PT100 reading too high at higher temps



  • Those probe thermocouples aren't terribly accurate, because there's very little conducting area since you're jamming a sphere between two parallel surfaces - you only get a tiny contact area. But the rest of the probe (the wires) acts like a heatsink.

    As a result they tend to read 3-7% percent low, which is what you're seeing (~5% low).

    I print PLA at 235C. I suspect that your previous setup was reading incorrectly, and you're setting that (known to be less accurate) as the mental standard and using a measurement technique that is flawed to support your hypothesis.

    What happens when you print at 230C?


  • administrators

    I think the PT100 is probably reading correctly. There is no calibration involved with the PT100, the accuracy depends only on the chip (which is guaranteed to be accurate to 0.5C), a 0.1% tolerance low temperature coefficient resistor, the sensor, and the resistance of the PT100 connecting wires and any connectors involved (unless you use a 4-wire connection). Additional resistance causes an increase in the reading of about 0.4C per ohm. So if you are getting good readings at room temperature, you are probably getting good readings at higher temperatures too. You can always try the other channel if you suspect a fault.

    It's hard to get an accurate reading from a thermocouple on the outside of the hot end, because it's difficult to get good thermal contact and the thermocouple leads conduct heat away from it. A better way to measure the temperature with a thermocouple is probably to feed the thermocouple into the hot end in place of the filament, so that it sits in a pool of molten filament at the bottom. Even then, it won't be at quite the same temperature as the PT100 in the heater block.

    You can check the accuracy of the PT100 interface by substituting a fixed resistor for the PT100 and comparing the reading you get with what the tables give for that resistance.

    Also bear in mind that if your printer was previously using a thermistor, then its temperature reading probably wasn't very accurate.

    BTW, 215C seems to me rather high for regular PLA. I use 205C first layer and 195C after that, using PLA from either RigidInk or Esun and a E3Dv6 hot end. But filaments and hot ends vary, in particular there are some modified PLA filaments that need higher temperatures.

    HTH David



  • @DjDemonD:

    Yeah I'd say you are about as close as you normally get with a K type placed somewhere on the heater block. You can't read the actual temperature without inserting the K type into the hole where the pt100 goes and the thermal conductivity to/from the K type tip just isn't that great.

    Makes me wonder why they don't put two sensors into each cartridge?

    Turn it up to 230 (indicated) is the problem solved?

    Yea I definitely expect some level of reduction of course as the probe isn't making fantastic physical contact..that's a duh. 😉
    And yes I did actually insert the probe into PT100 cartridge hole, so it sat there with the probe, but again without better thermal transfer…idk exactly what to expect for the offset. I debated on using some thermal transfer compound, but I'm not convinced that would yield much better results. I even ran it down the filament path as far as it would go.

    Either way with the probe RIGHT AGAINST the heater cartridge I would have expected higher temp readings than that of the PT100, especially since I can actually see light around the PT100 cartridge through the probe hole, so even it isn't making superb thermal contact. Plus as the heat rises, the PT100 reading grows farther away.

    So I just swapped out PT100 cartridges, JUST remembered we had ordered a couple spares, and set nozzle to 260C. I let it sit there a moment and then I unplugged the PT100 and took Ohm reading on it, got ~197 Ohm which falls pretty close to the resistance tables. I also see and feel PLA flowing as I'd expect it to @215C...and at @260C ha. Yet the other PT100 also read 108.4 at room temp...so idk.



  • @dc42:

    I think the PT100 is probably reading correctly. There is no calibration involved with the PT100, the accuracy depends only on the chip (which is guaranteed to be accurate to 0.5C), a 0.1% tolerance low temperature coefficient resistor, the sensor, and the resistance of the PT100 connecting wires and any connectors involved (unless you use a 4-wire connection). Additional resistance causes an increase in the reading of about 0.4C per ohm. So if you are getting good readings at room temperature, you are probably getting good readings at higher temperatures too. You can always try the other channel if you suspect a fault.

    It's hard to get an accurate reading from a thermocouple on the outside of the hot end, because it's difficult to get good thermal contact and the thermocouple leads conduct heat away from it. A better way to measure the temperature with a thermocouple is probably to feed the thermocouple into the hot end in place of the filament, so that it sits in a pool of molten filament at the bottom. Even then, it won't be at quite the same temperature as the PT100 in the heater block.

    You can check the accuracy of the PT100 interface by substituting a fixed resistor for the PT100 and comparing the reading you get with what the tables give for that resistance.

    Also bear in mind that if your printer was previously using a thermistor, then its temperature reading probably wasn't very accurate.

