How can I calibrate the temperature of my bed

axiom · 26 Jul 2022, 17:31

dc42 · 26 Jul 2022, 17:43

@axiom when you measured the resistance of the sensor at 20C using a multimeter, are you sure it read 106 ohms, not 106 kohms? If it's 106 ohms, it's a PT100. If it's 106 kohms, it's a 100K thermistor.

axiom · 26 Jul 2022, 17:55

@dc42 You are right, it is 106 kilo ohms and not ohms... sorry for the wrong statement..

axiom · 26 Jul 2022, 18:00

@dc42 wenn i am starting the bed heater it shows "hardware error no sensor" without starting it shows 2000 degrees

Phaedrux · 26 Jul 2022, 21:57

@axiom said in How can I calibrate the temperature of my bed:

@dc42 You are right, it is 106 kilo ohms and not ohms... sorry for the wrong statement..

So if it's 106 kilo ohms it is a thermistor and should not be connected to the PT100 daughterboard. Connect it to the mainboard instead and change your config.g to use values for a thermistor.

infiniteloop · 26 Jul 2022, 22:53

@axiom

it is 106 kilo ohms and not ohms

Ok, thermistor. So, for a single heater with thermistor, this is what works:

M308 S0 P"bedtemp" Y"thermistor" R4700 T100000 B3950 ; configure sensor 0 as thermistor on pin bedtemp

Now, you have to decide what to do with four thermistors and four heaters. Let's assume you want to control the bed as a single unit - I've understood that you wired all heaters to "Bed Heat", i.e. this connector:

As you have four 24V PSUs, one for each heater, how do you control these? The proper way to do this is to put a SSR (type DC/DC) between the outcome (-) of each PSU and its heater - if you use a single SSR to switch mains power of all PSUs, you risk their early demise: as the signal from "Bed Heat" is pulsed, it switches rapidly between on and off. You can however use the SSR on mains to power the PSUs. How to do this is described in the last paragraph of this link.

Now, the thermistors: You should use all of them for a combined reading. How this works is outlined in the documentation under Using multiple temperature sensors for a single heater.
I tend to recommend solution 1 (connect them in series), but never tried that with 4 thermistors… at 400 kOhm, risk of interference with power signals is high. Maybe a serial/parallel combination is better in this case: two thermistors each in parallel, i.e. connected as pairs in series.

axiom · 27 Jul 2022, 03:43

@infiniteloop said in How can I calibrate the temperature of my bed:
Unfortunately I'm not at the output yet. I have now connected the PT100 daughterboard (see photo above) and entered the following value:

; Heaters
M308 S0 P"spi.cs1" Y"rtd-max31865" R4700 T100000 B3950 ; configure sensor 0 as PT100 on pin spi.cs1
M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B1 S1.00 ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M308 S1 P"e0temp" Y"thermistor" T100000 B4138 ; 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 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H1 S280 ; Set temperature limit for heater 1 to 280C
M308 S2 P"e1temp" Y"thermistor" T100000 B4138 ; configure sensor 2 as thermistor on pin e1temp
M950 H2 C"e1heat" T2 ; create nozzle heater output on e1heat and map it to sensor 2
M307 H2 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H2 S280 ; Set temperature limit for heater 2 to 280C

2000 degrees and the error message: failed to read seonsor: sensor hardware error are displayed in the console

axiom · 27 Jul 2022, 03:51

@infiniteloop said in How can I calibrate the temperature of my bed:
or do I have to send back the 2 daughter boards because they are not suitable for these thermistors?

Phaedrux · 27 Jul 2022, 04:04

The PT100 daughterboards are of limited value unless you have PT100 sensors to go with them. You can't just configure them into being something else.

axiom · 27 Jul 2022, 04:16

@axiom Then I omit the daughterboardas.
Then the safest thing is to connect the thermistors in series?
However, I didn't quite understand the description of how to declare all 4 pieces in the code

axiom · 27 Jul 2022, 04:18

@infiniteloop said in How can I calibrate the temperature of my bed:

The proper way to do this is to put a SSR (type DC/DC) between the outcome (-) of each PSU and its heater

The same should also work with mosfets for each part?

infiniteloop · 27 Jul 2022, 08:57

@axiom said in How can I calibrate the temperature of my bed:

mosfets for each part?

Moin. Yes, absolutely.

Daughterboards: as @Phaedrux told you, these are of "limited value" with thermistors. That's an understatement - you can't attach thermistors to them. Instead, attach the thermistors to "bedtemp".

