Introduction to Instrumentation

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: 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 5: 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 6: 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 7: 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 8: 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 9: Electrical 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 10: 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 11: 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 12: Fundamentals of Control Loops

Topics: Definitions; Process sensors; Sensor characteristics; Controllers; Recorders; Signal conditioners; Final control elements

Learning Objectives:

• Explain the difference between an open loop and a closed loop.
• Define error, feedback, disturbance, and feedforward control.
• List several kinds of process sensors and describe the operation of each.
• Explain how accuracy, resolution, sensitivity, linearity, and step response affect sensor operation.
• Describe the functions of process controllers, recorders, signal conditioners, and final control elements.
• Explain the basic operation of a typical control loop.

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