Damage to NI equipment due to overvoltage/overcurrent.

Question

I am curious to how far an overvoltage or high current input to my data acqusition system (DAS) would travel through my hardware and how many components could be potitially damaged. I guess what I need is a probability of damage to those parts. Following is a discription of my hardware and for now lets say I am sampling an analog input current from an electronics board. The analog input is to a SCXI 1308 terminal block which is connected to the following series of hardware: SCXI 1308 --> SCXI 1102B --> SXCI 1001 (12 slot chassis) --> PXI 6052E Daq card --> PXI chassis with an 850 MHz embedded processor. How many hardware components could be potentially damaged if a current higher than 20mA hits the equipmen
t... for instance if there was a short in my electronics board causing a high current/wattage signal to hit the DAS? Also, additional input cards I have in the SCXI chassis are the 1102, the 1180 feedthrough module, the 1121, and the 1163R. In your explanation please explain why the component(s) would or would not be damaged.

Answer 1

Hi TAC,
I will take a crack at this question.
In an extreme case, everything can be damaged.
The case I have in mind when saying this follows.
If the current should suddenly (i.e. < 1ns) increase to say 100 Amps (this is larger than 20mA) you must take into concideration the effects of the RF response of the various devices (ever hear of an EMP weapon?). In the simplest case, let us concentrate on just the ground paths. At RF frequecies the wires must be analyzed as transmision lines. Depending on the diferences in wave propogation due to the difference in length and the materials used, there may be some very large potential differences in the what we normal concider ground planes ( put a gold embosed coffee cup in an old microwave and watch what happens)
. I think you figure out where I am going with this.
So, if you will buy this arguement that everything is suspect under the these extreme conditions, and we recall that nothing should be suspect when everything is within spec, then there may be some threshold in-between these cases where the reliability drops off. Where that point is I cannot specify without all the details.
In closing, I would like to invoke a variation on an old quote;
"There are only two types of electronic devices in the world,
those that are bad,
and
those that are not bad yet".
Trying to help,
Ben
Ben Rayner
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