Ghost pulses?

Hey All,

I’m kinda of lost right now. Looking for some advice. I’ve purchased a emonTX v4 and a emonBase to monitor hot water consumption. The water meter has a reed switch pulse counter, where each pulse represents 10 gallons. I have a 40 gallons water heater.

My issue is that it makes no sense that I see over 70 pulses in around 10 minutes. It would mean I used 700 gallons of hot water in 10 minutes…

I’ve connected the pulse counter to the rj45 port of the emonTX v4 using a Ethernet cable I’ve repurposed.

I’ve added a simple “log to feed” process in the input.
Any insight of what is happening? What do I need to change?


What is the pulse counter you are using? Are you just using the emonhub pulse counter interfacer? This was designed for the shop optical pulse meter.

My suspicion is that the counter is probably ‘bouncing’.

I had a magnetic reed switch connected to an emonTH for my gas meter, that counted approximately 2.5 per pulse. The addition of a 0.1 µF capacitor across the reed switch completely eliminated the problem.

In your case, for “reed switch” read “water meter terminals”.

The software should have a “contact debounce” algorithm, but even if it’s activated (which it should be by default), it’s not totally foolproof.

Reed switches are well known for bouncing, both when making and breaking, the real problem is the software is so fast that it is able to count every tiny glitch as the contacts move over each other.

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Pulse Output Standard on All Models Sensor Type:
Dry contact Reed switch Pulse Rates: 1 pulse per 10 Gallons
Max. Current: 100mA
Max. Voltage: 24 VAC/DC
Cable Length: 9’ standard (2000’ maximum run)

Hi Robert,

What do you mean “adding a 0.1uF capacitor to the reed switch”. Would I have to remove the switch and solder the capacitor or I could do this off the cables coming out the switch?



You do it wherever it’s convenient, either at the reed switch, somewhere along the cable if there’s an accessible joint, you can even do it on the pulse input on the front of the emonTx4 (the left and middle pins - you’ll need the plug but then it’s easy with screw terminals.)

(If you had the 2000’ of cable, there might be enough capacitance there and you wouldn’t need any more :rofl: )

I have an accessible joint where the cable from the switch is attached to the Ethernet cable. Is orientation of the capacitor important? Or having it connected to the 2 cables is enough?



If it’s a polarised capacitor, then you must observe the correct polarity (pin 5 on the RJ45 is the earthy side, pin 6 will 0 V or +3.3 V). But at 0.1 µF, your capacitor is not likely to be polarised.

Thank you Robert!