PID Tuning help needed
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Hi
I have started to PID tune my hotend heater, but it has been going for 20 minutes now, without finishing up - also I am at a P parameter of 0.1; am using an external mosfet driving my 24V heater (I want as little as possible current through my control board).
I am using a Duet2 board, with firware V 3.2.2; and Duet wifi server verion 1.25. I have included the text from the configuration at the end of this post.
Other strange thing is, there are quite a lot of oscillations with regards to the temperature being sensed. (Up to 3 to 4 degrees up and down)
Any/all help appreciated!
Tinus
CONTENTS OF CONFIG.G
; Configuration file for Duet WiFi (firmware version 3)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v3.1.4 on Tue Nov 03 2020 07:37:18 GMT-0800 (Pacific Standard Time); General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"Ender3" ; set printer name
M918 P1 E4 F2000000 ; configure direct-connect display; Network
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet; Drives
M569 P0 S0 ; X Stepper
M569 P1 S0 ; Y Stepper
M569 P2 S0 ; Z Stepper
M569 P3 S1 ; E Stepper
M569 P4 S0
M584 X0 Y1 Z2:4 E3 ; set drive mapping
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z1200.00 E401 ; set steps per mm
M566 X800.00 Y800.00 Z800.00 E300.00 ; set maximum instantaneous speed changes (mm/min)
M203 X15000.00 Y15000.00 Z1500.00 E6000.00 ; set maximum speeds (mm/min)
M201 X500.00 Y500.00 Z250.00 E5000.00 ; set accelerations (mm/s^2)
M906 X800 Y1000 Z850 E1500 I50 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout
M671 X-24.2:250.8 Y0:0 S1.0; Axis Limits
M208 X-77.2 Y-13 Z0 S1 ; set axis minima
M208 X270 Y258 Z360 S0 ; set axis maxima; Endstops
M574 X1 S1 P"!xstop" ; x-end stop with inverse operation
M574 Y1 S1 P"!ystop" ; y-end stop with inverse operation
M574 Z1 S2 ; z-end stop with inverse operation; Z-Probe
M950 S0 C"exp.heater3" ; define servo
M558 C"zprobe.in" P9 H10 F120 T3000 S1 I1 ; set Z probe type to switch and the dive height + speeds
G31 X40.0 Y-4.5 Z2.35 ; set Z probe trigger value, offset and trigger height // Z2.35
M557 X15:215 Y15:195 S20 ; define mesh grid; Heaters
M308 S0 P"bedtemp" Y"thermistor" T100000 B4092 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B1 S0.6 ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S150 ; set temperature limit for heater 0 to 150C
M308 S1 P"e0temp" Y"thermistor" T100000 B4092 ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S0.6 ; disable bang-bang mode for heater and set PWM limit
M302 S180 R180 ; Set retraction/extruding temperature limits. Extruding 180, Retraction 180.
M143 H1 S320 ; Set maximum heater temperature to 320C; Fans
;M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S0.85 ; disable bang-bang mode for heater and set PWM limit
M302 S180 R180 ; Set retraction/extruding temperature limits. Extruding 180, Retraction 180.
M143 H1 S320 ; Set maximum heater temperature to 320C; Fans
M950 F0 C"e1heat" ; create fan 0ler Fan" H-1 ; set fan 2 value. Thermostatic control is turned on @ 0.8Factor and 180C
M106 P0 C"Part Cooler Fan" H-1
M950 F1 C"fan0"
M106 P1 C"Fan unknown 0" H-1
M950 F2 C"fan1"
M106 P2 C"Hot End Fan" H1 T40
M950 F3 C"fan2"
M106 P3 C"Extruder Stepper Fan" H1 T60; Tools
M563 P0 D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C; Custom settings are not defined
; Miscellaneous
M501 ; load saved parameters from non-volatile memory
T0 ; select first tool; Signal to user that probe and loading is complete
M501 ; Load EEPROM details
M575 P1 S1 B115200 -
the oscillations are normal and it can take up to an hour or more to PID tune something. just let it run its course
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@jay_s_uk said in PID Tuning help needed:
the oscillations are normal and it can take up to an hour or more to PID tune something. just let it run its course
Thanx, but is it normal to shoot 30+ degrees Pas target, and the oscillations do not get smaller!?
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@Reefwarrior yes. its measuring cooling and heating times
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@jay_s_uk Thank you - I will try again and let you know. Weird is that I started the PID process with a temperature of 240C, but on initial heating now it went past 320C. I suspect that the glass thingy (I forgot the name now!) that measures the temperature may not be calibrated/defined correctly.
