Circuit Note

CN-0359

analog.com

Rev. C | 9 of 10

such, Analog Devices, Inc. also offers other reference designs with

varying form-factors and features. One of these is the CN0349,

which features a high precision conductivity measurement data

acquisition system with an 8-pin I2C Pmod interface that is ideal for

industrial environments that require a small, low cost, fully isolated

solution. Other examples are the CN0411 and the CN0428, which

are designed to measure conductivity for water quality monitoring

applications.

CIRCUIT EVALUATION AND TEST

This circuit uses the EVAL-CN0359-EBZ circuit board, an external

power supply, conductivity cell, and an RTD. The EVAL-CN0359-

EBZ comes preloaded with the code required to make the con-

ductivity measurements. For complete information on the system

hardware and software operation, refer to the CN0359 User Guide.

EQUIPMENT NEEDED

The following equipment is needed:

►

The EVAL-CN0359-EBZ circuit board

►

A 6 V power supply or wall wart (EVAL-CFTL-6V-PWRZ)

►

A conductivity cell

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Pt100 or Pt1000 2-wire, 3-wire, or 4-wire RTD (if the RTD is not

connected, the conductivity measurement is referenced to 25°C)

SETUP

Use the following steps to setup the CN0359 for evaluation:

1. Connect the 6 V power supply (EVAL-CFTL-6V-PWRZ) to the

EVAL-CN0359-EBZ.

2. Enter parameters for EXC Voltage, EXC Frequency, TEMP

Coefficient, and Cell Constant that are appropriate for the

probe.

3. Disconnect the EVAL-CFTL-6V-PWRZ power supply.

4. Connect the conductivity cell as follows:

a. 4-wire cell: connect an outside current electrode to J5 Pin 1

and the closest inner voltage electrode to J5 Pin 2. Connect

the second outside current electrode to J5 Pin 4 and the

closest inner voltage electrode to Pin 3.

b. 2-wire cell: connect one electrode to J5 Pin 1 and Pin 2 and

connect the second electrode to J5 Pin 2 and Pin 4.

c. If the conductivity cell has a shield, connect it to J5 Pin 5.

5. Connect the RTD as follows (if used):

a. 4-wire RTD (see Figure 7): Pair up the four wires according

to their color (or other identifying characteristic). Connect

one pair of wires to J3 Pin 1 and Pin 2, and the other pair

to J3 Pin 3 and Pin 4. Only one wire should be connected to

each pin.

b. 3-wire RTD (see Figure 8: Connect the odd wire to J3 Pin 1,

and the two common wires to J3 Pin 3 and Pin 4. Only one

wire should be connected to each pin.

c. 2-wire RTD (see Figure 9): connect one RTD wire to J3 Pin

1 and the other wire to J3 Pin 4.

d. If the RTD wires are shielded, connect the shield to J5 Pin

5.

6. Reconnect the EVAL-CFTL-6V-PWRZ power supply to the

EVAL-CN0359-EBZ.

7. Wait for the ADuCM360 to flush the buffers and display the

conductivity and the temperature. If the screen shows an error

and the buzzer beeps more than 20 times, check the sensor

connections.

Figure 12 shows a typical conductivity measurement setup.

Figure 12. Test Setup Functional Diagram