Thermocouple daughter board

The Duet range of machine controllers support one or more temperature daughter boards which provide expanded temperature sensor connectivity using Maximum integrated ICs. These daughter boards connect to the Duet digitally over SPI.

The Duet 3 6HC and 3HC each support up to two temperature daughter boards stacked. PT100 and Thermocouple daughter boards can be mixed and matched. The Duet 3 Toolboard 1LC does not support a temperature daughter board.

The Duet 2 WiFi and Duet 2 Ethernet support up to two temperature daughter boards stacked, with a further two stacked on the Duex2 or 5. This provides a total of 8 digital temperature inputs. PT100 and Thermocouple daughter boards can be mixed and matched.

The Duet 2 Maestro supports 1 temperature daughter board for two SPI temperature input channels. On the Maestro either a Thermocouple or PT100 daughter board can be connected, but not both.

There have been two versions of the thermocouple board. the change from version 1.0 to 1.1 was to made to move to the MAX31856 sensor IC.

• MAX31856-based daughter boards each supporting two thermocouples of type B, E,J K, N, R, S or T.

• MAX31855-based daughter boards, each supporting two K-type thermocouples

For setting up Duet controllers to use thermocouple sensors see: Connecting thermocouples

The MAX31856 performs cold-junction compensation and digitizes the signal from any type of thermocouple. The output data is formatted in degrees Celsius. This converter resolves temperatures to 0.0078125°C, allows readings as high as +1800°C and as low as -210°C (depending on thermocouple type), and exhibits thermocouple voltage measurement accuracy of ±0.15%. See the Maxim integrated website for more details on the MAX31856.

The Duet range of machine controllers support various other temperature sensors. See:

• A comparison of temperature sensors
• PT100 temperature sensor daughter board
• Connecting thermistors or PT1000 temperature sensors