CONDUCTIVITY

1. What is the difference between cation conductivity and specific conductivity?

To increase the sensitivity of conductivity measurement, the sample is first passed through a column of cation exchange resin in the hydrogen form, which converts all cations in sample into hydrogen ions. As a result of salts like NaCl and magnesium sulphate (which may enter into condenser through leakage) get converted into hydrochloric acid and sulphuric acid which have much higher conductivity than the salts. In such treatment,CO2 is unaffected. but amononia, / hydrazinc and caustic soda are completely removed from sample.. This type of measurement known is cation conductivity measurement.( and is proportional to

The mineral carryover and independent of CO2 hydroxides,carbonates,NH3 or amines concentration) and the conductivity measurement made directly without passing the sample through the cation exchange resin is known as specific conductivity measurement

Why are we measuring both of them in DM plant?

In GCU, only specific conductivity measurement done. Depends upon requirement, conductivity measurement selected.

2.What is potential free contact? What is the significance and application of this contact? Contacts having not potential. E.g. Relay contacts/ field switches contacts. They are used in logic circuits. A potential free contact is usually wired into an electrical circuit. However it must be ensured that the contact ratings are suitable for the service in which it is used.

3.What are the different types of torque measurement?( techniques )

There are two different types of torque measurements: 1) actual instantaneous torque 2) dynamic torque where primary objective is to measure variations of torque rather than the torque itself e.g. torque measurement in case of centrifuge. Torque can be measured by 1) using an appropriately connected strain gauge transducer, 2) measuring the twist (angular) of an elastic element e.g.. The power transmitting shaft of a rotating machine or the twisting of torque tube in a displacer type level transmitter. In case of power transmitting rotating shafts, two identical slotted discs are installed at opposite ends of the shaft. Optical pickups are used to generate electrical pulses. Speed of the shaft is also measured. The phase difference between two pulse trains is related to the twist in the shaft, which in turn is related to the torque transmitted.

4.Why cooling fins are required in level switches?

          Cooling fins are used to prevent transfer of heat of the process medium to the electrical parts of the switch and maintain their temperature within suitable limits.

5.What is meant by smart tuning and how is it done?

              Smart tuning, also known as self-tuning, refers to the ability of a controller to adjust its parameters/response automatically for optimum control loop performance when process parameters/respones/characteristics change.

Typically this is performed by a combination of mathematical calculations and heuristics (intelligent decisions based on the designer’s experience) and continual measurement of process characteristics.

6.What does NPT stand for and what does it signify?

 National Pipe Thread

               

Compressor Controls QUESTIONS & ANSWERS

1. Why anti surge control is not required in reciprocating compressors?

In Reciprocating Compressors Non return valves (NRVs) are present in the Suction Line and Discharge line, which prevents flow reversal. In case of high discharge pressure the pressurized gas gets accumulated in the cylinder and cannot go back through the NRV of suction line. So anti surge system is not required.

2. What do you understand by Surge Limit Line and Control line?

For any particular operating curve the point of minimum flow and max pressure is known as Surge limit point and the locus of all such points defines a curve called as Surge Limit line.

The Surge control line is the locus of set points of minimum flow and max pressure at operating conditions. The manufacturer normally gives these.

3. Why Cooling water is used for Lube Oil System?

The Lube Oil System is used for Lubrication of the bearings. The outlet of the system i.e the high temperature lube oil is cooled by means of cooling water. This is because if high temperature lube oil is sent back to compressor then the compressor may get damaged if the internals in the compressor are not suitable for high temperatures.

4.      What are Recycle and Vent valves and where are they used?

The Recycle valves are used in case of hazardous gases while Vent valves are  

Used in case of non-hazardous gases. Recycle valves are used for

both types of gases  for reducing the cost of the gas or fuel vent valves thereby  

the operating cost and also to recover the gas otherwise vented  to flare. Actually  

Vent or Blow Off valves should be used in the first place so as to prevent fast

5.      What are the systems associated normally with the compressor?

   Vibration monitoring, DCS, Lube Oil system

SURGE PROTECTION/CAPACITY CONTROL FOR CRITICAL COMPRESSORS IN JAMNAGAR

·        HEAT PUMP COMPRESSOR

Ø MIN FLOW CONTROLLER IN DCS WITH OPERATOR ENTERED SET POINT

Ø MANUAL SPEED CONTROL THROUGH DCS

·        PLAT FORMER/ISOMAR GAS COMPRESSORS

Ø MIN MECHANICAL STOP IN SUCTION VALVES

Ø SURGE DETECTION AND TRIP MOTOR LOW CURRENT

Ø IGV CONTROL FROM DCS

·        TAIL GAS COMPRESSOR

Ø DEDICATED CONTROL SYSTEM "TURBOLOG" FROM GHH BASED ON COMPRESSOR PERFORMANCE MAP

Ø SURGE CONTROL BY RECYCLE VALVE

Ø MIN OPENING BY OPERATOR

Ø SUCTION PRESSURE CONTROL BY IGV IMPLEMENTED IN GHH

Ø TRIP ON SURGE

·        VGO HT COMPRESSOR

Ø DEDICATED CONTROL SYSTEM "TURBOLOG" FROM GHH BASED ON COMPRESSOR PERFORMANCE MAP

Ø SURGE CONTROL BY RECYCLE VALVE

Ø TO HASNDLE DIFFERENT PROCESS CONDITIONS (MOL WT CHANGE) SELECTION SWITCH IS PROVIDED IN THE UCP. MOL WT-2.0,4.3,7.2 28

Ø VISUALIZATION IS PROVIDED IN THE PIB.

