opens up a new

PVSS Plant panel. The panels associated with the CO2 plant are described below:

Plant Panel This is by default the first screen of the user interface showing a schematic of the plant. It allows the

user to start-up and stop the plant, control the various parameters and monitor (in real time) the

status of the various components and sensors.

The plant panel is shown below along with the various parts that make up the panel:

Figure 12. Plant Screen PVSS Panel overview.

1. UNICOS Menu

2. PCO Alarms Display

3. Alarms Row

4. Quick Access Toolbar

5. Menu Bar

6. Log-in box

7. CO2 Circuit

8. Enthalpy Calculation box

9. Previous Actions Message box

10. Panel buttons

11. Chiller Circuit

12. Accumulator Parameters

13. Start/Stop box with Run-Order Button

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1 2

3 4 5 6

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8

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To open up the Plant panel, simply click the home button from the Menu bar in any panel:

A short description of these parts is given below:

UNICOS Menu

This menu allows user to Configure and Manage the PVSS Interface. It is only rarely used by the user,

and hence its full description is omitted here.

PCO Alarms Display

This displays the status of PCO Alarms.

Alarms Row

Figure 13. Alarms Row

The Alarms Row bar displays the status of the system with respect to alarms. A green box indicates

that the system is in a “healthy” state, with no interlocks currently triggered, while a red box

indicates an unhealthy system. The box also displays if the cause is an interlock (indicated by “Bad”)

or limits of parameters exceeding (indicated by an “L” or “H”; see Figure 13).

To cycle through previous alarms, the user can scroll pages with the page-up/down buttons:

The row can be minimised by selecting the double arrows:

Quick Access Toolbar

Figure 14. Quick Access Toolbar

It includes the following buttons (From Left to Right):

Window Tree: Shows all currently opened windows

Trend Tree: Opens the Trend Tree window for managing plots Alarms List: Displays the list of previously triggered alarms (see page 21)

Events List: Displays the history of events occurred in the PVSS

Device Tree Overview: Opens the Device Tree panel Front End Diagnostics: Opens the Front End Diagnostics panel (This panel is not important

for a lower level user, and is not discussed in the manual)

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Menu Bar

Shows the common menu buttons

Log-in box

Displays the user access level currently active, the time and the date. The “Key” symbol allows

logging in. The System Status box shows the current system status (green being “healthy” and red

being “unhealthy”)

CO2 Circuit

Schematic of the CO2 circuit is shown.

Enthalpy Calculation box

Shows the parameters which are involved in calculating the inlet enthalpy to the experiments.

Figure 15. Enthalpy Calculation Box

The “Enthalpy Request” is the inlet enthalpy to the small experiment.

The Enthalpy Is calculated at the inlet of the internal heat exchanger (IHX). This is the enthalpy at

Point 2 in the p-h diagram (Figure 22, page 25). The green box, when filled, displays that inlet

enthalpy can be calculated because CO2 is in liquid phase at the inlet to the IHX.

Previous-Action Message box

Shows the two previous messages (which could be events or alarms). Users can scroll with the arrow

buttons to view older/newer messages.

Panel Buttons

Shows the buttons associated with the current panel. If an object is selected, it shows the buttons

associated with the object.

Chiller Circuit

Schematic of R404a circuit is shown.

Accumulator Parameters

Shows the parameters involved in control of the accumulator.

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Start/Stop box with Run-Order Button

Shows the run-order button, the option mode currently selected and whether the system is in auto

mode or manual mode. It allows the user to Start and Stop the system and navigate to the

sequencer panel.

Sequencer

The theoretical start-up procedure (described on page 26) is implemented by the PVSS using a

sequencer. The whole operation has been divided into four operating stages internally by the

Control System.

The Sequencer screen allows the user to view the steps associated with the start-up of the system. It

is opened by clicking the “s” button near the start button. It is shown below:

Figure 16. Stepper/Sequencer

The four steps (marked 0, 1, 2 and 3 within PVSS) are:

1. Safety Position 2. Start-Up 3. Cool Down Loop 4. Cool Down Accumulator

A more detailed description of the process is given on page 26.

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Alarms Screen The Alarms screen shows the status of all the alarms and interlocks of the system. The user can find

out which alarm was triggered and can acknowledge and (if required) reset the alarm buttons.

To learn how to acknowledge alarms, go to the “Acknowledging Alarms” section (page 42).

Figure 17. Alarms Panel

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Alarms List The Alarms List panel allows users to view the history of previously triggered alarms.

Figure 18. Alarms List Panel

The user can view all alarms which are active, and also whether they have been acknowledged or

not. If an alarm is blinking, this indicates that it has not been acknowledged yet, whereas a steady

red display shows an acknowledged but active alarm.

The panel displays the number of triggered alarms, the number of unacknowledged alarms, and

allows the user to acknowledge them. If multiple pages of alarms are present, the user can

acknowledge them page-by-page.

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Pressure Enthalpy Diagram This screen allows the user to see a constantly-updated p-h diagram of the CO2 cycle. Having this

screen open in a separate window makes for easy visualization of the performance of the system. A

snapshot of the screen is shown below:

Figure 19. Pressure Enthalpy diagram of CO2 showing the system status

The enthalpies at various points are calculated by interpolating from the NIST refprop tables. These

tables give different properties of the fluid at a large number of set-points. The PVSS measures the

pressure and temperature of a point and determines the enthalpy by looking them up from the table

(or interpolating if exact point is not in table) . However, in the two-phase region, pressure and

temperature are not enough to determine enthalpy. The system instead shows all points in the two

phase region on the saturated vapour line (vapour quality = 1). This does not mean that all CO2 has

been evaporated, but is simply PVSS’s way of representing two-phase fluid. The points on the p-h

diagram are listed below:

1. Point 1 - Outlet of experiment lines 2. Point 2 - Outlet of return line of internal heat exchanger 3. Point 3 - Pump inlet 4. Point 4 - Pump outlet 5. Point 5 - Outlet of supply line of internal heat exchanger

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Diagnostic Panel This panel gives a more detailed description of the status of different objects. It also allows users to

reset the Full Stop Interlocks, if they are triggered. It is opened from the “Diagnostic” button from

the Plant panel. Figure 20 shows the Diagnostic panel, with the reset button highlighted.

Figure 20. Diagnostic Panel. Red circle shows Reset button

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SYSTEM SUMMARY

Two-Phase Accumulator Controlled Loop (2PACL) The test bench at building 158 is a closed-loop, two-phase cooling system using CO2 as the secondary

refrigerant and R404a as the primary refrigerant. It works on the principle of 2PACL (Two Phase

Accumulator Controlled Loop), which has also been used on the AMS-02 on the International Space

Station and the LHCb experiment at CERN.

This system has proven to be very successful in solving the problem of detector cooling. It minimises

the number of control parameters in the system to just three; the pump mass flow rate, the

pressure drop across the needle valve and the accumulator temperature. Additionally, it requires

the changing of only one parameter (Accumulator set point) to completely control the detector

temperature. Aside from the simplicity of usage, it has also shown good results in terms of the

temperature variation over the detector.

