Not-too-conductive material

Robert Scott · 2008-07-24T19:50:35+00:00

I am designing a very cost-sensitive and low-power water level sensor using aPIC microcontroller. The idea is to run pulse an RC network and measure thetime constant to indicate water level in a reservoir. The resistance is theeffective resistance between two conductive probes partially covered with water.The trouble is when the water is any more than 2 inches deep, the resistance isso low that the PIC cannot source that much current directly from a digitaloutput - not without severely dropping the applied voltage. So I would like theresistance to be higher. I tried replacing the solid metal probes with verythin bare wire (wire-wrap size). That helped a little, but the resistance isstill too low. What I would really like is to make the probe out of a materialthat has much less conductivity - about 100K for a 6-inch length. I canconsider placing a coating on a plastic substrate, but only if that coating isrugged enough to stand up to occasional cleanings with a damp rag. Can anyonesuggest a good probe material for this purpose?Robert ScottYpsilanti, Michigan

Jul 24, 2008 23 Replies

Rate this thread:

RST Engineering (jw) 17 years ago

Or two flat plates held together with nylon hardware and a nylon washer separating the plates at each screw.

Jim

Vote

bill.sloman 17 years ago

Rich's concentric pipes are potentially a lot better shielded than two flat plates (particularly if the outer pipe is grounded).

Three flat plates (with the two outer plates grounded) is even better, and has the advantage that the plates can be double-sided printed circuit boards, with the bridge-driving and monitoring circuitry on the middle board (preferably out of the water and embedded in a tolerably water-resistant encapsulent).

-- Bill Sloman, Nijmegen

Vote

LVMarc 17 years ago

water.

the

If this is for a commercial project please contact me, I can supply probes molded in a robust metal and offer a resistance that you can "RC" for water detection. Marc

Vote

Don Klipstein 17 years ago

water.

the

material

Keep in mind how the conductivity of the water will vary with temperature. Also, you should know how much or how little you have variations of concentration of substances in your water that affect its conductivity.

- Don Klipstein ( snipped-for-privacy@misty.com)

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required