Ground Loops...

[sameenkhan]

Hi Guys,

Ground loops is biggest problem for most of the instrument engineers...

What are typical problems that can raise from presence of ground loops??

Is there any guidelines/standard/RP available to rectify problems of ground loops??

Regards,
Sameen

[ali.abbas]

Speaking from the perspective of an Instrument Engineer, problems arising from ground loops include
- erratic indications
- bad PV indications
Depending on the application, incorrect PV can lead to anything between merely an incorrect indication to plant/unit tripping.

And yeah, there are definitely recommended practices to avoid presence of ground loops. Moreover, OEMs also generally provide recommended grounding techniques for their specific equipment.

Regards,
Ali Abbas

[sameenkhan]

Hi Ali,

You are right...
But do you have any info only how to troubleshoot ground loops... OEMs do provide recommended procedures/techniques to avoid ground loops.. but I haven't seen any ground loop troubleshooting methods/procedures/recommendations etc...

Regards,
Sameen

[ali.abbas]

Sameen,

I havent yet come across any guide that could help troubleshoot ground loops' existence. However, the only logical thing to do would be to review the signal loop in light of the best practices. The main reason for ground loops is the existence of more than one ground connection in a single loop. Therefore, any troubleshooting technique should actually target at eliminating any unwanted ground points if possible. From experience, I can tell you that these are a few things you might wanna check in order to troubleshoot ground loops.
1- Check for termination tightness; verify that termination leads are not in electrical contact with any metallic body or with any other signal loop wiring
2- Check insulation of instrument cable - damaged insulation can produce points where signal can easily be grounded. In fact we have had cases where damaged insulation has resulted in grounding of signals for conventional 4 - 20mA as well as for thermocouples
3- Check that each shield wire of each signal loop is grounded only at one end, that is either at the transmitter end or at the control system end. General practice is to have all shields being terminated at the control system (DCS, PLCs etc) end and left open at the transmitter end.
4- Use of signal isolators can be very helpful in doing away with ground loop problems, especially for externally powered devices like anaylsers.

Im not sure if thats answered your question, but I hope it does help.