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24vdc digital signal cable length limit

24vdc digital signal cable length limit

24vdc digital signal cable length limit

(OP)
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 ?

RE: 24vdc digital signal cable length limit

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

RE: 24vdc digital signal cable length limit

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!
 

RE: 24vdc digital signal cable length limit

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

Keith Cress
kcress - http://www.flaminsystems.com

RE: 24vdc digital signal cable length limit

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.

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