Ignore intermittent errors in the MAX31855K (and MAX6675) thermocouple sensor.

[mobilinkd]

Description

Ignore intermittent errors in the MAX31855K (and MAX6675) thermocouple sensor. This replicates behavior in Sailfish firmware for handling thermocouple sensors on the Makerbot Replicator & numerous clones.

Require a number of errors from a thermocouple sensor in series before triggering a fault. The default is set to 15 as this is the default in Sailfish firmware.

Benefits

Current behaviour of Marlin is that a single error event in a thermocouple sensor will cause the printer to halt with a MAXTEMP error. This change ignores intermittent errors from a thermocouple sensor due to noise. Marlin will no longer halt with an MAXTEMP error due to a spurious error report.

Safety is still maintained. The error is reported within 3 seconds when a failure resulting in a persistent error condition occurs.

Related Issues

See #18025

I have tested this code by shorting the thermocouples to GND and to VCC. I verified that the error condition is reported and that max_temp_error() is still called.

[Grogyan]

// Set this value to 0 to fail on the first error to occur.
#define THERMOCOUPLE_MAX_ERRORS 15
Line #408

Should be in conditionals_post.h so that it isn't called for all temperature settings.

[Grogyan]

Tested this PR on the SKR1.3 and, it causes immediate MIN_TEMP

[mobilinkd]

Tested this PR on the SKR1.3 and, it causes immediate MIN_TEMP

What thermocouple amplifier are you using? The SKR1.3 does not have a thermocouple amplifier built into it.

What happens when you use the same configuration without the patch?

[Grogyan]

I use the Max31855 breakout board from Adafruit.
Prior to this change, thermal settings work as expected
With this change, MIN Temp is called.
Reverting to 2.0.5.3 bugfix 19-5-2020, works as expected again

[mobilinkd]

Can you attach your config settings?

Also, can you try with

#define THERMOCOUPLE_MAX_ERRORS 0

and let me know if you still have the same problem?

[Grogyan]

I cannot right now

[Grogyan]

Currently at work.
I will go through this tomorrow.

[thinkyhead]

Thanks for the update, @Grogyan. Now merged.