Ø MIN OPENING BY OPERATOR

Ø CAPACITY CONTROL IS BY SPEED CONTROL BY OPERATOR.

·        HYDROGEN RFG COMPRESSOR

Ø DEDICATED MULTI VARIABLE CONTROL FROM CCC SERIES 3+ CONTROLLER

Ø SURGE CONTROL BY RECYCLE VALVE

Ø CAPACITY CONTROL BY DISCHARGE PRESSURE CONTROLLER

·        COKER GAS COMPRESSOR

Ø DEDICATED MULTI VARIABLE CONTROL FROM CCC SEREIS 3+ CONTROLLER

Ø SURGE CONTROL BY RECYCLE VALVE  SEPARATELY FOR FIRST AND SECOND STAGE

Ø ASC HAS PRESSURE OVERRIDE CONTROL(POC) FOR THE FIRST STAGE DISCHARGE PRESSURE

Ø AUTO CAPACITY CONTROL  BY SPEED VARIATION BASED ON SUCTION PRESSURE/COLUMN OVERHEAD PR.

Ø DECOUPLING BETWEEN PERFORMANCE AND ANTI SURGE CONTROLLER

·        PRT

Ø DEDICATED CONTROL SYSTEM FROM CCC

SERIES 4 SYSTEM

Ø CONTROL SYSTEM IS DUAL REDUNDANT AND FAULT TOLERANT

Ø SPEED/IGV POSITION CHANGE IS  TAKEN CARE BY USING INVARIANT CO ORDINATE SYSTEM

Ø FALL BACK STRATEGY IS IMPLEMENMTED

Ø PRT CONTROLS ARE VERY COMPLEX DUE TO MULTIPLE INTERACTING CONTROLS SUCH AS

          EXPANDER CONTROL

          DELTA P CONTROL RX/RG

          STEAM TURBINE CONTROLS

          BLOWER CAPACITY CONTROL

          LOAD SHARING CONTROL

          M/G CONTROL( LIMIT CONROL)

                  

Ø GHH TURBOLOG CONTROL SYSTEM FOR START UP AND MACHINE PROTECTION

Ø GHH SPECIAL SURGE DETECTOR BASED ON DP REVERSAL/ 'T' REVERSAL( FAST T/C) ACROSS SUCTION AND DISCHARGE OF THE BLOWER

Turbine / Compressor Control System Concept (Typical)

Turbine / Compressor Control System Concept (Typical)

COMPRESSOR CONTROL SYSTEMS

COMPRESSOR CONTROL SYSTEMS page 3

 SALIENT  FEATURES OF DESIGN :

·        For the control and monitoring of each machine, a dedicated control  panel (UCP) is supplied by the OEM which is located in respective PIB.

·        For all Reciprocating compressors & majority of the Centrifugal compressors, the interlocks and control of the machine are implementated in UCP using Allen Bradley (PLC 5/40) PLCs.

·        All machine condition monitoring & protection parameters (vibration, speed, temperature etc.) are connected to MCM system supplied by B-N (3500/3300 series).

·     For steam turbine driven compressors, Woodward governer (505)  is used for speed control system and Protech (203) is used for over speed  protection system.

·        Each UCP is connected to DCS by dual redundant serial link for remote monitoring and control (e.g. speed setpoint) by control room operators.

·        ESD and MCMS provide shutdown signal to UCP (through hardwired link) based on machine protection interlocks to trip the compressor. 

·        For implementation of advanced control algorithams (anti surge control, load sharing, performance control etc.) for Reciprocating compressors, M/s CCC supplied controllers are used in all machines except for Borsig where Turbolog is used.

·        For operator interface during start up and shutdown, a panel mounted display unit (Panelview 900) is provided on UCPs housing Allen Bradley PLCs and a table top mounted MMI is provided for UCPs containing Turbolog and CCC controllers.

·        For each machine, a local control panel is provided in field for status monitoring and control by field operator. In general, these local panels are provided with the following pushbuttons and lamp indications.

a)     Start PB

b)    Stop PB

c)     Reset PB

d)    Emergency stop PB

e)     Selector switch for capacity control

f)      Permissive lamps

g)     Status indication lamps

h)    Speed Indication (as applicable)

i)       Alarm Hooter

·        For local indication of machine protection parameters, a local display unit (MTL make) connected to MCM system is provided in field for each compressor.

CONTROL SYSTEMS FOR COMPRESSORS page 2

·        CONTROLS FOR RECIPROCATING COMPRESSORS

Ø START UP (PERMISSIVES FROM PROCESS/MACHINE CONTROL SYSTEM, SIGNAL TO DRIVER)

Ø SHUT DOWN(MACHINE  PARAMETER TRIPS,PROCESS TRIPS, NORMAL STOP)

Ø CONDITION MONITORING ( INCLUDING ROD DROP)

Ø LOAD VARIATION  CONTROL

·        CONTROL FOR CENTRIFUGAL COMPRESSORS

Ø START UP -PERMISSIVE, RAMP CONTROL

Ø SHUT DOWN( NORMAL ,EMERGENCY)

Ø PROTECTION SYSTEMS(MCMS, BEARING TEMP,LO CONTROL OIL,SEAL GAS ,PROCESS TRIPS)

Ø CAPACITY CONTROLS( SPEED,IGV,CONTROL VALVES)

