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Instrumentation and Control

DOE Fundamentals Handbook - Instrumentation and Control $17.95

 

The Instrumentation and Control Fundamentals Handbook discusses information on temperature, pressure, flow and level detection systems, position indication systems, process control systems and radiation detection principles. The information in the handbook is presented to provide a foundation for applying engineering concepts. It presents more than enough information to provide YOU with a fundamental knowledge level sufficient to understand the construction, operation and failure modes of various types of instrumentation and control systems, as well as the principles and theoretical concepts behind them.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DOE FUNDAMENTALS HANDBOOK INSTRUMENTATION AND CONTROL

 

VOLUMES 1-2

The Department of Energy (DOE) Fundamentals Handbooks consist of ten academic subjects, which include Mathematics; Classical Physics; Thermodynamics, Heat Transfer, and Fluid Flow; Instrumentation and Control; Electrical Science; Material Science; Mechanical Science; Chemistry; Engineering Symbology, Prints, and Drawings; and Nuclear Physics and Reactor Theory. The handbooks were first published as Reactor Operator Fundamentals Manuals in 1985 for use by DOE category A reactors. The subject areas, subject matter content, and level of detail of the Reactor Operator Fundamentals Manuals were determined from several sources and prepared by the DOE Training Coordination Program. Each handbook contains an abstract, a foreword, an overview, learning objectives, and text material, and is divided into modules.

The Instrumentation and Control Fundamentals Handbook was originally developed to assist nuclear facility operating contractors provide operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of instrumentation and control systems. The handbook includes information on temperature, pressure, flow, and level detection systems; position indication systems; process control systems; and radiation detection principles. This information will provide you with an understanding of the basic operation of various types of DOE nuclear facility instrumentation and control systems. The Instrumentation and Control handbook presents more than enough information to provide the reader with a fundamental knowledge level sufficient to understand the advanced theoretical concepts presented in other subject areas, and to better understand basic system and equipment operations.

The Instrumentation and Control handbook consists of seven modules that are contained in two volumes. The following is a brief description of the information presented in each module of the handbook.

 

 

 

 

 

 

 

 

Volume 1 of 2


Module 1 - Temperature Detectors

-Explanation- This module describes the construction, operation, and failure modes for various types of temperature detectors and indication circuits.

 

 

 

RTD elements are usually long, spring-like wires surrounded by an insulator and enclosed in a sheath of metal. Figure 2 shows the internal construction of an RTD.

This particular design has a platinum element that is surrounded by a porcelain insulator. The insulator prevents a short circuit between the wire and the metal sheath.

Inconel, a nickel-iron-chromium alloy, is normally used in manufacturing the RTD sheath because of its inherent corrosion resistance. When placed in a liquid or gas medium, the Inconel sheath quickly reaches the temperature of the medium. The change in temperature will cause the platinum wire to heat or cool, resulting in a proportional change in resistance.

This change in resistance is then measured by a precision resistance measuring device that is calibrated to give the proper temperature reading. This device is normally a bridge circuit, which will be covered in detail later in this text.

 

 

 

 

 

 

 

 

 

 

RESISTANCE TEMPERATURE DETECTORS (RTDs)

Temperature
RTD Construction
Summary

THERMOCOUPLES

Thermocouple Construction
Thermocouple Operation

Summary

FUNCTIONAL USES OF TEMPERATURE DETECTORS

Functions of Temperature Detectors
Detector Problems
Environmental Concerns
Summary

TEMPERATURE DETECTION CIRCUITRY

Bridge Circuit Construction
Bridge Circuit Operation
Temperature Detection Circuit
Temperature Compensation
Summary


Module 2 - Pressure Detectors

-Explanation- This module describes the construction, operation, and failure modes for various types of pressure detectors and indication circuits.

