The Duet WiFi supports up to two MAX31865-based daughter boards. Each daughter board supports two PT100 temperature sensors:
On the lower board, the terminal blocks labelled RTD1 and RTD2 will be temperature measurement channels 200 and 201 respectively. If you stack two daughter boards, the terminal blocks on the upper board will be channels 202 and 203. The Duex5 &Duex2 have an additional 4 channels allowing two more boards to be stacked for channels 204-207.
Each channel has a 4-position terminal block. We'll number the terminals 1, 2, 3 and 4 in order (it doesn't matter which end you start from, because PT100 sensors don't care about polarity). Terminals 1 and 4 supply current to the sensor, and the voltage developed across the sensor is measured between the terminals 2 and 3.
To connect a 2-wire PT100 sensor:
- Connect the PT100 wires to terminal 2 and 3
- On production PT100 daughter boards, you need to either bridge each pair of solder pads next to the terminal block, or add a wire between terminals 1 and 2, and another between terminals 3 and 4. On pre-production PT100 boards there is already a trace bridging each pair of solder pads.
To connect a 4-wire PT100 sensor:
- Connect the two wires that go to one end of the PT100 resistance element to pins 1 and 2 (it doesn't normally matter which wire in each pair goes to which terminal)
- Connect the two wires that go to the other end of the PT100 resistance element to pins 3 and 4
- If you have a pre-production daughter board, cut the fine traces that bridge each pair of solder pads next to the terminal block
See https://miscsolutions.wordpress.com/2016/06/25/more-delta-printer-upgrades-wifi-and-silence/ for additional information about using a 4-wire PT100 connection.