inductive Z probe problem

[RRinOz]

I'm new to this. I have just assembled my first 3D printer. A Voron 2.4 with Duet 2 V1.04 and Duex5 V0.11 running RepRap 3.4.5 - a steep learning curve. My config.g file describes the Z probe thus: M558 P5 C"!zprobe.in" H5 F120 T3000
I'm currently 'commissioning' and when I Send an M119 command to check the endstops, X,Y and Z microswitches all report OK when manually triggered, but the Z probe always reports 'probe at min stop' - whether triggered or not. The Z- probe is a ZHONGDE PL-08N2. I can manually trigger it by holding my wire cutters under it and when I do so a red LED inside the probe is turned off. All this time the DWC Status displays 'Z-Probe = 1000' or 'Z-Probe = 0" as appropriate!
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Why is the M119 command apparently lying to me?

[T3P3Tony]

@RRinOz Plase link to the datasheet for that probe and show how you have wired it at both the probe end and the Duet end.

[RRinOz]

@T3P3Tony Tony, thanks for the prompt reply. The probe has a 3 wire cable encapsulated into the body - so no connection at that end. I connected the 3 wires at the Duet2 WiFi end thus: Brown wire to + 24 v at the power terminal of the board; The Blue wire to Ground at the dedicated Probe socket and the Black wire to the signal pin of the same socket via a reverse biased diode. See diagram. Without the diode, the LED incorporated in the probe body would only dim when triggered. This mod was suggested for early Duet2 boards. I attach a copy of the spec sheet for the PL-05 probe family. Cheemi Inductive Proximity Sensor Series CJD-PL-05.pdf The PL-05 is the same as the PL-08 but with higher definition and less sensitivity (5mm compared to 8mm).

[T3P3Tony]

@RRinOz looking at this:
https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_connecting#npn-output-normally-open-inductive-or-capacitive-sensor

it looks to be wired ok and configured ok, other than the diode is not necessary on the v1.04 and later duet 2s, does it work without the diode?

Also worth checking that you see a change in the signal line from the probe (relative to ground) when you trigger it measuring with a multi meter when the signal line is not connected to the Duet.

[RRinOz]

Hi Tony, I have tried another probe with the same result (they are only cheap). If I insert a dress makers pin in beside the zprobe signal pin and short the diode, the voltage at the pin toggles between +0.7 volts and +24 volts with respect to Ground. With the diode in circuit, the signal voltage toggles between approx +1 and +2 volts. It never goes to zero. However, if I unplug the probe at the zprobe socket and jumper the signal pin to Ground (the adjacent pin), I get the same results running command M119 i.e. 'z probe at min stop'.
Late Extra: I just tried it after re-plugging the z probe plug on the Duet board and presto, it's working properly! I've wriggled all the connectors but can't make it fail now. Thanks for walking me through this mysterious problem. I can now proceed to the stepper motors. Cheers, Ralph