Figure 21 shows the schematic of the CO2 test bench with major components highlighted. The red

circles mark the expansion valves.

Figure 21. Schematic of the CO2 test-bench

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The detector is connected either on the large experiment line or the small experiment line. It is

cooled by the constant-pressure evaporation of CO2. First, the CO2 is condensed and sub-cooled to

below the saturation temperature inside the condenser (heat exchanger) by the R404a chiller. The

pressure at the evaporator and the condenser is the same since the return lines are designed to

minimise pressure drop. The membrane pump pumps this sub-cooled CO2 towards the detector. The

internal heat exchanger heats up the incoming CO2 to bring it to the saturation temperature

corresponding to the accumulator pressure. The expansion valve then reduces the pressure of the

CO2 to the accumulator pressure, giving saturated liquid at the detector inlet (in practice, the fluid

might have evaporated a little already). The CO2 then evaporates, taking up the detectors heat as

latent heat of vaporization, at the accumulator temperature. In this way, setting the accumulator

pressure enables the user to control the evaporation temperature. For a more detailed explanation,

consult the “Two Phase Accumulator Controlled Loop” (Verlaat, 2007) publication.

Figure 22 shows the p-h diagram representation of the system, with a description of the processes in

the following table:

Path Description Path Description

1-2 Pump 4-5 Evaporator

2-3 Internal Heat Exchanger (In) 5-6 Internal Heat Exchanger (Out)

3-4 Expansion Valve 6-1 Condenser

Figure 22. p-h diagram of CO2 showing the system cycle.

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In figure 22 above, a properly working experiment will have point 4 on or slightly after the saturated

liquid line.

Start-Up Principle

While the system is at rest, environmental heat leak makes the temperature of the CO 2 equal to the

room temperature (which we assume for this discussion is 20°C). The system is in two-phase, but we cannot determine the vapour quality. In the p-h diagram (Figure 22), this is somewhere along the

20°C isotherm (condition “A” in figure 22).

At start up, the accumulator is set at its highest set point of 27°C (saturation pressure 67 bars). The

temperature of the CO2 is still 20°C and hence the loop becomes filled with liquid. Upon liquefaction

of the system fluid, the pump can be switched on. Sub-cooled liquid of 20°C is now flowing through the system. This is represented by condition “B”. Since there is no heat addition, the chiller is not yet required.

Figure 23. Start Up Procedure

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Once the liquid circulation is achieved, the chiller is switched on. The chiller always sub-cools the CO2 to the minimum temperature achievable in the chiller. This temperature is much lower than room temperature, and hence heat circulation is achieved. Heat is added into the system through the environmental leak, and removed by the chiller. The system is now at condition “C”. Finally, the cooling down of the accumulator to the desired set point can be initiated. The accumulator temperature (and thereby, the pressure) decreases till it reaches the user set -point. Before starting the accumulator cool-down, the mass flow rate can be adjusted through the needle (expansion) valve. After reaching the desired set point of evaporation temperature and mass flow rate, the fluid flowing through the unloaded evaporator is in two-phase region. Therefore, we can control the evaporation temperature by controlling the accumulator set point. This is condition “D”. We can now load the experiment. The evaporation of CO2 begins and we are now in stable operating conditions.

System Control The PVSS has a Master PCO (Process Control Object) which is the highest level of control in the

system hierarchy. It has three modes, called Option Modes, which determine the overall system

operation status. These modes establish the state in which the system is at, depending on which

certain things can or cannot be accomplished. The states are:

Stop Mode: All objects are in off (safety) position. The user cannot run the

system in this mode. Manual manipulation is possible, but not

advised. If an object is put in manual mode in this level, pushing

the stop button DOES NOT return it to auto mode.

Standby Mode: The sequencer can be turned on to start-up the system, and stable

flow can be achieved. The user can also manually manipulate

individual components in this mode.

Run Mode: The accumulator cool-down is initiated in this mode, at the end of

which, the system attains the required evaporation temperature

set-point. The experiment can be tested with desired inlet

conditions (mass flow etc.)

Alarms and Interlocks The cooling plant is protected from hazards by several levels of protective interlocks and alarms.

PCO Alarms At the highest levels of protection are the PCO alarms. They are divided into three categories

Start Interlocks (SI1) This is triggered in case no “Option Mode” (Stop/Standby/Run) is selected. When Start Interlock is triggered, the system cannot be turned on.

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Temporary Stop Interlock (TS1) This is triggered when the Status of the 24V power supply of the Actuator+Commands Power Supply is not “OK”. When triggered, it sends an “Off” request to the object. This interlock is automatically reset once the error has been removed, and does not require Operator intervention (unless the system is in Manual or Forced mode). In other words, if the Run-Order had been given prior to interlock, it is reactivated upon removal of the interlock.

Full Stop Interlock If these interlocks are triggered, they send an off request to the object, and must be reset by the operator before allowing system operation

o FS1 - triggered if the Emergency Stop button is pressed, or after releasing the Emergency Stop button, the Reset button is NOT Reset (see alarm acknowledgement section for more details: Page 42)

o FS2 – triggered if the pressure in the system goes above 95 bars on any sensor. This might indicate a failure of the safety valves, and hence is essential

o FS3 – triggered if the pump’s Thermal Switch is triggered. This indicates an overheating in the pump.

PLC Alarms These alarms are intended to ensure that if any object goes out of the operating range, any

hazardous situations are avoided. They are categorised on the following page according to the object

associated with them:

Membrane Pump

Pump ST1 – Oil bath temperature (TT 1101) goes below its threshold value of 10 degree

Celsius.

Pump ST2* – Pressure between pump membranes (PT1101) exceeds 6.0 bars Pump ST3 – No liquid phase before the pump inlet (i.e. TT1110 < Tsat1104 – 2 deg C) Pump ST4 – Circuit breaker status = ‘False’ Pump ST5 – Pressure at PT1105 greater than 95 bars Pump ST6 – Pump on for more than 1 minute, but flow (FT1101) less than 0.25 g/s Chiller Circuit Chiller ST1 – TT1110 < -50 deg C; There is a risk of freezing the CO2. Resets itself when TT1110 > -50 deg C + 1 Chiller ST2 – ‘Pressure Switch Low’ or ‘Pressure Switch High’ is activated (=1) Chiller ST3 – Compressor Circuit Breaker status = ‘False’

OR Radiator Fan Circuit Breaker status = ‘False’

Accumulator Control Valve CV1105ST1 – Pressure in Accumulator (PT1103) < 6 bar, or the pressure sensor has I/O error Oil Pump Heater EH1101ST1 – Circuit Breaker status= ‘False’

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EH1101ST2 – TT1101 > 40 deg C EH1101ST3* – Thermal Switch TS1101 = ‘OFF’,

OR Any Heater PT100 sensor or Thermal Controller > threshold (EH1103 threshold = 50 deg C)

