Current Over a distance

Hi Nick, well as i know the resistance of the media ur transfering the current in, is the most important reson to this voltage drop.

but was it still 20mA at the other end?

that is the point of a current source,,,

the current is held constant (or tried to be held within the voltage limits of the current source) but the voltage may vary depending upon the resistance...

The current source will try to force 20 mA through whatever resistance you attach to it... Mark

Better show your circuit for V/I converter and the load. Lots of things (simple tghings) could be wrong. 7m is no distance at all.

Paul Burke

A number of possibilities: Voltage limits of the driving device. If (for instance), you were only using 5v, to drive your 'loop', and the op-amp involved can swing within

0.5v of the +ve rail, then the maximum resistance of the whole loop (source resistor, target resistor, plus the wiring), can only be 225R. Offset errors in the op-amp circuit itself. Errors in your measurements/references used - remember the loop accuracy will depend on the accuracy of the resistor used to measure the current both at the source, and at the target. Oscillation. It is very 'easy', when building a circuit to drive into a load of this sort, to end up building something that oscillates.... A problem with the driver/target, not being properly isolated. Done properly, a 4-20mA loop, can be excellent. If you look at the Siemens application note, number 54, which shows how to build opto-coupled drivers/receivers, using their IL300 opto-coupler, with the right op-amps, and references, this comfortably gives a complete driver, which gives better than 1% accuracy, driving loops with resistances varying from a few ohms to several hundred ohms.

Best Wishes

Either your V->I or I->V converters has an error. Simple to check really if you have suitable meters.

Hi everbody,

i think i will have to check my circuit and find current drop also..

Thanks for the help...

Current drop? Someone here doesn't understand what a current loop is. It's either you or me.

Hi,

I meant to say to check the transmitted current Vs the Received current...

With regards..

In which case, you were either doing something silly with the connections, or your wires between, have a massive DC leakage....

Best Wishes