Salty water resistivity is no-ohmic. It is related to ions movements, and so you'll get different values when me= asured with CC or CA, and also depending on the sensing current frequency a= nd amplitude, among others (temperature, salt content, type of ions present= , and a long etc.) You can do a simple experiment. Fill a glass with tap water and put your te= ster probes into it. Read the "resistance". You will see it is changing. Th= en shake the water a little and see what happens. Then remove the tips from= the water, wait some seconds and put them back in contact with water.=A0 You will see ever changing resistance values. That is due to salt ions trav= eling from one tip to the other (your "electrodes"). If you wait long enoug= h you can see litle bubles starting to accumulate in one or both of your te= ster tips: You are producing water electrolysis... To have a kinda usable resistance value use alternating current at a freque= ncy of some kilocycles. Hope it helps. Marcelo Fornaso ________________________________ From: Adam Field To: Microcontroller discussion list - Public. Sent: Friday, September 9, 2011 8:20 PM Subject: Re: [EE]Resistivity of water. 2011/9/9 mark springer : > unit resistivity per area/length > > resistance has to be ? expressed over a Volume. can you have > dimensionless resistance that is not infinite? I do not see it Resistivity of metal films used for capacitor construction is measured in ohms per square, and it is dimensionless. See here for a good explanation: http://www.esdjournal.com/techpapr/ohmmtr/ohm.htm I don't know how that relates to water though, which would have to be ohms per cube. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .