voltge current converter output to current loop receiver?

[seyyah]

I have a circuit that converts voltage into current referenced to ground of the circuit. Output is 4-20mA. What happens if i connect this output to a current loop receiver? Should all current receivers supply supply voltage? If so, two different voltage sources will be combined i think. Should we use current loop transmitter with the current loop receiver and current transmitter with the related receiver? Can you enlighten me about this subject?

 

[sathiya.ks@tekbridge.in]

can you please upload ur circuit... Because i am lookin for such kind of circuit which converts PWM output (0-5 VDC) to current loop (4-20 mA) output....

 

[@t]

Hello Seyyah,
A current loop output tries to maintain (the same) current regardless of the resistance of the transmission line. The resistance (of the loop) should be low enough to make that possible of course.
Several receivers can be connected in serial, as long as the (max) loop resistance allows that. Each receiver devellops a small voltage over its input resistor, and uses that as data (1 if present, 0 if not).
To enable the transmitter to function properly (as a constant current source), the sum of al these voltages, taken by the input circuits, should be lower than the supply voltage that the transmitter current-source is using.
To prevent loop problems an (isolated) optocoupler circuit in the receiver input is very handy, the detection is passive, a few hundred ohms, and the opto circuit (MCT2 f.i.). Each receiver will take about 3 volts or so, and if the source (driver) is fed with 12 to 24v, about 4 to 8 detectors can be connected.

Succes, At.