Liquid Level Sensors

Liquid level sensors are used to detect liquid levels or interfaces between liquids such as oil and water or liquids and solids.  Liquid level sensors can be defined as a sensor or transducer, or an integrated system, with instrumentation and control capabilities. Continuous or point level sensing can be chosen depending upon the application.  Point liquid level sensors often trigger an alarm or turn off the system based upon a specific limit.  

Some applications rely upon continuous liquid level monitoring.   Continuous liquid level sensing can use a number of methods including pressure, ultrasound, and vibration.  Pressure membrane liquid level sensors and differential liquid level sensors measure the pressure or change in pressure in a vessel such as a holding or storage tank.  Ultrasonic / sonic liquid level sensors measure the length of time it takes for a reflected sound wave to return to a transducer. Vibrating / tuning fork liquid level sensors use a piezoelectric crystal or other technology to vibrate a probe, then constantly monitor the presence, absence, increase or decrease of that vibration. In some applications, it is necessary to measure the level of a fluid without having direct contact with the media.  In applications where the liquid is highly corrosive, non-contact meter technologies such as ultrasonic / sonic liquid level sensors and/or radar / microwave liquid level sensors may be optimal. Media type, surface properties, and temperature are a consideration when choosing ultrasonic liquid level sensors.  For example, if a mixer is a part of the tank assembly, the fluid surface may include foam, waves, or additional turbulence. 

Some liquid level sensing systems are programmable and will filter the variations in signal that are due to these factors.  Radar / microwave liquid level sensors measure the microwave pulse emitted toward the process material; the pulse is reflected back by surface of material and picked up by a receiver.  Level is inferred from the time of flight. This is a non-invasive method that is effective in various applications where suspended solids, slurries, and sludge are part of the fluid that is measured such as in the pulp and paper and wastewater industries.  Radio frequency (RF) liquid level sensing is dependent upon the materials used to measure the capacitance or impedance of the liquid present or absent.  In contact applications, a probe is top mounted or side mounted in a tank or vessel.  A radio signal is emitted from a source.  When the liquid media covers the probe, the liquid acts as an insulator between the wall and the probe.  A change in the modulated signal is relayed to a switch for an alarm, or to a remote location where level status can be monitored or controlled.  A material with a high dielectric constant will have a higher conductivity.  The interaction of the chemical, the vessel wall material, and/or the material chosen for the sheath of the probe affects the total circuit.  Instead of a radio frequency, electrical conductivity / resistance liquid level sensors use a low-voltage power source applied across separate electrodes.  A conductive liquid contacting both probes completes a conductive circuit.   Other liquid level sensors include mechanical / magnetic floats, air bubblers, and rotation paddles.  These liquid level sensors may have an analog or digital output with an indicating display or other user interface.

• Magnetostrictive Level Sensors by David Nyce and Adrian Totten
  Many types of industrial processes utilize Liquid Level sensors to provide the information needed to monitor and control the process. This enables the design parameters to be maintained in order to...
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• Accurate Measurement of Spirits (.pdf)
  Seeking a new method of liquid level measurement, the Seagram's US distillery is retrofitting its facility to utilize magnetostrictive liquid level sensors to measure its spirit and carbonated...
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• Seagram's
  Seeking a new method of liquid level measurement, the Seagram's US distillery is retrofitting its facility to utilize magnetostrictive liquid level sensors to measure its spirit and carbonated...
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Part Numbers for Liquid Level Sensors