Measuring resistance of an electrolyte such as salt water
has been a thread some time back.  Any DC biased
measurement system such as a ohm meter will build up
a cloud of ions around it that will render the measurement
useless in a few seconds.  Just put the leads in a glass
of salt water and watch the reading.  Now stir and see
what happens.

Pardon the trailer junk.  I am a Microsoft victim

-----Original Message-----
From:   Wayne Foletta [SMTP:wayne@ELECTROTEK.COM]
Sent:   Thursday, January 22, 1998 11:40 AM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        Re: inclinometer

Michael:

I needed a inclinometer sensor also. After research I found these
sensors are fairly expensive ($50 bucks and up - not a mainstream market
part).
You may want to build one yourself if you have the components in your
lab. The one I built is a variable resistance three terminal device.
Find or form a curved tube of glass or plastic about 1" - 2" long. The
curve radius depends on the angles you want to measure. Lay bare wires
straight in parallel along the tube length and attach to tube ends. Seal
one end of tube and fill 50% with an electrolyte (use tap water with few
grains of table salt). Seal tube and connect sensor wires to an ohmmeter
to test the sensor operation. For long term use the electrolyte must be
compatible with the sensor wires. Also the sensing current should be as
low as possible. Three or fours wires could be used for higher accuracy
in ratiometric mode.

See this site for a capacitive version:
http://www.euronet.nl/users/ragman/robot1.html

- Wayne Foletta
        BMI - Saratoga, CA