Level Gauges
(Part 2 of 4)

E-Zine October 2008

Click here to review Part 1

Level measurement systems that have mechanical sensors that contact the material include float, magnetostrictive, and retracting level measurement technologies. In general, these level measurement systems use level sensors that have moving parts that are exposed to the material during normal operation.

Float sensors are typically suspended in the vessel whereby its location (height) reflects the location of the surface of the material. Various transmitter designs are available to sense the height of the float and generate a level measurement.

Magnetostrictive level sensors generally consist of a probe on which a float moves so as to locate itself at the surface of the material. Electrical pulses within the probe are reflected back to the transmitter by a magnetic field formed around the probe by a magnet embedded in the float. The level measurement is derived from the amount of time measured for the pulses to travel to and return from the float.

Retracting level sensors are typically floats or weights that are removed from the material during normal operation. Periodically, the float/weight is lowered into the vessel until contact with the material is made. The level measurement is derived from the distance measured prior to the sensor reaching the material.

Level measurement systems that have non-mechanical sensors that contact the material include capacitance, hydrostatic, contact radar, and submerged ultrasonic level measurement technologies. In addition, ultrasonic level sensors that measure liquid level while submerged in the liquid are also available.

Capacitance sensors are typically probes that are inserted into the material, however other shapes and arrangements are available. As the material level increases, the probe becomes more covered, and the capacitance between the probe and the material increases. The increase in capacitance is proportional to the covering of the probe and related to the electrical conductivity (of conductive materials) or the dielectric constant (of insulating materials). The transmitter electronics processes this information and produces a signal proportional to the material level.

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Excerpted from Excerpted from The Consumer Guide to Non-Contact Level Gauges

ISSN 1538-5280