LED pulse sensor problems

I installed the LED pulse sensor to electricity meter Landis + Gyr E450. Sensor´s green LED flashes according to the meter pulse, but the output pulse does not appear on PLC. When I unplug the sensor from the electricity meter and I give light by flashlight, output works, and the pulses are applied in to the PLC.
I wonder what is wrong with it. Is the meter led too fast or too dim? However, the sensor reacts when I turned over it in my hand towards the ceiling lamp.

Try moving the sensor around very slightly on the meter, also rotate it on it’s axis (ie cable entry down, up,left and right etc) and/or angling it slightly whilst watching the LED.

Since you have now observed this odd behavior I shall also share my findings (I didn’t want anyone thinking I’m even more nuts than they already did)

I have noticed a strange situation, where I can move a sensor and position it to give anyone one of 3 outputs from the same pulsed light source,

  1. LED flash only, no pulse via wiring,
  2. Pulse via wiring only, no LED flash or
  3. Both and LED flash and pulsed output from wiring.
    (obviously not including the 4th possibility of no led flash or pulse output if not positioned anywhere near correctly)

I had tested this further with a standard led controlled by Arduino blink.ino in free air (this rules out any possibility of 2 different light frequencies/intensities being the cause) and found that once located by moving the sensor. I can switch between the 3 results at will by moving very slightly. I assume either there are 2 actual sensors on board (which makes no sense) or the switching circuitry for the LED or pulse are independent of each other and have different characteristics (but that doesn’t directly explain the effect that positioning has, but may indirectly?), since my findings were done in free air with a gap between them, ambient light may play a part too.

I have only tested this on one sensor, the first and only one I had at that time so whether it is apparent on all sensors I couldn’t say, I know it sounds bizarre.

Bottom line is if what you are seeing is the same as I found, then you should be able to play with the positioning and find that “sweet spot” in which both the LED and pulse output work.

I had asked for a circuit diagram but @glyn.hudson has said the manufacturer will not provide one and as they are sealed units, I never got to the bottom of it.

All that sounds to me like a pulse duration / pulse amplitude issue.

What voltage were you (each of you) supplying the sensor with?

I can’t really believe that the LED output and the pulse output are independent, but a slight cause for concern is the claim that it has a “TTL” output, which it can’t be if it’s run off 3.3 V. If you are running it off 3.3 V, then maybe it’s worth trying 5 V and dividing down the output to 3.3 V?

Now there’s a question, I cannot recall. I use a USB connected Arduino nano for my pulse detection and have tried both 3v3 and 5v, which I was using at that time I do not recall, but if I was getting odd results I am also pretty sure I would have tried the other, since they are easily switched over. Plus as I was using a 5v powered nano I’m not sure I would have had any reason to opt for 3.3v, but cannot be 100%.

your thinking is similar to mine at the time, and what stumped me was the ability to invert the result, I understand intensity and/or frequency etc not hitting the mark for one the other, but that should result in one output being fairly consistent and the other being erratic, but not reversible at a tweak of the position. that’s the bit that got me.

I wonder what shape the output pulse is? I think we’re all tacitly assuming there’s some level detection mechanism inside, but that’s not necessarily the case. The sensor is often biased by a feedback mechanism to minimise the effect of ambient light, and if that’s the case here, there could be untold analogue effects influencing it. Until somebody reverse-engineers the device, we’ll probably never know.