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Liquid Level Detection - Sensing Application

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Capacitive sensors are suitable for liquid level detection and can detect liquid level either directly or through non-metallic container walls, sight glasses or non-metallic level tubes.

Capacitive sensors if suspended above a liquid can detect level directly at relatively low ranges with an additional fail-safe feature of capacitive sensors which is that they are more and more likely to detect the liquid the closer it gets to the sensor. In fact a capacitive sensor will still positively detect the proximity of a liquid when it has been immersed in that liquid. This means there will in many instances be less likelihood of a failure and possible overflow than for example if using a single transducer ultrasonic device which features a dead band close to the active sensor head in which nothing will be detected.

Non-invasive liquid level detection can be achieved using capacitive sensors when the material in front of the sensor with liquid present is greater than the material in front of the sensor when liquid is absent and when both fall within the sensors active detection range.

Capacitive sensors can detect through non metallic container walls, glass or perspex sight glasses or level tubes. Effectively the initial material in front of the sensor (perhaps a sight glass or tube) is compensated for in the sensor set up, thus the additional material presented when the liquid is present triggers the sensor. The sensor can consist of a single sensor with analogue output or an array of sensors.

Residue build up inside a container has long provided potential challenge for capacitive sensors in this through wall application.

Compensation for residue build up can be achieved using time values such that the slow build up of residue increases the set point of the sensor and is therefore ignored, while more rapid appearance of the target material will trigger the sensor.

Capacitive probes - probes that are partially immersed in liquid can be used to detect liquid level, the more the probe is immersed as the liquid rises, the greater the output of the sensor. Such probes can also be compensated for residue build up.

Sensatech would be pleased to discuss your liquid level sensing applications if you are having problems resolving them. Sensatech does not at this time produce a standard range of liquid level sensors, all solutions at this stage will therefore be custom.

See Also: Solder Wave Height Sensor

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