Flomec-qs100 Open collector output

[samBH]

Hi,
We are using multiple of these flowmeters (Flomec-qs 100, please see the link: https://fluidhandlingpro.com/great-...the-flomec-qs100-turf-irrigation-flow-sensor/). Now these have only two output wires and they are supposed to be connected as a open collector output. So connecting a pull-up resistor should work between the collector and the Vcc (power supply, 10-20 V). However, we are unable to display the output pulses on a oscilloscope even when we use a pullup resistor (we used 4.7k, 10 k, etc. see the connection diagram below). We have used a PLC before and it was able to count the pulses. But my question is how can I display the pulses in a scope or sample them with a National Instrument DAQ device. Thanks.
Samik

 

[rjenkinsgb]

I'd try 1K or less for the pullup.

The specifications I've found are confusing - on sheet says 200uA in the "off" state, but the photos show both power and signal LEDs on the unit, which I would expect to take rather more than that?

With a pullup resistor in place, check that there is more than 7.5V across the sensor when the output is "off" - that's the minimum rated operating voltage.

The output pulses are apparently 4mS long and presumably low-going, so should be visible on a scope?

 

[danadak]

But my question is how can I display the pulses in a scope or sample them with a National Instrument DAQ device. Thanks.
Samik

On a scope use either edge, + or -, set trigger for a couple 100 mV to trigger, trigegr mode "normal".


Regards, Dana.

 

[Nigel Goodwin]

We do a LOT of work with similar devices, and manufacture various equipment that connects to them - they are pretty well universally either open-collector (or open-source), or a simple reed relay.

So, as you've drawn the connections - you need a pull-up to a +ve supply (we normally use 3.3V, 5V, or non-rechargeable Lithium batteries at 3.6V) - the actual voltage isn't usually of any importance. We also normally use two x 22K resistors in series as a pull-up - but it's not usually supplying power.

The issue with this one is that it requires power, and that it has LED's (using more power) - I eventually found a datasheet, but it's incredibly poorly written, and not at all clear what's required.

But from what I can gather, there's a 50 ohm resistor in series with the collector/source (commonly 100 ohm is used - this could be lower though because of the added power requirement, and doesn't really matter).

Also it lists the voltage required as 7.5V to 36V - which I surmise suggests it's intended to connect to a PLC, which are normally 24V - with a 12V supply I'd suggest trying a 1K as rjenkinsgb suggested, and see what happens?.

You say you're not seeing pulses?, but what DC voltage is on the output - is it 0V, 12V, or somewhere in between?.

 

[samBH]

Hi Nigel,
Many thanks for your detailed reply. I will test with a 1k pullup resistor and let you know the result soon. The DC voltage on the output was almost same as the supply which meant the device was not drawing enough current. I will post a detailed note with different resistors soon. My life will be really simple if I can get a pulse transmitter and display device. This may work
rainbird_controller
But I am not sure.

 

[Nigel Goodwin]

I presume you had water flowing through it?.

 

[samBH]

Yes, of course. We have them in a plumbing network and the pump was running all the time.

 

[Nigel Goodwin]

Yes, of course. We have them in a plumbing network and the pump was running all the time.

Just checking