CB3: what type of temperature sensor
Hi, what type of temperature sensor does the craftbot 3 uses on the nozzles? Is it a pt100 or a thermocouple?
It is definitely not a thermocouple. I'm pretty sure it's a standard glass bead thermistor, probably a 3950 100K.
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
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.
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!
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,