Termocouple board necessary??

akrepsianka · 27 Jan 2018, 10:23

I just finish my new 3d printer setup. i have strange problem with termistor. I heated up to 210 C degree hearter block and i try to extrude pla filament. (my other 2 printer extrude at 210 C without any problem) it wasnt extruding properly. so i heated up to 235 C degree and start to extrude properly. My question is:
My termistor cable is around 2.5m long and i guess because its too long it dosent read properly. so in this case will thermocouple board solve my problem??

dc42 · 27 Jan 2018, 10:45

Long leads have very little effect when using a thermistor. Are you sure that your M305 P1 parameters on config.g are set correctly for the type of thermistor you are using?

If you want very accurate temperature readings, then unless you will be using very high temperatures I suggest a PT100 sensor rather than a thermocouple.

akrepsianka · 27 Jan 2018, 10:52

Here is my config for termistor. i copied it from my other printer because they use absolutly same termistor.
M305 P1 T100000 B3950 R4700 ; Set thermistor + ADC parameters for heater 1

Here is termistor parameters
Thermistor:100K NTC B 3950 ±1% ,1m long,2 pin connect

dc42 · 27 Jan 2018, 11:06

Thermistor B values are typically quoted at low temperatures, e.g. 25/75C or 25/100C. Using them is OK for the bed thermistor but will give inaccurate readings at the higher temperatures of the hot end. That doesn't matter too much if you find out the extrusion temperature that works for you by experiment.

akrepsianka · 27 Jan 2018, 11:09

if i get pt100 sensor ca i attached directly to the duet wifi board. or need to buy thermocouple board?
and what should be my config if i have pt100 sensor?

dc42 · 27 Jan 2018, 11:11

If you get a PT100 sensor then you will need the PT100 daughter board (assuming your Duet is a Duet WiFi or Duet Ethernet).

The latest firmware also supports PT1000 sensors connected directly to thermistor inputs, however PT1000 sensors in a form factor suitable for use in hot ends are not as readily available.

akrepsianka · 27 Jan 2018, 11:30

where i can find pt1000 sensors??? look better and cheaper solution.

dc42 · 27 Jan 2018, 12:03

Many PT1000 sensors are unencapsulated thin film types, which would not be suitable. Here's one that is encapsulated: http://uk.farnell.com/honeywell/hel-705-u-0-12-00/resistance-temp-detector/dp/1653390.

Please note, the use of a PT1000 connected directly to a Duet thermistor input is still experimental and we are unable to guarantee its accuracy.

akrepsianka · 27 Jan 2018, 12:21

thanks for the information