Ø ANTI SURGE CONTROL

Ø LOAD SHARING CONTROL

·        CONTROL SYSTEMS BY MACHINE VENDOR- GHH

·        BOUGHT OUT SYSTEMS- CCC

·        CONTROL OF THE MACHINE IS POSSIBLE FROM THE UCP

AT PIB AND FROM DCS ( THROUGH SERAIL LINK /HARD WIRED)

·        FACILITIES DEVELOPED AT THE CES

CCC TRAINING AT SITE FOR  10 INST ENGINEERS 20 OPERATION ENGINEERS

MODEM CONNECTIVITY FOR REMOTE DIAGNOSTICS BY CCC

TESTING /TRAINING FACILITY  AVAILABLE AT CES FOR CCC SERIES 3+ CONTROLLER /WOODWARD SPEED CONTROLLER

TESTING /TRAINING FACILITY  PLANNED  AT CES FOR CCC SERIES 4+ CONTROLLER / GHH CONTROLLER

CENTRIFUGAL COMPRESSOR

CONTROL SYSTEMS FOR COMPRESSORS

·        MAJOR TYPES OF COMPRESSORS

RECIPROCATING

CENTRIFUGAL

·        CONTROLS FOR  COMPRESSORS

Ø START UP (PERMISSIVES, SIGNAL TO DRIVER)

Ø SHUT DOWN(MACHINE  PARAMETER TRIPS,PROCESS TRIPS, NORMAL STOP)

