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Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0287. Devices Connected/Referenced AD7193 4-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA ADT7310 ±0.5°C Accurate, 16-Bit Digital SPI Temperature Sensor AD8603 Precision Micropower, Low Noise CMOS R-to-R Input/Output Operational Amplifiers ADR3440 4.096 V, Micropower High Accuracy Voltage Reference ADG738 CMOS, Low Voltage, 3-Wire Serially- Controlled, Matrix Switch ADG702 CMOS Low Voltage 2 Ω SPST Switch AD5201 33-Position Digital Potentiometer ADuM1280 3 kV RMS Dual Channel Digital Isolators ADuM5401 Quad-Channel, 2.5 kV Isolators with Integrated DC-to-DC Converter Isolated 4-Channel, Thermocouple/RTD Temperature Measurement System with 0.5°C Accuracy Rev. C 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 determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2013–2014 Analog Devices, Inc. All rights reserved. EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN-0287 Circuit Evaluation Board (EVAL-CN0287-SDPZ) System Demonstration Platform (EVAL-SDP-CB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials CIRCUIT FUNCTION AND BENEFITS The circuit shown in Figure 1 is a completely isolated 4-channel temperature measurement circuit optimized for performance, input flexibility, robustness, and low cost. It supports all types of thermocouples with cold junction compensation and any type of RTD (resistance temperature detector) with resistances up to 4 kΩ for 2-, 3-, or 4-wire connection configurations. The RTD excitation current are is programmable for optimum noise and linearity performance. RTD measurements achieve 0.1°C accuracy (typical), and Type-K thermocouple measurements achieve 0.05°C typical accuracy because of the 16-bit ADT7310 digital temperature sensor used for cold-junction compensation. The circuit uses a four-channel AD7193 24-bit sigma-delta ADC with on-chip PGA for high accuracy and low noise. Input transient and overvoltage protection are provided by low leakage transient voltage supressors (TVS) and Schottky diodes. The SPI-compatible digital inputs and outputs are isolated (2500 V rms), and the circuit is operated on a fully isolated power supply.
Figure 1. 4-Channel Thermocouple and RTD Circuit (Simplified Schematic: All Connections and Decoupling Not Shown) with 3- or 4-wire connections. millivolt depending on the temperature difference.
microamps to prevent self heating. dc over-voltage conditions are important design considerations. resistance compensation for the 3-W RTD configuration.
4.096 V reference connected to REFIN1(+)/REFIN1(−) of the
AD7193 for the thermocouple measurements. same ADC core, saving both space and cost. switch, and the ADG738 eight-channel matrix switch. Figure 2. External Programmable Current Source and Bias Voltage Generator 4.096 V reference for accuracy. AD8603 generates the RTD excitation current, IEXC = VW/RREF.
to compliment the IC’s internal integrated protection circuitry. circuitry is shown in Figure 5. Figure 5. Transient and Overvoltage Protection Circuit the case where long thermocouple leads have significant resistance. current that could flow into the AD7193 or the ADG738. printed circuit board (PCB) layout to meet emissions standards.
50 Hz/60Hz noise reduction enabled, and filter word FS[9:0] =
Figure 6. Noise Distribution Histogram of CN-0287 (VDD = 5 V, VREF =
4.096 V, Differential Input, Bipolar, Input Buffer Enable, Output Data rate =
50 Hz, Gain = 32, Chop Enable, 60 Hz Rejection Enable, Sinc4)
decreased by a factor of 2.24 V/8.192V.
Rev. C | Page 9 of 9 LEARN MORE CN-0287 Design Support Package: www.analog.com/CN0287-DesignSupport SDP-B User Guide Measurement, Analog Devices. and Practical Techniques, Analog Devices. Using an ADuC706x Microcontroller, Analog Devices. CN-0172, High Accuracy Multichannel Thermocouple Measurement Solution, Analog Devices. CN-0206, Complete Type T Thermocouple Measurement System with Cold Junction Compensation, Analog Devices. CN-0209, Fully Programmable Universal Analog Front End for Process Control Applications, Analog Devices. CN-0221, USB-Based Temperature Monitor Using the ADuCM360 Precision Analog Microcontroller and an External Thermocouple, Analog Devices. CN-0271, K-Type Thermocouple Measurement System with Integrated Cold Junction Compensation, Analog Devices. Kester, Walt. 1999. Sensor Signal Conditioning. Analog Devices. Chapter 7, "Temperature Sensors." Matthew Duff and Joseph Towey. Two Ways to Measure Temperature Using Thermocouples Feature Simplicity, Accuracy, and Flexibility, Analog Dialogue 44-10, Analog Devices. Mary McCarthy, AN-615 Application Note, Peak-to-Peak Resolution Versus Effective Resolution. MT-049 Tutorial, Op Amp Total Output Noise Calculations for Single-Pole System. Analog Devices. MT-004 Tutorial, The Good, the Bad, and the Ugly Aspects of ADC Input Noise—Is No Noise Good Noise? Analog Devices. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of “AGND” and “DGND”, Analog Devices. MT-035, Op Amp Inputs, Outputs, Single-Supply, and Rail-to- Rail Issues, Analog Devices. MT-101 Tutorial, Decoupling Techniques, Analog Devices. Data Sheets and Evaluation Boards CN-0287 Circuit Evaluation Board (EVAL-CN0287-SDPZ) System Demonstration Platform (EV AL-SDP-CB1Z) AD7193 Datasheet AD8603 Datasheet ADG738 Datasheet ADG702 Datasheet ADT7310 Datasheet ADuM5401 Datasheet ADuM1280 Datasheet AD5201 Datasheet ADR3440 Datasheet
REVISION HISTORY
2/14—Rev. B to Rev. C 9/13—Rev. A to Rev. B 8/13—Rev. 0 to Rev. A 8/13—Revision 0: Initial Version (Continued from first page) Circuits from the Lab reference designs are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab reference designs in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab reference designs are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any im plied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab reference designs at any time without notice but is under no obligation to do so. ©2013–2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10926-0-2/14(C)