Damper Heater EH1102_ST1 – Circuit breaker status = ‘False’ EH1102_ST2 – TT1102 > 120 deg C EH1102_ST3 – Thermal Switch TS1102 = ‘OFF’ OR Any Heater > threshold (EH1102 threshold = 160 deg C) EH1102_ST4 – Flow Rate FT1101 < 0.25 g/s Accumulator Heater EH1104_ST1 – Circuit Breaker = ‘False’ EH1104_ST2 – TT1111 > 120 deg C EH1104_ST3 – Thermal Switch TS1104 = ‘OFF’ OR Any Heater > threshold (EH1104 threshold = 160 deg C) EH1104_ST4* – PT1103 > 68 bar Chiller Oil Heater EH1301_ST1 – Circuit Breaker = ‘False’ EH1301_ST2 – Chiller is OFF Small Experiment Pre-Heater EH1903_ST1 – Circuit Breaker = ‘False’ EH1903_ST2 – TT1903 > 80 deg C EH1903_ST3* – Thermal Switch TS1903 = ‘OFF’ OR Any Heater > threshold (EH1104 threshold = 120 deg C) EH1903_ST4 – FT1101 < 0.25 g/s By-Pass Heater EH1904_ST1 – Circuit Breaker = ‘False’ EH1904_ST2 – TT1904 > 80 deg C EH1904_ST3* – Thermal Switch TS1904 = ‘OFF’ OR Any Heater > threshold (EH1904 threshold = 120 deg C) EH1904_ST4 – FT1101 > 0.25 g/s

Note: Heater Protection The heaters have a strong heating capacity, and can damage the system and destroy themselves. For this reason, all heaters in the system have a “thermal box” as hardware protection (independent of conditioner, PVSS or PLC status). The thermal box uses its own Thermal Switch for temperature control. Additionally, the heaters are connected to “conditioners” which can (independent of the PVSS) switch off the

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heaters if temperature exceeds a programmed threshold (through the PLC). Finally, they also have two software stop interlocks, one when the temperature of the heater exceeds threshold and the other when the Circuit Breaker for ANY heater is tripped.

* Interlocks marked with the asterisk require manual resetting of the Reset button before they

can be removed. The reset button is shown below:

Figure 24. Reset Button The red circle marks the Reset button. To Reset the switch:

1. Double click the Reset Button 2. Select “Manual Mode” in the panel that appears 3. Select “Off” to turn off the switch 4. Restart the switch by clicking “On” 5. Select “Auto mode” to put the switch on PVSS Regulation again 6. Deselect the “Reset” panel

Note: The fill button in the “Cause” dialog box (“Status of TS1101” in Fig.7. is NOT a reset button. It represents the status of the condition represented alongside it. Note 2: For a more detailed explanation on dealing with triggered alarms and interlocks, go to the “Acknowledging Alarms” section in the SYSTEM OPERATION chapter on page 42.

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SAFETY PRECAUTIONS

This section gives safety advice and precautions to be observed.

Emergency Stopping To stop the system in case of an emergency, the first step should be to press the “Stop” but ton on

the plant panel (Figure 25). If that does not work, the user should push the Emergency Stop button

on the control rack (Figure 26) to cut the power to the components. This button is on the control

rack next to the accumulator, and with the “Arret D’Urgence” symbol below it.

Figure 25. Stop button at top-left of panel.

Figure 26. Emergency Stop button highlighted in blue circle.

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Once the emergency stop button has been pushed, the system cannot be restarted without resetting

it. To reset the system, contact an expert.

System Operation While operating the system, keep in mind the following points:

Always isolate the experiment line before connecting an experiment to it. The “Connecting The Experiment” section (page 33) describes which valves to close before connecting experiments.

Ball valves are destroyed almost immediately if they are not completely closed but left open partially. This must be avoided. Close valves all the way until you hit the stop.

Needle valves are NOT intended to act as closing valves (NV2102 and NV2104). Do NOT turn them forcefully all the way in.

Valves installed in the system are open if the handle points in a direction parallel to the direction of fluid flow. If the handles are perpendicular to the direction of flow, this indicates a closed valve.

Always put heaters in auto mode, and check that they are off, before closing the system.

Always log off, and lock the computer, before leaving the lab.

33

GETTING STARTED

Requirements From The Client The experiment to be tested must conform to some basic requirements to ensure that it can be

safely and properly connected to the plant, and useful measurements can be taken:

Please inform the CO2 cooling team well in advance to book the plant, and ensure that there are no delays.

The test-bench has been tested against destruction to a system pressure of 140 bars. The safety valves of the plant are rated at 96 bars, which is the operating limit. The client’s experiment should either conform to this rating, or, in case of a lower rated pressure, should include its own safety valve. In case of confusion, please get in touch with the CO2 cooling team for clarification.

Connection to the small experiment requires two ¼” Swagelok VCR Fittings. Connection to the large experiment requires two ½” Swagelok VCR Fittings.

To connect to the large experiment, please provide an expansion valve on your own setup.

The heaters in the experiments should include their own stop interlocks, which should cut -off heater power at a maximum temperature of 150 deg C.

The clients are required to bring their own SCADA (Supervisory Control and Data Acquisition) system for their experimental setup.

The client should note that the CO2 test bench does NOT have pressure and temperature sensors AFTER the expansion valve. As a result, you are advised to make arrangements for your own sensors (pressure and temperature) to record inlet conditions.

Connecting The Experiment To connect your system to the experiment, the following procedure is to be followed:

Before connecting the experiment to the plant, please make sure that it is purged by a cycle of [vacuum -> pressurizing with CO2 to more than 6 bars -> vacuum] 3 times. This is to prevent contamination of the plant. If you are unaware of how to use a vacuum pump, or don’t have one, please contact an expert to help you out.

The large experiment and small experiment connections are shown in the Figure 8 (page 12). Determine which experiment you should connect to. (See Operating Range section, page 3)

Isolate the experiment by closing the inlet and outlet valves to the experiment. o For the small experiment: Valves MEV2104 and HV1107 o For the large experiment: Valves MEV2103 and HV1107

These valves can be identified with the labels on the mounting panel. (See Figure 7 on page 12)

Connect the system to the VCR Fittings.

34

Please use the “Swagelok VCR Fitting Installation Instructions” manual found on the Swagelok website to learn how to attach VCR fittings.

Open and quickly close one of the two valves connecting the experiment; to let a small amount of CO2 into the experiment. Then, on your pressure sensor, check for at least ten minutes to ensure that there is no leak from the system. The pressure reading should remain constant.

If you do not have a pressure sensor to check system pressure, please contact the experts to provide you with a “sniffer” to check the fittings for leaks. They will tell you how to use the sniffer.

Logging In Depending on the user’s familiarity and requirements from the system, he/she may be allowed

access to one of the four Access Levels described earlier. The user will be given a password for the

appropriate access level.

To log in, simply click on the log-in icon shown below. In the window that opens, type in the

username and password and click “OK”.

Figure 27. Log-In Icon

Note: To log-off from the system, simply right click on the text-box that displays the username and

click “Log Off”. Make sure that you log off before leaving the system unattended.

