Filament sensor "calibration" doesn't really calibrate the filament sensor?
I've discovered something unexpected about the filament sensor calibration function kf the MK4S.
Today, one of my MK4S printers started exhibiting some weird behavior with the filament sensor not detecting inserted filament.
I checked the "Sensor Info" / "filament sensor" option and watched as I inserted and removed filament. The value of the sensor very clearly and reliably changed from about 110,000 when not inserted to 140,000/160,000 when inserted. It's a solid and totally reliable separation of values. But the reported status of the filament sensor is "NINS" when not inserted and varies between "INS" and "NINS" when inserted, especially if I kind of wiggle and apply lateral pressure on the filament just above the extruder.
Here's the problem. I re-ran filament calibration, and it continued to behave erratically when filament was inserted, switching between "INS" and "NINS" depending on my lateral pressure against the filament sensor.
It seems that the "filament calibration" function does not do what I expected - i.e., measure the filament sensor values when filament is inserted vs. not inserted and select new sensor values to set the status of the sensor. Rather, it looks like the firmware has a certain hard-coded thresholds - e.g., a threshold around 145,000 - and the calibration function either verifies that the printer performs well with these values or raises an error if it doesn't.
Since the fixed, predetermined threshold is out of whack with my apparently fully filament sensor, I'm forced to turn it off to avoid spurious "oops, the filament is stuck" messages. Very frustrating.
Is this experience consistent with anyone else's experience? And is there any way to set or adjust the filament sensor INS/NINS cutoff?