 

 

 

Bourdon Tube-Type Detectors

The bourdon tube pressure instrument is one of the oldest pressure sensing instruments in use today. The bourdon tube (refer to Figure 2) consists of a thin-walled tube that is flattened diametrically on opposite sides to produce a cross-sectional area elliptical in shape, having two long flat sides and two short round sides. The tube is bent lengthwise into an arc of a circle of 270 to 300 degrees. Pressure applied to the inside of the tube causes distention of the flat sections and tends to restore its original round cross-section. This change in cross-section causes the tube to straighten slightly.

Since the tube is permanently fastened at one end, the tip of the tube traces a curve that is the result of the change in angular position with respect to the center. Within limits, the movement of the tip of the tube can then be used to position a pointer or to develop an equivalent electrical signal (which is discussed later in the text) to indicate the valve of the applied internal pressure.

 

 

 

 

 

 

PRESSURE DETECTORS

Bellows-Type Detectors
Bourdon Tube-Type Detectors
Summary

PRESSURE DETECTOR FUNCTIONAL USES

Pressure Detector Functions
Detector Failure
Environmental Concerns
Summary

PRESSURE DETECTION CIRCUITRY

Resistance-Type Transducers
Inductance-Type Transducers
Capacitive-Type Transducers
Detection Circuitry
Summary


Module 3 - Level Detectors

-Explanation- This module describes the construction, operation, and failure modes for various types of level detectors and indication circuits.

 

 

 

 

Steam Generator Level Instrument

Figure 14 illustrates a typical steam generator level detection arrangement. The ÄP detector measures actual differential pressure. A separate pressure detector measures the pressure of the saturated steam. Since saturation pressure is proportional to saturation temperature, a pressure signal can be used to correct the differential pressure for density. An electronic circuit uses the pressure signal to compensate for the difference in density between the reference leg water and the steam generator fluid.

 

 

 

 

 

 

 

 

LEVEL DETECTORS

Gauge Glass
Ball Float
Chain Float
Magnetic Bond Method
Conductivity Probe Method
Differential Pressure Level Detectors
Summary

DENSITY COMPENSATION

Specific Volume
Reference Leg Temperature Considerations
Pressurizer Level Instruments
Steam Generator Level Instrument
Summary

LEVEL DETECTION CIRCUITRY

Remote Indication
Environmental Concerns
Summary

Module 4 - Flow Detectors

-Explanation- This module describes the construction, operation, and failure modes for various types of flow detectors and indication circuits.

 

 

 

 

Venturi Tube

The venturi tube, illustrated in Figure 3, is the most accurate flow-sensing element when properly calibrated. The venturi tube has a converging conical inlet, a cylindrical throat, and a diverging recovery cone. It has no projections into the fluid, no sharp corners, and no sudden changes in contour.

The inlet section decreases the area of the fluid stream, causing the velocity to increase and the pressure to decrease. The low pressure is measured in the center of the cylindrical throat since the pressure will be at its lowest value, and neither the pressure nor the velocity is changing. The recovery cone allows for the recovery of pressure such that total pressure loss is only 10% to 25%. The high pressure is measured upstream of the entrance cone. The major disadvantages of this type of flow detection are the high initial costs for installation and difficulty in installation and inspection.

 

 

 

 

 

Pitot Tube

The pitot tube, illustrated in Figure 5, is another primary flow element used to produce a differential pressure for flow detection. In its simplest form, it consists of a tube with an opening at the end. The small hole in the end is positioned such that it faces the flowing fluid. The velocity of the fluid at the opening of the tube decreases to zero. This provides for the high pressure input to a differential pressure detector. A pressure tap provides the low pressure input.

 

 

 

 

 

 

 

 

 

 

 

 

For the precise measurement of gas flow (steam) at varying pressures and temperatures, it is necessary to determine the density, which is pressure and temperature dependent, and from this value to calculate the actual flow. The use of a computer is essential to measure flow with changing pressure or temperature. Figure 10 illustrates an example of a computer specifically designed for the measurement of gas flow. The computer is designed to accept input signals from commonly used differential pressure detectors, or from density or pressure plus temperature sensors, and to provide an output which is proportional to the actual rate of flow. The computer has an accuracy better than +0.1 % at flow rates of 10% to 100%.

