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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