12-bit 4-20mA loop-powered thermocouple measurement system using Cortex-M3

Test probe P100-M3

C-4

PJSRV05-4

Circuit function and advantage

This circuit uses the ADuCM360 precision analog microcontroller in precision thermocouple temperature monitoring applications and controls the output current from 4 mA to 20 mA accordingly. ADuCM360 integrates dual 24-bit ∑-Δ analog-to-digital converter (ADC), dual programmable current source, 12-bit digital-to-analog converter (DAC), 1.2 V internal reference and ARM Cortex-M3 core, 126 KB Flash, 8 KB SRAM and various digital peripherals such as UART, Timer, SPI and I2C interfaces.

In this circuit, the ADuCM360 is connected to a T-type thermocouple and a 100 platinum resistance temperature detector (RTD). RTD is used for cold junction compensation. The low-power Cortex-M3 core converts the ADC readings to actual temperature values. The supported T-type temperature range is −200°C to +350°C, and the temperature range for this temperature range is 4 mA to 20 mA.

This circuit provides a complete solution for thermocouple measurements with minimal external components and loop power for loop voltages up to 28 V.

Figure 1. ADuCM360 with thermocouple interface for temperature monitor controller (schematic diagram, not shown)