    BTW, 215C seems to me rather high for regular PLA. I use 205C first layer and 195C after that, using PLA from either RigidInk or Esun and a E3Dv6 hot end. But filaments and hot ends vary, in particular there are some modified PLA filaments that need higher temperatures.

    HTH David

    Ok, yea I couldn't find ANY info on 'tuning' a PT100 so it definitely seemed like it either works or doesn't. After reading your info on 2 wire vs 4 wire I concluded that 4 wasn't necessary for my setup as I wasn't seeing any notable increase in resistance.

    Because I know getting thermal contact is a PITA for a tiny probe bead, that's why I used the IR cam as a backup, but that has its own faults when measuring shiny things like the ultra shiny copper alloy heater block!

    As far as 215 being high, you may be right due to all previous experience being with thermistors! 215 (in this case SeeMeCNC brand PLA) was derived at via testing and tuning. I don't print ANY filament at recommended settings blindly. I run multiple test prints for layer adhesion at a wide range of temps and speeds. 215 is what has worked to get the best combination of strength and quality of print. I use this method on multiple Rostock machines at home and work. And at home on Maker Select and CR10. Some other brands of PLA I get good results at 205, but NEVER have I had 195 yield good layer adhesion and end part strength…ever. But...up till now ALL machines I've used are SEMITEC 104GT2...soo...idk Only recently have I used RigidInk and it did well at 205 and I've seen OK results from Hatchbox at 205. I've never used Esun. I mostly print in PETT/PETG anyhow.
    I know what burning filament looks and smells like...so I know 215 isn't TOO hot.

    I may try the other channel just for the sake of thorough evaluation...but that will have to wait till next week post holiday.



  • @superpotatofudge:

    Ok, yea I couldn't find ANY info on 'tuning' a PT100 so it definitely seemed like it either works or doesn't. After reading your info on 2 wire vs 4 wire I concluded that 4 wasn't necessary for my setup as I wasn't seeing any notable increase in resistance.

    Because I know getting thermal contact is a PITA for a tiny probe bead, that's why I used the IR cam as a backup, but that has its own faults when measuring shiny things like the ultra shiny copper alloy heater block!

    As far as 215 being high, you may be right due to all previous experience being with thermistors! 215 (in this case SeeMeCNC brand PLA) was derived at via testing and tuning. I don't print ANY filament at recommended settings blindly. I run multiple test prints for layer adhesion at a wide range of temps and speeds. 215 is what has worked to get the best combination of strength and quality of print. I use this method on multiple Rostock machines at home and work. And at home on Maker Select and CR10. Some other brands of PLA I get good results at 205, but NEVER have I had 195 yield good layer adhesion and end part strength…ever. But...up till now ALL machines I've used are SEMITEC 104GT2...soo...idk Only recently have I used RigidInk and it did well at 205 and I've seen OK results from Hatchbox at 205. I've never used Esun. I mostly print in PETT/PETG anyhow.
    I know what burning filament looks and smells like...so I know 215 isn't TOO hot.

    I may try the other channel just for the sake of thorough evaluation...but that will have to wait till next week post holiday.

    I have pretty much the same setup as you, E3D V6 with Copper heat block and copper nozzle .4mm with PT100 board in 2 wire configuration. While I agree with others you cannot accurately measure temp with that external sensor (I own one and used one during my setup of this printer). My experience is that this combo is dead on accurate with its temp readings and does a really good job of maintaining temp within .1 degree

    As soon as my hotend reaches the 190 mark my PLA begins a slight ooze from the nozzle and by the time it hits 205c it is ready to print (my preferred temp so far with this combo). I have it setup so it homes after heating the nozzle then moves off to the side and extrudes 30mm of filament before moving back to the bed to begin printing. I am getting insanely clean and accurate prints. One thing I did add in to the setup that has seemed to make very noticeable improvements is a Capricorn PTFE tube, I ordered the low friction version https://www.filastruder.com/products/capricorn-ptfe-tubing?variant=45539850511 I also printed a bowden coupler clip to keep the coupler from bouncing up and down during high retraction https://www.thingiverse.com/thing:1330497

    Here are my settings:[c]
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80.00 Y80.00 Z2560.00 E100 ; Set steps per mm
    M566 X3600 Y3600 Z3600 E7000 ; Set maximum instantaneous speed changes (mm/min)
    M203 X18000 Y18000 Z400 E7000 ; Set maximum speeds (mm/min)
    M201 X3600 Y3600 Z3600 E7000 ; Set accelerations (mm/s^2)
    M906 X765 Y850 Z850 E850 I30 ; Set motor currents (mA) and motor idle factor in per cent[/c]

    My extruder is a bowden and not geared and the extrusion coming out the other end is exactly 100mm

    So my question: are you sure with hotend detached that with your current settings, your hotend pushes exactly 100mm of filament? Also do you have pressure advance enabled? [c]M572 D0 S0.1[/c]

    If you do then you should know that pressure advance if configured incorrectly can cause a lot of grinding…. i had that issue when I accidentally had M572 D0 S1.0 in my slicer start script instead of M572 D0 S0.1 and was doing a retract heavy print.