Ø CONDITION MONITORING

Ø LOAD VARIATION  CONTROL

Next

INSTRUMENTATION EQUIPMENT

2.0 INTRODUCTION
Instrumentation is the art of measuring the value of some plant parameter,
pressure, flow, level or temperature to name a few and supplying a signal
that is proportional to the measured parameter. The output signals are
standard signal and can then be processed by other equipment to provide
indication, alarms or automatic control. There are a number of standard
signals; however, those most common in a CANDU plant are the 4-20 mA
electronic signal and the 20-100 kPa pneumatic signal.
This section of the course is going to deal with the instrumentation
equipment normal used to measure and provide signals. We will look at
the measurement of five parameters: pressure, flow, level, temperature,
and neutron flux.
2.1 PRESSURE MEASUREMENT
This module will examine the theory and operation of pressure detectors
(bourdon tubes, diaphragms, bellows, forced balance and variable
capacitance). It also covers the variables of an operating environment
(pressure, temperature) and the possible modes of failure.
2.1.1 General Theory
Pressure is probably one of the most commonly measured variables in the
power plant. It includes the measurement of steam pressure; feed water
pressure, condenser pressure, lubricating oil pressure and many more.
Pressure is actually the measurement of force acting on area of surface.
We could represent this as:
Pressure Force
Area
P F
or A
The units of measurement are either in pounds per square inch (PSI) in
British units or Pascals (Pa) in metric. As one PSI is approximately 7000
Pa, we often use kPa and MPa as units of pressure.
2.1.2 Pressure Scales
Before we go into how pressure is sensed and measured, we have to
establish a set of ground rules. Pressure varies depending on altitude above
sea level, weather pressure fronts and other conditions.
The measure of pressure is, therefore, relative and pressure measurements
are stated as either gauge or absolute.
Note
Science and Reactor Fundamentals – Instrumentation & Control 8
CNSC Technical Training Group
Revision 1 – January 2003
Gauge pressure is the unit we encounter in everyday work (e.g., tire
ratings are in gauge pressure).
A gauge pressure device will indicate zero pressure when bled down to
atmospheric pressure (i.e., gauge pressure is referenced to atmospheric
pressure). Gauge pressure is denoted by a (g) at the end of the pressure
unit [e.g., kPa (g)].
Absolute pressure includes the effect of atmospheric pressure with the
gauge pressure. It is denoted by an (a) at the end of the pressure unit [e.g.,
kPa (a)]. An absolute pressure indicator would indicate atmospheric
pressure when completely vented down to atmosphere - it would not
indicate scale zero.
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
Figure 1 illustrates the relationship between absolute and gauge. Note
that the base point for gauge scale is [0 kPa (g)] or standard atmospheric
pressure 101.3 kPa (a).
The majority of pressure measurements in a plant are gauge. Absolute
measurements tend to be used where pressures are below atmosphere.
Typically this is around the condenser and vacuum building.
Absolute
Scale
Atmospheric
Pressure
Perfect
Vacuum
101.3 kPa(a)
0 kPa(a)
Gauge
Scale
0 kPa(g)
-101.3 kPa(g)
Figure 1
Relationship between Absolute and Gauge Pressures
2.1.3 Pressure Measurement
The object of pressure sensing is to produce a dial indication, control
operation or a standard (4 - 20 mA) electronic signal that represents the
pressure in a process.
To accomplish this, most pressure sensors translate pressure into physical
motion that is in proportion to the applied pressure. The most common
pressure sensors or primary pressure elements are described below.
Note
Science and Reactor Fundamentals – Instrumentation & Control 9
CNSC Technical Training Group
Revision 1 – January 2003
They include diaphragms, pressure bellows, bourdon tubes and pressure
capsules. With these pressure sensors, physical motion is proportional to
the applied pressure within the operating range.
You will notice that the term differential pressure is often used. This term
refers to the difference in pressure between two quantities, systems or
devices
2.1.4 Common Pressure Detectors
Bourdon Tubes
Bourdon tubes are circular-shaped tubes with oval cross sections (refer to
Figure 2). The pressure of the medium acts on the inside of the tube. The
outward pressure on the oval cross section forces it to become rounded.
Because of the curvature of the tube ring, the bourdon tube then bends as
indicated in the direction of the arrow.
Pressure
Motion
Cross
Section
Figure 2
Bourdon Tube
Due to their robust construction, bourdon are often used in harsh
environments and high pressures, but can also be used for very low
pressures; the response time however, is slower than the bellows or
diaphragm.
Bellows
Bellows type elements are constructed of tubular membranes that are
convoluted around the circumference (see Figure 3). The membrane is
attached at one end to the source and at the other end to an indicating
device or instrument. The bellows element can provide a long range of
motion (stroke) in the direction of the arrow when input pressure is
applied.
Note
Science and Reactor Fundamentals – Instrumentation & Control 10
CNSC Technical Training Group
Revision 1 – January 2003
Pressure
Motion
Flexible
Bellows
Figure 3
Bellows
Diaphragms
A diaphragm is a circular-shaped convoluted membrane that is attached to
the pressure fixture around the circumference (refer to Figure 4). The
pressure medium is on one side and the indication medium is on the other.
The deflection that is created by pressure in the vessel would be in the
direction of the arrow indicated.
. Pressure
Motion
Flexible
Membrane
Figure 4
Diaphragm
Diaphragms provide fast acting and accurate pressure indication.
However, the movement or stroke is not as large as the bellows
Capsules
There are two different devices that are referred to as capsule. The first is
shown in figure 5. The pressure is applied to the inside of the capsule and
Note
Science and Reactor Fundamentals – Instrumentation & Control 11
CNSC Technical Training Group
Revision 1 – January 2003
if it is fixed only at the air inlet it can expand like a balloon. This
arrangement is not much different from the diaphragm except that it
expands both ways.
Pressure
Motion
Flexible
Membranes
continuous
seam
seam
Figure 5
Capsule
The capsule consists of two circular shaped, convoluted membranes
(usually stainless steel) sealed tight around the circumference. The
pressure acts on the inside of the capsule and the generated stroke
movement is shown by the direction of the arrow.
The second type of capsule is like the one shown in the differential
pressure transmitter (DP transmitter) in figure 7. The capsule in the bottom
is constructed with two diaphragms forming an outer case and the interspace
is filled with viscous oil. Pressure is applied to both side of the
diaphragm and it will deflect towards the lower pressure.
To provide over-pressurized protection, a solid plate with diaphragmmatching
convolutions is usually mounted in the center of the capsule.
Silicone oil is then used to fill the cavity between the diaphragms for even
pressure transmission.
Most DP capsules can withstand high static pressure of up to 14 MPa
(2000 psi) on both sides of the capsule without any damaging effect.
However, the sensitive range for most DP capsules is quite low. Typically,
they are sensitive up to only a few hundred kPa of differential pressure.
Differential pressure that is significantly higher than the capsule range
may damage the capsule permanently.
2.1.5 Differential Pressure Transmitters
Most pressure transmitters are built around the pressure capsule concept.
They are usually capable of measuring differential pressure (that is, the
Note
Science and Reactor Fundamentals – Instrumentation & Control 12
CNSC Technical Training Group
Revision 1 – January 2003
difference between a high pressure input and a low pressure input) and
therefore, are usually called DP transmitters or DP cells.
Figure 6 illustrates a typical DP transmitter. A differential pressure
capsule is mounted inside a housing. One end of a force bar is connected
to the capsule assembly so that the motion of the capsule can be
