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ST L4620 Liquid Sensor Probe Design

Kart31

Member
Does anyone have a source for information on the probe design or requirements for the ST L4620 Liquid Level Alarm IC? The datasheet says "a very simple sensor (two electrodes) can be used". I'm not having any luck with that. Nor am I having any luck with the keywords I'm using in Google. Does anyone else have any better luck or know where to get more information?
 

Diver300

Well-Known Member
The idea is that the sensor is connected to a simple metal rod that just dips into the liquid at whatever liquid level is to be sensed.

If the liquid doesn't conduct electricity, and the sensor isn't close to the side of a metal tank, you will need a second electrode, to provide an earth path, parallel to the first electrode and near it.
 

Kart31

Member
The idea is that the sensor is connected to a simple metal rod that just dips into the liquid at whatever liquid level is to be sensed.

If the liquid doesn't conduct electricity, and the sensor isn't close to the side of a metal tank, you will need a second electrode, to provide an earth path, parallel to the first electrode and near it.
I opted for the 2 probe option as the bulk of the system is plastic/PVC. One probe connected to Sensor Output (2) and the other to Sensor Input (3). I have also tried picking some (random) values for the external R-C circuitry shown on page one, then tried with only one probe and with a second probe to ground.
 

dr pepper

Well-Known Member
Most Helpful Member
Interesting chip, the st datasheet shows some values for the osc, and implies the freq is 50hz, probably a good place to start.
The liquid will probably at least some condutivity for it to work.
 

dr pepper

Well-Known Member
Most Helpful Member
The drawing I'm looking at just says rosc and cosc.
 

dr pepper

Well-Known Member
Most Helpful Member
Looks like some kind of high pass on the o/p and low pass on the i/p.
Maybe you could see if you can find an application note for that device.
 

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