EVAL-CN0300-EB1Z: Thermocouple Interface

This circuit uses the ADuCM360 precision analog microcontroller in an accurate thermocouple temperature monitoring application and controls the 4 mA to 20 mA output current accordingly. The ADuCM360 integrates dual 24-bit sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), dual programmable current sources, a 12-bit digital-to-analog converter (DAC), and a 1.2 V internal reference, as well as an ARM Cortex-M3 core, 126 kB flash, 8 kB SRAM, and various digital peripherals such as UART, timers, SPIs, and I2C interfaces.

In the circuit, the ADuCM360 is connected to a Type T thermocouple and a 100 Ω platinum resistance temperature detector (RTD). The RTD is used for cold junction compensation. The low power Cortex-M3 core converts the ADC readings to a real temperature value.

The Type T temperature range supported is −200°C to +350°C, and this temperature range is converted to an output current range of 4 mA to 20 mA. The circuit provides a complete solution for thermocouple measurements with a minimum requirement for external components, and it is loop powered for loop voltages up to 28 V.