transmitted to outside the housing. A sealing mechanism is used where the
force bar penetrates the housing and also acts as the pivot point for the
force bar. Provision is made in the housing for high- pressure fluid to be
applied on one side of the capsule and low-pressure fluid on the other.
Any difference in pressure will cause the capsule to deflect and create
motion in the force bar. The top end of the force bar is then connected to a
position detector, which via an electronic system will produce a 4 - 20 ma
signal that is proportional to the force bar movement.
Detector
4-20mA
Seal and Pivot
Force Bar
Silicone Oil Filling
High Pressure Low Pressure
D.P. Capsule
Metal Diaphragm
Housing
Backup Plate
Figure 6
Typical DP Transmitter Construction
This DP transmitter would be used in an installation as shown in
Figure 7.
Controlled Vessel
Pressure
(20 to 30 KPa)
Impulse Line
Isolation
Valve
H L
Pressure Transmitter
Vented
4-20mA
Note
Science and Reactor Fundamentals – Instrumentation & Control 13
CNSC Technical Training Group
Revision 1 – January 2003
Figure 7
DP Transmitter Application
A DP transmitter is used to measure the gas pressure (in gauge scale)
inside a vessel. In this case, the low-pressure side of the transmitter is
vented to atmosphere and the high-pressure side is connected to the vessel
through an isolating valve. The isolating valve facilitates the removal of
the transmitter.
The output of the DP transmitter is proportional to the gauge pressure of
the gas, i.e., 4 mA when pressure is 20 kPa and 20 mA when pressure is
30 kPa.
2.1.6 Strain Gauges
The strain gauge is a device that can be affixed to the surface of an object
to detect the force applied to the object. One form of the strain gauge is a
metal wire of very small diameter that is attached to the surface of a
device being monitored.
Force Force
AREA AREA AREA
Resistance Ω Increases
Cross Sectional Area Decreases
Length Increases
Figure 8
Strain Gauge
For a metal, the electrical resistance will increase as the length of the
metal increases or as the cross sectional diameter decreases.
When force is applied as indicated in Figure 8, the overall length of the
wire tends to increase while the cross-sectional area decreases.
The amount of increase in resistance is proportional to the force that
produced the change in length and area. The output of the strain gauge is a
change in resistance that can be measured by the input circuit of an
amplifier.
Strain gauges can be bonded to the surface of a pressure capsule or to a
force bar positioned by the measuring element. Shown in Figure 9 (next
page) is a strain gauge that is bonded to a force beam inside the DP
capsule. The change in the process pressure will cause a resistive change
in the strain gauges, which is then used to produce a 4-20 mA signal.
Note
Science and Reactor Fundamentals – Instrumentation & Control 14
CNSC Technical Training Group
Revision 1 – January 2003
Field Terminals
Electronics
Feedthrough
Electronics Enclosure
Electronic
Amplifier
Compensation
Circuit Board
Strain Gauge
Beam
Overpressure
Stop
Process Seal
Diaphragm
Sensing Capsular
Element
Liquid Fill
Figure 9
Resistive Pressure Transmitter
2.1.7 Capacitance Capsule
Similar to the strain gauge, a capacitance cell measures changes in
electrical characteristic. As the name implies the capacitance cell measures
changes in capacitance. The capacitor is a device that stores electrical
charge. It consists of metal plates separated by an electrical insulator. The
metal plates are connected to an external electrical circuit through which
electrical charge can be transferred from one metal plate to the other.
The capacitance of a capacitor is a measure of its ability to store charge.
The capacitance of the capacitance of a capacitor is directly proportional
to the area of the metal plates and inversely proportional to the distance
between them. It also depends on a characteristic of the insulating material
between them. This characteristic, called permittivity is a measure of how
well the insulating material increases the ability of the capacitor to store
charge.
d
C = ε A
C is the capacitance in Farads
A is the area of the plates
D is the distance of the plates
ε is the permittivity of the insulator
By building a DP cell capsule so there are capacitors inside the cell
capsule, differential pressures can be sensed by the changes in capacitance
of the capacitors as the pressure across the cell is varied.
Note
Science and Reactor Fundamentals – Instrumentation & Control 15
CNSC Technical Training Group
Revision 1 – January 2003
2.1.8 Impact of Operating Environment
All of the sensors described in this module are widely used in control and
instrumentation systems throughout the power station.
Their existence will not normally be evident because the physical
construction will be enclosed inside manufacturers’ packaging. However,
each is highly accurate when used to measure the right quantity and within
the rating of the device. The constraints are not limited to operating
pressure. Other factors include temperature, vapour content and vibration.
Vibration
The effect of vibration is obvious in the inconsistency of measurements,
but the more dangerous result is the stress on the sensitive membranes,
diaphragms and linkages that can cause the sensor to fail. Vibration can
come from many sources.
Some of the most common are the low level constant vibration of an
unbalanced pump impeller and the larger effects of steam hammer.
External vibration (loose support brackets and insecure mounting) can
have the same effect.
Temperature
The temperature effects on pressure sensing will occur in two main areas:
The volumetric expansion of vapour is of course temperature dependent.
Depending on the system, the increased pressure exerted is usually already
factored in.
The second effect of temperature is not so apparent. An operating
temperature outside the rating of the sensor will create significant error in
the readings. The bourdon tube will indicate a higher reading when
exposed to higher temperatures and lower readings when abnormally cold
- due to the strength and elasticity of the metal tube. This same effect
applies to the other forms of sensors listed.
Vapour Content
The content of the gas or fluid is usually controlled and known. However,
it is mentioned at this point because the purity of the substance whose
pressure is being monitored is of importance - whether gaseous or fluid –
especially, if the device is used as a differential pressure device in
measuring flow of a gas or fluid.
Higher than normal density can force a higher dynamic reading depending
on where the sensors are located and how they are used. Also, the vapour
density or ambient air density can affect the static pressure sensor readings
Note
Science and Reactor Fundamentals – Instrumentation & Control 16
CNSC Technical Training Group
Revision 1 – January 2003
and DP cell readings. Usually, lower readings are a result of the lower
available pressure of the substance. However, a DP sensor located in a hot
and very humid room will tend to read high.
2.1.9 Failures and Abnormalities
Over-Pressure
All of the pressure sensors we have analyzed are designed to operate over
a rated pressure range. Plant operating systems rely on these pressure
sensors to maintain high accuracy over that given range. Instrument
readings and control functions derived from these devices could place
plant operations in jeopardy if the equipment is subjected to over pressure
(over range) and subsequently damaged. If a pressure sensor is over
ranged, pressure is applied to the point where it can no longer return to its
original shape, thus the indication would return to some value greater than
the original.
Diaphragms and bellows are usually the most sensitive and fast-acting of
all pressure sensors.
They are also however, the most prone to fracture on over-pressuring.
Even a small fracture will cause them to read low and be less responsive to
pressure changes. Also, the linkages and internal movements of the
sensors often become distorted and can leave a permanent offset in the
measurement. Bourdon tubes are very robust and can handle extremely
high pressures although, when exposed to over-pressure, they become
slightly distended and will read high. Very high over-pressuring will of
course rupture the tube.

