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

　　Advantages and features:

T-type thermocouple measurement system, capable of loop power supply for 4-20mA output

Typical temperature range is -200C to +400C

Single-chip solution using Cortex processing core

Cold junction compensation

　　Products used in this circuit

ADP1720

ADUCM360

　application:

Field instrumentation and smart transmitters

Temperature Controller

Sensors and sensor interfaces

　　Circuit functions and advantages

This circuit uses the ADuCM360 precision analog microcontroller in a precision thermocouple temperature monitoring application and controls the output current from 4mA to 20mA accordingly. ADuCM360 integrates dual-channel 24-bit Σ-Δ analog-to-digital converter (ADC), dual-channel programmable current source, 12-bit analog-to-analog converter (DAC), 1.2V built-in reference voltage source, ARM Cortex-M3 core, and 126KB flash memory , 8KB SRAM and various digital peripherals such as UART, timers, 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. A low-power Cortex-M3 core converts ADC readings into actual temperature values. The supported T-type temperature range is −200°C to +350°C, and the output current range corresponding to this temperature range is 4mA to 20mA.

This circuit provides a complete solution for thermocouple measurements, requires minimal external components, and can be loop powered for loop voltages up to 28V.