I'll post how to wire the four thermistors - give me a minute …

infiniteloop · 27 Jul 2022, 09:30

@axiom Here are two of the "better" options how to wire the thermistors:

Left, it's a serial arrangement, resulting in a high impedance of 400 kOhm. As I wrote earlier, risk of interference with power signals may be high.

To the right, you see a serial/parallel combination: to the Duet, that arrangement looks exactly like a single thermistor.

In either case, the "open ends" at the bottom of my artwork are meant to be connected with "bedtemp".

axiom · 27 Jul 2022, 17:21

@infiniteloop II opted for the serial/parallel combination, but where exactly do I have to specify half the resistance in the code (that's what it says in the description)?
Here my code:
Heaters
M308 S0 P"bedtemp" Y"thermistor" R4700 T100000 B3950 ; 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 S1.00 ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M308 S1 P"e0temp" Y"thermistor" T100000 B4138 ; 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 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H1 S280 ; set temperature limit for heater 1 to 280C
M308 S2 P"e1temp" Y"thermistor" T100000 B4138 ; configure sensor 2 as thermistor on pin e1temp
M950 H2 C"e1heat" T2 ; create nozzle heater output on e1heat and map it to sensor 2
M307 H2 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H2 S280 ; set temperature limit for heater 2 to 280C

I stopped the autotuning because the cables got so hot!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

axiom · 27 Jul 2022, 17:59

@infiniteloop My mistake, I did the math again...I have to solder on a thicker cable extension...

infiniteloop · 27 Jul 2022, 21:00

@axiom said in How can I calibrate the temperature of my bed:

I opted for the serial/parallel combination, but where exactly do I have to specify half the resistance in the code (that's what it says in the description)?

The description talkes of two thermistors, not four. Two thermistors in series double their resistance (2 x 100k = 200k), wired in parallel it's half of the resistance (100k / 2 = 50k). In your case, you have two times two thermistors in series (TH_Heater_1 + TH_Heater_2 = 200k, TH_Heater_3 + TH_Heater_4 = 200k). These pairs (of 200k each) are wired in parallel, et voilà: you get 100k (200k / 2). That's why I wrote:

To the right, you see a serial/parallel combination: to the Duet, that arrangement looks exactly like a single thermistor.

As I see from your config snippet above, you've entered the proper values for this thermistor array:

M308 S0 P"bedtemp" Y"thermistor" R4700 T100000 B3950 ; configure sensor 0 as thermistor on pin bedtemp

Now to the heaters:

I stopped the autotuning because the cables got so hot!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

OK, you've then used a thicker cable extension, but I wonder: how did this work initially when you tuned just one single heater? Don't you connect each heater individually to its dedicated PSU? If so, the currents should only add up on the mains side… have I missed something?

One last thing: please post the tuning report. If the bed heats up as fast as last time, maybe we should reduce power a bit by limiting the PWM to less than 1.0 (that's the S parameter in M307). Finally, you build a 3D printer, not a pizza oven

axiom · 28 Jul 2022, 02:55

@infiniteloop Hello, pizza oven was a separate project :-). When I first tested the single mat, I just didn't pay attention to the heat from the cable. I have now ordered a thicker cable for the extension...will probably not arrive until Saturday....I would rather not do the tuning until then.
My nozzles are still an open construction site...I have the Volcano Tunig set (2 heads) https://www.3djake.com/e3d/supervolcano-upgrade-kit-300-mm?sai=7419 . I also started the autotuning...at 180 degrees the heating process breaks off...can you help me there too or should I open a new topic?

infiniteloop · 28 Jul 2022, 07:27

@axiom Better keep this thread focussed on your array of bed heaters, so that other readers with similar questions can reference it. And in case you want to limit PWM a bit, feel free to return to this thread.

Tuning your volcanos is a different topic. BTW, did you have a look at other threads dealing with hotend tuning under RRF 3.2 ff? With a quick forum search, you’ll find several discussions of 'tuning a heater' vs. 'tuning a tool'. For an in-depth treatment of the topic, you might also want to look at this here: Tuning the Heater Temperature Control.

axiom · 28 Jul 2022, 15:14

@infiniteloop Ok I understand, I can only continue with the bed when the new cable extensions are hopefully there on Saturday, then I will report back

infiniteloop · 28 Jul 2022, 15:16

@axiom

The new cable extensions are hopefully there on Saturday, then I will report back

That's fine. CU