Thermocouple measuring system with cold junction compensation

The circuit shown in the figure below is a complete thermocouple system based on the 24-bit Σ-Δ ADCAD7793. The AD7793 is a low-power, low-noise, complete analog front-end suitable for high-precision measurement applications. It has a built-in PGA, reference voltage source, clock and excitation current, thereby greatly simplifying thermocouple system design. System peak-to-peak noise is approximately 0.02°C.

The maximum power consumption of the AD7793 is only 500μA, making it suitable for low-power applications such as smart transmitters where the power consumption of the entire transmitter must be less than 4mA. The AD7793 also has a shutdown option. In this mode, the entire ADC and its auxiliary functions are shut down, reducing the maximum power consumption of the device to 1μA.

The AD7793 provides an integrated thermocouple solution that interfaces directly with thermocouples. Cold junction compensation is provided by a thermistor and a precision resistor. The circuit only requires these external components to perform cold junction measurements, and some simple RC filters to meet electromagnetic compatibility (EMC) requirements.

Thermocouple measuring system with cold junction compensation