Circuit Note CN-0394 Devices Connected/Referenced Circuits from the Lab reference designs are engineered and tested for quick and easy system integration to help solve todays Low Power, Precision Analog analog, mixed-signal, and RF design challenges. For more ADuCM360 Microcontroller with Dual information and/or support, visit www.analog.com/CN0394. Sigma-Delta ADCs, ARM Cortex-M3 Flexible, Low Power, 4-Channel Thermocouple System with Arduino-Compatible Analog Interface The circuit can process up to four independent thermocouple EVALUATION AND DESIGN SUPPORT channels, and the software linearization algorithms support eight Circuit Evaluation Boards different types of thermocouples (B, E, J, K, N, R, S, and T). The CN-0394 Circuit Evaluation Board (EVAL-CN0394-ARDZ) four thermocouples can be connected in any combination, and ADICUP360 Evaluation Board (EVAL-ADICUP360) resistance temperature detectors (RTDs) on each thermocouple Design and Integration Files channel provide cold junction compensation (CJC). No extra Schematics, Layout Files, Bill of Materials compensation is needed. Thermocouple measurements using CIRCUIT FUNCTION AND BENEFITS this system cover the full operating range of the various types of thermocouples. The circuit shown in Figure 1 is a flexible, integrated, 4-channel thermocouple measurement system based on the Arduino- The circuit interfaces to the EVAL-ADICUP360 Arduino- compatible EVAL-ADICUP360 platform, which contains compatible platform for rapid prototyping. With a USB to UART the ADuCM360 low power, precision analog microcontroller. The interface and open source firmware, the EVAL-CN0394-ARDZ ADuCM360 has an ARM Cortex-M3 processor core, a number and EVAL-ADICUP360 combination can be easily adapted to a of peripherals, and also precision analog functions including a variety of thermocouple applications. dual, 24-bit, - analog-to-digital converter (ADC) multiplexer programmable gain amplifier (PGA) and voltage reference. Rev. 0 Circuits from the Lab reference designs from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 2016 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) CN-0394 Circuit Note EVAL-ADICUP360 ARDUINO-COMPATIBLE PLATFORM EVAL-CN0394-ARDZ TC1 P1 AIN0 C1 0.47F CH0 AIN4/IEXE C6 R1 0.1F TC2 P2 AIN1 C2 ADuCM360 0.47F CH1 AIN5/IEXE C7 R2 0.1F TC3 P3 USB AIN2 C3 PC 0.47F CH2 AIN6/IEXE C9 R3 0.1F TC4 P4 AIN3 AIN11/VBIAS C5 C4 CH3 0.47F 0.47F AIN7/IEXE R4 AIN8 C8 C10 0.1F 0.1F R5 VREF+ 1.6k 0.1% VREF AV EP SS Figure 1. Thermocouple Measurement System (Simplified Schematic: All Connections and Decoupling Not Shown) V V TC CJ T CJ METAL A V V TC CJ T V ADC TC TC METAL B ITS-90 R5 RTD AT IEXE V T TC TC INVERSE 1.6k T CJ EQUATION 0.1% V RTD V TO T TC TC R = R5 RTD V REF V CJ V , RTD T V CJ ITS-90 V V REF REF RTD EQUATION R TO T ADC RTD CJ T TO V CJ CJ Figure 2. Thermocouple Connection Showing Measurement and Reference Junctions for One Channel The junction is placed where the temperature is to be measured, CIRCUIT DESCRIPTION T , and is referred to as the measurement junction. The other TC Temperature Measurement Introduction end of the thermocouple is connected to a precision voltage Thermocouples are one of the most frequently used sensors for measurement system, and this connection is referred to as the temperature measurements in industrial applications because of reference junction, or alternately the cold junction (CJ). The their low cost, ruggedness, repeatability, as well as wide operating temperature difference between the measurement junction, TTC, temperature range and fast response time. Thermocouples are and the cold junction, TCJ, generates a voltage, VTC VCJ , that especially useful for making measurements at high temperatures is caused by the difference between the temperatures of the (up to 2300C for Type C thermocouples). two junctions. The voltage generated is typically from several A thermocouple consists of the junction of two wires of different microvolts to tens of millivolts and is dependent on the metal types, as shown in Figure 2. temperature difference and the thermocouple type. Rev. 0 Page 2 of 8 15303-001 15303-002