page3

explain the reasons for power control using ion chambers at low
power and in-core detectors at high power;
Control
• identify the controlled and manipulated variables;
• sketch a simple block diagram and indicate set point,
measurement, error, output and disturbances;
• state the difference between open and closed loop control;
• state the basic differences between feedback and feed forward
control;
• explain the general on/off control operation;
• explain why a process under on/off control is not controllable at
the set point;
• explain why on/off control is suitable for slow responding
processes;
• explain the meaning of proportional control in terms of the
relationship between the error signal and the control signal;
• explain why offset will occur in a control system, with
proportional control only;
• choose the controller action for corrective control;
• convert values of PB in percentage to gain values and vice-versa;
• determine the relative magnitude of offset with respect to the
proportional band setting;
• state the accepted system response, i.e., ¼ decay curve, following a
disturbance;
• explain the reason for the use of reset (integral) control and its
units;
• sketch the open loop response curve for proportional plus reset
control in response to a step disturbance;
• state two general disadvantages of reset control with respect to
overall loop stability and loop response if the control setting is
incorrectly adjusted;
• calculate the reset action in MPR or RPM given a control system’s
parameters;
• state, the purpose of rate or derivative control;
• state the units of derivative control;
• justify the use of rate control on slow responding processes such
as heat exchangers;
• explain why rate control is not used on fast responding
processes.
• sketch the open loop response curve for a control system with
proportional plus derivative control modes;
• state which combinations of the control modes will most likely
be found in typical control schemes;
Note
Science and Reactor Fundamentals – Instrumentation & Control 6
CNSC Technical Training Group
Revision 1

page 2

This module covers the following areas pertaining to instrumentation and
control.
• Pressure
• Flow
• Level
• Temperature
• Neutron Flux
• Control
At the end of training the participants will be able to:
Pressure
• explain the basic working principle of pressure measuring devices,
bourdon tube, bellows, diaphragm, capsule, strain gauge,
capacitance capsule;
• explain the basic operation of a differential pressure transmitter;
• explain the effects of operating environment (pressure,
temperature, humidity) on pressure detectors;
• state the effect of the following failures or abnormalities:
over-pressuring a differential pressure cell or bourdon tube;
diaphragm failure in a differential pressure cell;
blocked or leaking sensing lines; and
loss of loop electrical power.
Flow
• explain how devices generate a differential pressure signal: orifice,
venturi, flow nozzle, elbow, pitot tube, annubar;
• explain how each of the following will affect the indicated flow
signal from each of the above devices:
change in process fluid temperature;
change in process fluid pressure; and
erosion.
• identify the primary device, three-valve manifold and flow;
transmitter in a flow measurement installation;
• state the relationship between fluid flow and output signal in a
flow control loop with a square root extractor;
• describe the operation of density compensating flow detectors;
• explain why density compensation is required in some flow
measurements;
• state the effect on the flow measurement in process with
abnormalities: Vapour formation in the throat, clogging if throat by
foreign material, Leaks in HI or LO pressure sensing lines;
Note
Science and Reactor Fundamentals – Instrumentation & Control 4
CNSC Technical Training Group
Revision 1 – January 2003
Level
• explain how a level signal is derived for: an open vessel, a
closed vessel with dry reference leg, a closed vessel with wet
reference leg;
• explain how a DP cell can be damaged from over pressure if it
is not isolated correctly;
• explain how a bubbler derives level signal for an open and
closed tank;
• explain the need for zero suppression and zero elevation in level
measurement installations;
• describe the effects of varying liquid temperature or pressure on
level indication from a differential pressure transmitter;
• explain how errors are introduced into the DP cell signal by
abnormalities: leaking sensing lines, dirt or debris in the sensing
lines;
Temperature
• explain the principle of operation of temperature detectors: RTD,
thermocouple, bimetallic strip & pressure cylinders;
• state the advantages and disadvantages of RTDs and
thermocouples
• state the effect on the indicated temperature for failures, open
circuit and short circuit;
Flux
• state the reactor power control range for different neutron sensors
and explain why overlap is required: Start-up instrumentation, Ion
Chambers, In Core detectors;
• explain how a neutron flux signal is derived in a BF3 proportional
counter;
• explain the reasons for start-up instrumentation burn-out;
• explain how a neutron flux signal is derived in an ion chamber;
• state the basic principles of operation of a fission chamber
radiation detector;
• state and explain methods of gamma discrimination for neutron ion
chambers;
• explain how the external factors affect the accuracy of the ion
chamber’s neutron flux measurement: Low moderator level, Loss
of high voltage power supply, Shutdown of the reactor;
• describe the construction and explain the basic operating principle
of in-core neutron detectors;
• explain reactor conditions factors can affect the accuracy of the incore
detector neutron flux measurement: Fuelling or reactivity
device movement nearby, Start-up of the reactor, long-term
exposure to neutron flux, Moderator poison (shielding);

