Circuit Note

CN-0359

analog.com

Circuits from the Lab™ circuits 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)

Rev. C | 1 of 10

Circuits from the Lab

® refer-

ence 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/CN0359.

Devices Connected/Referenced

Devices Connected/Referenced

AD8253

10 MHz, 20 V/μs,

G = 1, 10, 100, 1000, iCMOS

Programmable Gain Instrumen-

tation Amplifier

ADuCM360

Low Power, Precision Analog

Microcontroller with Dual Sigma-

Delta (Σ-Δ) ADCs, ARM Cortex-

M3

ADA4627-1

30 V, High Speed, Low

Noise, Low Bias Current, JFET

Operational Amplifier

AD8542

CMOS Rail-to-Rail General-

Purpose Amplifiers

ADA4622-1

30 V, 8 MHz, Low Bias

Current, Single-Supply, Rail-to-

Rail Output Precision Op Amp

ADP2300

1.2 A, 20 V, 700 kHz/1.4 MHz,

Nonsynchronous Step-Down

Regulator

ADA4638-1

30 V, Zero-Drift, Rail-to-Rail

Output Precision Amplifier

ADP5072

1 A/0.6 A DC-to-DC Switching

Regulator with Independent

Positive and Negative Outputs

ADA4528-2

Precision, Ultralow Noise,

RRIO, Dual, Zero-Drift Op Amp

ADG1211

Low Capacitance, Low Charge

Injection, ±15 V/+12 V, iCMOS

Quad SPST Switches

ADA4077-2

4 MHz, 7 nV/√Hz, Low Offset

and Drift, High Precision

Amplifiers

ADG1419

2.1 Ω On Resistance, ±15 V/

+12 V/ ±5 V, iCMOS SPDT

Switch

AD8592

CMOS, Single-Supply, Rail-to-

Rail Input/Output Operational

Amplifiers with Shutdown

Fully Automatic High Performance Conductivity Measurement System

EVALUATION AND DESIGN SUPPORT

►

Circuit Evaluation Boards

►

CN0359 Circuit Evaluation Board (EVAL-CN0359-EBZ)

►

Design and Integration Files

►

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTIONS AND BENEFITS

The circuit shown in Figure 1 is a completely self-contained, mi-

croprocessor controlled, highly accurate conductivity measurement

system ideal for measuring the ionic content of liquids, water quality

analysis, industrial quality control, and chemical analysis.

A high performance combination of precision signal conditioning

components yields an accuracy of better than 0.3% over a conduc-

tivity range of 0.1 μS to 10 S (10 M to 0.1 Ω) with no calibration

requirements, using either 2- or 4-wire conductivity cells.

The circuit automatically detects either 100 Ω or 1000 Ω platinum

(Pt) resistance temperature devices in 2-, 3-, or 4-wire configura-

tions, allowing for added flexibility when measuring the temperature

of the liquid.

The circuit generates a precise AC excitation voltage with minimum

dc offset to avoid a damaging polarization voltage on the conductiv-

ity electrodes. The amplitude and frequency of the AC excitation is

user-programmable.

A synchronous sampling technique converts the peak-to-peak am-

plitude of the excitation voltage and current to a DC value for

accuracy and ease in processing using the dual, 24-bit Σ-Δ ADC

integrated within the precision analog microcontroller.

The user interface consists of an LCD display and an encoder

push button. The circuit can also communicate with a PC using a

USB-to-UART bridge if desired, and operates on a single 4 V to 7 V

power supply.