Unterminated control port inputs

DeltaXRay

I'm looking for some assistance in being assured of reliable results when operating BLUs from contact closures on the end of very long cables, please.

I've got 150mtr + runs of unscreened conrol cables in an old and electrically 'noisy' building (a large traditional theatre). The switches are simple contact closures, and those switches are on user control panels which can be unplugged, leaving very long cable lengths unterminated.

I am wonderng if these long, low impedance and unterminated cables may lead to false input states. I have observed false states (apparently 'off' persisting after a remote contact closure has been opened). Occassionally, there have been other unexplained states which do not correspond with the actual position of the switches.

I've measured low (e.g. 0.6v) voltages on an input port in the minutes after the contact closure has been opened.

Should I add a pull-up resistor to 5v on these long runs, to overcome any persistence due to capacitance or exposure to electrical 'noise'?
Should I adopt any other measure to protect the integrity of the input ports?

Thanks

Cinch

Well if you have only closure contacts and no resistor leaders or similar, I'd suggest another solution. Use an external 24V power supply and some 24V relais (you can get those soldered to standard \"euro board\" size or mount them on \"rail-mounts\"). Then you wire the 24V to your switch and the switched side to the relay coil. Then use the closure contact of the relay to operate the soundweb port.
This works perfect, I've upgraded some old 100V systems with complex relay structures using soundwebs and are always triggering soundweb control inputs by relays.