Circuit Note CN-0359 Devices Connected/Referenced 10 MHz, 20 V/s, G = 1, 10, 100, Low Power, Precision Analog AD8253 1000, iCMOS Programmable Gain ADuCM360 Microcontroller with Dual Sigma- Instrumentation Amplifier Delta ADCs, ARM Cortex-M3 30 V, High Speed, Low Noise, Low Bias CMOS Rail-to-Rail General- ADA4627-1 AD8542 Current, JFET Operational Amplifier Purpose Amplifiers Circuits from the Lab reference 1.2 A, 20 V, 700 kHz/1.4 MHz, designs are engineered and Low Cost, Precision JFET Input ADA4000-1 ADP2300 Nonsynchronous Step-Down tested for quick and easy system Operational Amplifiers Regulator integration to help solve todays 30 V, Zero-Drift, Rail-to-Rail Output 650 kHz/1.3 MHz, Step-Up PWM analog, mixed-signal, and RF ADA4638-1 ADP1613 Precision Amplifier DC-to-DC Switching Converters design challenges. For more Low Capacitance, Low Charge information and/or support, visit Precision, Ultralow Noise, RRIO, ADA4528-2 ADG1211 Injection, 15 V/+12 V, iCMOS www.analog.com/CN0359. Dual, Zero-Drift Op Amp Quad SPST Switches 4 MHz, 7 nV/Hz, Low Oset and 2.1 On Resistance, 15 V/+12 V/ ADA4077-2 ADG1419 Drift, High Precision Amplifiers 5 V, iCMOS SPDT Switch CMOS, Single-Supply, Rail-to-Rail 3.3 V Slew Rate Limited, Half AD8592 Input/Output Operational ADM3483 Duplex, RS-485/RS-422 Amplifiers with Shutdown Transceivers Fully Automatic High Performance Conductivity Measurement System the conductivity measurement to be referenced to room EVALUATION AND DESIGN SUPPORT temperature. Circuit Evaluation Boards CN-0359 Circuit Evaluation Board (EVAL-CN0359-EB1Z) The system accommodates 2- or 4-wire conductivity cells, and Design and Integration Files 2-, 3-, or 4-wire RTDs for added accuracy and flexibility. Schematics, Layout Files, Bill of Materials The circuit generates a precise ac excitation voltage with minimum dc offset to avoid a damaging polarization voltage on CIRCUIT FUNCTION AND BENEFITS the conductivity electrodes. The amplitude and frequency of the The circuit shown in Figure 1 is a completely self-contained, ac excitation is user-programmable. microprocessor controlled, highly accurate conductivity An innovative synchronous sampling technique converts the measurement system ideal for measuring the ionic content of peak-to-peak amplitude of the excitation voltage and current liquids, water quality analysis, industrial quality control, and to a dc value for accuracy and ease in processing using the dual, chemical analysis. 24-bit - ADC contained within the precision analog A carefully selected combination of precision signal conditioning microcontroller. components yields an accuracy of better than 0.3% over a The intuitive user interface is an LCD display and an encoder conductivity range of 0.1 S to 10 S (10 M to 0.1 ) with push button. The circuit can communicate with a PC using an no calibration requirements. RS-485 interface if desired, and operates on a single 4 V to 7 V Automatic detection is provided for either 100 or 1000 supply. platinum (Pt) resistance temperature devices (RTDs), allowing Rev. B 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 20152016 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-0359 Circuit Note +3.3V J2 J4 S1 ADM3483 ENCODER AVDD J-LINK R13 RS-485 PEC11R-S AIN0 ADC0 PWM0 J3 1.5k 1 100 OR +15V AIN7/IEXC AIN1 PWM1 ADC1 1000 J1 AIN8 Pt RTD 15V 2 AIN2 ADC2 PWM2 +4V TO +7V AIN6 +3.3V AIN3 ADC3 128 64 ADuCM360 POWER LCD +1.65V AIN5/IEXC P0.0 R U2WRI X SUPPLIES MCCOG128064A6S-SPTLY +3.3V P2.0 AIN6 U4WRI AIN5/IEXC 3 +VEXC P1.2 A0 1k AIN7/IEXC A1 VEXC P2.1 +0.115V 4 AIN8 AIN9 AIN9 DAC 36 AGND EP R20 1.2k ADG1419 ADG1211 820pF R23 +VEXC R34 +15V 430 R19 J5 1 1k G1 = 1, 10, 100, 1000 VEXC + ADA4638-1 7.5k +3.3V PWM0 +15V C50 AD8253 U10 24 2 A0, A1, 4.7F PWM1 U12B ADC3 U2WRI 15V V1 P-P ADA4528-2 + 10nF U15 +1.65V 1k 430 5 R31 + REF Y X 1.2k 1nF ADG1211 15V ADA4000-1 VOUT1 = R36 820pF +3.3V 3 +15V G1 0.16 V1 P-P 430 +15V + R29 + + 4 ADA4638-1 7.5k C73 U14 +1.65V U13 U22B 4.7F 24 PWM2 U12A ADC2 15V CONDUCTIVITY 15V CELL + ADA4528-2 10nF 470k +1.65V 1k 1nF AD8542 1nF R38 IP-P 1nF 1.2k ADG1211 820pF R41 R47,1.0k G2 = 1, 10, 100, 1000 430 +15V R37 + 7.5k ADA4638-1 +15V +3.3V +15V AD8253 C84 U16 24 4.7F A0, A1, PWM1 U20B ADC1 U19 ADA4627-1 + U4WRI 15V V2 P-P + ADA4528-2 10nF + U18 +1.65V 1k 430 15V R52 REF 1nF ADG1211 1.2k VOUT2 = 15V R42 G1 0.16 V2 P-P 430 +15V R48 G2 VOUT2 820pF + Y = 1mS + ADA4638-1 7.5k X G1 VOUT1 C93 +1.65V U22A U21 24 4.7F PWM2 U20A ADC0 15V + ADA4528-2 +1.65V 10nF 1k 1nF AD8542 Figure 1. High Performance Conductivity Measurement System (Simplified Schematic: All Connections and Decoupling Not Shown) R14 CIRCUIT DESCRIPTION 110k The excitation square wave for the conductivity cell is generated 1nF by switching the ADG1419 between the +VEXC and VEXC R15 +15V 15k voltages using the PWM output of the ADuCM360 G = 8.33 +VEXC R16 microcontroller. It is important that the square wave has a U9A DAC 13k 0V TO +10V FROM + ADA4077-2 precise 50% duty cycle and a very low dc offset. Even small ADuCM360 0V TO +1.2V dc offsets can damage the cell over a period of time. R27 27k The +VEXC and VEXC voltages are generated by the 1nF ADA4077-2 op amps (U9A and U9B), and their amplitudes are R24 controlled by the DAC output of the ADuCM360, as shown in 27k Figure 2. VEXC R22 U9B 13k 0V TO 10V + ADA4077-2 15V Figure 2. Excitation Voltage Sources Rev. B Page 2 of 10 12970-002 12970-001