Calibrating inductive sensor, problem with Z axis movement

I've got a cartesian reprap with Marlin 1.1.8, and I've just added an inductive sensor to my extruder carriage for z probing. I changed all the settings in Marlin to set it up and enable bilinear meshing, and the printer executes the bed meshing perfectly. My problem is that when the sequence ends, the z height raises ~5-10mm. I'm in the middle of trying to fine-tune the z height offset for the probe, so I'm trying to figure out where the instructions for this movement are in the firmware, or at least disable them temporarily while doing the fine tuning. Sending a G92 Z10 command doesn't allow me to move the Z height any lower, and I don't know how much the Z height raised to begin with.

I tried changing the default Z height movement between probe attempts from 5mm to 0, which kind of worked (it didn't raise at the end of the sequence but also didn't raise between probing). Then I sent the G92 Z10 command to allow me to lower the nozzle in small increments, but the Z axis still will not move down despite registering Z height as 10mm.

I'm just trying to get the final Z height offset value then I'll be all done setting up "auto bed levelling," but there's something I'm missing. Any suggestions?

Okay, sorry my original question was very scattered. I was able to find decent solutions to my problems, so here they are. The two issues I was having were:

1. The machine refused to move below 0 on Z axis, and since the probe obviously triggers before the nozzle reaches the bed, I needed to be able to move to negative Z values to see what my Z Probe Offset value needed to be.

I solved this by commenting out "#define MIN_SOFTWARE_ENDSTOP_Z". I was then able to move below 0 on the Z axis and confirm Z Offset as -1.8mm.
I changed the Z Offset with the following, as you would expect:
"#define Z_PROBE_OFFSET_FROM_EXTRUDER -1.8"

2. But I was still encountering my second problem, which is that for some reason the printer was not recognizing the Z Offset value even after it was set and uploaded. Sending an M851 command returned this:

SENT: M851
READ: echorobe Z Offset: 0.00
Probe Z Offset: 0.00

I'm still not sure why the printer was ignoring the Z Offset value, but I solved it by sending M851 Z-1.8 to set Z offset manually, then saving with the M500 command. Now, the printer displays the proper offset value constantly.

Any idea why it seems to be ignoring the Z Offset value without the workaround? I would love to not have to remember to enter M851 Z-1.8 and M500 every time I re-flash the controller.

Just a short question, but what happens when you send a G1 Z0? Does it move to Z0?

---

http://www.marinusdebeer.nl/

Just tested, using G1 Z0 does move it to Z0. After setting the Z Offset with M851 Z-1.8 and saving with M500, the movement to Z0 does account for the Z Offset value as well. But the weird thing is, when I change Z Offset using "#define Z_PROBE_OFFSET_FROM_EXTRUDER (value)" and reflash, an M851 command still shows the old Z Offset.

Example:
I moved the probe down closer to the bed, so needed to recalculate the new offset value. My new Z Offset is -2.65. So, I change "#define Z_PROBE_OFFSET_FROM_EXTRUDER -1.8" to "#define Z_PROBE_OFFSET_FROM_EXTRUDER -2.65" and reflash the controller. Once done, using M851 shows my Z Offset value is still -1.8 even after flashing. So, is "#define Z_PROBE_OFFSET_FROM_EXTRUDER" not operating properly? Or am I doing something wrong? I can't figure out why it is ignoring the changes I make to this value.

After re flashing, you must issue a M502 and M500 to update the eeprom values with the new values from the configuration.h

eeprom allways has preference over the config.h file.

Ah okay, that makes sense. I will update the eeprom values tonight. Thank you!

Just FYI, you don't need to edit your configuration to be able to move past the probe point when figuring out what to set Z_PROBE_OFFSET_FROM_EXTRUDER. "M211 S0" will temporarily disable software endstops ("M211 S1" will re-enable them) so you can make your measurement.

Thank you for the tip! That will make things much easier. I'm going to brush up on the full list of gcode commands so I don't have to reflash every time I tweak something. Thanks again!