Ultimaker reading consistently ~20°C temperatue off

[SandervG 1,521]

Well i guess it is never too late to learn and today i have learned a new lesson which i would like to share.

On rare occasions i have gotten some tickets saying the Ultimaker was reading a temperature which was consistently too low..

Room temperature it read ok, but when heating your UltiController would display 210°C (for instance, or whatever you set), but in real life it would be only 190°C or something close. This can go unnoticed for a while, and it might get you thinking that there is something wrong with your feeder, or a plug in your hot end.

While in fact it is the thermocouple causing trouble.

Usually this happens after some attempts to fix the hot end, and it required to remove the thermocouple. If you pull the iron cover you can pull it off without excessive force. This can leave the wires open and they can get damaged now, or later due to high temperatures. What will happen is that your thermocouple will start reading temperatures outside your heater block, right where the wires are touching. Resulting in an accurate room temperature, but since the source of the heath is a few cm away from your point of reading it will be off by 20/30°C.

In order to diagnose this, you should inspect your thermocouple for damage and use a temperature laser gun or something similar to double check the temperature. However i must add, a laser temperature gun is also not always accurate, since the hot end is shiny and this may interfere with a proper temperature reading. If anybody has some good test on how to read the actual read the temperature, feel free to share them with the rest

An example of this issue, can be found here: http://umforum.ultimaker.com/index.php?/topic/2447-hotend-no-longer-reaching-correct-temperatures/

Therefore i also would like to advice, if you would ever need to remove your thermocouple, do it while the hot end is hot, and push it from the other side with a screwdriver, while holding your aluminum heater block secured with some pliers.

 

[illuminarti 18]

This is definitely useful info, Sander. In the past I've measured my hot end temperature by using kapton tape to attach an external thermometer's thermocouple probe to the side of the aluminium block, adjacent to the nozzle, and then also wrapping some insulation around it.

I found I got temperatures that were very consistently 5% below the temperature the UM was reporting, across the entire 180-260 working range I tested. I'm not sure if this is explainable solely in terms of thermal gradient from the inside to the outside of the block, or whether one or other measurement is really off by 5%. Based on my tests printing some plastics with fairly narrow working temperature ranges, I suspect that my printer may indeed be reading 5% - roughly 10-15 degrees - too high.

Has anyone else compared external/internal block temperatures and can give me a sense of whether a 5% difference seems legitimate?