Pre Start-up Checks Before starting the system, the user is required to examine several valves and ensure that they are in

an open position.

The valves which are mounted on the stainless-steel panel have markings which point the direction

of on/off. For the valves which are not mounted on the panel, the following test is an effect ive way

of determining if it is open or closed. If the black-coloured handle of the valve is aligned (parallel)

with the direction of the piping attached to the valve, the valve is open. If it is perpendicular to the

piping direction, the valve is closed.

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The following valves must be examined:

HV1105 and HV1102 They are used to isolate the pump section while vacuuming the plant.

MEV1103 This controls the accumulator line. It is shown below (Figure 28)

Figure 28. Accumulator Valve

If the small experiment is connected, the flow through bypass line and small experiment line should be open. Therefore:

o MEV2102 - Open (Bypass) o MEV2104 - Open (Small Experiment) o MEV2103 - Closed (Large Experiment)

If the large experiment is connected, the flow through the bypass and small experiment should be closed. Therefore:

o MEV2103 - Open o MEV2102 - Closed o MEV2104 - Closed

Pressure sensor PT1102 should be read to ensure that pressure is within safe limits (generally,

pressure should be lower than 75 bar on PT1102).

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These valves are shown in Figure 29 below:

Figure 29 (a) MEV2104 (Top) and MEV2103 (Bottom)

Start-Up Procedure

To start-up the system, use the following method:

1. Log in. 2. Acknowledge all pending alarms. You can do this through the “Alarms List” panel by clicking”

“Ack. Visible” (see “Acknowledging Multiple Alarms, page 44) 3. Set the Accumulator Set-Point. To do this, double-click on the User Set Point Value (Figure 30) on

the main Plant screen. You will get the accumulator set-point panel. On the panel, click on “Set Value”. A window opens which allows you to enter the desired evaporation temperature. Enter the value and click “OK”.

Figure 29 (b) MEV2102 (Bypass)

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Figure 30. Accumulator Set-Point

4. Change the system Option Mode to “Stand-By”. To do this, double click on the Run-Order button. From the panel that opens up, click on the “Option Modes” button. Select “Stand -By” from the window that opens up (Figure 31).

5. Click the “Start” button on the Plant panel. The system should begin heating up the accumulator and the chiller should be turned on. You will also see the run-order being given. This is displayed as the Run-Order box turning green.

6. The accumulator continuously calculates an automatic set-point*. This set point is always 6 (six) degrees above to the pump inlet temperature (TT1110 + 6 degree C), which is considered a safe value to ensure that pump only receives sub-cooled liquid at inlet, and there is no cavitation.

7. The accumulator now heats up (at full heater power) to reach the automatic set-point. At the same time, the chiller is running and cooling the fluid at pump inlet (TT1110).

8. The PVSS checks if the temperature at the pump inlet (TT1110) is two degrees below the saturation temperature (“TTsat1104 calc.”) corresponding to pump inlet pressure (PT1104). This is done to ensure no vapour is seen by the pump during operation. When this condition has been achieved stably for at least 30 seconds, the pump is switched on. Standby mode operations are now completed, and the system is stable in standby mode

9. The system will now continue at the automatically calculated set point. To move the system to the user set point, the system must be put in the “run” mode. To get the system from the stand-by mode to the run mode, double click on the run-order object (Figure 31). From the window that opens up, click on the “Option Modes” button. A pop-up window showing all the modes available will open. From the window, select “run” mode. Doing so transitions the system from stand-by to run mode, which means the system can now be used for testing experiments.

10. The Accumulator cool-down should begin once the system is in “run” mode. This is indicated on the PVSS panel as an opening up of the Control Valve CV1105. The Accumulator will now reach the set point indicated by the user. This process is slow due to the large size of accumulator so kindly be patient.

11. The Accumulator cool-down should begin once the system is in “run” mode. This is indicated on the PVSS panel as an opening up of the Control Valve CV1105. The Accumulator will now reach the set point indicated by the user. This process is slow due to the large size of accumulator so kindly be patient.

* The accumulator set point calculations are active only once the system has been started. If the

system is on off position, the user might see random auto set-point values.

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Figure 31. Run-Order button and the Run-Order window showing Option Modes.

The following table lists the status of different components during the various stages of start-up.

Component Stop Standby Run

Status ->

Safety

Position

All

components

off

Accumulator Heating

Accumulator heated

to automatically

calculated

accumulator set

point, while system

checks if TT1110 <=

Tsat1104 calc – 2 C

Pump Start

when TT1110 <=Tsat1104

calc. – 2.0 degree C

For at least 30 seconds

Accumulator

Cool Down

Accumulator

cooled down

to user set

point

Chiller Off On On On

Pump Off Off On (after 30 seconds) On

CV1105

(Accumulator

Cooling

Valve)

Off Off

PVSS Regulation

Intermittently turned on/off

to regulate temperature at

Automatic Set-Point

On until set

point

achieved, then

on PVSS

regulation

EH1104

(Accumulator

Heater)

Off On (Full Power)

PVSS Regulation

Intermittently turned on/off

to regulate temperature at

Automatic Set-Point

Off

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Stopping The System Before stopping the system, please ensure that all objects (especially heaters) that you have put in

manual or forced mode are put back in auto-mode for PVSS regulation.

To stop the system, simply click on the “Stop” button on the Plant PVSS panel. You should note the

following:

The compressor and the pump stop. All control valves are set to zero position.

All heaters are turned off and put on Auto Regulation mode (You will see an “A” next to them).

The run-order (filled green box) should become transparent. This means that the run-order is no longer active

Now, put the system on “Stop” Option Mode, using the Run-Order box.

Note: When the system is stopped, due to the logic of the programming, the chiller heater alarm

EH1301_ST2 is always triggered. This is not an indication that something has gone wrong with the

system while stopping. The alarm can be acknowledged from the Alarms panel.

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SYSTEM OPERATION

This section discusses how to operate the system once it has been started-up. Running the small

experiment, adjusting mass flow rates, acknowledging alarms and so on, are discussed

Running the small experiment If the system is connected to the small experiment, all the flow cannot pass through the small

experiment line, since it has been designed for lower mass flow rates. However, the pump is

pumping at a constant, much larger mass flow. Therefore, the remaining liquid is made to pass

through the bypass line. The bypass line has a 2 kW dummy heater to provide heat-load to the

chiller.

The bypass line also has an actuator mounted on the expansion valve NV2102. This ensures that the

pressure before the expansion valve is always high enough to ensure purely liquid phase before

the expansion. This is necessary to ensure accurate readings from the mass flow meters.

While running the small experiment, always ensure that the bypass line sees load through the

heater. If the heater power is too low, the compressor does not see enough load and starts

switching on and off because of excess sub-cooling (CO2 temperature threatens to go below freezing

point of -56 deg C). On the other hand, if the heating is too high, the heater temperature shoots up

regularly, activating the heater interlocks. The user should look for a heating power through which

both these conditions are avoided. This is explained in the next section:

Selecting the bypass heater power The bypass heater power is calculated as follows:

1. Calculate the mass flow through the bypass. This is the difference between the flow generated by the pump and the flow through the small experiment (both read through their respective flow meters). For this example, let us assume that the pump mass flow is 9 g/s and that through the small experiment is 3 g/s. Therefore, the mass flow rate through the bypass is 6 g/s.

