Short leading to autofill failure

is about as close as I have come to finding a homebrew autofill circuit. Just got a LSM-85 that has a blown brain box; I think that I will do a small circuit board to drive 3 ssr's - autofill solenoid, group solenoid, and motor. This is my third Hx and this controller would be about as simple as it gets - if I can find a reliable circuit for autofill.

Anyone found one? The above link was about as close as I have seen.

Thanks
Joe

try this
http://www.alliedelec.com/search/produc ... U=70158794

Crouzet actually makes 4 variants of this control, 3 of which are in a relay housing.

I believe Omron automation makes a similar kind of product.

Sean

I think your choices are either measuring the resistance to see if it changes enough to monitor or some sort of oscillator who's frequency changes when water touches the probe. I'd certainly try resistance first.

Ira

Thanks guys,

Sean, I am concerned that the spec sheet calls for about 25K ohm sensitivity, I think that would work for a solution containing electrolytes in greater quantities that typical "mountain spring water". From what I have seen elsewhere on this board, a typical resistance to ground is in the megohm range for an autofill probe sitting in a tank.

I'm going to play a little with this over the weekend. I would like to do it as simply as possible; the big question is how real the risk of electrolysis is - scaling is enough of a problem. if you don't push as much charge out as pull charge in to a probe, stuff either leaves or builds up on the probe. The easiest way to do that is with some kind of charge pump, and I haven't thought about those things in decades.

I think I can do a simple resistance measurement circuit with three 2n3904 transistors and a couple of pots to create a latching output with hysteresis; key thing is to have the pump turn on at a different level than it turns off at. It may be that a JFET is needed for one of those transistors.

I am also looking at sensing the water level in the sight glass with a pair of wires taped on either side of the sight tube and using it to sense capacitance. I think that may be a more robust signal and not subject to scaling.

Thank you for the suggestions-

Joe