[solved] help needed to understand this diagram of a water flow sensor (from a boiler)
[solved] help needed to understand this diagram of a water flow sensor (from a boiler)
cross-posted from: https://lemmy.dbzer0.com/post/26703241
This diagram is from the service manual of a combi boiler. It’s a flow sensor which detects whether hot water is running, which is then used to trigger on-demand heat and switch a diverter to take radiators out of the loop.
In English, the diagram shows:
- X ⅔ red wire (+5V)
- X 2/2 black wire (ground)
- X 2/6 green wire (signal)
I need to know what those fractions mean. I took the voltage measurements in this video:
I cannot necessarily trust the model in that video to have the same specs as mine. My voltmeter detected 4.68 V on the red input wire showing that the sensor is well fed. The green “signal” wire is supposed to be 0 V at rest and 2 V with water running (or I think the reverse of that is used in some models). In my case the green wire is ~1.33 V at rest and ~0.66 V when water is running. I need to know if these readings are normal as I troubleshoot this problem.
update
@unexposedhazard@discuss.tchncs.de and a couple others gave the answer I was after. Then @tofubl@discuss.tchncs.de helped solve the underlying problem. The theory that the sensor was fine but the board was not drove me to test the sensor in isolation. The sensor gave correct output in isolation. Then I connected it back to the motherboard to retest and reconfirm that it’s still broken. But it actually worked. The hot water suddenly and mysteriously works now. I guess the act of draining the water and unplugging the connector then reconnecting and repressurizing caused it to work. It may be temporary, since in the past it was hit or miss whether it would work.
I dont know how it works in france but here in germany i would expect X 2/2 to just be a label for that contact so you can reference it in a larger diagram. I doubt there is any electrical meaning to it.
Thanks for the feedback. I see that that’s indeed the case.
My first thought: connector two, pin two?
Looking at the attached videos, these are usually connected up with wide rows of quick plug thingies that you can just push cables into. So yeah X indicating its a connector, 2 being the number of the mumber of the connector row and the last number being the pin. Thats how i have seen it done many times.
Just from the wording, ignoring the numbers, this looks like the control connection (red +5v,black ground and the last one signal).
From your description is guess this connects to the boiler on a dedicated port which provides the DC and reads the signal. 5v is quite common for sensors so that doesn't seem off.
That is probably inspired by EN IEC 81346-2 where "X" indicates a connector of some kind and the numbers following the X identify the connector and the relative position on the connector (for connectors with multiple contacts).
These flow sensors are usually hall effect sensors, with two or four magnets attached to a rotor with a little water wheel. When water flows, the magnets turn and create something like a PWM signal at the output (actually it's high level when magnet is there and low level when magnet is not there or vice versa). Measuring the pin with a slow multimeter, this would indeed give you approximately half the supply voltage when water is flowing, depending on a few other factors. So- readings sound sensible to me. To note that if the rotor stops with a magnet close to the hall effect sensor, you will read 5V (or VCC) at the output, but always VCC/2 when flowing.
Most of these sensors employ an open collector output stage, but that doesn't need to bother you with the readings you're getting, I think.
Read your post again, and your readings are of course not in line with what I laid out. Are you measuring the sensor in-system?
If you are, the sensor might indeed be faulty. If you aren't, you probably need a pullup resistor on the output pin.
Yeah, if by /in system/ you mean connected to the board. I didn’t mess with anything other than to stick my probes onto the wires. The boiler is not switching on to heat water and it acts just as if it is not detecting that water is running. So a broken flow sensor was one of the theories. And since the readings seem quite off from what’s expected I guess buying a new sensor is the right move.
Once I get it removed I’ll see if it looks like I can rebuild it but I don’t expect that to go well. I may not have to waste it though. Considering the at rest voltage is double the running water voltage, it’s still detecting water running. It’s just not giving the voltage the board expects. So one idea is maybe I can repurpose this to turn on a shower light when the shower water is running.
If I had an electronics background I would probably try to do a makeshift gadget that converts 0.66 V to 2V and 1.33 V to 0 V. Then I wouldn’t need a new sensor (which could cost €100.. i’ve not checked locally yet but online prices are looking terrible).