Heater Temperature Excursion

[Phaedrux]

@Leav said in Heater Temperature Excursion:

I hope this isn't bad form, but it seems this question slipped by so I'm tagging @dc42 again...

No that's fine. Keeps us from forgetting. Thanks for giving it a couple days.

[Leav]

Still chasing this, and I've worked on a few things since I last posted:

• New Thermistor (cartridge style, to rule out issues with wires shorting in the heater block)
• New heater cartridge
• Successfully replaced wifi module with esp-07s - Signal went from ~-70dbm to ~-55dbm

Started a five hour print, temperature graph was smooth, minus a few blips which seemed to indicate that the heating process gets "stuck" (??) either in "on" or "off" mode for a second, and the then recovers:

I let it be, thinking this is a minor issue, but after a few hours the excursion hit again:

I was able to resume the print (thanks for such a robust recovery mechanism!), and there was still a bit of noise:

But now it is very smooth (minor blip still shows up):

Does anyone have any clue what could cause this? I feel like this is some sort of random behavior that gets introduced and suddenly vanishes, making debugging very frustrating...

Here is a copy of the M122 response after the recovery:

M122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 3.1.1 running on Duet WiFi 1.02 or later
Board ID: 0JD0M-9K662-MGPSS-6J1FD-3S46N-TVU6Y
Used output buffers: 3 of 24 (11 max)
=== RTOS ===
Static ram: 27980
Dynamic ram: 93124 of which 48 recycled
Exception stack ram used: 576
Never used ram: 9344
Tasks: NETWORK(ready,268) HEAT(blocked,792) MAIN(running,1732) IDLE(ready,80)
Owned mutexes: WiFi(NETWORK)
=== Platform ===
Last reset 04:52:37 ago, cause: power up
Last software reset at 2020-10-16 16:27, reason: User, spinning module GCodes, available RAM 9376 bytes (slot 0)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0441f000 BFAR 0xe000ed38 SP 0xffffffff Task MAIN
Error status: 0
MCU temperature: min 22.3, current 36.8, max 43.8
Supply voltage: min 23.7, current 24.0, max 24.3, under voltage events: 0, over voltage events: 0, power good: yes
Driver 0: ok, SG min/max 42/430
Driver 1: ok, SG min/max 78/423
Driver 2: ok, SG min/max 0/416
Driver 3: ok, SG min/max not available
Driver 4: standstill, SG min/max not available
Date/time: 2020-10-17 12:48:30
Cache data hit count 4294967295
Slowest loop: 275.25ms; fastest: 0.12ms
I2C nak errors 0, send timeouts 0, receive timeouts 0, finishTimeouts 0, resets 0
=== Storage ===
Free file entries: 9
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest read time 2.9ms, write time 63.4ms, max retries 0
=== Move ===
Hiccups: 0(0), FreeDm: 161, MinFreeDm: 137, MaxWait: 455270ms
Bed compensation in use: mesh, comp offset 0.000
=== MainDDARing ===
Scheduled moves: 215624, completed moves: 215603, StepErrors: 0, LaErrors: 0, Underruns: 0, 0  CDDA state: 3
=== AuxDDARing ===
Scheduled moves: 0, completed moves: 0, StepErrors: 0, LaErrors: 0, Underruns: 0, 0  CDDA state: -1
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1 -1 -1
Heater 0 is on, I-accum = 0.0
Heater 1 is on, I-accum = 0.4
=== GCodes ===
Segments left: 1
Movement lock held by null
HTTP is idle in state(s) 0
Telnet is idle in state(s) 0
File is doing "G1 X-5.074 Y-103.468 E29.61163" in state(s) 0
USB is idle in state(s) 0
Aux is idle in state(s) 0
Trigger is idle in state(s) 0
Queue is idle in state(s) 0
Daemon is idle in state(s) 0
Autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 275.44ms; fastest: 0.00ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0), 0 sessions
HTTP sessions: 1 of 8
- WiFi -
Network state is active
WiFi module is connected to access point 
Failed messages: pending 0, notready 0, noresp 0
WiFi firmware version 1.23
WiFi MAC address 48:3f:da:45:74:de
WiFi Vcc 3.38, reset reason Unknown
WiFi flash size 4194304, free heap 24504
WiFi IP address 192.168.1.6
WiFi signal strength -55dBm, reconnections 0, sleep mode modem
Socket states: 4 0 0 0 0 0 0 0

[mendenmh]

Given that on both the negative and positive small excursion you show, the leading edge is 'instantaneous', followed by a real ramp to compensate, it looks like a thermistor issue. The actual temperature cannot change that fast. After a sudden change in the thermistor+wiring resistance, the heater initiates a real ramp + overshoot to compensate. There has to be a loose connection in the thermistor wiring somewhere, I think.

[Leav]

@mendenmh

This has been suggested before, but I'm willing to give it a try again.
I'll expose the electronics bay and jiggle everything around while holding at ~250c.
Will report back.

[Leav]

Embarrassed / Happy to say that I found a loose connection deep in the mines of moria electronics bay.

Below is the result of wiggling that cable... That cable is very much static during the print, but I guess the vibrations/heat expansion was enough to cause issues?

Lesson of the day: don't use bare wire in screw terminals! (not even "just temporarily to see if it works!")

Thanks all for bearing with me during my somewhat crazy tangents.