    If you have pressure advance configured in config.g go ahead and remove it from there and create yourself a macro to do some testing:

    [c]G1 E100 F300 ; Extrude[/c]

    Heat up your hotend first to 205c and then run this macro then increase the F parameter by increments of 50 until you notice grinding…. this will be your max flow rate for that temp, then repeat the same test with 210 and again with 215.... if all of these tests can do up to F300 then your flowrate is fine in those temps for 60mm/s and the problem is not with temperature or jamming.

    A great print to dial all this in is this model: https://www.thingiverse.com/thing:607968

    It is a serious torture test at high speeds so I would suggest starting with 40mm/s



  • Thanks for the input!! I'll look into the Capricorn PTFE. The only downer there is the lack of translucency for the ultra slick variety. But I suppose it is a worthwhile trade for being extra slick for long runs. So far I haven't had any issues with needing a clip, I always keep pressure on the tube when I push it in and use my fingernail to pull up on the built in clips and then double check from time to time that the tube has no play. Thus far I still haven't had a single instance of there being slop since I started that method.

    Looking at your settings I see some rather glaring differences to what I've gleaned for the Rostock!
    How do you get that Z2560 for M92 steps/mm?? That's crazy… most of my settings were either pulled from my RAMBo EEPROM or from mhackney's Duet config.

    Currently I have:
    M92 X80 Y80 Z80 E92.65

    My motor currents are based on the same 1 amp used with the RAMBo for the Automation Tech steppers.
    M906 X1000 Y1000 Z1000 E800 I30
    Acceleration is based on what was used on RAMBo and what I've seen from others on the SeeMeCNC forum
    M201 X1850 Y1850 Z1850 E6500
    Max speeds taken from previous firmware
    M203 X21000 Y21000 Z21000 E6000
    Jerk taken from previous firmware and not increased based on mhackney and others on SeeMeCNC forum settings
    M566 X2100 Y2100 Z2100 E1200

    I had pressure advance set, but I thought it may be causing problems since I've never used it before. So I commented it out to work on later.

    As for extrusion calibration... 99.443 is the average extrusion amount. So I'm pretty happy with that, but could be a little better. And my steps/mm for the extruder are 92.65.



  • @Whitewolf:

    @superpotatofudge:

    Ok, yea I couldn't find ANY info on 'tuning' a PT100 so it definitely seemed like it either works or doesn't. After reading your info on 2 wire vs 4 wire I concluded that 4 wasn't necessary for my setup as I wasn't seeing any notable increase in resistance.

    Because I know getting thermal contact is a PITA for a tiny probe bead, that's why I used the IR cam as a backup, but that has its own faults when measuring shiny things like the ultra shiny copper alloy heater block!

    As far as 215 being high, you may be right due to all previous experience being with thermistors! 215 (in this case SeeMeCNC brand PLA) was derived at via testing and tuning. I don't print ANY filament at recommended settings blindly. I run multiple test prints for layer adhesion at a wide range of temps and speeds. 215 is what has worked to get the best combination of strength and quality of print. I use this method on multiple Rostock machines at home and work. And at home on Maker Select and CR10. Some other brands of PLA I get good results at 205, but NEVER have I had 195 yield good layer adhesion and end part strength…ever. But...up till now ALL machines I've used are SEMITEC 104GT2...soo...idk Only recently have I used RigidInk and it did well at 205 and I've seen OK results from Hatchbox at 205. I've never used Esun. I mostly print in PETT/PETG anyhow.
    I know what burning filament looks and smells like...so I know 215 isn't TOO hot.

    I may try the other channel just for the sake of thorough evaluation...but that will have to wait till next week post holiday.

