Process Instrumentation I

Table of Contents

Chapter 1: The Nature of Process Control

Topics: Process variables; On-off control; Measuring data; Controlling variables, Error and feedback; Open- and closed-loop control

Learning Objectives:

• Define setpoint and error.
• Explain how measurement and control are related in industrial processes.
• Describe the four essential functions of an automatic control system.
• Discuss the functions of the CRT and PLC in control systems.
• Identify variables in industrial processes.
• Explain the importance of feedback in a closed-loop control system.

Chapter 2: Elements of Process Control

Topics: Analog and digital control signals; ASCII; Measuring pressure, level, and flow rate; Digital pulse control; System terminology; Controller action

Learning Objectives:

• Discuss the differences between modern automatic control systems and older ones.
• Identify the standard signals used in process control.
• Define the terms commonly used in control terminology.
• Explain the differences between open-loop control and closed-loop control.
• Describe on-off, proportional, integral, derivative, and PID controller action.

Chapter 3: Process Control Signals

Topics: Linear and nonlinear transducers; Signal operating values; Error; Controller output; Pneumatic and electrical signal transmission; Control loops

Learning Objectives:

• Discuss standard signals and linearity and explain how to calculate the value of a variable from an instrument's span and range.
• Describe five common sources of error in signal measurement.
• Discuss the basic principles governing pneumatic signal transmission and explain how a flapper-nozzle device works.
• Describe the function of the controller in a control loop.
• Discuss the basic principles governing electrical signal transmission, including Ohm's law, and list standard current and voltage signals.
• Explain the function of I/P devices in a typical control system and discuss the use of digital signals and optical signals.

Chapter 4: Process Measurement Fundamentals

Topics: The purpose of measurement; Kinds of signals; Measurement requirements; Kinds of displays; Remote vs local display; Errors in measurement systems; Calibration; Noise; Response time; Measurement system deterioration; Observation errors; Transmitters; Proportionality

Learning Objectives:

• Explain why measurement is necessary and discuss conditions that affect the degree of accuracy required.
• Compare the advantages of linear and nonlinear displays.
• Compare analog and digital devices and explain how each is applied to measurement.
• Name five sources of measurement error.
• Discuss proportionality and explain how it applies to transmitters.

Chapter 5: Principles of Transducer Operation

Topics: Outputs; Mechanical, electrical, and pneumatic elements and response; Resistance, voltage, and frequency devices; Combining elements

Learning Objectives:

• Discuss the need for linearity in a process.
• List examples of mechanical and electrical transducer elements.
• Compare pneumatic response and electrical/electronic response in transducers.
• Describe the operation of the bourdon tube, bellows, and diaphragm.
• Name examples of resistance, voltage response, frequency response, and electromechanical devices and explain how they work.
• Discuss the use of the Hall-effect transducer and the differential transducer.

Chapter 6: Basic Process Measurement Systems

Topics: Interaction of system elements; Transmitters; Electrical vs. pneumatic output; Converters; Signal conditioning; Indicators and recorders

Learning Objectives:

• Discuss the basic elements of measuring systems and explain how they interact.
• Describe how a physical quantity is translated into another quantity.
• Discuss the use of transmitters to relay information from one location to another and explain the transfer function.
• Describe the operation of at least five kinds of converters.
• Compare analog and digital indicators and recorders.

Chapter 7: Temperature Measurement Principles and Indicators

Topics: Temperature and temperature scales; Heat; Change of state; Measuring instruments; Color change and melting point indicators

Learning Objectives:

• Define thermal energy and explain the relationships among thermal energy, heat, and temperature in a substance.
• Correlate changes in temperature with changes in a substance's physical state.
• Compare four temperature scales, and convert temperature readings from one scale to another.
• Explain how primary and secondary temperature calibration standards are used.
• Describe various temperature-measuring devices and contrast thermometers and pyrometers.

Chapter 8: Bimetallic and Fluid-Filled Temperature Instruments

Topics: Bimetallic, liquid-in-glass, and filled-system thermometers; Liquid- and gas-filled systems; Vapor-pressure systems; Capillary and bourdon tubes; Temperature transmitters

Learning Objectives:

• Discuss the physical characteristics and operation of bimetallic thermometers.
• Describe how liquid-in-glass thermometers are constructed and how they operate.
• Compare liquid-, gas-, and vapor-filled systems and discuss their advantages and disadvantages.
• Explain how a mercury thermometer operates.

