Mini poll: what temperature sensor are you using?



  • Hi. I still can't decide what type to choose and decided to create "poll" for me and other noobs 🙂
    Answer please:

    1. What type? (Thermistor, Thermocouple K, PT100, PT1000, other?)
    2. Connection? (Straight to the board or connectors near extruder? 2 or 4 wires?(for PT100 and PT1000)

    Thank you!



  • I use a PT100, 2 wire sensor.

    The different sensors available in a little bit more detail:

    • Thermistor: They are a simple resistor (usually high resistance, like 10k or 100k), with the added property to change its resistance based on the temperature it is exposed to (actually all resistors will change, Thermistors simply follow a predictable curve). Since thermistors are resistors they can be connected using stranded wire, which allows bending (compared to solid core; useful if mounted on a head of a printer). Generally a maximum temperature of 285C.
    • Thermocouples: they are special solid core wires (2 different alloys, specified by the Type, most commonly used is the K-Type) that are fused together at a single point - this is the sensing point. When exposed to different temperatures, it creates a voltage (K-types have a 0.1V/*C graph). The thermocouple wires can't be soldered, as this would create additional sensing points, they can be crimped to different wires. Since the voltage it creates is extremely small, you need an amplifier close by to read it and provide a more useful signal to the controller. Since it is solid core, that part of the sensor may not flex or it will break off. Since it creates a voltage, polarity is very important. Generally for temperatures up to about 290C.
    • PT100: These contain a very small piece of actual Platinum inside. That piece is calibrated to be 100 Ohms at 0C and follows a predictable graph (though this resistance increases with the temperature, compared to decreasing with Thermistors). Since they are resistors, flexible wires can be used without issue. More accurate than Thermocouples. They can be used for temperatures over 300C without issue (though each manufacturer specify a maximum which should not be exceeded).
    • PT1000: Like the PT100 it is Platinum that is specially calibrated. Since it is in the 1k resistance range, the standard Thermistor inputs can be used for this (PT100 would allow too much current through, and actually affect the temperature by heating up). These can also handle the high temperatures. These are not readily available.

    Thermistors and PT1000 can be connected directly to a Duet mainboard using the same 2-pin connectors. For PT100 or Thermocouples, you will need a daughter board, sold separately.

    2-wire, 3-wire and 4-wire PT100 sensors:

    • 2-wire: Most commonly used and most readily available (though not in my country, I had to import mine). This provides better accuracy than Thermistors, but usually not more than a good thermocouple. The same wires that bring electricity to the sensor, also performs the measurement - this results in the wire resistance (very small, but it exists and makes a slight difference) also being taken into account.
    • 3-wire: This is the 1/2 way between 2-wire and 4-wire. Provides better accuracy since one of the wire's resistance is taken out of the equation. Since virtually no current flows through the 3rd wire, its resistance does not matter and the wire running next to it, which have all of the current running through is no longer used (the voltage drop over this wire is simply thrown out).
    • 4-wire: In this setup you have 1 for Power +, Power -, Sensor + and Sensor -; since no current flows through each of the Sensor wires, they don't add resistance (we get a full Before Sensor voltage and a After Sensor voltage on these 2 wires); the before and after sensor voltages might only differ with a few mV from the power and ground, but this provides more accurate results.

    Personally the 2-wire PT100 is good enough for me and allows me to use high temp filament without worrying (note that your hot-end should also be able to handle the high temperatures, if you need it). My other printer is happy with its Thermistor. I would avoid the Thermocouples - my big printer (with the PT100 sensor) came with one, and the amplifier board broke after 1.5 years (it broke due to flexing; requiring me to make massive changes, configure own firmware, since original firmware was not open source and it required changes inside firmware code etc - took a few months to get it back into service; now it is running a Duet and I no longer have to worry about it).



  • Bed: generic Chinese 100k thermistor
    Hotends: LerdeStore from Aliexpress: Thermistor HT-NTC100K B3950 that claims to be good up to 350C 😄

    Planning to upgrade to PT1000 sensors.



  • Problem is that PT1000 is very hard to find... Can't find in USA, can't find on Aliexpress(they are too big or to bad Class C there). And some stores has them but without telling the Class and temp range.
    I have found Class B PT100 on Aliexpress with 4 wires and Class A PT100 on eBay with 3 wires...

    I even thinking about making one by myself..



  • @jacotheron said in Mini poll: what temperature sensor are you using?:

    • Thermocouples: they are special solid core wires (2 different alloys, specified by the Type, most commonly used is the K-Type) that are fused together at a single point - this is the sensing point. When exposed to different temperatures, it creates a voltage (K-types have a 0.1V/*C graph). The thermocouple wires can't be soldered, as this would create additional sensing points, they can be crimped to different wires. Since the voltage it creates is extremely small, you need an amplifier close by to read it and provide a more useful signal to the controller. Since it is solid core, that part of the sensor may not flex or it will break off. Since it creates a voltage, polarity is very important. Generally for temperatures up to about 290C.

    This is probably the range that you may expect for 3D printing, but I have a couple of type K thermocouples measuring temperatures in my exhaust manifold and turbocharger, where I see temperatures in excess of 750 deg C (I get a bit worried when the turbocharger gets close to 800 deg C.) so the thermocouple itself is good to something over 1200 deg C. What may not be able to handle it would be the wire insulation.

    Additional note, what thermocouples measure is a temperature gradient. To be truely accurate, the sensing end should be immersed in an ice bath, but since that's not generally possible, most thermocouple readers have a mechanism to check the temperature at the sensing end, which it uses as part of the amplifier circuit to give an adjusted reading.

    For my response, I'm using regular thermistors in my printer for the time being. I'd like to upgrade to PT1000 sensors, but as stated, they're difficult to find. For the time being, the thermistor is accurate enough for the temperatures that I'm using, I generally subtract 5 degrees from the manufacturer recommended temperature for filament that I buy, and that seems to be about right.



  • I have found a place where I can order PT1000 Class A in 3mm x 15mm cases, MOQ 10pcs, $4.5 for each. But I don't need so many... )



  • I used to use 4 wire PT100s but the ones I bought had very fine leads which kept breaking so I changed to simple thermistors. I always do a temperature test print for any new filaments and use whatever temperature is best on my machine. So if my test indicates that the best temperature is (say) 205 deg C, that's what I use for that filament. I don't really care what the true temperature as measured by a more accurate would be.



  • @deckingman And this said temperature is stable until thermistor will die, right?



  • 4 wire PT100



  • @phaedrux Class and size please?





  • @briskspirit said in Mini poll: what temperature sensor are you using?:

    @deckingman And this said temperature is stable until thermistor will die, right?

    Seems to be. I've been using the same thermistors for about 18 months and don't have any wildly different temperature results from my test prints. For me, most reels of PLA print best at 195 degC on my machine. That's the values that my test prints showed to be best 18 months ago and I'm still getting the same values now.

    I have no idea when the thermistor is likely to die, but then I have no idea when a PT100 or thermocouple would die either. At least when it does die, it'll be cheap to replace.



  • @deckingman Hm, good point



  • ive just used the standard semitiec thermistor with the e3d for the last 2 years with no problem. Although i just bought a PT1000 from DJdemons site (https://www.precisionpiezo.co.uk/product-page/pt1000-sensor) that fits the standard E3d cartridge so im keen to print some higher temp filaments


 

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