EVAL-CN0319-EB1Z: -200°C ~ 350°C Thermocouple Interface

This circuit provides a low cost solution to temperature monitoring because most of the circuit functionality is integrated into the ADuCM360 precision analog microcontroller, including dual 24-bit Σ-Δ ADCs, the ARM Cortex™-M3 processor core, and the PWM/DAC features for controlling the 4 mA-to-20 mA loop for loop voltages up to 28V.

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 temperature value. The Type T thermocouple 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.

This circuit is similar to the circuit in Circuit Note CN-0300 with the additional benefit of the higher resolution of the PWM driving the 4 mA-to-20 mA loop. The PWM-based output provides 14 bits of resolution. For details on the temperature sensor interface to the ADC and on linearization techniques for the RTD measurements, see Circuit Note CN-0300 and the AN-0970 Application Note.