This liquid sensor from Comus has two gold plated metal probes fitted close to the body. When the probes detect the presence of liquids the change in resistance will activate the internal reed switch contacts and cause the contact to close and the circuit to be made.
Liquid drains away from the probes and resistance will drop and the switch contacts will open
Liquids of very poor viscosity may not drain away from the probes and will cause the switch contacts to remain closed
Q. Based on it's method of operation, I assume that the device is only suitable for use with a conductive liquid like water. Would it be ok for the sensor to be continuously immersed in water and does it have to be maintained horizontal or would it operate at any angle?
A. Hi Joe, thank you for your question. The liquid must be conductive but not corrosive. The orientation is not critical. The data sheet can be found here.
Q. I wish to operate this from a 1.5 volt supply.
Will it function?
If it has a reed relay within what is the minimum voltage it will operate from?
A. Thanks for your enquiry Donalex. This product does not appear to have a minimum voltage rating so 1.5 volts will be fine. This product switches a reed switch over only at the presence of liquids, so in effect the contact will simply just switch over when sensing liquids thus making the complete circuit.
Reviews
Actual operation
Reviewed by: Steve W - Monday, June 18, 2012
We have been using these for a little while and to understand properly we disected one. The device is a transistor (or could be an FET) switch where the base current is supplied by the resistance across the external pins (by liquid) and an internal series resistor. The transistor also has a series diode in the collector circuit so that when 'ON' the lowest voltage you get is about 1v ... not 0v. No reed switch!!
Quite Good, but...
Reviewed by: Ralph Bolton - Sunday, May 27, 2012
I've been using a couple of these for a little while. The spec says there's a reed switch inside these, but I've found no evidence of one. Instead, these things work a little like variable resistors (low resistance in water). I wouldn't try and put them in series with a load.
In terms of water level measurements, unlike float switches these have no hysteresis, which may be what you want, or maybe not.
The other thing to note is that these aren't isolated, so start to do strange things if you put them in earthed water (most domestic/commercial plumbing is earthed, so all the water in it is too). However, all said and done, with a bit of care, you can make these things work for you.
