ThermokUSB-RTD2

Introduction

The ThermokUSB-RTD2 is a small module that plugs into your USB port and provides two precision RTD inputs. Versions are available for PT100 or PT1000 RTDs. Two wire, three wire and four wire RTDs are supported. Communications with the computer is via Modbus RTU format. The ThermokUSB-RTD2 is a Serial CDC device, so no drivers are needed with modern operating systems.

Internally the ThermokUSB-RTD2 uses two of Maxim Integrated's MAX31865 RTD to digital converters. These converters are high resolution (0.03125°C nominal resolution) and high accuracy (0.5°C across all operating conditions). Built-in fault detection shows open RTD elements, RTD shorted to out-of-range voltage and shorts across RTD. +-50V input protection is provided. The inputs are not isolated from the computer. A Microchip PIC18F14K50 is used to provide Modbus communications and USB interface.

The ThermokUSB-RTD2 is open source hardware and software. Schematic and PCB files are available in open formats. Firmware source code is open source, however it requires CCS's PCH compiler to compile.