2. Note the evaporation temperature (which is the accumulator saturation temperature “Accu_Tsat”). We assume an evaporation temperature of -20 degree C.

3. We take a 50% evaporation of CO2 as an adequate value (Vapour quality = 0.5). Higher vapour qualities risk dry-out.

4. The inlet to the bypass heater is assumed to be saturated liquid. This is true if the internal heat exchanger has been designed properly, which in this case, it has. Thus we have a 0.0 inlet vapour quality.

5. Calculate the enthalpy difference between 0.0 and 0.5 vapour qualities. This can be read from the x-axis of the pressure enthalpy diagram of CO2 at the evaporation temperature desired by the user. For -20 degree C, this value is 141.22 kJ/kg

6. Now, use the following relation to calculate the heater power required: Heater Power (kJ/s or kW) = Enthalpy Difference (kJ/kg) x Mass Flow Rate (kg/s) Here, the mass flow rate is the rate through the bypass valve. For our example, we get Power as the product (141.22 x 6 x 10-3) = 0.85 kJ/s = 0.85 kW Thus, a power of about 800 to 900 watts should be sufficient for this case.

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Important Note: The dummy heater has an internal control program which calculates heater

output power based on the power requested by the user. This output power may not exactly

match the user’s requested power, but might vary by up to 0.1 Watt

Adjusting Mass Flow Rates The membrane pump from Lewa has a knob similar to a micrometre to regulate the mass flow. By

turning it, the stroke length of the piston can be altered, and thereby the mass flow rate. However,

to adjust mass flow rates of the system, the user is advised not to change the pump settings. This is

because the pump, due to its operating mechanism, adds some enthalpy into the fluid. At low

mass flow rates, this enthalpy is enough to cause evaporation of the CO2 at the pump outlet itself.

Thus, a minimum mass flow rate of 5 g/s should be maintained through the pump. Instead of

altering the pump settings, the experiment’s needle valve should be controlled to adjust mass flow

rate.

For the small experiment:

Adjust the valve NV2104 to achieve the required mass flow rate.

Ensure that the pressure at PT1102 is high enough. The pressure should be higher than the

saturation pressure of CO2 at temperature TT1104. If this condition is true, it ensures that

you have pure liquid before the expansion valves, and allows accurate readings from the

mass flow meter.

For the large experiment:

Adjust the expansion valves on your experiment to achieve the required mass flow rate.

Getting Required Vapour Quality at experiment outlet At a specified evaporation temperature, it is possible to adjust the mass flow rate in such a manner

that you get a specific vapour quality at the outlet of your experiment. To accomplish this , follow the

following steps:

1. Calculate the enthalpy difference, between saturated liquid and required vapour quality, at the evaporation temperature. This is calculated by reading the x -axis reading in the p-h diagram between the saturated liquid line and the required vapour quality line.

2. Use the following relation to get the mass flow rate: Mass Flow Rate (kg/s) = Cooling load (kW) / Enthalpy Difference (kJ/kg)

Acknowledging Alarms Alarms are triggered if the PVSS notes that some aspect of the system is not working properly, or is

dangerous. Some alarms, once triggered, do not allow the user to run the component they are

associated with, until they are acknowledged. These are the alarms which are considered important

enough to be brought to the operator’s attention, before restarting the component.

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Once an alarm is triggered, it will be displayed with an “s” symbol next to it to indicate a Stop

Interlock.

The following symbols are associated with alarms:

Blinking Steady Blinking

Cause of alarm no longer

active, but alarm not

acknowledged.

Alarm triggered and

acknowledged, but cause still

active

Alarm triggered, not

acknowledged, and cause still

active

Alarms not requiring resetting These are the PLC alarms that do not have a Reset button next to them in the Reset column in the

Alarms panel. To acknowledge such alarms, following method should be used:

1. If the cause of the alarm is still active, determine the cause (you may use the Troubleshooting section), and determine what must be done to eliminate the cause of the alarm.

2. Once the cause of the alarm has been eliminated, simply right click on the alarm ’s symbol and select “Ack. (Acknowledge) Alarm”.

3. On the Plant panel, right click on the object’s symbol and again click “Ack. Alarm”.

Alarms requiring resetting The PLC alarms which require resetting are the following:

Stop Interlock 3 (ST3) of all heaters: These are triggered when the Thermal Switch of the heater is

not working, or if the threshold temperature of any heater is exceeded. If any heater triggers its ST3

all heaters will be shut down, and their interlocks are triggered simultaneously.

EH1104_ST4: This is the interlock triggered if accumulator pressure exceeds its upper limit of 68

bars.

These objects cannot be used without resetting. To reset these alarms:

1. Determine the cause of the alarm, and eliminate it. 2. Now double click on the Reset button (green button in Reset column). The button’s window

should open up. 3. Click on “Forced Mode”. Select “Off”. Then, turn it on by selecting “On” again. 4. Put the button back on PVSS regulation by clicking on “Auto Mode” button. 5. Deselect the heater. 6. Acknowledge the conditions by right clicking on both the blinking, red boxes in the “Cause

column” and selecting “Ack. Alarm” 7. The Alarm symbol should now be a red blinking annulus indicating that the cause for the

alarm has been eliminated. You can now right click on the symbol and select “Ack. Alarm”. This is the last step to resetting the alarm. The heater may now be started again.

43

Resetting PCO Full Stop Interlocks The PCO temporary interlocks do not require resetting, and can be acknowledged by the above

mentioned method for alarms which don’t require resetting.

To reset the PCO Full Stop Interlocks, follow the following steps:

1. Ensure that the cause for the interlock has been removed. 2. Open the Diagnostic panel by clicking the “Diagnostic” button from the plant pane l (Figure

32)

Figure 32. Diagnostic Button

3. In the Diagnostic window, double click the reset button. (Figure 33)

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Figure 33. Diagnostic Panel with Reset button highlighted.

4. In the window that opens, select the “Manual Mode” button from the bottom of the

window. Then, click on “Off” to turn off the button off. Then click “On” and finally, put the button back on “Auto” mode. This resets the Full Stop Interlock.F

5. Acknowledge the alarm by right clicking on the alarm symbol and selecting “Ack. Alarm” from the drop-down menu.

Acknowledging Multiple Alarms If the Alarm Status button at the top of the screen shows a “Bad” status, it indicates that an alarm

has been triggered in the past, and it has not been acknowledged and/or is still active.

Figure 34. “Bad” icon indicating triggered interlocks

1. Click on the “Alarms List” button near the top of the Panel:

2. You will get a list displaying (in reverse chronological order) the list of alarms triggered in the past. This page gives a full description of the alarms triggered, number of

45

acknowledged and unacknowledged alarms, and allows the user to filter the results to view the specific alarms based on category.