BASIC INSTRUMENTATION MEASURING DEVICES AND BASIC PID CONTROL

Section 1 - OBJECTIVES.................................................................... 3
Section 2 - INSTRUMENTATION EQUIPMENT ...................... 7
2.0 INTRODUCTION ......................................................................... 7
2.1 PRESSURE MEASUREMENT .................................................... 7
2.1.1 General Theory ................................................................... 7
2.1.2 Pressure Scales.................................................................... 7
2.1.3 Pressure Measurement ........................................................ 8
2.1.4 Common Pressure Detectors............................................... 9
2.1.5 Differential Pressure Transmitters .................................... 11
2.1.6 Strain Gauges.................................................................... 13
2.1.7 Capacitance Capsule ......................................................... 14
2.1.8 Impact of Operating Environment .................................... 15
2.1.9 Failures and Abnormalities ............................................... 16
2.2 FLOW MEASUREMENT........................................................... 18
2.2.1 Flow Detectors .................................................................. 18
2.2.2 Square Root Extractor....................................................... 25
2.2.3 Density Compensating Flow Detectors ............................ 29
2.2.4 Flow Measurement Errors................................................. 31
2.3 LEVEL MEASUREMENT ......................................................... 33
2.3.1 Level Measurement Basics ............................................... 33
2.3.2 Three Valve Manifold...................................................... 34
2.3.3 Open Tank Measurement.................................................. 36
2.3.4 Closed Tank Measurement ............................................... 36
2.3.5 Bubbler Level Measurement System ............................... 42
2.3.6 Effect of Temperature on Level Measurement ................. 44
2.3.7 Effect of Pressure on Level Measurement ....................... 47
2.3.8 Level Measurement System Errors.................................. 47
2.4 TEMPERATURE MEASUREMENT......................................... 49
2.4.1 Resistance Temperature Detector (RTD)......................... 49
2.4.2 Thermocouple (T/C) ........................................................ 52
2.4.3 Thermal Wells.................................................................. 54
2.4.4 Thermostats......................................................................... 55
2.5 NEUTRON FLUX MEASUREMENT ....................................... 59
2.5.1 Neutron Flux Detection..................................................... 59
2.5.2 Neutron Detection Methods.............................................. 60
2.5.3 Start-up (sub-critical) Instrumentation............................. 61
2.5.4 Fission neutron detectors .................................................. 63
2.5.5 Ion chamber neutron detectors......................................... 64
2.5.6 In-Core Neutron Detectors............................................... 70
2.5.7 Reactor Control at High Power......................................... 77
2.5.8 Overlap of Neutron Detection........................................... 78
REVIEW QUESTIONS - EQUIPMENT ............................................. 81
Science and Reactor Fundamentals – Instrumentation & Control ii
CNSC Technical Training Group


NEXT

F&G Block Diagram

  

Control Systems Engineering Design Criteria

TABLE OF CONTENTS

G-i

Appendix G - Control Systems Engineering Design Criteria

G.1 Introduction.

G.2 Codes and Standards.

G.3 Control Systems Design Criteria .

G.3.1 General Plant Control Philosophy .

G.3.2 Pressure Instruments .

G.3.3 Temperature Instruments 

G.3.4 Level Instruments.

G.3.5 Flow Instruments .

G.3.6 Control Valves 

G.3.7 Instrument Tubing and Installation.

G.3.8 Pressure and Temperature Switches

G.3.9 Field-Mounted Instruments..

G.3.10 Instrument Air System 

G.1 INTRODUCTION

This appendix summarizes the codes, standards, criteria, and practices that will be generally used

in the design and installation of instrumentation and controls for the Bullard Energy Center

(BEC). More specific project information will be developed during execution of the project to

support detailed design, engineering, material procurement and construction specifications.

G.2 CODES AND STANDARDS

The design of the control systems and components will be in accordance with the laws and

regulations of the federal government, the State of California, County of Fresno, and local

ordinances and industry standards. The most current issue or revision of rules, regulations,

codes, ordinances, and standards at the time of filing this Application for Certification (AFC)

will apply, unless otherwise noted. If there are conflicts between cited documents, the more

conservative requirements will apply.

The following codes and standards are applicable to the mechanical aspects of the power facility:

• The Institute of Electrical and Electronics Engineers (IEEE)

• Instrument Society of America (ISA)

• American National Standards Institute (ANSI)

• American Society of Mechanical Engineers (ASME)

• American Society for Testing and Materials (ASTM)

• National Electrical Manufacturers Association (NEMA)

• National Electrical Safety Code (NESC)

• National Fire Protection Association (NFPA)

G.3 CONTROL SYSTEMS DESIGN CRITERIA

G.3.1 General Plant Control Philosophy

An overall distributed control system (DCS) or programmable logic controller (PLC) will be

used as the top-level supervisor and controller for the project. DCS/PLC operator workstations

will be located in the control room of the Administration and Control Building. The intent is for

the plant operator to be able to completely run the entire power island from a DCS/PLC operator

station, without the need to interface to other local panels or devices. The DCS/PLC system will

provide appropriate hard-wired signals to enable control and operation of all plant systems

required for complete automatic operation.

Each combustion turbine generator (CTG) is provided with its own microprocessor-based control

system with both local and remote operator workstations, installed on the turbine-generator

control panels and in the remote main control room, respectively. The DCS/PLC shall provide

supervisory control and monitoring of the turbine generator.

Appendix G

Control Systems Engineering Design Criteria

G-2

Several of the larger packaged subsystems associated with the project include their own PLCbased

dedicated control systems. For larger systems that have dedicated control systems, the

DCS/balance-of-plant (BOP) PLC will function mainly as a monitor, using network data links to

collect, display, and archive operating data.

Pneumatic signal levels, where used, will be 3 to 15 pounds per square inch gauge (psig) for

pneumatic transmitter outputs, controller outputs, electric-to-pneumatic converter outputs, and

valve positioner inputs.

Instrument analog signals for electronic instrument systems shall be 4- to 20- milliampere (ma)

direct current (dc).

The primary sensor full-scale signal level, other than thermocouples, will be between 10

millivolts (mV) and 125 volts (V).

G.3.2 Pressure Instruments

In general, pressure instruments will have linear scales with units of measurement in psig.

Pressure gauges will have either a blowout disk or a blowout back and an acrylic or shatterproof

glass face.

Pressure gauges on process piping will be resistant to plant atmospheres.

Pressure test points will have isolation valves and caps or plugs. Pressure devices on pulsating

services will have pulsation dampers.

