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

 

How are you powering the flow meter? The data sheet (https://s3-us-west-2.amazonaws.com/catsy.467/qs100-data-sheet.pdf) implies that the two wires are used for both pulse and power:

A simple two wire connection for pulse and power make installation easy

What are the LED's on the flow meter doing? Refer to page 12 in the User's Manual (https://s3-us-west-2.amazonaws.com/catsy.467/qs100-owners-manual.pdf) for a description of the LED behavior.

How do you know the output is open collector? I can't seem to find anything in the manual or data sheet above that mentions this. And if it is indeed open collector, is it NPN or PNP? I believe using a pull-up resistor like you've shown would assume the output is NPN.

 

Hi
jschulze
Thanks for your reply. I was told by the company tech representative that it is a NPN open collector output. Accordingly I used a 22k pullup resistor between the power supply +ve terminal and the red wire of the flowmeter. I am using a techpower DC power supply to power the flow meter and it is set at 24 V. I have attached the connection diagram that I used.

 

And what are the LED's on the flow meter doing?

You may need to contact that company tech rep again. If the flow meter indeed uses those two wires for both power and a pulse, I don't see how you could put such a large resistor (22k) on the positive supply voltage. Any significant current draw would drop the voltage well under the required voltage level for the flow meter.

Completely conjecturing here, but perhaps the pulse output is a current pulse, not a voltage pulse. Maybe the flow meter uses an NPN transistor to connect a resistor to the positive power supply terminal to pulse current, and therefore varies its current draw from the power supply for the pulses.

I recommend that you confirm this with the tech rep.

If this is indeed the case, you could use a very small resistor (1 ohm or less) in place of where you have the 22k ohm resistor and measure the voltage drop across the resistor (oscilloscope + probe on the power supply side of the resistor and the - probe on the other side of the resistor) in order to measure the current and see the current pulses in the oscilloscope.

 

Great Discussion. Any one can help me about this https://control.com/forums/threads/output-reversing-of-transmitter.24409-dia/

I am confused that's why asking about this.

 

Great Discussion. Any one can help me about this https://control.com/forums/threads/output-reversing-of-transmitter.24409-dia/

I am confused that's why asking about this.

Start a new thread and ask specific questions. The more details and context you provide in your questions, the better answers you will receive.

 

what is the controller model number and its input details.

 

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

View attachment 3401

Samik,

Did you ever get this to work?

I'm looking to use this on my home irrigation system.