3. You can acknowledge these alarms, one page at a time, by clicking the “Ack. Visible”

button near the top left of the panel.

4. The alarms listed on the current page will be acknowledged. This process takes some time, and the progress is displayed in the Previous Action Message Box (#9 in Figure 12 on page 16)

46

TAKING MEASUREMENTS AND RECORDING DATA

PVSS allows users to read and record a wide variety of data related to the system. This section

describes how a user can utilize the system to take measurements. The PVSS archives data for

roughly the previous three months.

Viewing Parameter Trends Quickly Very often, the user is interested only in viewing the trend of few variables over a short period of

time to determine some aspect of system performance. In these situations, it becomes tedious to

create a completely new plot just to view a small amount of data. In addition, it also uses up more

memory, leading to a slower system. To quickly view one or more parameters, two methods are

available:

Single DPE Trend A Single DPE Trend refers to a plot of only one variable. It functions like a normal plot, but shows

only one variable.

To create a new Single DPE Trend, simply right-click on the parameter you want to measure and

select “Single DPE Trend” from the menu. Then select the signal that you want to measure from the

sub-menu (for example “OutOV”, “PosSt” etc.)

The created plot now works exactly like a normal plot. You can export data as csv files, manipulate

the axes, and even add further variables to the trend through the “plot configuration” option.

Note: This plot is only active and recording data until the plot window is opened. Upon closing the

window, the plot is not stored in memory.

Figure 35. Example of a Single DPE Trend.

47

Dynamic DPE Trend With a Dynamic trend, the user has the option of viewing multiple parameters at the same time.

To create a dynamic trend:

1. Right-click on one of the variables you want to add to the trend and select “Add to dynamic trend”. From the sub-menu, select the signal associated with the parameter that you want to view.

2. Successively select on the remaining variables and add them to the Dynamic Trend.

The trend now works in a similar manner to a created plot.

The user is advised to prefer this option to creating a new graph if possible, since the dynamic trend

(like the Single DPE trend) does not use up memory when it is closed, thus saving memory space.

Figure 36. Example of a Dynamic Trend

Deleting a Dynamic Trend The dynamic trend can only accommodate up to eight variables. These can be configured like in a

normal plot, but sometimes a user may wish to start from scratch while creating a plot. This involves

deleting the previous trend and starting anew. To delete a dynamic trend, right click on any object

on the PVSS plant panel and select “Delete Dynamic Trend”.

Zooming a Single or Dynamic Trend The single and dynamic trend windows that appear by default are compact. To see enlarged versions

of the trend, click on the “Other” menu button and select “Zoomed Window” from the sub -menu.

48

Creating A New Plot To create a new plot, use the following steps:

1. On the Plant panel, click on the CERN-UNICOS icon near the top left hand side of the panel. 2. From the drop down menu, select “Configuration” 3. Click on “Trend Tree (local)” (Figure 37)

Figure 37. CERN-UNICOS Menu. Note that the “Monitor” user cannot create new plot.

4. The trend tree window should now open up (Figure 38) 5. In the left-pane of the window, navigate to the Folder where you want the new plot to appear. 6. Click on the “Hierarchy” button at the top of the window and select “New Plot” from the drop -

down menu. Alternatively you can right-click in the right-hand-side pane and select “New Plot” from the drop-down menu.

7. Input the desired plot-name in the window that comes up and click “OK”. Your created-plot should now appear in the Trend Tree pane.

49

Figure 38. Trend Tree (local) Window showing the left and right window panes.

Configuring Plot Variables A plot page in the PVSS interface can record eight variables at a time. These variables can be a wide

variety of objects from pressure and temperature sensors, heaters, interlock-statuses, object-

statuses and so on.

To add/modify plot variables, use the following method:

1. Click on the plot in the left-pane of the trend-tree window. The right pane should now show the “Plot-Configuration” panel (Figure 39).

2. Click on the button in front of one of the variable-name boxes.

3. The DPE Selection window (Figure 40) should open up. 4. From the window, you can narrow down your search by changing the Filter Options. For

example, if you know which type of Device you want to add, you can select the appropriate device type from the “Device Type” option. (As an example, we select the “AnaDig” device type.) Note: For a guide on how to select device types, see Appendix A on page 61.

5. After filling out the Filter Options, click on search. A list of objects which match your filtering criteria will be displayed.

6. From the list, click on the parameter that you wish to record. 7. In the window that opens up, select the appropriate signal that you wish to record and click

“OK”. (Two of the commonly obtained options are: “PosSt” and “OutOv”. The former refers to the input signal into the object, while the latter is the feedback signal from the object.) (Figure 41)

8. Click OK in the “DPE Selection” window.

50

9. In the “Plot Configuration” panel, you can now enter the desired name for the parameter in the “Legend Text” area. This is the name with which the parameter will be referred to on the graph axes and in the plot in general.

10. Enter/Modify the remaining variables as you desire. 11. Click on “Apply” in the Plot Configuration panel once you have finished. The step by step

procedure is shown in the Figures 39 to 41.

Figure 39. Plot Configuration Pane.

Figure 40. DPE Selection Pane Figure 41. Select Device DPE Window

51

Viewing A Created Plot It is not possible to view the plot from the “Trend Tree (local)” window. To view a created plot, use

the following method:

1. On the Plant panel, click on the “Trend Tree” button from the button-bar near the top of the panel.

2. From the window that opens up, navigate to the correct folder and left-click on the appropriate

graph.

Note: This opens up the plot page in place of the Plant Panel. Therefore, open up a new PVSS window

to keep the Plant panel simultaneously with the Plot.

Configuring Created Plots This section describes how to manipulate created plots.

Displaying The Y-Axes To view the Y-Axes of the plotted parameters, on the Plot panel, click on the “Y-Axes” button near

the top-left of the panel. From the drop down menu, select the parameters whose axis you want

displayed.

Viewing/Hiding Parameters To view or hide a particular parameter, click on the check-marks of the parameters at the bottom of

the screen.

Note that hiding a parameter does not exclude it from being exported as part of the data-exporting

procedure, but simply hides it from view

Zooming in and out Use the mouse wheel to zoom in and out of the graph. Hold the mouse over the graph

region to zoom the time axis and the Y-axis simultaneously

Keeping the mouse hovering on the X-axis (time) will only change the time range, without altering the Y-axis. The time range will change with respect to the value at which the mouse is kept. That is, if you keep the mouse over, say, 3:00 P.M. value, then the time range will change on either side of 3:00 P.M.

Keeping the mouse hovering over any of the Y-axis will change the Y-axis without changing

the time range. Only the variable whose Y-axis is zoomed will vary, without changing the other axes. This feature is useful if the scale is too short or too large to allow conclusions to be derived.

52

To zoom in on a particular range of X and Y axes in the graph, left click on the start point and

(while keeping the left-mouse-button clicked), drag a rectangle over the required range.

Manipulating Axes

To move an axis left or right (or up-down), without changing the scale or zooming, simply left-click

on the axis, and while keeping the mouse button pressed, drag it in the direction desired.

