Can anyone identify the classification of this data signal?

[mscottdoran@gmail.com]

Hi, I'm an elevator technician. The attached oscilloscope display picture is from a digital elevator hall arrival lantern data signal. We have been having problems with “ghost signals” causing intermittent hall arrival lanterns to illuminate randomly when the elevator is not actually due to arrive at the floor.

The tech support of the hall arrival board manufacturer (CE Electronics) is blaming the elevator controller manufacturer (MCE), and the tech support of the elevator controller blames the hall arrival board manufacturer.

The boards are powered by a ground referenced 24vdc, and data is transmitted to the board via a ground referenced single data wire (not a twisted pair). CE Electronics calls this their “Micro Comm data network”. It generally works extremely well and has relatively short transmission lengths (a few hundred feet, depending on the height of the building).

I have an email in to their tech support, but haven't heard back from them yet.

I was wondering if anyone on this forum could identify the data signal from the oscilloscope waveform. It appears to me to be a lower frequency square carrier wave carrying packets of higher frequency “data” square waves. Is this just pulse code modulation using a square carrier wave instead of a sine carrier wave, or something different? It's about 2.4 volts peak to peak above ground.



Thanks, Matt

[stj]

does the 24v come from a mains transformer?
maybe it's some type of powerline remote control.
not wifi-plugs or the scope wouldnt catch it

[sam_sam_sam]

I could be wrong but to me it looks like noise of some kind because it is not consistent in nature

I once worked on a machine that had some kind a switching power supply that buss type of control chip in it and just before it went out it causing havoc on the machine not powering things on correctly or turning things off and unfortunately you could not just buy the ic chip you had to buy the hole switching power supply for it but there was nothing wrong the switching power supply it self with out that special ic chip in it worked just fine

I wondering if you might have the same issue with a switching power supply that has some kind of buss system on it

[mscottdoran@gmail.com]

I have attached the relevant areas of the schematics. The building 3 phase 480vac powers the elevator controller, it is then transformed down to single phase 120vac, which is again stepped down and full wave rectified to unfiltered 24vdc. The unfiltered 24vdc gets plugged into the car and hall fixture driver board, and is filtered at the driver board to a steady 24vdc with about 200-300 mVac ripple. This filtered 24vdc goes to each floor's serial hall fixture as power. Each floor's serial hall fixture has a unique address that can be set by an onboard dip switch. Not 100% sure but the data signal must activate the board at whatever address the driver board sends out in order to turn on a floor output and sink some of the 24vdc power to ground through the fixture's LED thus illuminating the hall arrival lantern.

I can definitely see noise getting on the data signal as it is not a shielded twisted pair, but rather just a single 18awg copper wire run down the elevator shaft bundled with other high voltage ac wires (about 120vac max). The manufacturer tech support doesn't see this as a problem though, and in my experience it usually isn't.

[sam_sam_sam]

Are there any filtering capacitor or capacitors on the 24 volts circuit because the circuit diagram does not show it that is why I am asking
The only thing that comes to mind is that there might be issue with the Dlink circuit that it is transmitting a signal when it should not be
On rare occasions I seen issues with buss link modules do weird things so do not rule it out I sure that it is rare but I weird things happen before

[stj]

maybe one of the nodes on the network is fucked and glitching the line.

[sam_sam_sam]

maybe one of the nodes on the network is fucked and glitching the line.

I was thinking the same thing

[mscottdoran@gmail.com]

Yes there is a big filtering cap on the driver board. I don't have a board level schematic, but I have attached a picture of the board from the MCE elevator controller website:

[sam_sam_sam]

I would check the big filtering capacitor with a ESR meter to see if the resistance has gone high compared to a new one the same value

[mscottdoran@gmail.com]

maybe one of the nodes on the network is fucked and glitching the line.

yeah, I think this is most likely the case too. It's only four cars and eleven stops so 44 potential culprits, lol!

[mscottdoran@gmail.com]

I would check the big filtering capacitor with a ESR meter to see if the resistance has gone high compared to a new one the same value

That's a good idea, I'll check that out next week, Thanks