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

Test probe P100-M3

C-4

PJSRV05-4

Advantages and features:

T-type thermocouple measurement system for loop powering of 4-20mA output

Typical temperature range is -200C to +400C

Single-chip solution with Cortex processing core

Cold junction compensation

Products used in this circuit

ADP1720

ADUCM360

application:

Field instrumentation and intelligent transmitter

Temperature Controller

Sensor and sensor interface

Circuit function and advantage

This circuit uses the ADuCM360 precision analog microcontroller in precision thermocouple temperature monitoring applications and controls the output current from 4mA to 20mA. ADuCM360 integrates dual 24-bit ∑-Δ analog-to-digital converter (ADC), dual programmable current source, 12-bit digital-to-analog converter (DAC), 1.2V internal reference and ARM Cortex-M3 core, 126KB flash 8KB 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 4mA to 20mA.

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