Chapter 9: Electrical Temperature Instruments

Topics: Resistance thermometers; Wheatstone bridge circuits; RTD elements; Thermistors; Thermocouples; Compensation

Learning Objectives:

• Discuss the relationship between temperature and electrical resistance.
• Describe the function of RTD bridge circuits and explain how to calculate lead-wire errors.
• Compare the accuracy, response time, stability, and circuit complexity of RTDs and thermistors.
• Describe the operation of a thermocouple and explain how to compensate for changes in the reference junction temperature.

Chapter 10: Pyrometry

Topics: Principles; Effects of emittance and temperature; Wavelength of radiated energy; Pyrometers

Learning Objectives:

• Discuss the principles that govern noncontact thermal measurements.
• Define electromagnetic radiation and emittance.
• Discuss the characteristics of a blackbody.
• Describe the effects of temperature and emittance on radiation intensity.
• Describe the operation of optical and radiation pyrometers.

Chapter 11: Principles of Pressure in Liquids and Gases

Topics: Properties of matter; Units of pressure; Density; Specific gravity, Gauge, absolute, and atmospheric pressure; Pressure and flow

Learning Objectives:

• Compare the three forms of matter.
• Define pressure and explain the difference between gauge pressure and absolute pressure.
• Discuss the conditions that affect the pressure of a liquid.
• Describe how changes in volume affect the pressure of a gas at a constant temperature.
• Describe how changes in temperature affect the volume of a gas at constant pressure, and the pressure of a gas with a constant volume.
• Discuss the two causes of pressure drop in a pipe carrying liquid from a tank.

Chapter 12: Pressure Sensors

Topics: Manometers; Bourdon tubes; Diaphragm sensor construction and capsule elements; Bellows sensors; Maintaining accuracy; Calibration

Learning Objectives:

• Explain how a manometer works.
• Describe four kinds of bourdon-tube sensors.
• Discuss construction details of bourdon tubes, diaphragms, and bellows.
• Explain how bellows pressure sensors work.
• Describe how calibration may be accomplished and list the steps in calibrating a pressure gauge.
• Explain how normally open and normally closed pressure switches work.

Chapter 13: Pressure Transducers

Topics: Pressure conversion; Potentiometric pressure transducers; P/I, P/P, reluctive, servo, straingauge, and piezoelectric transducers; Response

Learning Objectives:

• Discuss the advantages and disadvantages of the potentiometric pressure transducer.
• Explain how a P/I transducer works.
• Describe the operation of capacitive, reluctive, and servo pressure transducers.
• Compare the three kinds of strain gauge pressure transducers.
• Describe the operation and advantages of the piezoelectric pressure transducer.
• Discuss three environmental conditions that can affect transducer operation.

Chapter 14: Low-Pressure Measurement

Topics: Low pressure; Methods of conversion; DP transmitters, Pressure, slack-diaphragm, ionization, McLeod, thermal conductivity, Pirani, and thermocouple gauges

Learning Objectives:

• Define the pressure unit torr and calculate pressure in specified units when given the pressure in other units.
• Explain the operation of a differential-pressure transmitter and a slack-diaphragm gauge.
• Name two kinds of ionization gauges and describe how they work.
• Explain how the McLeod gauge works.
• Describe the capacitance manometer.
• Compare the operation of the Pirani gauge and the thermocouple gauge.

Chapter 15: Principles of Level Measurement

Topics: Surface-sensing and storage tank gauges; Sight glasses; Magnetic and displacer gauges; Buoyancy; Level, mercury, and magnetic reed switches; Switches with multiple displacers

Learning Objectives:

• Define datum point, and contrast direct and indirect level measurement.
• Describe the main kinds of surface-sensing gauges.
• Define buoyant force and explain how it is used in displacer gauges to measure liquid level.
• Describe maintenance procedures for float devices, displacer gauges, and sight glasses.
• Compare the use of sight glasses, mercury level switches, and magnetic reed switches.

Chapter 16: Electrical Level Instruments

Topics: Conductivity and liquid level; Capacitance probes; Zero and span adjustments; Ultrasonic, resistance, and photoelectric level detectors

Learning Objectives:

• Differentiate between continuous and point level measurements, and between direct and indirect level measurement.
• Describe the operation of a conductance probe in a conducting liquid.
• Describe the operation of a capacitance probe in a dielectric liquid.
• Explain the operation of ultrasonic, resistance, and photoelectric level sensors.
• Describe conductance point level probes, capacitance point level probes, and ultrasonic point level detectors.

