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Distance for Analog Signal Transmission

Distance for Analog Signal Transmission

Distance for Analog Signal Transmission

(OP)
Question came up as to what distance can a 4-20 mA analog signal from a transmitter can be run if terminating to a card on a DCS or PLC.

RE: Distance for Analog Signal Transmission

Depends on if there is enough voltage available to overcome the resistance (wire length and resistance of DCS, etc).

RE: Distance for Analog Signal Transmission

buzzp is right. Say a transmitter will accept a 500 ohm max load. If you drop the signal across a 250 ohm resistor (creating a 1-5 VDC internal signal), that leaves you with 250 ohms to work with. If 18 ga. copper wire was the only resistance, you could install the transmitter over 3 miles away!

However, intermediate connections, bends in the wire, internal resistance (control system and transmitter), power supply, etc. all contribute to resistance.

A more practical max distance is 1 mile, and that's only under ideal circumstances.

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