Is my Thermister under-reading

Not really done many prints yet, but I am noticing that with pronterface pla setting of 200 , I am not getting temperature values much greater than 189. Is this my thermister under-reading or is it a lack of power from the interface? What do I trust, should I tinker with pronterface setup to up the temp to 210 or leave everything alone? Normally prints are ok except for some extruder motor stuttering which I understand from this list is my head too near the bed.

Alan

1. How have you measured the temperature? The thermistor is embedded within the heater block, so it is likely to be at a temperature very close to the temperature of the block. If you put e.g. a thermocouple on the surface of the block, it is going to be difficult to get it up to the same temperature as the block unless you clamp it securely in place and put insulation around it.

2. What version firmware are you using? Versions prior to 0.53 over-read the temperature.

3. Ultimately, it doesn't matter if the temperature reading is not accurate, what matters is that you know what temperature to set to get good prints. Most of us set the temperature to about 195C for the first layer (using recent firmware), and somewhat lower for subsequent layers. The original Ormerod settings from RRP were for the older firmware.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I have not used any external instrument, I am just relying on the temperature readings displayed on pronterface. Also using firmware 057h-dc42.

Alan

Sorry, I misunderstood. Are you commanding the temperature to 200C directly in Pronterface, or are you printing a gcode file that you only think sets the temperature to 200C? If you are commanding it in Pronterface, then I suggest you check the 6-pin connector at the hot end for poor connections (either poor pin/socket connections or poor crimp connections). Mine can get up to more than 300C, although I suggest you don't test it above 250.

Edited 1 time(s). Last edit at 02/02/2014 06:14PM by dc42.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks,
I looked at the gcode file and it is setting the temperature to 195. The heat drop-down in pronterface is set to 200 and the set button is in its pressed state. Despite both of those the temperature reported is 189. So I guess that the loaded gcode file overrides the pronterface UI setting. But I will check the 6 pin connector as I did not make a very good job of the connection in the first place. If there is not a good connection will that cause an increase in resistance and maybe cause the connection to warm up a bit. I just felt mine and the connection is quite cool.

Alan

Yes, the loaded gcode file will override the Pronterface setting. Also the gcode file may command one temperature for the first layer and then reduce it to a lower temperature for subsequent layers. The current Ormerod firmware considers the head and/or bed to be up to temperature if it is within 5C of the commanded temperature.

To test it, don't print a gcode file, just command the temperature in either Pronterface or the web interface and watch it.

Edited 1 time(s). Last edit at 02/02/2014 06:42PM by dc42.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

To take a reading of the hotend with an external thermocouple thermometer, you can either jam the thermocouple head into the hole next to the thermistor (my thermocouple fits OK, but careful you don't damage the sleeving over the thermistor), or remove the filament and take the clip and Bowden tube out of the extruder block, then feed the thermocouple down the Bowden tube until it bottoms inside the nozzle.

While knowing the real temperature is not necessary once you find the setting that works for you, it is a lot better to know the real temperature of the hotend when trying out different types of plastic so you can start off knowing that you are extruding at the recommended temperature for that plastic. Maybe set up a thermometer once, and take readings at various set temperatures so you can draw up a table or graph of indicated vs actual temperatures.

Dave
(#106)