Probe-type LWCO question.

kevin coppinger_4

a set of alligator clips?

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JohnNY

Hi, everyone.

I'm trying to fool a probe type LWCO into working while mounted on a wooden board as part of a complete burner circuit.
I thought I would just have to ground the probe to the control's casing.
That doesn't seem to be the case.

Any ideas?

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Brad White

Is the idea to

get it to make or break, John? I would think you would have trouble getting it to "make" without water.

Would inserting it into a tube you fill with water and have a base drain valve work?

Sounds like a nice demo board you are preparing but that is just my guess. Sorry of not much help.

JohnNY

You guessed it, Brad.

I could conceivably screw a tube of water onto the probe but I feel like I shouldn't have to do that.
A circuit is a circuit, no?

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Brad White

A circuit is a circus....

In principle, yes, but the probe types I have seen have a shielded probe inside the sheath and the protruding one into the pipe. The internal contactor is isolated from the sheath so you would have to get into the works to make a connection.

They are designed this way to minimize shorting out the circuit (keeping the boiler operating without water) if contact is inadvertently made.

I think what you are trying to do is defeat this feature for the purposes of demonstration. As to how that would be done without water? I will shut up now. I have no idea.

Unknown

I'd say,,,

rig yourself a small tank to mount the probe into and fill with water, then you can drain the water in some fashion and the students can watch as the level goes below the probe and the "boiler" shuts down on LWCO.

JohnNY

Yeah...

...I tried that.
What should I be clipping to?

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Hvacman

A direct short...

A direct short won't work, that would simulate the probe grounding against the pipe it is screwed into... Think about a resistor between the probe and ground to simulate the conductivity of water, not steel! The rating of the resistor, I have no idea, they are cheap thru Radio Shack, you may also find a multi pack there. Keep trying different values till the LWCO makes. I hate to recommend them but there really is no other place to put your hands on small electronic components.

martin

Probe LWCO

Just had 2 MM probe cutoffs where water was such that it said we had a shorted probe. MM tech help told me to replace lead to probe with 100 ohm 1/2 watt resister, fixed it. I dont know if that would work on the other end or not.

JohnNY

Ahh-HAAAA!

That sounds like the answer.
Just one question: I should put the resistor between the end of the probe and...what?....the 3/4" threads?



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JohnNY

Well done.

PLUMBARIS and Brian K:

The 100 ohm, 1/2 watt resistor worked like a charm.
Learning stuff every day.

Thank you both VERY MUCH.

Hope to see you(s) at a Big Ugly soon.

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martin

Big Ugly

not a term I've heard before other than a referance to a few of my clients, what is it

JohnNY

It's a thing....

...where everyone gets even more more stupider than usual.
Haha.

It's just a get-together of people that participate here usually involving much food and drink.


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Hvacman

Glad to help...

No problem... I was slated to go to the MA seminar and Big Ugly but work got in the way! It was held not 5 minutes from my house. I'm looking forward to putting faces to names at the next one.