I know in Marlin you can choose the different options, but I haven't come across it in the duet firmware yet. Or am I missing something?
Tinus
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@Reefwarrior yea, it shouldn't go as high as 320 on a 240 degree tune.
The M308 line in config sets the thermistor. best finding out what you had in marlin so you can replicate it here -
@Reefwarrior It sounds to me like you have a very over powered heater. Might it be 12V heater running in a 24V system? Are you able to measure the resistance of the heater cartridge? If so, post the value here and one of us will work out the wattage.
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@deckingman Hi, I get 4.1ohm. I don't know if this can be correct, as it 'feels' too little?
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@Reefwarrior typical resistances
P\V --------------------- 12V---- 24V
40w (Red Leads) 3.6Ω 14.4Ω
25w (Blue Leads) 5.76Ω 23.04Ω -
@Reefwarrior said in PID Tuning help needed:
@deckingman Hi, I get 4.1ohm. I don't know if this can be correct, as it 'feels' too little?
So, if my maths serves me correctly, V=IR, so I=V/R = 24/4.1 = 5.8536Amps. Wattage = VI = 24 x 5.853 = 140.48 Watts !!
If the voltage was 12, then the current becomes 2.9 Amps so the wattage would then be 12 x 2.9 = 35 Watts.
So it looks you have a nominal 40 watt \ 12V cartridge so when you put 24V through it, you get roughly 4 x the heating power.
Note. A 40 Watt/24V cartridge would have a resistance of about 14.5 Ohms.
Edit. A 40W/ 24v heater cartridge would draw about 1.65 Amps which is perfectly safe to use with the onboard MOSFETs - no need to use an external one.
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Thank you all for the feedback. Yes seems I am running a 12V then at 24V. I take it I can't just put in a power factor of P0.25 to fix this? Or will it be better to rather just swap it out for a 24V cartridge?
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@Reefwarrior said in PID Tuning help needed:
Thank you all for the feedback. Yes seems I am running a 12V then at 24V. I take it I can't just put in a power factor of P0.25 to fix this? Or will it be better to rather just swap it out for a 24V cartridge?
Running 25% PWM is bad idea IMO. The problem is that, if a MOSFET fails, then you could end up with the full ("permanent" as in non PWM switched) 24V which could be a fire risk.
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@Reefwarrior swap it. it will be unsafe until you do so
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Cool thank you. I will swap it out this afternoon then, and see if it is better.
With regards to the temperature measurement. Is it normal for it to jump up and down a few degrees? The graphs show spikes, instead of a normal flat line....
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@Reefwarrior said in PID Tuning help needed:
Cool thank you. I will swap it out this afternoon then, and see if it is better.
With regards to the temperature measurement. Is it normal for it to jump up and down a few degrees? The graphs show spikes, instead of a normal flat line....
I think you'll find it's a lot more stable with a cartridge that is a better match to the hot end. The PID control can only do so much and when you have a heater that is over powered by a factor of 4 then you are likely to get overshoots when it turns on.
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@Reefwarrior said in PID Tuning help needed:
Is it normal for it to jump up and down a few degrees?
No, check your wiring. Either it's picking up interference (usually from stepper motor or endstop wiring), or there's a poor joint. It will also cause the PID tuning to fail, as it can't get a consistent reading, and it's probably why it's taking so long to tune.
Are you using a thermistor PT1000, PT100 or thermocouple? There are ways to make the last two more reliable, by using four wires rather than just two.
Ian
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@droftarts Hi Ian,
It looks like one of those little glass bead thingies that measures the temperature....
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@Reefwarrior Sounds like a thermistor. Check your wiring, and make sure the leads of the thermistor aren't grounding on the heater block, and that the thermistor bead is making good contact with the heater block (ie not flapping about in a big hole!). Cartridge thermistors, or PT1000, are generally easier to use and get good contact with. What kind of hot end is this?
Ian
Cartesian bed-slinger with Duet 3 Mini 5+ WiFi and 1LC : RRP Fisher Delta v1 with Duet 2 Maestro : TronXY X5S with Duet 3 MB6HC and Roto toolboard
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@droftarts E3d v6 clone. I will take a look at the hotend too....
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@droftarts Did you check the earlier posts? It transpires the OP has a 12V cartridge and a 24V system. So around 140 Watt instead of 35. Methinks, that's more likely to cause the oscillations.
