FP-AI-111 channel protection circut w/resister,diode and 16th amp fuse for inputs

[Wayne.C]

Luther,

Can you post a diagram of what you built up to protect the inputs?  Curious to see what the NI hardware guys came up with.

[lexluther]

Sure i'll get it posted tomorrow. Thanks for listening.

Luther

[lexluther]

Heres the circut in PDF form

[AnalogKid2DigitalMan]

Ahh:

Current limiting input resistor, and when Vin exceeds the Zener voltage, it conducts and blows the fuse.

Have you tested it for your scenario and does it save $400?

-AK2DM

[lexluther]

Yes for 4 years it's saved my ass. Works perfectly.

Thanks for the reply

[Wayne.C]

A simple 6.2V  zener diode.  Very cheap.  Does the zener seem to affect the offset of the 4-20 input?  I guess that would depend on how much the zener conducted below the zener voltage.

Message Edited by Wayne.C on 04-02-2009 02:57 PM

[lexluther]

It doesn't give much of an offset .02ma at most . MAX itself shows this. We also have the ability through our program to calibrate all instruments separately anyway so any offset will be absorbed.(which we do when ever and input item changes which makes this circuit invaluable)

Its a pain to have to add the circuit which I might add "NI should inform all in there spec's that this could be a catastrophic failure". It cost me dearly in the past before the circuit

Thanks all for your help