Automatic Tank Gauge
Tank Level Measurement
There are many methods for measuring tank levels, so identifying which technology or instrument to use can be difficult. Some of the common types of level measurement methods include RF capacitance, conductance, hydrostatic tank gauging, radar and ultrasonic.
- Radio Frequency capacitance uses the electrical characteristics of a capacitor to measure the level. The amount of capacitance is determined by the spacing and area between two conductors and the electrical characteristic of the insulating medium between them.
- Conductance is based on the electrical conductivity of the liquid, used for point level detection.
- The radar or microwave method uses electromagnetic waves for continuous level measurement. A sensor beams down a microwave from the top of the vessel. The time it takes for the beam to reach the bottom is used to calculate the level.
- Ultrasonic and sonic methods uses sound waves to determine the level of a liquid. A transducer sends waves downwards onto the surface of the material, then the echoes return to the trasducer which calculates the distance and converts it into a measurement.
Automatic Tank Gauge (ATG)
Hydrostatic tank gauging with an automatic tank gauge (ATG) is one of the oldest and most common methods of measuring liquids. The density of liquid varies with temperature, so the pressure exerted by a column (or head) of liquid in the tank is measured and expressed in relation to the actual temperature of the measured liquid. Through hydrostatic tank gauging transfers in tank farms can be monitored, and accurate information on tank level, mass, density and volume can be provided.
Semrad Pty Ltd provides level transmitters that measure hydrostatic pressure using an air purge connection to the tank. A downpipe or ‘bubbler’ of open ended pipe that extends downward into the tank measures the differential pressure.