Measuring The Value At A Specific Time-Point To find out the values of the plot parameters at any specific instance of time, simply left-click on the

graph above that time-value. A yellow pop-up box will come up showing the values of those

parameters.

Measuring The Difference In Parameter Value Between Two Points Sometimes, you may wish to find out the difference between the values of a specific parameter at

two different time-points. To do this, zoom in/out such that both time-points are visible on the plot.

Click on the graph on the region above the first time-point. Now, while holding the <<shift>> key,

click on the region above the second time-point. A yellow pop-up box will appear, this time showing

the difference in all values between the two points.

Changing the Y-Axis Range To display the Y-axis only between exact points, use the following method:

1. Click on the “Other” menu on the plot page. 2. From the drop-down, select “Plot Configuration”. 3. On the “Plot Configuration” window, you can input the Y-axis min and max limits for the

different parameters in the Y-axis section. (Figure 43)

Figure 42. Zooming In On A Range Rectangle dragged over range on

which to zoom

53

Figure 43. Y-Axis Range

4. Click OK.

Changing Time Range Again, using the mouse-wheel on the time-axis offers the simplest way of changing the time range.

However, to obtain a more exact range, the following method should be used:

1. Click on the “Time Range” button at the top of the window. 2. From the drop down menu, you can select one of the predefined options to get the range

for the last 10 minutes, 1 hour, 8 hours and so on

To specify a more detailed time range:

1. Click on the “Time Range” button at the top of the window. 2. From the drop-down menu, select “User-Specified” time range. 3. The “Specify a Time Range to Display” window should open up. 4. Specify the date for the time range which you want to display. 5. Input the Hours and Minutes. 6. Input the range of time over which you want the data displayed.

Note: The Hours and Minutes should mark the mid-point of the time range that you want to

display. The range of time that you specify will add half the range on either side of the mid-point.

For example, if you want to display the data between 12:00 and 14:00 on the 3rd July 2011, enter

the date as “3/7/2011”, the hours and minutes as “13” and “0” respectively. Finally, in the time

range, input “2” hours and “0” minutes.

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Exporting Data Data that has been archived by the PVSS can be exported in a CSV (Comma Separated Values) file

which can be opened in Excel, and further used in programs like Matlab.

To export data, use the following method:

1. Ensure that the time range displayed on the screen is the range over which you want to export the data. The PVSS exports only the data displayed on the screen.

2. Click on “Other” and click “Export plot to CSV” from the drop-down menu.

Figure 44. Export Plot To CSV Option

Figure 45. Export Plot To CSV

3. In the window that opens up, click on the button to browse to the folder in which you want to save the file. Also specify the name of the plot in the window that opens. Click “OK”. The default folder in which the file is saved is on the CERN server. You can save the file on the desktop, on the computer, or even directly to a USB device.

4. Click “OK” on the “Export data to CSV” window. 5. A busy-status-bar will appear on the window informing you that exporting is in progress.

Exporting a large amount of data may take up to a few minutes. Please be patient.

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Creating A Plot Page It is possible that the total parameters that need to be recorded for an experiment are more than

the maximum accommodated by a single plot (Eight). Also, the user might wish to group separate

and related parameters in their individual graphs. In such cases, it is handy to create a plot page

instead of a single plot.

A plot page allows a user to add six graphs (with 8 variables each) as a single unit called “plot page”.

This page is equivalent to a single plot, such as while exporting data, all the plots are exported into

one csv file.

To create a plot page, follow the given method:

1. On the Plant panel, click on the CERN-UNICOS icon near the top left hand side of the panel. 2. From the drop down menu, select “Configuration” 3. Click on “Trend Tree (local)” 4. The trend tree window should now open up. 5. In the left-pane of the window, navigate to the Folder where you want the plot page to

appear. 6. Click on the “Hierarchy” button at the top of the window and select “New Page” from the

drop-down menu. Alternatively you can right-click in the right-hand-side pane and select “New Page” from the drop-down menu.

7. Input the desired name in the window that comes up and click “OK”. Your created page should now appear in the Trend Tree pane.

8. The created Plot Page shows by default only one graph. To add more graphs, (up to a maximum of six) increase the number of rows and columns to get the desired layout (Figure 46, next page). Click on “Apply” once done.

To view the created plot page, follow the same steps as for a single plot.

Adding Pre-Existing Plots To A Plot Page For created plot pages, it is possible to add already existing single-plots as one of the plots of the

created page. For example, if you create a plot page called “Example_Page”, and you wish to add a

plot that you had previously created called “Example_Plot”, use the following steps:

1. On the trend tree (local) page, opened through the Unicos menu, click on the plot page on the left pane.

2. Click on the button at the location where you want the Example_Plot to be. A “Choose Plot” window should open up, listing all the existing plots stored in the PVSS memory. Scroll to the plot that you wish to select, and click “OK”.

3. The plot name should now be visible on the window. 4. Even if none of the existing plots are the ones that you require, you should still fill up all the

rows and columns with graphs. This is necessary to tell the PVSS that you wish to utilize all the rows and columns that you have added. You can modify the plot variables later on.

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Figure 46. Plot Page shown in the right pane

Figure 47. Choosing a pre-existing plot called “qweqwe”

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Configuring Plot Variables in a Plot Page The method to add/modify variables in a plot page is similar to the method for a single plot.

Individual plot variables can be added/ modified by first opening the plot. Use the following method:

3. On the Plant panel, click on the “Trend Tree” button from the button-bar near the top of the panel.

4. From the window that opens up, navigate to the

correct folder and left- click on the appropriate plot

page.

5. The plot page should now open up. The plots on the plot page are displayed as individual plots,

with their own menu bar and so on (Figure 48).

6. To modify the variables of a particular graph, click on the “Others” button on the menu -bar of

the correct plot. Select “Plot Configuration” from the drop down sub-menu. The plot

configuration panel should open up.

7. Click on the button in front of one of the variable-name boxes.

Figure 48. Example Plot Page. The individual menu-bars can be seen for each plot.

8. The DPE Selection window should open up. 9. From the window, you can narrow down your search by changing the Filter Options. For

example, if you know which type of Device you want to add, you can select the appropriate device type from the “Device Type” option. (As an example, we select the “AnaDig” device type.) Note: For a guide on how to select device type, see Appendix A on page 61.

10. After filling out the Filter Options, click on search. A list of objects which match your filtering criteria will be displayed.

11. From the list, click on the parameter that you wish to record.

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12. In the window that opens up, select the appropriate signal that you wish to record and click “OK”. (Two of the commonly obtained options are: “PosSt” and “OutOv”. The former refers to the input signal into the object, while the latter is the feedback signal from the object.)

13. Click OK in the “DPE Selection” window. 14. In the “Plot Configuration” panel, you can now enter the desired name for the parameter in the

“Legend Text” area. This is the name with which the parameter will be referred to on the graph axes and in the plot in general.

15. Enter/Modify the remaining variables as you desire. 16. Click on “OK” in the Plot Configuration panel once you have finished.