    I have pretty much the same setup as you, E3D V6 with Copper heat block and copper nozzle .4mm with PT100 board in 2 wire configuration. While I agree with others you cannot accurately measure temp with that external sensor (I own one and used one during my setup of this printer). My experience is that this combo is dead on accurate with its temp readings and does a really good job of maintaining temp within .1 degree

    As soon as my hotend reaches the 190 mark my PLA begins a slight ooze from the nozzle and by the time it hits 205c it is ready to print (my preferred temp so far with this combo). I have it setup so it homes after heating the nozzle then moves off to the side and extrudes 30mm of filament before moving back to the bed to begin printing. I am getting insanely clean and accurate prints. One thing I did add in to the setup that has seemed to make very noticeable improvements is a Capricorn PTFE tube, I ordered the low friction version https://www.filastruder.com/products/capricorn-ptfe-tubing?variant=45539850511 I also printed a bowden coupler clip to keep the coupler from bouncing up and down during high retraction https://www.thingiverse.com/thing:1330497

    Here are my settings:[c]
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80.00 Y80.00 Z2560.00 E100 ; Set steps per mm
    M566 X3600 Y3600 Z3600 E7000 ; Set maximum instantaneous speed changes (mm/min)
    M203 X18000 Y18000 Z400 E7000 ; Set maximum speeds (mm/min)
    M201 X3600 Y3600 Z3600 E7000 ; Set accelerations (mm/s^2)
    M906 X765 Y850 Z850 E850 I30 ; Set motor currents (mA) and motor idle factor in per cent[/c]

    My extruder is a bowden and not geared and the extrusion coming out the other end is exactly 100mm

    So my question: are you sure with hotend detached that with your current settings, your hotend pushes exactly 100mm of filament? Also do you have pressure advance enabled? [c]M572 D0 S0.1[/c]

    If you do then you should know that pressure advance if configured incorrectly can cause a lot of grinding…. i had that issue when I accidentally had M572 D0 S1.0 in my slicer start script instead of M572 D0 S0.1 and was doing a retract heavy print.

    If you have pressure advance configured in config.g go ahead and remove it from there and create yourself a macro to do some testing:

    [c]G1 E100 F300 ; Extrude[/c]

    Heat up your hotend first to 205c and then run this macro then increase the F parameter by increments of 50 until you notice grinding…. this will be your max flow rate for that temp, then repeat the same test with 210 and again with 215.... if all of these tests can do up to F300 then your flowrate is fine in those temps for 60mm/s and the problem is not with temperature or jamming.

    A great print to dial all this in is this model: https://www.thingiverse.com/thing:607968

    It is a serious torture test at high speeds so I would suggest starting with 40mm/s

    Just learned that trick on the e3d v6 ptfe retainer today! thanks for the link to the clip, could come in handy! Looking at ptfe upgrade too 🙂



  • printed e3d ptfe tube clip and it works great, Thanks! The retract settings are now 6mm so that helps with jamming but still leaving a blob at start\ stop points(retract and wipe enabled)… kills print quality so got to figure that out... slowly but surely Thanks again Whitewolf! I will be watching to see how that pressure advance pans out. I am thinking i want to give it a try.



  • Do this next…. turn off all retraction.... print 40 mm cube with 0 top layers and 0 bottom layers and 1 perimeter. Adjust your pressure advance until you find the sweet spot.... then and only the start increasing your retraction little by little... start with a low retraction like 0.75 and move up little by little it shouldnt be 6mm retraction if you have done this



  • So Whitewolf, why are you using such a drastic Z steps/mm??

    I've recalibrated my extruder steps/mm and now I'm bang on to 100mm, minus flex/takeup inside the Bowden tube as there is some internal slop. I'm still not using pressure advance, but my prints look like absolute crap.

    Somehow suddenly square corners aren't square. And by that I mean they aren't 90 degrees anymore. And my bed still seems high on the right side. I thought autocalibration was supposed to handle that leveling.



  • @Whitewolf:

    Do this next…. turn off all retraction.... print 40 mm cube with 0 top layers and 0 bottom layers and 1 perimeter. Adjust your pressure advance until you find the sweet spot.... then and only the start increasing your retraction little by little... start with a low retraction like 0.75 and move up little by little it shouldnt be 6mm retraction if you have done this

    Thanks Whitewolf! the blobbing is killing print quality. if i print with "aligned" at least the blob is in the same spot, "random" makes prints look terrible… I am not using pressure advance but think i might need to make the switch. 1 thing I am pretty sure of is extruder is calibrated and i do get 100mm exactly at end of bowden tube so should be good there. I also tried reducing extrusion % but that just leaves gaps in parts so i dont think it is over extruding issue, got to be something with retract and restart of print after move. I can see slop in my tube so am looking forward to replacement to see if that helps too.



  • @superpotatofudge:

    So Whitewolf, why are you using such a drastic Z steps/mm??

