Isolated Input - Instrumentation

If one applies an ohm meter between the terminals of two inputs that are galvanically isolated, it reads >Megohms off-scale.

Isolated input/output has used in the MCC to PLC/DCS.

Non isolated system has used filed terminal to DCS/PLC

Hi there,

You need to supply more information.

There are two types of isolation used.

For intrinsic safety - galvanic isolation or zener barrier.

There is another form which is often incorrectly called signal isolation, which is in fact signal conversion (signal conditioning). This is when you have the plc card powering the loop, and the transmitter powereing the loop. In this case you have both parts trying to put 24VDC into the signal wires. Here you would use a signal converter (signal conditioner).

For intrinsic safety, there are certain rules coverning how much energy (voltage vs current) you can put into the field (non safe zone). The point of the galvanic isolator or barrier is to limit this energy in the loop so that you can in no way cause ignition from the loop, even if you were to short the two wires together causing sparks.

The main thing to bear in mind between the two, barriers require an IS (intrinsic safe)earth and the signals are not electrically isolated. Galvanic isolators also provide surge protection from the field as the signals are electrically isolated.

For more information do a google search for MTL barriers. You can download the schematics and brochures that depict how the different barriers/isolators work.

For more information on the signal converters (sometimes known as signal conditioners) goto www.weidmuller.com and do a search for signal converters. You can download the manuals and brochures that explain this in greater detail.

Regards,

Craig

Thanks.

But i need more information about isolated, because when i see the rockwell automation drawing example 1756IA16 & 1756IA16I both have termianl in the I/O module and terminal number only changed.

So where it is isolated.

Another technique for isolation is optical isolation. Various techniques are used to do this but in essence a light source is detected by a light detector. Only photons travel from one circuit to the other, for the most part.

Without knowing what type of signals are getting isolated and only having cryptic part numbers, I cannot elaborate.