AC Current into an analog input card?

hd_coop

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Join Date
Jul 2002
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Belgium, WI
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Hi all,

I am working on a machine right now which is spinning a flywheel past a sensor. The sensor is creating an AC voltage everytime a tooth goes by. This voltage is about 400 mV max at the speed we are running the flywheel at. We have this going into an AB 1746-NIO4V analog card. We are getting a usable signal right now which works well.

My question is if there will be any adverse effects of sending AC into a DC analog card? Will the life of the card be reduced? The frequency of the wave is 30 Hz

Thanks for your help
 
The Input Specification for this module in Voltage Mode is -10 to +10 VDC. As long as the peak AC voltage does not exceed 10 volts, you won't damage the module. I can not say how the module will respond to the AC voltage.
 
you may get a more stable reading if you put a rectifying diode and smoothing capacitor in circuit.

If you can envision a sine wave, 30 times per second it is rising from 0V, to a peak voltage determined by your alternator, back down to zero, down to the negative of your peak, back up to zero. e.g. 0V -> 400mV -> 0V -> -400mV -> 0V.

Depending on when in this cycle your input card makes its sample, your voltage reading will change.

I am actually surprised that you do get a useful reading from it, as is.

Check out this result from my quick google search on half-wave rectifiers...

http://engineering.dartmouth.edu/other/3Dcircuits/animations/rectc.html
 
Last edited:

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