    I've recalibrated my extruder steps/mm and now I'm bang on to 100mm, minus flex/takeup inside the Bowden tube as there is some internal slop. I'm still not using pressure advance, but my prints look like absolute crap.

    Somehow suddenly square corners aren't square. And by that I mean they aren't 90 degrees anymore. And my bed still seems high on the right side. I thought autocalibration was supposed to handle that leveling.

    Z step per mm will be drastically different for every machine…. I have a 1.25 pitch leadscrew direct driven 400 is as fast as i can get it before it stalls... DC said his can only do 100 based on his configuration.

    Not sure what is causing the rounded corners... are you sure pressure advance is off both in config.g and config override as well as start g code in your slicer



  • @FrankNPrinter:

    @Whitewolf:

    Do this next…. turn off all retraction.... print 40 mm cube with 0 top layers and 0 bottom layers and 1 perimeter. Adjust your pressure advance until you find the sweet spot.... then and only the start increasing your retraction little by little... start with a low retraction like 0.75 and move up little by little it shouldnt be 6mm retraction if you have done this

    Thanks Whitewolf! the blobbing is killing print quality. if i print with "aligned" at least the blob is in the same spot, "random" makes prints look terrible… I am not using pressure advance but think i might need to make the switch. 1 thing I am pretty sure of is extruder is calibrated and i do get 100mm exactly at end of bowden tube so should be good there. I also tried reducing extrusion % but that just leaves gaps in parts so i dont think it is over extruding issue, got to be something with retract and restart of print after move. I can see slop in my tube so am looking forward to replacement to see if that helps too.

    it will help a lot just a warning you will have to recalibrate everything once getting that new tube…. just follow my above post to dial in calibration once you do.

    It helps to do this for every filament... I have a filament that pressure advance does not play nice with at all.



  • @Whitewolf:

    @superpotatofudge:

    So Whitewolf, why are you using such a drastic Z steps/mm??

    I've recalibrated my extruder steps/mm and now I'm bang on to 100mm, minus flex/takeup inside the Bowden tube as there is some internal slop. I'm still not using pressure advance, but my prints look like absolute crap.

    Somehow suddenly square corners aren't square. And by that I mean they aren't 90 degrees anymore. And my bed still seems high on the right side. I thought autocalibration was supposed to handle that leveling.

    Z step per mm will be drastically different for every machine…. I have a 1.25 pitch leadscrew direct driven 400 is as fast as i can get it before it stalls... DC said his can only do 100 based on his configuration.

    Not sure what is causing the rounded corners... are you sure pressure advance is off both in config.g and config override as well as start g code in your slicer

    Ahhh ok, for some reason I thought you were also running a Rostock so I was like..whaaaat? That's why it didn't make sense to me.

    Pressure advance definitely disabled in config.g and doesn't even exist in config-override.g. The odd thing about the square issue is that the outside corners are fine. I've put my machinist squares on them and they're basically perfect 90. As well as an FDM plastic 90 can be anyhow. It's just the inside corners on a hollow square column that made me notice in the first place.

    I just checked belt tension and the X tower has almost 2oz more tension than the others, with Z being lightest of all of three. I have no clue how much tension differential could be playing a part, but my other Rostocks I all have within .5oz of each other. Not sure what happened to this one to make it this far off, but I'll rectify that shortly.



  • its funny how that works… I had everything dialed in then about a week ago everything went bad but only on two corners of a square. It was acting like an extrusion issue. At first i thought it was something i changed so i went through a lot of cubes and settings trying to get it to extrude correctly. Then i tried a cold pull with nylon.... then i realized it was a flaw in the x carriage design which the faster speeds put a small crack in my x carriage that allowed flex but only affected it when moving from x minima and y minima due to carriage design.



  • Well I just ran
    Room temp bed G32
    Bed probe heights: 0.345 -0.136 0.308 0.302 -0.233 -0.201 -0.018 -0.385 -0.098 -0.021 0.223 0.127 -0.085 -0.134 -0.135 -0.095, mean -0.015, deviation from mean 0.208

    60C bed G32
    Bed probe heights: 0.495 0.039 0.471 0.477 -0.095 -0.076 0.132 -0.260 0.015 0.091 0.335 0.227 0.053 -0.047 -0.035 -0.008, mean 0.113, deviation from mean 0.219

    So that doesn't look great. And I just noticed that the X carriage seems to have a lot more friction and resistance to movement than the other two carriages. I didn't notice before I guess because the belt tension was so much higher than the other belts. Now it is quite obvious so…off to figure out why it is significantly worse.


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