Suspected static discharge

[Steve Ford]

Hi, i have a duress button connected to a dry contact panel via a cable run of about 89mtrs.
Every so often I am getting "phantom" activations which i believe are caused by the length if the cable run.
I have been advised that placing a capacitor across the button contacts may resolve this issue
The cable being used is fig 8. 24 awg

Any advise appreciated.

Thanks.

 

[(*steve*)]

It could be static, but it is far more likely to be pickup of interference on your long antenna.

I guess that your long run of wire isn't shielded cable.

Replacing the cable with coax would probably help, but you might get away with a capacitor at one or both ends. These will reduce the speed of operation, but for a button press i don't think that is an issue. Try 0.1uF at the end furthest from the switch first, that may be all you need.

 

[Bluejets]

If all else fails, fit a small interposing relay.

 

[dorke]

89 Meters is a long nice antenna.
It can pick-up fluorescent light ignition,old car ignition, working tool (like a drill) etc.

Do you know what type of "input" there is at the dry contact panel?

The Coax solution would be very costly,twisted pair may be o.k.
A capacitor filter like Steve suggested may help,
you can add(depending on "input type") a series small resistor(say 100) near the input to create a more effective filter.