12-Bit, 4-20mA Loop-Powered Thermocouple Measurement System Using ARM Cortex-M3 (CN0300)
This circuit uses theADuCM360 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.
Figure 1. ADuCM360 as a Temperature Monitor Controller with a Thermocouple Interface (Simplified Schematic, All Connections Not Shown)
- T-type thermocouple measurement system, to loop powered 4-20mA output
- Typical temperature range of -200 C to +400 C
- Single chip solution using a Cortex processing core
- Cold junction compensation
Схемы и диаграммы
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