 

 

 

 

 

 

 

 

 

 

 

HEAD FLOW METERS

Orifice Plate
Venturi Tube
Dall Flow Tube
Pitot Tube
Summary

OTHER FLOW METERS

Area Flow Meter
Displacement Meter
Hot-Wire Anemometer
Electromagnetic Flowmeter
Ultrasonic Flow Equipment
Summary

STEAM FLOW DETECTION

Summary

FLOW CIRCUITRY

Circuitry
Use of Flow Indication
Environmental Concerns
Summary

Module 5 - Position Indicators

-Explanation- This module describes the construction, operation, and failure modes for various types of position indicators and control circuits.

 

 

 

 

Control transformer synchros are used when only a voltage indication of angular position is desired. It is similar in construction to an ordinary synchro except that the rotor windings are used only to generate a voltage which is known as an error voltage. The rotor windings of a control transformer synchro are wound with many turns of fine wire to produce a high impedance. Since the rotor is not fed excitation voltage, the current drawn by the stator windings would be high if they were the same as an ordinary synchro; therefore, they are also wound with many turns of fine wire to prevent excessive current.

During normal operation, the output of a control transformer synchro is nearly zero (nulled) when its angular position is the same as that of the transmitter.

A simple synchro system, consisting of one synchro transmitter (or generator) connected to one synchro receiver (or motor), is shown in Figure 2.

 

 

 

 

 

 

 

Position detection devices provide a method to determine the position of a valve or control rod. The four types of position indicators discussed were limit switches, reed switches, potentiometer valve position indicators, and LVDTs (Figure 7). Reed and limit switches act as ON/OFF indicators to provide open and closed indications and control functions. Reed switches can also be used to provide coarse, incremental position indication.

The indicating and control circuitry provides for remote indication of valve or rod position and/or various control functions. Position indications vary from simple indications such as a light to meter indications showing exact position.

Control functions are usually in the form of interlocks. Pump isolation valves are sometimes interlocked with the pump. In some applications, these interlocks act to prevent the pump from being started with the valves shut. The pump/valve interlocks can also be used to automatically turn off the pump if one of its isolation valves go shut or to open a discharge valve at some time interval after the pump starts.

Valves are sometimes interlocked with each other. In some systems, two valves may be interlocked to prevent both of the valves from being opened at the same time. This feature is used to prevent undesirable system flowpaths.

Control rod interlocks are normally used to prevent outward motion of certain rods unless certain conditions are met. One such interlock does not allow outward motion of control rods until the rods used to scram the reactor have been withdrawn to a predetermined height. This and all other rod interlocks ensure that the safety of the reactor remains intact

 

 

 

 

 

 

 

 

HEAD FLOW METERS

Orifice Plate
Venturi Tube
Dall Flow Tube
Pitot Tube
Summary

OTHER FLOW METERS

Area Flow Meter
Displacement Meter
Hot-Wire Anemometer
Electromagnetic Flowmeter
Ultrasonic Flow Equipment
Summary

STEAM FLOW DETECTION

Summary

FLOW CIRCUITRY

Circuitry
Use of Flow Indication
Environmental Concerns
Summary


Volume 1 of 3


Module 6 - Radiation Detectors

-Explanation- This module describes the principles of radiation detection, detector operation, circuit operation, and specific radiation detector applications.

 

 

 

 

 

The newest electroscope utilizes a quartz fiber and has many advantages over the gold-leaf type. It is portable, less dependent on position, much smaller in size, and more sensitive. The capacity of the quartz fiber electroscope is about 0.2 pico-farads, and its voltage sensitivity is about one volt per division on the scale. The sensitive element is a fine gold plated quartz fiber mounted on a parallel metal support. Figure 22 illustrates a quartz fiber electroscope.

