Low Pass Filter Counter Input Compact DAQ

[ASTDan]

Hello,

I need to put a 10kHz Low pass filter on a counter input.

I have a CDAQ 9178

and a 9421 Digital Input module

Acording to the documentation and my own experience I can't enable the filter on the Digital input card.

Is there another way to do this?  I need to filter the signal in hardware.

Thanks

Dan

[Adam G]

Hello Dan,

You are correct in thinking you cannot set digital filters on the cDAQ-9178. If you wish to have a hardware filter you will need to build an external circuit that does the filtering for you. You can then run your signal through that filter before connecting it to the NI-9421.

Best Regards,

Adam G 

[ASTDan]

I am in the process of finding and or building an external filter

I just wanted to make sure there wasn't a simple fix from NI's end before I put a lot of effort into it.

Thanks for your response.

Dan

[ASTDan]

Just to follow up for posterity with what I am doing.

I am going to try this filter

I will post if this works or not.

Dan

[Henrik_Volkers]

Your filter might work, however it is build to filter power lines, with current rating 6A and powerline voltage. You pay a lot for a box with screw terminals and a lot of copper and high rated capacitors.

Have you tried a simple RC lowpass (costs less than 50 cent, even when purchased in a pharmacy 😉 ) ? R=1500Ohm, C=10nF gives a coarse 10kHz first order lowpass. The C fits between the ground and input terminals of your DAQ, the R in the signal line to the input.

Output impedance of your source?

If you explain more of your application, type of signal, we might find other solutions.

[ASTDan]

I verifed the filter would work up using a capaciter and resister. However time is money to wire up a resister aand capaciter in a nice enclosure with screw terminals would cost me several hundred in labor costs. Dan