AB Analog card

Hi All,
I have just installed a 1746-NI8 analog card to gather analog data from an old system, since doing this we have had several of the input devices fail.
We are guessing the issue is being caused by the fact that some of the inputs come from diffrent power supplies .
Now before we install the new input devices what do we need to do to protect them and the analog card?

Thanks in advance

Just a guess

http://www.redlion.net/Products/ProcessControl/SignalConditioning/ProcessInputs/AAMA.html

We all ready have some on order.What I realy want to know is why it all went so wrong ?

It could be coincidence.

You said the system was old so those components could just have been close to failure anyway.

Another thing to look at is position of the module and wiring, are they close to anything that could be producing EMI etc.

Are all the shields (I assume the analog inputs are using shielded cable) tied together at the module, if so you may want to separate them and use a meter and scope to see if one of them is placing voltage into the circuit.

AND THEN THERE IS GROUND, it would seem this would be a simple thing but it is not. You may want to look for potential differences in the ground circuit.

There was a time that an oscilloscope was rarely used on a plant floor, with today's technology their use has become a requirement. The new portable models that are available these days are awesome but have a tendency to grow legs, at least my Fluke 97 did. I still have a benchtop B&K 40Mhz unit though.

The different potentials between the different power supples with I guess different ground planes will result in ground loops through the device, if there is a big enough ground loop current then this will blow the device. I am assuming that you have powered any loop-powered devices from the NI8 power supply source. So the devices you are talking about are 4-wire.

One of the possibilities is floating grounds ( a pet hate of mine) , could create a problem . Go round with your meter and see what the voltage difference is on the analogue grounds , and also signals - don't worry about the signal level , just check the voltages between signal grounds and signal inputs (does that make sense ?)