Mass Portal Pharaoh ED, RADDS 1.5 , Thermistor problems

Comments

• Repetier

  July 2022

  That place is not for thermistors. It is for thermo-couple if firmware is configured for it. You need to connect a shield then there that converts e.g. PT100 signals to correct voltage as there is no thermocouple chip build in.
  
  If it used a thermistor the normal connector for first extruder is T0 in the Thermistors header. Just hope it was configured for it. 
• blysprutan

  July 2022

  Repetier said:

  That place is not for thermistors. It is for thermo-couple if firmware is configured for it. You need to connect a shield then there that converts e.g. PT100 signals to correct voltage as there is no thermocouple chip build in.
  
  If it used a thermistor the normal connector for first extruder is T0 in the Thermistors header. Just hope it was configured for it. 

  Thanks mate!
  I have a Thermo-Couple from a multimeter and when connecting it i get the right values :-)
  So far so good. 
  I hope i can get it up and running soon.
  The printer have some kind of chip for it since the Thermo-couple goes to before it enters the board.
  Do you have any advice on how to insulate the probe before putting it into the hotend?
  I read that putting it in there without insulation it will be shorted and not read anything correct.
• Repetier

  July 2022

  Ok getting shorts would in deed be a problem. We average several measurements so it can jump in temperature if it switches between short and correct resistance. Kapton tape is a good and thin insulator if you have. Electric tape should also work. Do you have also the correct Thermo-couple type? PT100 is most common but there are different types that would also behave different.
• RAyWB

  July 2022 edited July 2022

  Just for clearance , PT100 is a PTC thermistor(100 Ohms) which increases resistance by rising temperature ,

  most common in 3dPrinters  are the NTC thermistors (100KOhms) which decrease resistance by rising temperature.

  
  

  Thermocouple is a voltage-output sensor based on combination of alloys for example a (source:Wikipedia)

  
  

  "Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 µV/°C.[11] It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C (−330 °F to +2460 °F) range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point, which occurs for type K thermocouples at around 185 °C "

  
  

  i guess you have a Type-K thermocouple wich is very common and the most reliable way to isolate it is a galvanic islolation of the Thermocouple amplifier to printer electronic what means , separate power supply and galvanic isolation of data lines (guess its a spi-connection) with optocouplers or special digital isolatiors.

  
  

  edit: should be an analog signal in your case and the Chip should be AD595 (necessary thermocouple type K).
  

  
  

  Isolating with kapton tape may work , but not reliable as its temperature range ends at about 260°C whats close to hotend temperature.

  I guess there are thermocouples on the market which are isolated by aluminiumoxide or cement but i don´t know where to buy.

  I prefer the galvanic isolation as it´s a "clean" but high effort solution.

  
  

  to keep it simple my suggestion is to try to get original replacement or depending on your skills use standard 100K NTC , reconfigure and compile Firmware for use of the T0 input