resistance / resistivity of water and wort

Does anyone know the typical resistivity of wort and tap water?

I'm hoping to use several floatless level switches which operates using resistance. It switches on at 0-4kOhm (presence of liquid), and off at 15kOhm and above (no liquid). Its intended for use with general tap water, so it should work out of the box for water. I'm also thinking that wort with all the additional ions will also have lower resistivity, and so will also work.

Can anyone confirm this is in the ballpark with expected resistivity of water/wort, or shed some light with some figures?

I've done some simple experiments which have puzzled me. Using several different multimeters, I get resistance of a small glass of water of 50-100 KOhm, which seems much higher than I was expecting. Also, the resistance is not linear - it reduces when I bring the electrodes together, but a 10x reduction in distance reduces resistance by no more than 30%.

Any insight much appreciated!

The measured resistance of water (and of any liquid) will vary, according to several factors, some related to the liquid itself (level of purity, nature of impurities, etc), others to the circumstances (temperature), and others to the way you measure ( submerged surface of the electrodes, distance between them, shape, position of one electrode in relation with the other one), and maybe others that now escape me. So, if you want to measure it consistently, you have to start by eliminating the variables you can control (like the characteristics of the electrodes, and the temperature of the water, for example), and measure other variables (like pH) that can also affect your readings.
Even then, don't expect to get a single specific reading. Realistically you will most likely get a given range for each liquid, and I would imagine that for wort it would be quite wide, as its composition varies a lot from style to style, and sometimes even within the same style, just in 2 different recipes.

I'd think, if you want to have a fairly accurate idea of the resistivity of each, you're in for a whole lot of work...

A Practical Guide to Conductivity Measurement

http://www.mbhes.com/conductivity_measurement.htm

My water supply tank with three electrodes





Cheers,
ClaudiusB

Thanks for the responses (and the cool pic!).

I understand there are many variables that affect conductivity, and thankfully I don't need to get an accurate measurement myself - the floatless level switch is doing all that. I was just hoping to try to get a measurement that's in the region of what the level switch is expecting, 0-4kOhm.

Claudius, if you have one, could you post a link to your setup? I'm keen to see how you mounted the electrodes and what you are using as a sensor!

I'm keen to see how you mounted the electrodes and what you are using as a sensor!

Click to expand...

The probes are from:
http://www.lumenite.com/sanitrodethreelevel.html
The monster connector is model 3J-jack with cable



My current controller is an old Warrick.
New model # Warrick series 16D from Gems Sensors.

Claudius, if you have one, could you post a link to your setup?

Click to expand...

http://s238.photobucket.com/albums/ff156/ClaudiusB/Water/


Cheers,
ClaudiusB