long distance analog signals


Thread Starter

J-F Portala

hi listers,

I make analog measurements with a PC and an analog acquisition board.

The problem is that my PC must be at 30 meters from my sensors they delivers 4-20mA or 0-10V.
How can I do to preserve the quality of signals for this distance.

thank you

J-F Portala
[email protected]
1- use shielded wires
2- run them away from others cables likes mains, or on/off signals
3- 4-20 mA is better than voltage

Vitor Finkel

Use 4 to 20 mA, and adequate instrumentation wires/cables. Ground all wiring shields in the PC, insulate shield in the other end.

This should do.


P.S. In industrial environment, 30 m is not a long distance, and using the procedures listed above is more than adequate for this distance, if you dont have any strong "interference generator"
near by.
Thank for your answer.

My acquisition board accepts only voltage (0-10V, -5/+5V)... I have sensors wich have 0-10V outputs and other wich has 4-20mA output. I convert the last one to 2-10V thanks to a 500ohms resistor.

I understand that 30 meter is not a long distance for 4-20mA, but for a 0-10V signal?

I have founded isolated DC input/output module (adam 3014 advantech) which accepts curernt or voltage in input and gives current or voltage in output.

Can I use this module to protect my voltage signals, or is it better to convert 0-10V to 0-20mA then converts back 0-20mA in 0-10V.

Can I make this with simple resistor?

thank you for your help.
J-F Portala

Michael R. Batchelor

Is it easy to move the 500 ohm resistor to the board and do the conversion there? 30m of 4-20ma and a few cm of 2-10VDC makes a much better solution.

Vitor Finkel

Depending upon Input Impedance on the measuring circuit, 0-10 Vdc may become quite noisy, with a 30 m line. Of course that depends upon wiring
characteristics, shielding, twisting, gage, distance between conductors, and noise level and type in your field (Electrostatic, Magnetic and/or
Electromagnetic ?) Definitively I would try to go to 4 -20 ( or 0-20) mAdc.

To convert current into voltage, a simple resistor will do (mind the precision, or this can lead to large errors), to convert from voltage to current, is an entirely different and more expensive story. Remember, each converter adds errors to your measurement.


Vitor Finkel [email protected]
P.O.Box 16061 Tel (+55)21 2285-5641
22221-971 Fax (+55)21 2205-3339