4/20ma loop or 5V solution Expert opinion ..

[dark]

Hi ,I have a Voltage sensor outputting 4/20ma signal . Its to be placed inside panel box. My meter is to be placed 3meters away from the sensor/panelbox. I need to know;

1) Should I place a shielded cable and drop 4/20ma by 250E resistor and feed it to ADC of MCU directly .

2) Do I require expensive Instrumentation amplifier solution? BUT the distance of signal travel is too less .

4) Should I use a sensor with 0~5V output directly with shielded cables.

Please note around the process , I could see alternator and other DC motors (Big one in about 100KW)operating .

Expert advice is most desirable . Rgds

 

[ericgibbs]

Hi ,I have a Voltage sensor outputting 4/20ma signal . Its to be placed inside panel box. My meter is to be placed 3meters away from the sensor/panelbox. I need to know;

1) Should I place a shielded cable and drop 4/20ma by 250E resistor and feed it to ADC of MCU directly .

2) Do I require expensive Instrumentation amplifier solution? BUT the distance of signal travel is too less .

4) Should I use a sensor with 0~5V output directly with shielded cables.

Please note around the process , I could see alternator and other DC motors (Big one in about 100KW)operating .

Expert advice is most desirable . Rgds

hi,
For long cable runs in electrically noisy environments I would always use a 4-20mA loop, connected using twin screened cable.

Terminate with a 250R resistor at the receiving end, this will give a 1V thru 5V signal output across the 250R.

If the 1V offset is a problem, use a OPA to remove the 1V and make the OPA output 0 to 5V == 4 to 20mA.

 

[dark]

Thanks for the reply, I will get the twin screened cable earlier I was planning for single shielded cable. Should I terminate it at sensor end or the MCU/ADC end. Regards

 

[ericgibbs]

Thanks for the reply, I will get the twin screened cable earlier I was planning for single shielded cable. Should I terminate it at sensor end or the MCU/ADC end. Regards

I would initially terminate at the 250R end.

Obviously avoid any ground loops in the cabling.

EDIT:
added pdf