ST L4620 Liquid Sensor Probe Design

[Kart31]

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]

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]

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]

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.

 

[Kart31]

Interesting chip, the st datasheet shows some values for the osc, and implies the freq is 50hz, probably a good place to start.

The R-C Circuit? There are a lot of Rs and Cs there. How to narrow down what is what?

The liquid will probably at least some conductivity for it to work.

This is not for a dehumidifier, so the chances are much better of having some.

 

[dr pepper]

The drawing I'm looking at just says rosc and cosc.

 

[Kart31]

The drawing I'm looking at just says rosc and cosc.

But those have values. I'm questioning the sensor input circuit in the upper right, with 3 caps and 3 resistors...and no information on how to specify them.

 

[dr pepper]

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.

 

[rjenkinsgb]

Here you go, and example circuit with all the component values:

**broken link removed**