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Revision to Connecting thermistors or PT1000 temperature sensors

David Crocker

Parameter B3950 in the above example means that the thermistor B value over the temperature range of interest is 3950.
 
The R parameter is the value (in ohms) of the series resistor on the controller electronics, which is always 4700 ohms onelectronics. You do not need to specify this value unless you are using a Duet WiFi and06 or a DueX4 expansion board. If you do specify it, the correct value is:

* Duet 2 WiFi,
Duet 0.8.5 controllers, as well as Duex22 Ethernet, DueX2 and Duex5DueX5 expansion boards - but see the note further down this page. It defaults toboards, and Duet 085: 4700 in the
*
Duet WiFi firmware, and 1000 in RepRapFirmware for the2 Maestro: 2200
*
Duet 0.8.5 and 0.6. The06: older generation Duex4 expansion boards have a series resistor value of 1000.1000, newer boards 4700
* DueX4 version 0.2: 1000
* DueX4 version 0.2a: older boards 1000, newer boards 4700
The R parameter is the value (in ohms) of the series resistor on the controller electronics, which is always 4700 ohms onelectronics. You do not need to specify this value unless you are using a Duet WiFi and06 or a DueX4 expansion board. If you do specify it, the correct value is:

* Duet 2 WiFi,
Duet 0.8.5 controllers, as well as Duex22 Ethernet, DueX2 and Duex5DueX5 expansion boards - but see the note further down this page. It defaults toboards, and Duet 085: 4700 in the
*
Duet WiFi firmware, and 1000 in RepRapFirmware for the2 Maestro: 2200
*
Duet 0.8.5 and 0.6. The06: older generation Duex4 expansion boards have a series resistor value of 1000.1000, newer boards 4700
* DueX4 version 0.2: 1000
* DueX4 version 0.2a: older boards 1000, newer boards 4700
 
For the E0 thermistor, the command is similar except that P0 is replace by P1, for example:
}
 
1) The C parameter can be written in [https://en.wikipedia.org/wiki/Scientific_notation] as shown here or in normal decimal notation (in this example C0.0000000706, just be careful to use the right number of zeros) see below for an explanation of the C parameter.</small>parameter.
1) The C parameter can be written in [https://en.wikipedia.org/wiki/Scientific_notation] as shown here or in normal decimal notation (in this example C0.0000000706, just be careful to use the right number of zeros) see below for an explanation of the C parameter.</small>parameter.
 
If you have a datasheet for the thermistor you are using, and if it provides a resistance-versus-temperature table, you can calculate the correct value for the B and C parameters. The simplest way is to use the calculator on the heater tab of [https://configurator.reprapfirmware.org/].
For the technically minded: firmware 1.17 and later uses the Steinhart-Hart thermistor model. The M305 C parameter is the Steinhart-Hart '''c''' parameter, the M305 B parameter is the reciprocal of the Steinhart-Hart '''b''' parameter, and the Steinhart-Hart '''a''' parameter is calculated from the resistance at 25C. If you don't provide a C parameter, then C defaults to zero and the Steinhart-Hart equation reduces to the beta-value equation.
 
'''Warning''': Some thermistors meant for high-temperature work (for example those provided with the Dyze hot end) may have such a high resistance at room temperature that they read as open. This will generally cause heater faults as soon as you start heating. There has been discussion of a number of workarounds; a search of the forum may yield some good suggestions. For really satisfactory results you may need to switch to a thermocouple,PT100thermocouple, PT100 or PT1000 sensor.
'''Warning''': Some thermistors meant for high-temperature work (for example those provided with the Dyze hot end) may have such a high resistance at room temperature that they read as open. This will generally cause heater faults as soon as you start heating. There has been discussion of a number of workarounds; a search of the forum may yield some good suggestions. For really satisfactory results you may need to switch to a thermocouple,PT100thermocouple, PT100 or PT1000 sensor.
 
=== PT1000 sensors ===
[code]M305 P1 X501 R4700 ; heater 1 uses a PT1000 connected to thermistor channel 1 which has a 4.7K series resistor[/code]
 
Note: '''PT1000 sensors connected to thermistor inputs will generally be less accurate and havehave lower resolution than PT100 sensors connected via the RTD daughter board''', especially when used withboard'''. The accuracy of PT1000 sensors should be very good on the Duet 2 Maestro and generally good on the Duet Wifi and Duet Ethernet. However, it may be poor on the Duet 06, Duet 085 and other SAM3X8E-based Duets (0.6/0.8.5)electronics.
Note: '''PT1000 sensors connected to thermistor inputs will generally be less accurate and havehave lower resolution than PT100 sensors connected via the RTD daughter board''', especially when used withboard'''. The accuracy of PT1000 sensors should be very good on the Duet 2 Maestro and generally good on the Duet Wifi and Duet Ethernet. However, it may be poor on the Duet 06, Duet 085 and other SAM3X8E-based Duets (0.6/0.8.5)electronics.
 
=== Note for users of Duet 0.6 boards and DueX4 boards ===
=== Correcting the temperature calibration of Duet 0.6 and 0.85. boards ===
 
The ADC on the Duet 0.6 and 0.8.5 is not calibrated automatically, so you may need to calibrate it in order to get accurate readings, especially at low temperatures.Here'stemperatures or when using PT1000 sensors. Here's how:
The ADC on the Duet 0.6 and 0.8.5 is not calibrated automatically, so you may need to calibrate it in order to get accurate readings, especially at low temperatures.Here'stemperatures or when using PT1000 sensors. Here's how:
 
* With the machine cold, see what temperatures the are displayed for the bed and hot end(s), and compare that with room temperature.

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