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TROUBLESHOOTING

This section discusses some unexpected errors or stoppages that you may encounter while using the

system, lists the likely causes for it and gives solutions for them.

Compressor stops suddenly The system continues to pump CO2 while the compressor has suddenly stopped. This could be due to

two reasons:

Cause: The most likely cause is the CO2 temperature falling below -50 degree C. This is because there

is very little heat load on the CO2, and it is getting highly sub-cooled. The compressor will restart

itself once the CO2 temperature becomes -49 degree C.

Solution: If the bypass line is being used, adding more heat load through the dummy heater can

resolve the problem.

Cause: It could also be caused by the Pressure switch of the compressor being too high. This is often

seen immediately after start-up of compressor when, due to environmental heat-leak overnight, the

system pressure and temperature is high.

Solution: To solve this problem, when the chiller is started, the dummy heater for the chiller should

also be switched on (to a power of about 500W). The compressor might still continue to stop and

start, but it stabilises after about 5 minutes of operation.

Compressor makes shuddering noises during start-up On starting the chiller, the compressor seems to vibrate vigorously for 3 or 4 seconds before

stabilizing. Afterwards, it releases a steady whirr of noise.

Cause: This is caused by liquid R404a refrigerant entering the compressors. Compressors cannot

compress liquids, which causes the noise to be made

Solution: This condition can be safely ignored unless it persists for longer than 15-20 seconds. In

case of persistence, stop the system and contact an expert.

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Blue “o” symbols appear in front of all objects, and readings freeze. A blue “o” appears in front of all sensors/valves/heaters etc. on the PVSS panel, and the readings

become static. It may disappear after some time, or may continue.

Cause: This indicates a network problem. The PVSS is unable to receive the signal from the PLC

through the network.

Solution: If the problem occurs, contact an expert.

Note: This problem might not exist anymore since the network cables were replaced with newer

ones.

Pressure Enthalpy diagram shows ALL the CO2 evaporating in evaporator The p-h diagram shows vapour quality = 1 at the end of the evaporator.

Cause: This is due to the method used to calculate the enthalpy of a point in the system. Since the

PVSS uses pressure and temperature to get enthalpy, it is unable to calculate enthalpy in the two-

phase region. Thus, to represent two-phase fluid, the point is displayed on the saturated vapour line.

Sometimes, the fluid might also be displayed beyond the vapour quality = 1 line. Usually, this does

not mean that all the two phase fluid has been converted to vapour but is simply a display

inaccuracy.

Pressure/Temperature sensor is showing rapidly changing and widely rang ing values The sensor may show an I/O error with an “E” symbol alongside it.

Cause: This is caused by the sensor’s wires breaking, or touching each other,

Solution: Ask an expert to repair the sensor wires.

Temperature Sensor shows a cyclic variation in temperature A temperature sensor seems to show a periodic, cyclic trend varying between two points.

Cause: This is caused by the chiller temperature varying cyclically due to the thermostatic expansion

valve in the chiller.

Solution: This problem has no solution, because the valve is mechanically controlled, and suffers

from stick-slip. However, this does not affect the experiment since the evaporation temperature is

constant due to the accumulator and internal heat exchanger.

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APPENDIX A This appendix gives a brief description on how devices are categorised in PVSS. It will allow the user

to understand how to use the filters to narrow down the list of devices while selecting variables for

plots.

The PVSS system for the CO2 plant has the following categories of devices:

Digital Input Analog Input

Digital Output

Analog Output

Analog Object AnaDig Object

Controller Object

Process Control Object On/Off Object

Alarm

Analog Status Analog Parameter

Here, input means input into the PVSS (PLC) not input into the object.

Digital Input: These are the input signals into the PLC whose value is either 0 or 1. They typically

determine the true/false (or on/off) status of objects, for example Circuit Breaker status, heater

status or pump/chiller on/off status etc.

Analog Input: These are the objects that have an analog input into the PLC (which could be 0-100%,

4-20mA, 0-5 Volts and so on). All the pressure, temperature, flow rate readings etc. are analog

inputs.

Digital Output: These are the 0 or 1 signals which the PLC gives to the different components of the

cooling system. For example, if the user requests compressor start-up, the PLC gives a Digital Output

signal to the compressor requesting start-up.

Analog Output: These are analog outputs given by the PLC to components. They could be values, for

example, calculated by the PLC and then fed into the component in the form of a 4-20 mA signal.

Analog Object: These are objects which have analog input and analog output. The bypass heater

(EH1904) is an Analog Object.

AnaDig Object: These are objects which have an analog signal into the PLC, but a digital from output

from it. The heaters in the damper (EH1102), the accumulator (EH1104), the pump oil heater

(EH1101), and the accumulator control valve CV1105 are some examples of AnaDig objects.

Controller Object: These, as the name suggests, are objects which control a component (example

heater or valve) based on a threshold value. So, for instance, the pressure and temperature

controllers (e.g. PC1104, TC1102) are controller objects which can turn a component off if the

controlling parameter exceeds the threshold value.

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Process Control Object: PCOs are the highest level of control that is exerted over a system. If a large

project is being controlled, or multiple projects acting together, multiple PCOs can exist together.

For this CO2 plant however, there is only one PCO, whose function is to allow selection of option

modes, and check the PCO level interlocks.

On/Off Object: These are components which can only be turned on and off, and do not have

intermediary states. The pump, the MEV valves, the chiller, the chiller oil -heater are on/off objects.

Note that these are also physical components which are part of the system. The On/Off object is

therefore a representation of the component itself in PVSS, and not a signal associated with it (like

the Digital Input object).

Alarm: These are PVSS objects associated with alarms. That is, every alarm which has been designed

for the system is represented in PVSS with its corresponding Alarm object.

Analog Parameter: These are the parameters which are used to compare analog conditions. For

example, the Analog Parameter object QSMC_B158_EH1102_tST2 (associated with the damper

heater) is set to 120 degree C. This parameter is used by the EH1102_ST2 alarm as the reference

value above which the alarm should be triggered. In effect, if the value of the damper temperature

sensor exceeds this parameter (120 degree C), the alarm is triggered.

Analog Status: This object is intended for use by administrators only, and serves no purpose for a

new user. It is not explained here.

Viewing the objects in each of the Device Type categories Sometimes, the user may wish to see all the objects belonging to a particular, or multiple categories.

To do this, use the following method:

1. On the PVSS panel, click on the “Device Tree Overview” button, near the top: 2. The device tree overview panel should show up (Figure 49).

Figure 49. Device Tree Overview Panel.

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3. In the left pane, select the check box on the left of “device type:” 4. Select the green check mark for “OK” 5. The different categories of objects will now be listed in the lower half of the left

pane. (Figure 50)

Figure 50. Categories of Objects in PVSS

6. Click on the “+” symbol next to any category to display the list of objects in it. 7. Alternatively, you can simply left click on the text of the category. Doing so displays all the

objects of that category in the right pane, and also displays their current value/status. (Figure 51)

8. To scroll through multiple pages of objects, select the page from the drop down menu highlighted in red in figure 51.

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Figure 51. List of Digital Input objects.