SCADA Grounding question

[Jester]

The image below depicts the existing setup. Less than ideal, common ground for both power and signals, however the cable has long since been buried.

I'm not sure if the analog ground on the SCADA board is fully isolated or has some resistor or capacitor to earth ground.

The transducer board has 2 grounding links as shown. Am I better off closing link 1, link 2, or neither?

 

[HTA]

Hi Jester,

if you are not sure if ground and earth is really isolated on both sites, you have to measure it. I think it is critical if the cable has been watered(damaging the cable isolation) or if ground and earth is connected in the SCADA(might cause ground loop current). You might test reference measurements with link1 and link 2(each one closed, or both open).

Enjoy your trouble shooting work!

 

[Jester]

Hi Jester,

if you are not sure if ground and earth is really isolated on both sites, you have to measure it. I think it is critical if the cable has been watered(damaging the cable isolation) or if ground and earth is connected in the SCADA(might cause ground loop current). You might test reference measurements with link1 and link 2(each one closed, or both open).

Enjoy your trouble shooting work!

The site is remote, so I can't measure, I'm trying to provide advice.

It seems that closing Link 2 stands a decent chance of creating a ground loop (will be the case if analog and earth grounds are connected at the SCADA side.

Regardless there will be some coupling between analog and earth grounds at the SCADA side (even if electrically isolated). Is there any potential advantage to closing Link 1?

 

[FvM]

Consider what happens in case of a near by lightning strike, and I'm sure you'll want to keep the signal ground separated from cable shield and earth.

 

[Jester]

Consider what happens in case of a near by lightning strike, and I'm sure you'll want to keep the signal ground separated from cable shield and earth.

FmV,

Good point.

Do you see any advantage to the 1Meg resistor?

 

[FvM]

Do you see any advantage to the 1Meg resistor?

Not in this circuit, because the SCADA board can be expected to have already an earth connection (either high resistance or direct short).