Hi, what type of temperature sensor does the craftbot 3 uses on the nozzles? Is it a pt100 or a thermocouple?

June 29, 2019

vital vital
Beginner
2 posts

4 replies


It is definitely not a thermocouple. I'm pretty sure it's a standard glass bead thermistor, probably a 3950 100K.

June 29, 2019

mroek mroek
Revered
531 posts

mroek wrote:It is definitely not a thermocouple. I'm pretty sure it's a standard glass bead thermistor, probably a 3950 100K.


It is definitly a cartridge, if it's just a shitty thermistor then this was my last craftbot. For that price I expect a pt100 or similar. Something accurate. I can't understand why those are still used today. A pt100 amplifier doesn't cost much and paying 2$ for an accurate and reproducable temperate is way better than paying 0.20$ and and never knowing what temp you really have

June 29, 2019

vital vital
Beginner
2 posts

I guess that they could possibly have a PT100 inside that cartridge, I really don't know, but since they use standard thermistors on the older Craftbots, I was assuming that to reuse their code, they'd go for a similar setup.

June 29, 2019

mroek mroek
Revered
531 posts

It is definitly a cartridge, if it's just a shitty thermistor then this was my last craftbot.

I don't see that as reason to abandon craftbots. The used thermistor has a 1% deviation. So about +/-2 degrees at 200 degrees. Not that much of a dealbreaker. Nevertheless a thermocouple is much suitable at high temp as 300 degrees as for the CB3. So seen in that perspective a thermocouple is a better choice I think.
OTOH, in the long time a thermistor is more stable than a thermocouple. A thermocouple can be 2% off or so in the long term. Not a dealbreaker either I think.
From what I know a thermistor is more accurate than a thermocouple. A thermocouple can be 5 degrees off in the 200-300 degree range.

What is a good thing about thermocouples, is that they have a liniair readout. While a thermistor has an exponentional readout. An surely in the high temps, that is a disadvantage.
The build has to be stable, so each batch of thermistors and thermocouples should have the same characteristics.

So, after all that, in general I would think that until 250 degrees a thermistor is doing it's job allright. And probably until 300 degrees, as the CB3, a thermocouple is a better choice. But a well firmware tweaked thermistor of a good manufacturer can do it's job as well.

But it's surely not the reason you should leave the CraftBots alone, because of a thermistor or thermocouple. As that would make only a couple of degrees off in the high temp range. Not interesting at all.

What actually is a reason to leave CraftBots is that CraftUnique isn't getting the temperature table accurate in the firmware. With the CraftBot plusses we had a temp table off by abut 20 degrees for a year before the corrected that.
And as measured by Jan Houwers, the set and measured temperatures at the CB3 as well. That was a year ago way off as well: about 15 degrees at the hole temp range (se picture below). That has nothing to do with a thermistor of thermocouple, but all with a simple table in the firmware telling with which resistance a specific temperature belongs. Measure and put it in the firmware people!
CB3: what type of temperature sensor

So, I wouldn't give that much weight regarding thermocouple / thermistor as that is just a couple of degrees difference and with pro and cons at both sides.
I would actually blame CraftUnique, not making an accurate temperature table in the firmware, as that is between 15-20 degrees off in the 3D printing temp range.
I know the temp table of the CB+/XL is more accurate now, but I didn't check the CB3 firmware recently.
OTOH: what do I care. Even if it is saying 540 degrees to melt PLA when testing it with manual extrusion, than it's that value I put in the slicer. And with a new filament testing tells me that the min temp is -100 degrees, than I put that in the slicer. I don't care about actual temperatures with my 3D printer. I always test filament regarding the min melting temp and put that temp + 10 degrees in the slicer.
Nevertheless, it would be nice all printers would be in the same temp range and a specific filament, so you can set the slice temp for each printer the same and don't have to think about it.

Greetings to all,
Bart




July 19, 2019

Bartaar Bartaar
Service partner
1677 posts
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