24vdc digital signal cable length limit

[ronmarx]

what is the longest practical cable length for a 24vdc digital(on/off)siganl ?

I have a Piloteye 2000 flare monitor between 2500ft-3000ft away from control room and need to get digital(on/off) signal to control room. What problems might I encounter ?

 

[dpc]

The main issue would voltage drop due to current. If you going to a digital input or small relay, that should not be a problem.

I'd run shielded twisted pair cable and keep it away from any high current power circuits.

"The perfect is the enemy of the good." -- Voltaire

 

[ScottyUK]

I used a successfully used a solid state relay as an interface relay at a distance of nearly a mile from a switched 24V source. It was a solution to someone else's poor design, but worked very well. The key is that the SSR 'coil' - actually an opto-coupler - accepts anything from about 3V DC to about 32V DC as an 'on' state which means volt-drops which would cause problems for an electro-mechanical relay don't bother the SSR. It's worth including a burden resistance of a few hundred ohms or so in parallel with the SRR input to give a definite 'off', especially if you have anything carrying heavy current running along a parallel route.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

I concur with Scotty's OPTO + burden resistor suggestion.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

BTW: You'd want to use a DC output SSR.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[srbelec]

I have gone 1000m (3000 ft) with a standard On/Off signal to a controller. most controllers take about 45mA to sense a logic (1). I typically use #14awg for all my digital signals, so that voltage drop issues don't come into play.