There has been lots of discussion about the temperature readings of the Ultimaker. For some people they are spot on. While others need a measured temperature of 300C to print ABS (while 250C should be enough)
This page is not about general temperature reading problems. If your temperature doesn't read at all, see checking the temperature regulation.
What is the problem
Temperature readings seem to be off by more then 10% or 25C in some cases. This is a huge problem, as stable and accurate temperature really helps in 3D printing.
What can be causing this
There can be multiple causes for this, and there hasn't been a real answer yet on what's the main factor in the error.
- Thermocouple - The chances for this to be wrong are very slim. These are high quality parts
- AD597 - According to the datasheet this cannot give a bigger error then 5%, and has a typical error of 2%.
- ATMega2560 ADC - Datasheet only gives typical characteristics. And talks about 3 bits of error. The 3 lowest bits account for a 40mV measurement. Which is about 4C in error.
- Additional "thermocouple junctions" (TODO: Elaborate)
How can we fix it
Unless we know what is causing it. It's hard to really fix it. But as a workaround you can calibrate the temperature sensor. First you'll need some accurate measurements. See the measurements section for details.
After you have measurements, you can feed this into calibration (TODO)
There are a few ways to get real measurements to compare to the Ultimaker temperature measurements.
Pretty obvious, leave the printer in a room, it should be at room temperature after a while.
Laser temperature reader
There are laser based temperature readers, point it at the heater block to read the temperature. (TODO: Does the shininess of the heater block cause problems?)
Ice water (water that is near freezing) has a stable temperature of 0C Boiling water is 100C at sea level, if you are at higher elevation then water boils at a slightly lower temperature. A rule-of-thumb should be that you adjust 3.4 degrees for every 1000m (3000 feet).
- Google groups discussion: http://groups.google.com/group/ultimaker/browse_thread/thread/1d628422dbf1ce9/2f675e70d7a6d1e6
- Joergen Geerds temperature chart: https://picasaweb.google.com/lh/photo/CGoOli0YIIs5WpcCSxmrezIYJXjTqlQYmaNWFtjfw8o