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Brushless DC motor Tacho measurement cDAQ-9174


Hi Folks,


I’m trying to monitor the speed of brushless DC motor (Thomas 1410 series 12v). using a cDAQ -9174 chassis.

The motor runs as expected but when I attach an oscilloscope to the Tacho output I’m only seeing signals between 0.3v and 0 (but at the correct frequency).  

Is this enough of a signal to bring directly into the chassis (what module would people recommend)?

If not, what should I do to the signal to achieve the 0-5v TTL described in the spec sheet?

(again, what module would be best suited?)


Please excuse my inexperience as I’ve never played with frequency measurement before.





Spec sheet and Brochure attached 

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Message 1 of 4

Hi there,


No that is not enough voltage for cDAQ to read. Depends on your specific application, I would recommend you call your local NI Sales representative for module recommendation!



Message 2 of 4

Hi Winnie_G


Thanks for your interest.

My boss overcame the low voltage problem for me.

I not saying he's old school but he still laments the passing of the valve, he put together a small discrete amplifier.

I've run it against the scope and its noisy as hell but it works.


Many thanks



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Message 3 of 4

You may have partially solve your problem but the real problem is that from your specs you should be getting 0 to 5V from your tachometer, if you are getting 0.3 V then something is wrong check your circuit impedance.


Disconnect the tachometer just measure its otput with an osciloscope if the output is still 0.3 then its broken.



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Message 4 of 4