how to protect DAQ modules from inductive voltage spikes

[pnielsen@gplains.com]

I just ordered the USB 9221 DAQ module. It will read voltages up to 60 volts. My loads are inductive. I have been using diodes to prevent negative spikes. I used a scope on one of the inductive loads with out a diode. I recorder -560 volts. Is TVS type of diode better? If so how do I specify a part? I do not want to blow up the DAQ module.

Thanks

Philip

[johnsold · Accepted solution]

Philip,

It depends.  What is the source of your signal? What is the voltage and frequency range of the desired signal? How is it coupled to the inductive loads? How fast are the transients? How much energy do they contain?  What kind of grounding circuits do you have?

Diodes are often good protectors.  TVS diodes are usually specified and rated for transients while conventional diodes are typically rated fro rectification functions.  Some systems may require multiple protection devices selected to complement each other.  I have seen systems with gas discharge tubes, MOVs, diodes, and crowbars.

Lynn

[Ben]

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@johnsold wrote:

...

 I have seen systems with gas discharge tubes, MOVs, diodes, and crowbars.

Lynn

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In an old cabinet, recently removed from a physics lab, we found a mystery when playing "name that widget" inside a dumpster. Half of Pitt's Condensed Matter Physics Department was set back by a row of automobile spark plugs mounted in a fixture on the inside of the cabinet. We eventually decided they were being used as spark arrestors.

This lead me to investigate a related question with one of the Emeritus types, "What did you use for a vlotage reference before Zeners were invented?" Answer: Chemical cells.

Sorry about the trip down memory lane but sometimes the old ways of doing things can inspire new.

Ben 

[johnsold]

I have actually used saturated cells as voltage standards (1.0189 V/cell if memory serves correctly), although it has been quite a few years.

Lynn

[JÞB]

If you look on pg 17 of the manual you'll see the specs for the input protection of the 9221-  you seem to be OK but, its better to have too much input protection than too little.