Chapter 17: Pressure Head Instruments

Topics: Hydrostatic pressure; Relative density; Pressurized fluids; Air bellows; Air/liquid purge systems; Force-balance diaphragm system

Learning Objectives:

• Define hydrostatic pressure and explain how it is calculated by means of the relative density (specific gravity) of a liquid in a tank.
• Discuss the relationship between pressure head and the location of the pressure (level) indicator.
• Compare the air bellows and air purge systems and discuss advantages for each.
• Explain how a force-balance diaphragm system works.
• Describe the operation of a differential pressure transmitter and explain how it is used to measure level and density.

Chapter 18: Solid Level Measurement

Topics: Weight method; Ultrasonic, microwave, and radiation level detectors; Capacitance and resistance probes; Bob-and-cable tension method

Learning Objectives:

• List the data needed to compute the level of a bulk solid in a bin.
• Describe and compare the operation of wire strain gauges and semiconductor strain gauges.
• Compare the advantages and disadvantages of ultrasonic and microwave level measuring methods.
• Discuss the operation of capacitance probes, resistance probes, and bob-and-cable units in measuring bulk solids.
• Describe how diaphragm switches and tilt switches are used for point level detection in automatic bin fillers.
• Discuss the use of rotating paddle detectors in controlling level within a band.

Chapter 19: Other Level Measurement Instruments

Topics: Radiation level detectors; Ionization, semiconductor, and photoelectric radiation sensors; Infrared detectors; Interface levels

Learning Objectives:

• Explain how radiation level detectors are used for both continuous and point level measurement.
• Describe the operation of ionization radiation sensors, semiconductor radiation sensors, and scintillation counters.
• Discuss the operation of an infrared point level detector.
• Describe several methods of measuring interface levels.
• Explain how range suppression and range elevation are used.
• Discuss the important considerations in equipment selection.

Chapter 20: Properties of Fluid Flow

Topics: Fluids in motion; Establishing a pressure difference; Indicating flow; Factors affecting flow rate; Reynolds number

Learning Objectives:

• Explain the difference between density and relative density (specific gravity).
• Define fluid velocity, viscosity, and volume flow rate.
• Describe laminar flow and turbulent flow.
• Explain how static head, friction head, and velocity head differ from each other.
• Explain how pipe size, pipe friction, and fluid viscosity affect the measurement of fluid flow.

Chapter 21: Primary Measuring Devices

Topics: Flow measurement in filled pipes; Restricting flow; Pressure drop; Orifice plates; Flow nozzles; Turndown and rangeability; Pipe taps

Learning Objectives:

• Describe direct and indirect flow measurement methods.
• Describe how a primary device creates a differential pressure.
• Give at least three examples of common primary devices and explain how each works.
• Describe the significant features of orifice plates and explain their functions.
• Discuss the conditions that determine the length of straight pipe required for each kind of primary flowmeter.

Chapter 22: Secondary Measuring Devices

Topics: Manometers; Liquid pressure measurement; Hazards of mercury; Bellows meter; DP transmitter; Target meter; Deadweight tester

Learning Objectives:

• Explain why both accuracy and precision are required in a secondary measuring device.
• Describe how an inclined manometer differs from a conventional U-tube manometer.
• Explain how to calibrate dry and wet manometers.
• Give examples of secondary measuring devices and explain how they work.
• Explain how to calibrate a differential pressure transmitter and discuss the different outputs available.

Chapter 23: Variable-Area Instruments

Topics: Rotameters; Measuring gas flow; Specific gravity, pressure, and temperature; Float and tube shapes; Piston, vane, and special meters

Learning Objectives:

• Discuss the similarities and differences between rotameters and orifice instruments.
• Compare the benefits of linear and nonlinear scales and explain how a square-root extractor is used.
• Explain how calibration, relative density, viscosity, and temperature affect rotameter readings.
• Describe how changes in the pressure, temperature, and relative density of a gas affect the ability of a rotameter to measure its flow rate.
• Discuss the operation of piston- and vane-type flowmeters and explain why armored rotameters and orifice-plug flowmeters are used.

Chapter 24: Positive-Displacement Meters

Topics: Piston and rotating-vane meters; Nutating-disk, lobed impeller, oval, and helix flowmeters; Dry-gas bellows meter; Calibration

Learning Objectives:

• Describe the advantages and disadvantages of positive-displacement meters.
• Describe the operation of the reciprocating piston meter and the oscillating piston meter.
• Describe the operating principles of the sliding-vane rotary meter and the nutating-disk meter.
• Identify the elements in lobed impeller, oval, and helical flowmeters.
• Explain the operation of a dry-gas bellows meter.
• Discuss the calibration of positive-displacement meters.

