Ultrasonic Level Transmitters

Level transmitters provide continuous level measurements over the range of the system rather than at a single point and produce an output signal that directly correlates to the level in the vessel. The output signal generated can be used to display the depth or to actuate control functions.

Level Transmitter Technology:

Float
Float level instruments are mechanical devices that move in conjunction with the level of the liquid medium. The movement of the float indicates the level and can actuate a switch or create an output signal. Float level instruments are an economical and practical solution.

Depth / Pressure
Pressure based level instruments use pressure sensors at the bottom of a tank to measure the force exerted per unit area. For level applications, that force is the weight of the medium to be measured plus any pressure acting on the surface. By knowing the density of the medium and compensating for the effect of ambient pressure, the resulting value can be converted to a level measurement. The output signal generated can be used to display the depth or to actuate control functions.

Radar
Radar level instruments measure the time required for a microwave pulse and its reflected echo to make a complete round trip between the transducer and the sensed material level. That value is then converted into a level measurement.
Radar level instruments utilize non-contact measurement unaffected by changes in temperature, pressure or the presence of vapor. Accuracy of radar level instruments depend upon bandwidth and frequency but is unaffected by density, conductivity or dielectric constant of the medium.

Ultrasonic
Ultrasonic level instruments use sound waves to determine the level of liquids, solids, and slurries. Consisting of two elements, a high efficiency transducer and an electronic transceiver, these non-contact systems measure the time for an ultrasonic pulse and reflected echo make a complete round trip between the transducer and the sensed material level. Ultrasonic systems can also measure open channel flow, volumetric output, and differential level.

While highly accurate, ultrasonic level instruments must compensate for temperature. Applications involving heavy dust, foam or surface turbulence are not advised as the ultrasonic pulse can be absorbed or otherwise distorted affecting accuracy.

Capacitive
Capacitance level instruments operate on the electrical characteristics of a capacitor. A capacitor is made of two conductive plates isolated from one another by a dielectric. Capable of storing an electrical charge, that charge varies depending upon the conductivity of the dielectric.

In level applications, the medium to be measured serves the dielectric while the tank wall and sensor are the conductive plates. As the tank fills the sensor probe is exposed to a more conductive material than air and the capacitance value of the probe increases. This value is converted to an output signal that can be used to display the level or activate a switch or control.

Capacitance level instruments do not work well with low capacitance materials like plastic, sand, etc. or with materials having a large particle size (and thus a lot of air pockets). Material build-up along the probe can also make readings inaccurate.