PT100 temperature sensor 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.

The PT100 daughter board uses the Maxim Integrated MAX31865 RTD sensor IC. This IC supports 2,3 or 4 wire PT100 connections. The mode can be set using jumps on the board. With the jumpers on/bridged the board expects a 2 wire PT100 sensor. With the jumpers off/cut a 4 wire PT100 sensor can be used. The change between older versions and 1.1 was to move from solder jumpers to pin jumpers.

The following minor changes from v1.1 to 1.1a:

• The addition of a ground point between the two sets of screw terminals to make it easier to ground shielded wires.
• Added 0u1 filtering capacitors on RTDIN(+/-).
• Switched from 1x400R to 2x200R in series reference resistors for component availability reasons.

From version 1.1 on wards there are two pin jumpers per input channel.

Versions of the board before v1.1 had solder jumpers to convert from 2 wire to 4 wire.

For setting up the Duet us use PT100 sensors see: Connecting PT100 temperature sensors

An external resistor sets the sensitivity for the RTD being used (in the case of the Duet3d daughter board this is a PT100) and a precision delta-sigma ADC converts the ratio of the RTD resistance to the reference resistance into digital form. High Accuracy: 15-Bit ADC Resolution; Nominal Temperature Resolution 0.03125°C (Varies Due to RTD Nonlinearity). Total Accuracy Over All Operating Conditions: 0.5°C (0.05% of Full Scale) max. For more information see the Maxim Integrated MAX31865 product page.

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

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