Isolators at Analog Inputs


Thread Starter

Omer Aziz

Is it a standard practice to use isolators at analog inputs?

Can we use isolators before thermocouple signals?
Isolated Analog Inputs could be of several kind. Depending upon the type of industry, there exit (generaly) regulation about safety.
Presumably you mean floating input vs grounded input. Unless the cabling is short, all sensors of same brand as the receiving apparatus, then using floating inputs is current practice. That saves many problems, particularly if the instrument ground is inadequate. This suspicious ground is more than common.
I have also designed systems for client already badly organised. So, same phylosophy=same satisfaction ! Indeed.
Thermocouples are not different than other analog inputs. Look for instance a reputable supplier like Rosemount.

Vikas Meshram

In my opinion its not exactly the isolator. It is isolation amplifier.


Vikas W. Meshram
Scientific Officer,
Laser Instrumentation,
Center For Advanced Technology,
Indore- 452 013, MP,INDIA.
Email:[email protected]
Omer Aziz <[email protected]> asked :

>Is it a standard practice to use isolators at analog inputs?
>Can we use isolators before thermocouple signals?

Jim Pinto responds :

Always make sure your analog inputs (DC, t/c, RTD, etc.) are isolated 3-way : Input, output, Power/Ground.

If your analog signal (t/c mV signal, for example) wiring becomes wet and leaks to power or ground, this can cause inaccuracies and possibly damage.

I have a rule that has stood me in good stead :
When in doubt, isolate. Always be in doubt!

Action Instruments has an excellent application note on this subject, "Using signal-conditioners - Myths & Misconceptions" at :

Jim Pinto
email : [email protected]
San Diego, CA., USA

Andrew Chiang

We have many cases where optical isolation helps in an installation. The
additional cost is high. Can anyone recommend any cheaper isolators ?