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rustyshackleford
(@rustyshackleford)
Active Member
PT1000 high-temp question

I've got a MK3S with a Mosquito hotend and a PT1000. It works flawlessly below 300C, prints are perfect and everything works as it should. When I try to print PC at 300C, the hotend heats up and when it reaches 300C, it stays at exactly 300.0 for the duration of the print. I'm pretty sure that the hotend continues to heat up, because it takes 1-2 minutes after the print ends for the temperature to come back down from 300. When I modified the firmware, I changed the temp_sensor_0 setting to 1047 for the PT1000 and then changed the maxtemp setting from 305 to 400. Is there another firmware setting I missed that would cause the printer to stop reading anything higher than 300 and continue heating the hotend?

This topic was modified 2 weeks ago by rustyshackleford
Posted : 14/09/2021 11:21 pm
rustyshackleford
(@rustyshackleford)
Active Member
Topic starter answered:
Update

Just to check that there isn't something else happening that I'm missing, I re-sliced the file and changed the temp to 298C. This time it behaved as expected, printing beautifully until it warped off the bed and I had to cancel the print. In these images, the top pieces were printed at 300C and the bottom at 298C (though, clearly the 300C print was far higher at the end... basically producing a smooth pool of melted plastic on the topmost surfaces).

These were printed about an hour apart using the same spool, same PrusaSlicer settings, everything the same except the temperature.

Posted : 15/09/2021 1:19 am
JoanTabb
(@joantabb)
Moderator

Hi Rusty. 
standard Mk3 series printers do not use PT100 sensors. 
Are you sure you have a PT100? these normally need an amplifier/interface board to work with the Mk3, and I believe they require modified firmware!

As far as I understand 300C is the limit for a Semitec 104 gt-2 thermistor, which is usually used on a prusa mk3 printer. 

I believe Slice engineering offer a high temperature thermistor, to replace the standard Prusa thermistor, and to the best of my knowledge, this also needs revised firmware. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 15/09/2021 1:22 pm
rustyshackleford
(@rustyshackleford)
Active Member
Topic starter answered:

Thank you! To clarify, it is a PT1000, not a PT100. It does not require an amplifier but it does require modifications to the firmware. What I'm asking is whether anyone else has encountered similar issues when making this switch. I believe I updated what was needed in the firmware correctly but due to this odd 300C behavior I'm guessing I missed something Prusa-specific.

More background I should have included: I've just upgraded from the stock V6 setup to a Slice Mosquito hotend using the Slice 50W heater and the Slice PT1000. They did not have the high-temperature thermistor in stock and the PT1000 is supposed to work with just some minor firmware updates as described in my first post. Here is Slice's documentation on updating the firmware:

https://support.sliceengineering.com/portal/en/kb/articles/how-do-i-update-my-firmware-to-be-compatible-with-the-rtd-pt1000

Posted : 15/09/2021 1:53 pm
JoanTabb
(@joantabb)
Moderator

does your thermistor table have entries for temperatures above 300C (Appropriate for the PT1000)

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 15/09/2021 4:46 pm
rustyshackleford
(@rustyshackleford)
Active Member
Topic starter answered:

Ah - thanks, you may be right. Here are the relevant sections from thermistortables.h in the 3.10.0 firmware. It does look like it stops at 300. I'll add a 350 row and see if that solves it. For anyone else reading this at a later date, a separate file called Configuration_adv.h defines "thermistorheater_0" as "temp_sensor_0". So the change in the Configuration.h file to modify temp_sensor_0 from 5 to 1047 changes the relevant lookup table in thermistortables.h from 5 to 1047.

// Pt1000 and Pt100 handling

//

// Rt=R0*(1+a*T+b*T*T) [for T>0]// a=3.9083E-3, b=-5.775E-7

#define PtA 3.9083E-3

#define PtB -5.775E-7

#define PtC -4.183E-12

#define PtRt(T,R0) ((R0)*(1.0+(PtA)*(T)+(PtB)*(T)*(T)))

#define PtRtNew(T,R0) ((R0)*(1.0+(PtA)*(T)+(PtB)*(T)*(T) + (T-100)*PtC*(T)*(T)*(T)))

#define PtAdVal(T,R0,Rup) (short)(1024/(Rup/PtRt(T,R0)+1))

#define PtLine(T,R0,Rup) { PtAdVal(T,R0,Rup)*OVERSAMPLENR, T },

#if (THERMISTORHEATER_0 == 1047) || (THERMISTORHEATER_1 == 1047) || (THERMISTORHEATER_2 == 1047) || (THERMISTORBED == 1047) // Pt1000 with 4k7 pullup

const short temptable_1047[][2] PROGMEM = {

// only few values are needed as the curve is very flat

PtLine(0,1000,4700)

PtLine(50,1000,4700)

PtLine(100,1000,4700)

PtLine(150,1000,4700)

PtLine(200,1000,4700)

PtLine(250,1000,4700)

PtLine(300,1000,4700)

};

#endif

Posted : 15/09/2021 5:16 pm
JoanTabb
(@joantabb)
Moderator

Has that worked for you?

regards Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 16/09/2021 10:51 am
rustyshackleford
(@rustyshackleford)
Active Member
Topic starter answered:

It appears to have worked, though I haven't printed anything yet. I just set the nozzle temp to 305, then 310 yesterday and each time it stabilized and read temperatures greater than 300 with some +/- fluctuations as I'd expect. I will have time to actually print again this weekend. Thank you for your help with this!

Posted : 16/09/2021 10:57 am
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