Chapter 25: Turbine and Magnetic Flowmeters

Topics: Turbine flowmeter types, components, principles, construction, and installation; Magnetic flowmeter construction, output, and installation

Learning Objectives:

• Describe the operating principles governing turbine flowmeters.
• Discuss the construction of turbine flowmeters.
• Discuss the advantages and disadvantages of turbine flowmeters.
• Describe the operating principle governing magnetic flowmeters.
• Describe significant advantages and disadvantages of magnetic flowmeters.

Chapter 26: Introduction to Controllers

Topics: Process dynamics; Current, position, and time proportioning; Controller modes, actions, terminology, and options; Loop accuracy

Learning Objectives:

• Describe the kinds of controllers most often used in industrial applications.
• Discuss six important problems of process dynamics that controllers must overcome.
• Compare the actions of current proportioning, position proportioning, and time proportioning.
• Name four kinds of controller alarms.
• Discuss the importance of safety in control loops.

Chapter 27: Controller Operation

Topics: Automatic/manual control; Range and span; Direct-, reverse-acting, on/off, and proportional controllers; Current, time, and position-proportioning control; Control strategies

Learning Objectives:

• Explain why automatic/manual control is necessary.
• Explain how on/off controllers work and discuss the difference between on/off and proportional controllers.
• Describe a basic controller tuning process.
• Describe current-, time-, and position-proportioning controllers and name possible uses for each.
• Explain how split control works.

Chapter 28: Controller Modes and Tuning

Topics: Proportional mode; Offset; Integral mode (reset); Derivative mode (rate); Single, two, and three mode controllers; Loop tuning; Step-change response

Learning Objectives:

• Describe the effect of the proportional, integral, and derivative modes on a controller's response to process changes.
• Discuss proper uses for the proportional, integral, and derivative modes.
• Explain how the proportional, integral, and derivative modes affect the tuning of a controller.
• Describe the procedure for tuning a controller by the step-change response method.

Chapter 29: Final Control Elements in Process Loops

Topics: What is a final control element?; Compensation; Feedback loops; A typical system with feedback; Effects of disturbances on performance; Parts of a final control subsystem; Electrical control signals; Amplifiers; Digital signals; Fluidic control signals

Learning Objectives:

• Discuss the function of final control elements in process loops.
• Explain how an actuator is used with the final control element.
• Discuss the effect of a disturbance on the performance of a process loop.
• Describe the three parts of a final control element subsystem.
• Discuss the differences between electric and fluidic control signals in the operation of final control elements

Chapter 30: Pneumatic and Hydraulic Actuators

Topics: Pneumatic Actuators; Effects of changing pressure: Relationship of pressure, volume, and temperature; Effects of changing temperature; Diaphragm actuators; Piston actuators; Positioners; Hydraulic actuators; Hydraulic principles; Mechanical advantage; One-way hydraulic system; Two-way hydraulic system; Uses for hydraulic systems; Hydraulic fluid; Hydraulic maintenance

Learning Objectives:

• Describe the basic principles of operation for both pneumatic and hydraulic actuators.
• Discuss the relationships among pressure, temperature, and volume in a pneumatic system.
• Compare the operation of direct- and reverse-acting actuators.
• Describe the major components of a simple hydraulic system.
• Discuss the characteristics of proper hydraulic fluid and describe elements of hydraulic system maintenance.

Chapter 31: Control Valves

Topics: Control valve components; Kinds of control valves; Globe valves; Cage valves; Butterfly valves; Ball valves; Sliding-gate valves; Diaphragm valves; Split-body valves; Proportional/Servo valves; Other control valves; Control valve flow characteristics; Mechanical requirements; Selecting control vavles

Learning Objectives:

• Describe the components of a control valve.
• Compare the operation and advantages of glove, cage, butterfly, ball, sliding-gate, diaphragm, and split-body valves.
• Discuss the operation, advantages, and disadvantages, of proportional/servo valves.
• Explain the differences in linear, quick-opening, and equal-percentage flow characteristics.
• Discuss mechanical requirements for valves and valve actuator requirements.
• Explain the relationship of flashing and cavitation to proper control valve selection.

Chapter 32: Electric Actuators

Topics: Solenoids; Solenoid-operated valves; Electric motors; DC motors; AC motors; Three-phase induction motors; Single-phase induction motors; Stepper motors; Relay systems; Programmable logic controllers

Learning Objectives:

• Describe the operation of a solenoid with a valve.
• Name the basic components of dc and ac electric motors and explain how they work.
• Discuss the advantages of universal motors and stepper motors.
• Explain how an electromechanical relay works.
• Name at least three kinds of relays in use today and give typical applications for them.
• Discuss the applications and advantages of programmable logic controllers.

Request Exam Copies