This site uses cookies to deliver our services and provide a basic level of website functionality. The four different types of cookies are: Strictly Necessary cookies, Functionality cookies, Performance cookies and Advertising cookies. By checking the box and clicking the button below, you are informing Rapid Electronics Ltd that you agree to the use of these cookies as detailed in our Privacy Policy.

Industry Schools FE/HE Site: Industry Site: Schools Site: FE/HE Site: Mobile

Comus WS1 Liquid Sensor

Order Code:  


Brand: Comus  MPN: WS1 
 Report an error
Qty Was Unit Price (Ex VAT)
1+ £4.53   £3.71
25+ £4.11   £3.37
100+ £3.75   £3.08

Get a quote for large quantities here

Price per unit {{ IncVat ? 'Inc' : 'Ex' }} VAT
Contact us for lead times on larger quantities
7 in Stock, despatched same dayAdditional quantity lead time 14 days

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

Contact formForm A normally open
Switching voltage100V DC max.
Switching current0.5A max.
Switching capacity10W max.
Contact resistance0.5Ω
Operating temperature–5°C to +80°C
Case materialWhite plastic
LiquidsNon corrosive. Not heavy oils
CableTwin core insulated. 1.8m

To use this facility please Sign In. Alternatively use our Quotation page.

Sign In


*Question functionality currently disabled

12 April 2018 Question by: Joe | Product code: 78-2090
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.

02 January 2012 Question by: Donalex | Product code: 78-2090
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.


Actual operation

Reviewed by: Steve W - 18 June 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 - 27 May 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.