 

 

 

 

 

 

 

 

 

 

Scintillation counters are constructed by coupling a suitable scintillation phosphor to a light-sensitive photomultiplier tube. Figure 25 illustrates an example of a scintillation counter using a thallium-activated sodium iodide crystal.

There are three classes of solid state scintillation phosphors: organic crystals, inorganic crystals, and plastic phosphors.

Inorganic crystals include lithium iodide (LiI), sodium iodide (NaI), cesium iodide (CsI), and zinc sulfide (ZnS). Inorganic crystals are characterized by high density, high atomic number, and pulse decay times of approximately 1 microsecond. Thus, they exhibit high efficiency for detection of gamma rays and are capable of handling high count rates.

Organic scintillation phosphors include naphthalene, stilbene, and anthracene. The decay time of this type of phosphor is approximately 10 nanoseconds. This type of crystal is frequently used in the detection of beta particles.

Plastic phosphors are made by adding scintillation chemicals to a plastic matrix. The decay constant is the shortest of the three phosphor types, approaching 1 or 2 nanoseconds. The plastic has a high hydrogen content; therefore, it is useful for fast neutron detectors.

 

 

 

 

 

 

 

Gamma spectroscopy is a radiochemistry measurement method that determines the energy and count rate of gamma rays emitted by radioactive substances. Gamma spectroscopy is an extremely important measurement. A detailed analysis of the gamma ray energy spectrum is used to determine the identity and quantity of gamma emitters present in a material.

The equipment used in gamma spectroscopy includes a detector, a pulse sorter (multichannel analyzer)and associated amplifiers and data readout devices. The detector is normally a sodium iodide (NaI) scintillation counter. Figure 27 shows a block diagram of a gamma spectrometer.

 

 

 

 

 

 

 

 

RADIATION DETECTION TERMINOLOGY

Electron-Ion Pair
Specific Ionization
Stopping Power
Summary

RADIATION TYPES

Alpha Particle
Beta Particle
Gamma Ray
Neutron
Summary

GAS-FILLED DETECTOR

Summary

DETECTOR VOLTAGE

Applied Voltage Summary

PROPORTIONAL COUNTER

Summary

PROPORTIONAL COUNTER CIRCUITRY

Summary

IONIZATION CHAMBER

Summary

COMPENSATED ION CHAMBER

Summary

ELECTROSCOPE IONIZATION CHAMBER

Summary

GEIGER-MÜLLER DETECTOR

Summary

SCINTILLATION COUNTER

Summary

GAMMA SPECTROSCOP

Summary

MISCELLANEOUS DETECTORS

Self-Powered Neutron Detector
Wide Range Fission Chamber
Activation Foils and Flux Wires
Photographic Film
Summary


Module 7 - Principles of Control Systems

-Explanation- This module describes the principles of operation for control systems used in evaluating and regulating changing conditions in a process.

 

 

 

 

 

 

Example of a Proportional Process Control System

Figure 16 illustrates a process system using a proportional temperature controller for providing hot water.

Steam is admitted to the heat exchanger to raise the temperature of the cold water supply. The temperature detector monitors the hot water outlet and produces a 3 to 15 psi output signal that represents a controlled variable range of 100o to 300oF. The controller compares the measured variable signal with the setpoint and sends a 3 to 15 psi output to the final control element, which is a 3-in control valve.

The controller has been set for a proportional band of 50%. Therefore, a 50% change in the 200oF span, or a change of 100oF, causes a 100% controller output change.

The proportional controller is reverse-acting so that the control valve throttles down to reduce steam flow as the hot water outlet temperature increases; the control valve will open further to increase steam flow as the water temperature decreases.

 

 

 

 

 

 

 

 

 

 

 

The setpoint indicator, located in the center of the upper half of the controller, indicates the setpoint (desired value) selected for the controller. The scale may be marked 0% to 100% or correspond directly to the controlled variable (e.g., 0 - 1000 psig or -20°F to +180°F).

