With the wide variety of approaches to level measurement and as many as 163 suppliers offering one or more types of level-measuring instrument, identifying the right one for your application can be very difficult. In recent years, technologies that capitalized on microprocessor developments have stood out from the pack.

For example, the tried-and-true technique of measuring the head of a liquid has gained new life thanks to “smart” differential pressure (DP) transmitters. Today’s local level-measuring instruments can include diagnostics as well as configuration and process data that can be communicated over a network to remote monitoring and control instrumentation. One model even provides local PID control. Some of the most commonly used liquid-level measurement methods are:

• RF capacitance

• Conductance (conductivity)

• Hydrostatic head/tank gauging

• Radar

• Ultrasonic

Before you can decide which one is right for your application, however, you need to understand how each works and the theory behind it. (Each method has its own abbreviations, so you may find the sidebar, “Abbreviations for Common Flow Sensing Terminology,”, a useful reference during the discussions that follow.)