G.3.3 Temperature Instruments

In general, temperature instruments will have scales with temperature units in degrees

Fahrenheit. Exceptions to this are electrical machinery resistance temperature detectors (RTDs)

and transformer winding temperatures, which are in degrees Celsius.

Dial thermometers will have 4.5- or 5-inch-in-diameter (minimum) dials and white faces with

black scale markings and will be every-angle type and bimetal actuated. Dial thermometers will

be resistant to plant atmospheres.

Temperature elements and dial thermometers will be protected by thermowells except when

measuring gas or air temperatures at atmospheric pressure. Temperature test points will have

thermowells and caps or plugs.

RTDs will be 100 ohm platinum or 10 ohm copper, ungrounded, three-wire circuits (R100/R0-

1.385). The element will be spring-loaded, mounted in a thermowell, and connected to a cast

iron head assembly.

Thermocouples will be single-element, grounded, spring-loaded, Chromel-Constantan (ANSI

Type E) for general service. Thermocouple heads will be the cast type with an internal

grounding screw.

G.3.4 Level Instruments

Reflex-glass or magnetic level gauges will be used. Level gauges for high-pressure service will

have suitable personnel protection.

Appendix G

Control Systems Engineering Design Criteria

G-3

Gauge glasses used in conjunction with level instruments will cover a range that is covered by

the instrument. Level gauges will be selected so that the normal vessel level is approximately at

gauge center.

G.3.5 Flow Instruments

Flow transmitters will be the differential pressure type with the range matching the primary

element. In general, linear scales and charts will be used for flow indication and recording.

In general, airflow measurements will be temperature-compensated.

G.3.6 Control Valves

Control valves in throttling service will generally be the globe-body cage type with body

materials, pressure rating, and valve trims suitable for the service involved. Other style valve

bodies (e.g., butterfly, eccentric disk) may also be used when suitable for the intended service.

Valves will be designed to fail in a safe position.

Control valve body size will not be more than two sizes smaller than line size, unless the smaller

size is specifically reviewed for stresses in the piping.

Control valves in 600-class service and below will be flanged where economical. Where flanged

valves are used, minimum flange rating will be ANSI 300 Class.

Severe service valves will be defined as valves requiring anti-cavitation trim, low noise trim, or

flashing service, with differential pressures greater than 100 pounds per square inch differential

(psid).

In general, control valves will be specified for a noise level no greater than 90 A-weighted

decibels (dBA) when measured 3-feet downstream and 3-feet away from the pipe surface.

Valve actuators will use positioners and the highest pressure, smallest size actuator, and will be

the pneumatic-spring diaphragm or piston type. Actuators will be sized to shut off against at

least 110 percent of the maximum shutoff pressure and designed to function with instrument air

pressure ranging from 60 to 125 psig.

Handwheels will be furnished only on those valves that can be manually set and controlled

during system operation (to maintain plant operation) and do not have manual bypasses.

Control valve accessories (excluding controllers) will be mounted on the valve actuator unless

severe vibration is expected.

Solenoid valves supplied with control valves will have Class H coils. The coil enclosure will

normally be a minimum of NEMA 4 but will be suitable for the area of installation.

Terminations will typically be by pigtail wires.

Valve position switches (with input to the DCS for display) will be provided for motor operated

valves (MOVs) and open/close pneumatic valves. Automatic combined recirculation flow

control and check valves (provided by the pump manufacturer) will be used for pump minimumflow

recirculation control. These valves will be the modulating type.

Appendix G

Control Systems Engineering Design Criteria

G-4

G.3.7 Instrument Tubing and Installation

Tubing used to connect instruments to the process line will be 3/8- or 1/2-inch-outside diameter

copper or stainless steel as necessary for the process conditions.

Instrument tubing fittings will be the compression type. One manufacturer will be selected for

use and will be standardized as much as practical throughout the plant.

Differential pressure (flow) instruments will be fitted with three-valve manifolds; two-valve

manifolds will be specified for other instruments as appropriate.

Instrument installation will be designed to correctly sense the process variable. Taps on process

lines will be located so that sensing lines do not trap air in liquid service or liquid in gas service.

Taps on process lines will be fitted with a shutoff (root or gauge valve) close to the process line.

Root and gauge valves will be main-line class valves.

Instrument tubing will be supported in both horizontal and vertical runs as necessary.

Expansion loops will be provided in tubing runs subject to high temperatures. The instrument

tubing support design will allow for movement of the main process line

.

G.3.8 Pressure and Temperature Switches

Field-mounted pressure and temperature switches will have either NEMA Type 4 housings or

housings suitable for the environment.

In general, switches will be applied such that the actuation point is within the center one-third of

the instrument range.

G.3.9 Field-Mounted Instruments

Field-mounted instruments will be of a design suitable for the area in which they are located.

They will be mounted in areas accessible for maintenance and relatively free of vibration and

will not block walkways or prevent maintenance of other equipment. Freeze protection will be

provided.

Field-mounted instruments will be grouped on racks. Supports for individual instruments will be

prefabricated, off-the-shelf, 2-inch pipe stand. Instrument racks and individual supports will be

mounted to concrete floors, to platforms, or on support steel in locations not subject to excessive

vibration.

Individual field instrument sensing lines will be sloped or pitched in such a manner and be of

such length, routing, and configuration that signal response is not adversely affected.

Local control loops will generally use a locally-mounted indicating controller (flow, pressure,

temperature, etc.).

Liquid level controllers will generally be the non-indicating, displacement type with external

cages.

Appendix G

Control Systems Engineering Design Criteria