The setpoint adjustment, located right of the setpoint indicator, is a thumbwheel type adjustment dial that allows the operator to select the setpoint value. By rotating the thumbwheel, the scale moves under the setpoint index line.

The deviation indicator, located left of the setpoint indicator, displays any error (+10%
to -10%) between setpoint value and actual controlled variable value. With no error, the deviation pointer stays at mid-scale, in line with the setpoint index mark. If the controlled variable is lower than setpoint, the deviation indicator deflects downward. If higher, the indicator deflects upward. An example of this is shown in Figure 33.

The output meter is the horizontally positioned meter below the deviation and setpoint indicators. It indicates controller output signal in percent. This particular controller ranges from zero to 100% current. However, this will correspond to an air signal for pneumatic controllers.

Snap-in tabs, above each end of the output meter, indicate the direction the final control element moves for a change in the output signal. Tabs normally read "open-close" for control valves and "slow-fast" for variable-speed motors, or other appropriate designations.

The manual-automatic (M-A) transfer switch, immediately below the output meter, selects operating mode of the controller.

A manual output adjust knob, in the center of the M-A transfer switch, varies the controller output signal in manual mode of operation. The knob is rotated clockwise to increase the signal and counterclockwise to decrease the signal.

 

 

 

 

 

 

 

 

 

 

An important safety feature is provided by the spring in an actuator. It can be designed to position a control valve in a safe position if a loss of supply air occurs. On a loss of supply air, the actuator in Figure 36 will fail open. This type of arrangement is referred to as "air-to-close, spring-to-open" or simply "fail-open." Some valves fail in the closed position. This type of actuator is referred to as "air-to-open, spring-to-close" or "fail-closed." This "fail-safe" concept is an important consideration in nuclear facility design.

 

 

 

 

 

 

 

 

 

PRINCIPLES OF CONTROL SYSTEMS

Introduction

Terminology
Automatic Control System
Functions of Automatic Control
Elements of Automatic Control
Feedback Control
Summary

CONTROL LOOP DIAGRAMS

Terminology
Feedback Control System Block Diagram
Process Time Lags
Stability of Automatic Control Systems
Summary

TWO POSITION CONTROL SYSTEMS

Controllers
Two Position Controller
Example of Two Position Control
Modes of Automatic Control
Summary

PROPORTIONAL CONTROL SYSTEMS

Control Mode
Proportional Band
Example of a Proportional Process Control System
Summary

RESET (INTEGRAL) CONTROL SYSTEMS

Reset Control (Integral)
Definition of Integral Control
Example of an Integral Flow Control System
Properties of Integral Control
Summary

PROPORTIONAL PLUS RESET CONTROL SYSTEMS

Proportional Plus Reset
Example of Proportional Plus Reset Control
Reset Windup
Summary

PROPORTIONAL PLUS RATE CONTROL SYSTEMS

Proportional-Derivative
Definition of Derivative Control
Example of Proportional Plus Rate Control
Applications
Summary

PROPORTIONAL-INTEGRAL-DERIVATIVE CONTROL SYSTEMS

Proportional-Integral-Derivative
Proportional Plus Reset Plus Rate Controller Actions
Summary

CONTROLLERS

Controllers
Control Stations
Self-Balancing Control Stations
Summary

VALVE ACTUATORS

Actuators
Pneumatic Actuators
Hydraulic Actuators
Electric Solenoid Actuators
Electric Motor Actuators
Summary

 

 

 

 

 

 

 

DOE Fundamentals Handbook - Instrumentation and Control $17.95

 

 

 

The Instrumentation and Control Fundamentals Handbook discusses information on temperature, pressure, flow and level detection systems, position indication systems, process control systems and radiation detection principles. The information in the handbook is presented to provide a foundation for applying engineering concepts. It presents more than enough information to provide YOU with a fundamental knowledge level sufficient to understand the construction, operation and failure modes of various types of instrumentation and control systems, as well as the principles and theoretical concepts behind them.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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