How to check working of Water flow meter

Forums › Home Workshop DIY › How to check working of Water flow meter

PSLog

291 posts

Ultimate Geek

#306508 30-Jul-2023 10:32

I had set up a water-flow meter for my motorhome.
It comprised a sender unit installed in the pipe
https://www.aliexpress.com/item/32995826469.html?spm=a2g0o.detail.0.0.33a42ccaAvLpZR&algo_pvid=621883fd-8c59-45ea-904b-de067d3fff9b&algo_exp_id=621883fd-8c59-45ea-904b-de067d3fff9b-0&pdp_npi=3%40dis%21NZD%2115.31%2114.55%21%21%219.27%21%21%402103200516906688033467069eefeb%2166909330378%21sea%21NZ%21100777415&curPageLogUid=WZhwKqw02zoL
which generated a 5V pulse through Hall effect.
This was connected to a digital display of the accumulating pulse count
https://www.aliexpress.com/item/32631229860.html?spm=a2g0o.store_pc_allProduct.8148356.1.29c361428mvQeh&pdp_npi=3%40dis%21NZD%21NZ%24%2020.17%21NZ%24%2019.16%21%21%21%21%21%402101e9d416906678556475844ec101%2159442935839%21sh%21NZ%21100777415.
After 4 years it stopped working and I have just bought a replacement sender unit.

The new one doesn't work either - even with an independent test wiring set-up.

Can anyone suggest a way of testing the operation of the sender unit independent of the display meter - maybe using a multimeter. I don't have access to an oscilloscope.

I will try to answer any supplemental questions promptly.

Gordy7

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#3109729 30-Jul-2023 12:34

https://www.seeedstudio.com/Water-Flow-Sensor-YF-B7-p-2884.html

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

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PSLog

291 posts

Ultimate Geek

#3109748 30-Jul-2023 13:15

Thanks Gordy.
That site shows more details than I have seen before, but neither do I have access to a Raspberry or other processor.
It would be good if there was a way to detect pulses using a multimeter (or light bulb,pehaps)

Gordy7

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#3109756 30-Jul-2023 13:42

You should be able to check the thermister using a DMM on ohms.

The expected value at room temperature is likely stamped on the side of the sensor. (50k ohms shown in comments on my initial link)

On the flow sensor:

Apply 5 volts.... + to red wire, - to the black wire.

Using the DMM on volts, connect to black and yellow wires.

With a very very very slow water flow rate the DMM should flick between 0.5v and 4.7 volts.

With faster water flow rates the DMM would likely show about 2.5v.

Using a light bulb is not a very good idea and might damage the sensor electronics.

Edit: A good source of 5 volts for testing the sensor is an old USB cable plugged into a laptop or computer. The sensor only draws 15mA.

Cut off one cable end. The wires are likely red=+5v and black 0v. Check with a DMM to be sure.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

PSLog

291 posts

Ultimate Geek

#3109777 30-Jul-2023 15:42

Thanks for the suggestions, Gordy.

The thermistor is not used.

1. Applying 5V to red and black: with no rotation the voltage between yellow and black is also 5V
Then
2. Applying fast flow (rotation), the voltage reading changes not one iota.

???

Gordy7

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#3109826 30-Jul-2023 16:07

Not looking very good at all.

With fast flow the sensor is supposed to output square wave pulses.

The DMM should average these pulses and show approx 2.5v.

Maybe time to check your installation power supply and the display counter pulse input for problems.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

PSLog

291 posts

Ultimate Geek

#3109828 30-Jul-2023 16:30

I have 2 identical sender units:
One 4 years old (which has been working fine until 2 weeks ago - but maybe the sender is not the problem)
The other is a week old.

Both exhibit identical voltage readings during rest and rotation.

Maybe the problem is with the counter/display unit.

I would be happier shelling out for a replacement display unit, if I was confident that the sender units were functioning properly.

And I'm not.

Like you, I would have expected to read 2.5V during fast rotation.
I would have thought that there would be 0V when there was no rotation.

Gordy7

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#3109830 30-Jul-2023 16:45

With no sensor rotation you don't really know where the hall sensor and magnet is parked or aligned, so the output could either output 0v or 5v

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

PSLog

291 posts

Ultimate Geek

#3109895 30-Jul-2023 21:07

I don't think so, Gordy.

From your first link:
" Magnetic field rotation triggers the Hall sensor, which outputs high and low level square waves(pulse)."

No magnetic field rotation = no output.

I think the square wave is generated by field movement: not rotor position?
But I would have thought: no rotation = 0V - which is not what I have observed.

Danite

42 posts

Geek

#3109979 31-Jul-2023 10:35

You could also take a look at frequency if you looking at measuring pulses and voltage isn't helping, Hz or frequency on the meter might manage it. Unsure what type of meter you using and I wouldn't suggest buying one of these for the job Fluke 725 but this is what I have used in the past to check pulses out of turbine and vortex meters.

PSLog

291 posts

Ultimate Geek

#3110156 31-Jul-2023 16:40

Danite
That's a good idea.
I'll have a look tomorrow to see if one of my DMM's has that function.
I'll report back.
Thanks