Grounding Cable for Instruments

One of the reasons is to shield the signal, with may be very small, from the effects of induced currents from other things, like big motors. The other possibility is to provide earth grounding.

Do not remove them unless unavoidable, as the instrument reading, and safety, may be compromised.

You should also make sure that it is only grounded on one end. Not both. Typically it is grounded on the PLC/DCS end, but that is only convention and convenience - not an absolute.

the purpose of the grounding the shield cable with earthing cable the control cable and instrumentation cable will mixed up in an single tray

high voltage due to induction voltage will induced through the instrument cable also thats while we are connecting the shield cable it will bypass the interference voltage through ground

the earthing must have 0.3 ohms resistance value

Hello Guest,

Please also refer to my just-written reply at an associated Topic Thread: http://cr4.globalspec.com/comment/253476/Re-Problem-with-noise-on-data-cables

Hope that also assists you.

Kind Regards....

The other reason you would ground instruments to the same ground plane is to provide a solid reference point. This is especially true if the measurements at different instruments are going to be compared to each other.

static electrical build up then discharge can do damage to tiny parts and limit their life span.

....though 1MΩ is eqivalent to a short circuit when dealing with static electricity.

I think the question refers to grounding the body of transmitters ,positioners etc. to ground(earth).

To my knowledge this is not done in the US.

What about other countries?

Would be interesting to know.

We also do not ground the bodies but do use one-end grounded signal cables.

The same style is valid in Russia as i learned from my colleagues...

hi srini,

I meant the same . Ground to the tranmitter or positioner body. In our plant we are using grounding to the body of the instruments.What difference it makes if not grounded.Our all the signals are going to DCS through MTL isolator.