Aux input help

I have an Aux input unit that is trying to read an open/closed circuit on roller door motor to confirm that door is closed and display on shac interface.
Circuit is working fine when contact closed but when Circuit is open it still reads between 5 mohms and 12 mohms and aux unit sees this as a closed contact and won't switch.
I was of the understanding that it only needed about 1000 kohms to read open circuit.
Any suggestions would be greatly appreciated
Ash

 

What model is the aux unit, it may help others determine what tbe issue is.

 

It is a L5504AUX

 

I assume by "5 mohms " you mean 5 Meg Ohms. That will work fine. Anything over about 50K Ohms will give you an open reading. Have you checked that the input function is set to Aux On/Off and not just On/Off?

If you disconnect one of the input leads from the unit, does the group turn off?

 

Correct, when I disconnect 1 x lead into the aux unit it goes open circuit but with 5 Meg ohms it sees it as a closed circuit.
I didn't even get to try any programming of the unit because I couldn't get the dry contact of the aux unit to switch back and forth.

 

5 Meg Ohms will not pull the input down. There is something wrong with your measurements somewhere.

Try putting a resistor above 100K directly across the terminals. I doubt the group will turn on. If it does you have a very unusual fault the the unit.

 

Is the open/close circuit from the roller door motor dry contact, or is there a voltage across the pair?

 

Hi Ash,
Does this unit incorporate a cbus psu???
If so could that add to the problem???

 

No

However having stray voltage on the input could cause this type of problem. The input resistance is quite high at about 10K ohms so long cable runs near other cabling could induce enough stray voltage to be a problem.

Try disconnecting the two wires and see if you can measure any stray voltage with the switch open.

 

The roller door contact is not a dry contact, it has voltage across it.
I will measure for stray voltage when supposedly open circuit and also try a 100k plus resistor to get some clarity tomorrow

 

May be useful if you have any technical info on the Output of the roller door.
You could consider driving a relay coil from the door then using the relay contacts to the Aux input unit

 

The roller door output is supposedly a dry contact with ground, when open circuit it has between 50-150mv stray voltage.
Can this stray voltage cause the aux unit to play up?
Is there a way I can snub out the stray voltage?

 

Unlikely. Are you measuring AC or DC voltage though? Does your meter have a peak function?

I assume the aux input unit works fine if you disconnect the lines completely and just short the 2 inputs with a short piece of wire?

Also, check the voltage across the two inputs of the unit with nothing connected. You should see about 5.2 volts dc. Then connect back up the contact, open the door and check the voltage at the two inputs again.