E3D's PT100 Amplifier Board allows you to connect an E3D PT100 temperature sensor to a printer that doesn't normally support RTD sensing devices. The Amplifier Board connects to an analog input pin of a 3D printer controller board.
If your printer doesn't support RTD sensing devices, you'll need E3D's PT100 Amplifier Board to amplify the signal from a PT100 sensor to a voltage level that your printer controller can accurately read. The amplifier board requires a controller board running Marlin or Repetier that has a spare analog input pin.
E3D has derived the board from the circuit design of the Ultimainboard V2 controller board, so you can select temperature sensor '20' in the marlin firmware to get correct calibration values.