Circuit Note CN-0429 Devices Connected/Referenced Circuits from the Lab reference designs are engineered and tested for quick and easy system integration to help solve todays Precision Analog Microcontroller with analog, mixed-signal, and RF design challenges. For more ADuCM355 Chemical Sensor Interface information and/or support, visit www.analog.com/CN0429. Electrochemical Gas Measurement System with Sensor Diagnostics By utilizing built-in diagnostics features (such as impedance EVALUATION AND DESIGN SUPPORT spectroscopy or bias voltage pulsing and ramping) it is possible Circuit Evaluation Boards to inspect sensor health, compensate for accuracy drift due to Electrochemical Gas Sensor Board (EVAL-CN0429-EBZ) aging or temperature, and estimate the remaining lifetime of the Arduino Shield Interface Board (EVAL-M355-ARDZ-INT) sensor right at the edge of the sensor network without user ADICUP3029 Arduino Form Factor Ultra Low Power ARM intervention. This functionality allows smart, accurate sensor Cortex-M3 Development Platform (EVAL-ADICUP3029) replacement at the individual edge nodes. An integrated, ultra Design and Integration Files low power microcontroller directly biases the electrochemical Schematics, Layout Files, Bill of Materials, Software gas sensor and runs onboard diagnostic algorithms. CIRCUIT FUNCTION AND BENEFITS The circuit shown in Figure 1 shows how an electrochemical Gas detection instruments are used in a wide range of gas sensor is connected to the potentiostat circuit and how it is applications ranging from home air quality measurement biased and measured. Common 2-lead, 3-lead, and 4-lead devices to industrial solutions for detecting toxic gases. Many of electrochemical gas sensors can be used interchangeably. The these instruments use electrochemical gas sensors. This sensor integration of this signal chain dramatically reduces cost, size, technology requires specialized front-end circuitry for biasing complexity, and power consumption at the sensor node. and measurement. 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, determining its suitability and applicability for your use and application. Accordingly, in no event shall U.S.A. Tel: 781.329.4700 www.analog.com 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) Fax: 781.461.3113 2019 Analog Devices, Inc. All rights reserved. CN-0429 Circuit Note DNI EC SENSOR CHANNEL 0 C4 C2 30pF 0.1F DGND DGND M1 SE0 4 DE0 E3 E5 AE CE0 1 2 1 2 1 2 CE WE CO-A4 RE 600 AT 100MHz 600 AT 100MHz 1 3 D C1 R1 AVDD 3 CAP POT0 Q1 G 100k 2 S 0.1F MMBFJ270 E4 1 2 C3 600 AT 100MHz 30pF RE0 DGND VBIAS0 VZERO0 VREF2V5 AIN4/LPF0 SW 15 SW 12 SW 13 ULPBUF RE0 + SW 2 LPDAC0 CE0 PA SW 8 ULPREF SW 3 SW 14 SW 10 CAP POT0 TO CHANNEL 1 10k 10k SW 6 RE0 SW 4 + SW 11 LPTIACON0 TIA0 12:10 SW 7 SE0 LPTIACON0 SW 5 SW 9 R 15:13 LOAD FORCE/ R R TIA LPF SW 1 SENSE LPTIACON0 9:5 ADC MUX SW 0 RC00 RC00 RC01 Figure 1. Simplified Circuit Block Diagram CIRCUIT DESCRIPTION POROUS MEASURED WORKING GAS Fundamentals of Electrochemical Gas Sensors ELECTRODE The fundamental principle of electrochemical gas sensing is measuring the current generated due to oxidation or reduction at an electrode in response to a target gas. Most common ELECTROLYTE sensors have two or three electrodes. Some sensors utilize an additional fourth electrode. In 3-electrode configuration, the electrodes are referred to as a working electrode (WE), also known as sensing electrode (SE), a reference electrode (RE), and a counter electrode (CE). Figure 2 shows simplified diagram of such an electrochemical cell. COUNTER REFERENCE ELECTRODE ELECTRODE Figure 2. Electrochemical Gas SensorSimplified Rev. 0 Page 2 of 7 17302-001 17302-002