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Getting pulse from flow meter(NI 9401)

Dear all,

As part of my project I am trying to count pulses from an ultrasonic flowmeter (

However when I use the probe to see the pulses number (CTR6 in upper timed loop) I get numbers such as 0, 29, 45, 61, 76 every time I rerun the program. As it runs there is no change in the probe output no matter if there is flow through the flowmeter or no.

I am using NI 9401 module and CRIO 9074 and have the module configured in Counter Mode (Labview 2018). 

The picture attached indicates the measuring settings.

As part of the project I am also using an analog module NI 9205 to get signal from 3 analog pressure sensors and it works just fine

The input node of the timed loop used to take measurements is synchronized with the scan engine.

The module works fine when used in normal mode (when None is selected under Specialty Digital Configuration in Properties) so I assume it is not problematic.

The flow meter has been tested using an oscilloscope and works fine.

I tried to use a pulse generator to feed the module but when I use the probe to see what I get it is just 0 or other 2 or 3 digit integer numbers that do not fluctuate when I change the frequency of the pulse generator.

I would like to know if you have any ideas of what might be wrong here. Any suggestion is more than welcome.

Also I am curious if the slot I am putting the module on CRIO plays a role?

I attach the main vi used to take measurements for your review.

Thanks a lot for the your help and time in advance,

Kind Regards,




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Message 1 of 5

Hi amfe,


how did you connect the flowmeter to your 9401 module?

Best regards,

using LV2011SP1 + LV2017 (+LV2020 sometimes) on Win10+cRIO
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Message 2 of 5

Hi GerdW,

I connected the signal output of the sensor to pin 23 and the ground to pin 10.



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Message 3 of 5

Hi Georgios,


where does the sensor get its supply from?

Did you use any pullup/pulldown resistors for the PNP/NPN output of that sensor?

Best regards,

using LV2011SP1 + LV2017 (+LV2020 sometimes) on Win10+cRIO
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Message 4 of 5

I use a 660 0246 constant voltage led driver that outputs 12V into a circuit. The sensor ends up receiving 8,05V which inside its range. I am confident it is properly energized since the led indications of the sensor are according to the sensors datasheet when I let water flow through the sensor.

As far as the pulldown, pullup resistor I am not sure since  I didn't set up the electronics and it is impossible to reach the guy that did. But it looks that he has used one of the 2 if I judge from the cabling, but its covered. I can rip the cable off and have a look if u think it is vital. But  I also know that the sensor was working 2 years ago with the exact same cable so it should not be the problem.





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Message 5 of 5