Wrong Temp Monitored at Chamber Heater Fault

baua1024

I have a Duet 3 Mainboard and added a rather unconventional chamber heating setup.
I have a heating element in the back of the printer that gets air sucked in from the chamber by 2 fans and cycles it back into the chamber afterwards. I have a temp sensor at the printhead to monitor the chamber temperature that is configured with the heater. The heating element has a bimetal shutoff but to monitor the temp of the heating element itself I added a "fake" heater with another sensor that's attached directly to the heater. This is so the fans that suck in air are turning automatically on when the heater is getting hot.
When I turn on the chamber to let's say 60C it switches on H2 (which is the chamber) and as soon as the fake heater registers a temp above 80C the fans start to spin circulate air from the chamber into the heating cycle and back into the chamber.
Once the printhead registers 60C it shuts off the heating elements. In 3.3 that worked all fine but since I went to 3.4 I get an error: "Error: Heater 0 fault: temperature rising too slowly: expected 2.24°C/sec measured 0.01°C/sec".

This error is refering to heater 0 which is the bed. Since the bed already is at 100C the error makes sense. But the fault then is at the chamber. It's almost as if the Chamber monitors T0 although in DWC I can see the correct chamber temp. Not sure if this is a bug or I have some config error.

;Heated Bed
M308 S0 P"temp0" Y"thermistor" T100000 B3950 A"Bed" ; configure sensor 0 as thermistor on pin temp0
M950 H0 C"out0" T0 ; create bed heater output on out5 and map it to sensor 0
M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S115 ; set temperature limit for heater 0 to 110C
;heated Chamber
M308 S3 P"temp1" Y"thermistor" T100000 B3950 A"Chamber Heater" ;Sensor for Heating element
M308 S2 P"121.temp1" Y"thermistor" T100000 B3950 A"Chamber" ;Sensor for temp at printhead
M950 F2 C"out4" Q500 ;Create Fan2 and set its freqency
M950 H3 C"0.out3" T3 ; create fake chamber heater
M143 H3 S200 ;set fake chamber max temp to 200C
M106 P2 C"Chamber Fan" S0 H3 L255 T80 ;assign fan thermostatic control to fake chamber heater
M950 H2 C"0.out2" T2 ; create chamber heater
M307 H2 B1
M143 H2 S80 ;set max temp to 65
M141 H2 ;assign chamber heater to chamber

jay_s_uk

@baua1024 this has been raised as an error in the firmware. the incorrect heater number is being reported in the error
here is the original post where the issue has been raised https://forum.duet3d.com/topic/27766/wrong-number-in-heater-faults-in-3-4?_=1648447629117

In the meantime I suggest retuning your chamber heater

baua1024

@jay_s_uk Good to know that this is just a display issue. It's a weird issue then as the patchontes say that the reading time of the heater has been increased but it feels like it has been reduced as the chamber temp is rising VERY slowly as the heating element is not super powerfull. I even get negative readings due to fluctuation. Is there a way to disable this temp rising reading?

jay_s_uk

@baua1024 you might want to take a look at this https://forum.duet3d.com/topic/26733/3-4b7-7-chamber-heater-faults

baua1024

@jay_s_uk Thanks! I just had a read through it and unfortunately the C parameter got deprecated for the final 3.4 release. I will have to play with the E/K parameters although it reads like they have a different purpose(Cooling Curve) than the C.

baua1024

@jay_s_uk So I played around with E and K but I couldn't get the heater to stay on for longer without having the same error again. I also increased the dead time to 45 without any change. I think I don't understand how E and K fundamentally work. In the documentation there was the C parameter which simply said how long in seconds it would take for the heater to reach temperature but it was deprecated in favor for K and E. The docs say this is the formula: K*((Th-Ta)/100)^E. What is taken as the ambient temperature? I'm getting a bit frustrated as the only way I can heat the camber currently is manually increasing the temp by 1C at a time.

jay_s_uk

@baua1024 whats your current M307 line for the chamber heater?
I don't have one but I would suggest looking at changing the R value to something below 0.01 and increasing the dead time

baua1024

@jay_s_uk My current line is "M307 H2 B1 R0.016 D60" E&K value don't positively influence the successrate. Also all parameters seem to influence each other. So i can't go lower on R than 0.016 but if I set E&K on something i can't even go lower than 0.1.
I changed the Deadtime to 330 (that's the max) and this way it takes quite a bit longer until the fault occurs.

martin7404

@baua1024 With 3.4 I got this error only once for 48 hour printing already
My chamber heater is this link text
run trough SSR, I am using standard E3d V^ thermistor
this is my config line

M308 S2 A"Chamber" P"temp2" Y"thermistor" T100000 B4725 C7.06e-8
M950 H2 C"out2" T2                                 ;
M307 H2 A11 C99000 D2000 B1   ; 
M141 H2
M143 H2 S70

baua1024

@martin7404 Thanks! I will give it a shot. My heater element is 300W so it's fairly similar. I'm curious about the C parameter though as the docs say it's not supported anymore.

martin7404

@baua1024 it is left from older version, my point it trigered this error only during start of a print in a cold morning in the shop 20 minutes in.
Before that 20 hour print was finished

baua1024

@martin7404 Thank you Martin! With these values I can get it to heat up until 70C without any errors. I still wish there would be a better solution like a "dumb" heater but at least I can work with it now