Friday, July 01, 2016

12-Bit, 4-20mA Loop-Powered System

An Application note and Evaluation Kit from Analog Devices. This solutions helps you evaluate a part of a Process Control or Data Acquisition module that you may wish to design.

"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."

12-Bit, 4-20mA Loop-Powered Thermocouple Measurement System

12-Bit, 4-20mA Loop-Powered System

The thermocouple used in this application is a Type T (copper-constantan) that has a temperature range of −200°C to +350°C. Its sensitivity is approximately 40 μV/°C, which means that the ADC in bipolar mode, with a PGA gain of 32, can cover the entire temperature range of the thermocouple.


The RTD was used for cold junction compensation. The particular one used in this circuit was a platinum 100 Ω RTD, Enercorp PCS 1.1503.1. It is available in a 0805, surface-mount package. This RTD has a temperature variation of 0.385 Ω/°C.