IR Probe readings

[droftarts]

I recently fitted one of DC42's differential modulated IR Probes to a Cartesian machine I'm building up. It seems to work fine, and homing seems to be accurate, but I'm puzzled as to why it only shows 3 readings in DWC; 0 when far away from the bed, 456 about 0.5mm before the trigger height, and 531 (or 532) at the trigger height or closer. Is this normal?

Board: Duet WiFi v0.10 (Beta board)
Firmware: RepRapFirmware for Duet 2 WiFi/Ethernet 2.04RC1 (2019-07-14b1)
Duet WiFi Server Version: 1.23
Duet Web Control 2.0.0-RC7
Probe: Mini IR height sensor kit version 1.2

config.g:

; Z-Probe
M574 Z1 S2                   ; Set endstops controlled by probe
M558 P1 H5 F120 T6000        ; Set Z probe type to unmodulated and the dive height + speeds
G31 P500 X20 Y0 Z1.45        ; Set Z probe trigger value, offset and trigger height

Ian

[T3P3Tony]

@droftarts Yes i think having multiple values for the reading with an analog z probe like the IR sensor is expected behaviour. ideally that would be a linear ramp from where it can "just see" the bed to 1000 when its saturated. The trigger amount should be picked to give consistent results with your bed surface. You can jog the axis down in small increments to see the profile of the readings at different heights and then use that to select the trigger height, I would normally have it trigger some amount above the Z0 position and then adjust the z probe offset .