Connecting open collector pulse output of flow meter to NI 9361

[Naseemvp777]

Hi,
Acquiring the Pulse Signal output from a Flow meter (Flow meter Output: Passive open collector, 30V, 250mA) using NI 9361 and cDAQ 9185.
Initially I connected flow meter output +24 and -25 directly to an oscilloscope, I couldn’t see any pulse. And Just tried connecting to PFI0+- of NI 9361. My program is as attached below. The counter started counting but after few minutes it was displaying 0 forever.
The pulse details are Pulse width: 100ms and Pulse value: 1kg Max Range of flow is 36000kg\h.
Then with the help from forum went through the flowmeter manual found the connections for configuring Passive output as attached below. Applied this and could see the pulses on Oscilloscope (Red one channel A)

And went through the NI9361 Manual and realized the connections for open collector output to be as file attached as NI open collector

But, my flow meter doesn’t have separate pin for Vin and GND. It has only pin no +24 and -25. So connected Vout to +24 and then +24 to DI0+. -25 to DI0- and to ground.
And created a task to test. But the counter output remained always Zero.

Also tried connecting the ends +24 and -25 without Vsup to the NI card. But providing supply externally and the pulses were visible on oscilloscope. But, then the output was zero.

I have connected the external power supply of 5V through a load of 7kohms. The pulse output has 2.2V logic high and 0.8V logic low.

In short, with no external power supply, I could see some random counts in LabVIEW but nothing on oscilloscope and with external power supply, I could notice pulses on oscilloscope and nothing on LabVIEW Panel

Any help would be greatly appreciated

Thanks in advance

[Henrik_Volkers]

The 9361 has a internal 5k pullup resistor to (internal) 5V 🙂

So connect port (25) to DGND/COM and (24) to DIx  (single ended) of your 9361 and enable the internal pullup. (don't have that card, but I'm shure there is a property node (or setup vi) for that)

[Naseemvp777]

Thanks a lot for your reply.

I tried doing that, but still the value is Zero. please find the attached code below

Trial 1: external supply voltage and external pullup resisitor of 7k ohm, with logic high 2.2V and 0.7V logic low (with the help of oscilloscope viewed the pulse voltage) and connected DI+ and DI- respectively. The Counter Counts extremly fast upto 64k and stops. sometimes never Counts.

Trial 2: provided supply voltage NI 9361 and connected in diferential mode, No Output.

Trial 3: followed your suggested method, still no values.

Is the pulse voltage low,that the device couldnot recognise? I even connected LED in series, LED blinked, not brightly for 2.1V, But, I could see the lighting of LED. but,the PulseCount did not increase.

I am very much confused, how to proceed. Your Suggestions and advices would be a great help.

Thanks a ton in advance

[Henrik_Volkers · Accepted solution]

The vi looks ok for me, maybe a 20ms wait in the loop would be nice 😉

Just in case try the (25) and DI- to COM. 

If you connect a scope to com and DI+ (and (24) ) you should see the pulses ...

Your sensor has a photo coupler as output ... is it powered?

A sketch of your setup including all power/sensor wires/connections would be helpful (and needed for your documentation anyway 😉 )

[Naseemvp777]

Thanks a ton Henrik.

I just got the Output.

tried connecting (25) and DI- to COM.

Could you please reply to one of query regarding DIADEM.

https://forums.ni.com/t5/DIAdem/Plotting-Exponential-Curve-with-two-co-ordinates-automatically/m-p/3...

Once again thanks a ton 🙂

[Henrik_Volkers]

Sorry, I can't help you with Diadem, don't use it ..

[Naseemvp777]

No Problem. 🙂