Level Measurement

Course Number: 776

This course discusses the principles governing various methods of measuring level. It explains the operation of conductive, capacitive, resistive, ultrasonic, and photoelectric devices. It compares the operation of several kinds of pressure-head instruments. It explains the measurement of solids by ultrasonic, microwave, radiation, and other methods. It concludes with a discussion of several special-application devices for both continuous and point level measurement

Recommended Contact Hours - 8

Chapter 1: 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 2: 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 3: 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 4: 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 5: 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.