I'm trying to identify what's causing a false trigger on a zone and think it's possibly a contact that's not closing properly (When I close a window slowly, the contact doesn't close, so maybe the magnet is too weak for the spacing., or the reed switch is just gone bad. This is a new problem) Resistance is 9 MOhm for the loop open and 38 ohms it's closed. I would have thought that the 9 MOhm is low and the loop resistance should be higher on open circuit. Weather is really damp, so I'm thinking condensation on the insides of contacts or oxide deposits are contributing to the low reading. Interestingly, resistance is 7 MOhm with probes one way and 9 MOhm with them reversed, so maybe coupling of voltages or electrochemical action between wires and screws is responsible.

Edited February 7, 20224 yr by Eugene's DIY Den

Do tests with the contact removed on open and closed circuit, compare difference you'll find your answer.

Never do tests while circuits is connected to the controls.

Edited February 7, 20224 yr by sixwheeledbeast
typo

3 minutes ago, sixwheeledbeast said:

Do tests with the contact removed on open and closed circuit, compare difference you'll find your answer.

Never do tests while circuits is connected to the controls.

qfa

One leg of the loop is removed from the terminals in the control panel, I wouldn't be measuring the resistance of a circuit that's powered. So the circuit is open and no current can flow in the loop to influence the meter.

Edited February 7, 20224 yr by Eugene's DIY Den

How do you know there isn't cable damage and it's not looping back through mains earth?

4 minutes ago, sixwheeledbeast said:

How do you know there isn't cable damage and it's not looping back through mains earth?

That's possible. Is 0v on this panel connected on the board to earth? (or is this the case in general for panels?)

Edited February 7, 20224 yr by Eugene's DIY Den

No idea, but most panels you can get earth loops like this, hence a method of testing that rules it out.

4 minutes ago, sixwheeledbeast said:

No idea, but most panels you can get earth loops like this, hence a method of testing that rules it out.

Ok, I'll disconnect two legs of the loop and see what results I get.

3 hours ago, Eugene's DIY Den said:

Resistance is 9 MOhm for the loop open and 38 ohms it's closed.

 

you holding the conductors onto the test probes ?

9 minutes ago, MrHappy said:

 

you holding the conductors onto the test probes ?

No, I thought about that. I'm qualified in this area, so it rules out me doing all the silly things ? Good point though.

Edited February 7, 20224 yr by Eugene's DIY Den