CN0349 provides robust and complete solution for processing conductivity and temperature inputs into digital code. The design solution is optimized for high precision and low cost measurement, using five active devices, and has a total error less than 1% FSR after calibration. The output of the circuit is fully isolated, and therefore, the ground-loop interference is effectively reduced, making it ideal for industrial applications.

The circuit shown in Figure 1 incorporates the AD5934YRSZ 12 bit Impedance Converter, ADG715BRUZ Octal SPST Switch, AD8606ARZ Rail-to-Rail OpAmp, ADuM5000ARWZ Isolated DC-DC Converter, ADuM1250ARZ Dual I2C Isolator, to convert the conductivity and temperature inputs to digital code.

The circuit has 8pin Digilent Pmod I2C interface connector on board, which could be used for connection to a customer microprocessor or FPGA.

The CN0349 circuit note discusses the design steps needed to optimize the circuit shown in Figure 1 for a specific measuring range including accuracy analysis and component selection considerations.

The performance of the circuit can be demonstrated with the use of Analog Devices SDP controller EVAL-SDP-CB1Z and SDP-to-PMOD Interposer Board SDP-PMD-IB1Z, both optional purchase items.

This user guide discusses the use of the evaluation software to collect data from the EVAL-CN0349-PMDZ Evaluation Board CN0349

Figure 1. Data Acquisition system for conductivity measurements with isolation (All connections and Decoupling Not Shown)

• EVAL-SDP-CB1Z Controller Board (SDP-B Board)
• EVAL-CN0349-PMDZ Evaluation Board (CN-0349 Board)
• EVAL-CFTL-6V-PWRZ (+6V Power Supply) or equivalent
• SDP-PMD-IB1Z SDP-to-PMOD interposer board
• Resistance Decade Box (to simulate the input impedance, e.g. IET RS-200 Labs Resistance Substituter Decade Box) or real conductivity cell with integrated Pt100 sensor (e.g. Sensorex CS200TC-PT1)
  • CN0349 Evaluation Software
  • (download from above link)
• PC with the following Minimum Requirements
  • Windows® 7 (64-bit), Windows 8 (64-bit), or Windows 10 (64-bit)
  • USB type A Port
  • Processor rated at 1GHz or faster
  • 512 MB RAM and 500 MB available hard disk space
• USB type A to USB type mini-B cable (provided with the EVAL-SDP-CB1Z Controller Board)

• The EVAL-CFTL-6V-PWRZ (+6V DC Power Supply) powers the SDP-PMD-IB1Z (Interposer Board) via the DC barrel jack.
• The SDP-PMD-IB1Z (Interposer Board) connects to the EVAL-SDP-CB1Z (SDP-B Board) via the 120-Pin connector A.
• The EVAL-SDP-CB1Z (SDP-B Board) connects to the PC via the USB cable.
• The EVAL-CN0349-PMDZ (CN0349) connects to the EVAL-PMD-IB1Z (Interposer board) via the 8-pin header Digilent Pmod I2C interface connectors (J2 on both boards). Use the 4-pin MTE Cable (Digilent, Inc.) supplied with CN0349 board.
• The resistance decade box/the conductivity cell connects to the EVAL-CN0349-PMDZ (CN0349 Board) via the terminal block J1

1. Load the evaluation software by placing the CN0349 evaluation software disc in the CD drive of the PC. You can also download the most up to date copy of the evaluation software from www.analog.com/CN0349. Open the file setup.exe.
   
   

   NOTE: It is recommended that you install the CN0349 Evaluation Software to the default directory path C:/Program Files/Analog Devices/CN0349/ and all National Instruments products to C:/Program Files/National Instruments/

   
   
   
   
   
   

2. Click Next to view the installation review page
   
   
   
   
3. Click Next to start the installation
   
   
   
   
4. Upon completion of the installation of the CN0349 Evaluation Software, the installer for the ADI SDP Drivers will execute.
   
   

   NOTE: It is recommended that you close all other applications before clicking “Next”. This will make it possible to update relevant system files without having to reboot your computer.

   
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5. Press “Next” to set the installation location for the SDP Drivers.
   
   

   It is recommended that you install the drivers to the default directory path
   C:/Program Files/Analog Devices/SDP/DriversR2

   
   
   
   
   
   
   
   

6. Press “Next” to install the SDP Drivers and complete the installation of all software. Click “Finish” when done.
   
   
   
   

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1. Connect the +6V DC Power Supply (Wallwart) to the barrel jack J1 of the Interposer Board (Interposer Board ) as depicted below.
   
   

   NOTE: Make sure that the jumper is positioned as shown below!

   
   
   
   
   
   
   
   
   

2. Connect the 120-pin connector on the SDP-PMD-IB1Z (Interposer Board) to the 120-pin connector marked “CON A” on the EVAL-SDP-CB1Z (SDP-B Board)
   
   
   
   
3. Connect the USB cable supplied with EVAL-SDP-CB1Z (SDP-B Board) to the USB port on the PC and the SDP Board
   
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   NOTE: Verify that the SDP Drivers are loaded properly. For that purpose open the Device manager and check if the SDP Board is recognized. If not repeat steps 1-3

   
   
   
   
   

4. Connect the EVAL-CN0349-PMDZ (CN0349 Board) to the SDP-PMD-IB1Z (Interposer Board) via the 8 pin header Digilent Pmod I2C interface connector.
   
   
   
   
5. Connect the Resistance Decade Box/Conductivity Cell to pin4 and pin5 of J1 Terminal Block located on EVAL-CN0349-PMDZ (CN0349 Board). If a Conductivity Cell with integrated Pt100 sensor is used, the sensor should be wired to pin 3 and pin 2 of J1 Terminal Block. Pin 1 can be used to wire the ground shield of the Conductivity Cell.
6. After a proper connection of the hardware to the PC the CN0349 Evaluation Software can be used to calibrate the board and capture data.

1. Measure Button
   • When this button is pressed, the SDP-B Board will perform a measurement procedure and present the data in the measurement data indicators (3,4,5,6).
2. Control Tabs
   • Main - Clicking this tab brings the data collection graph to the front.
   • Calibrate System - Clicking this tab brings the system calibration settings to the front.
   • Register Value - Clicking this tab brings the AD5934 and ADG715 register value panel to the front.
   • SDP Revision - Clicking this tab brings the SDP board information window to the front.
3. Impedance Indicator
   • This indicator displays the measured input impedance in Ω).
4. Conductivity Indicator
   • This indicator displays the measured input conductivity in mS/cm. The measurement result is dependent on the applied probe corrections (7) and (9).
5. Conductivity Temperature Compensated Indicator
   • This indicator displays the temperature compensated input conductivity in mS/cm according to the chosen Temperature coefficient (8)
6. Temperature of the Solution Indicator
   • This indicator displays the measured temperature in °C, using external Pt100 RTD sensor
7. Cell Constant Control (Probe Corrections)
   • This control is used to apply the constant of the cell used for the measurement. The value of this control affects the measurement result presented in the Conductivity Indicator (4).
8. Temperature Coefficient Control (Probe Corrections)
   • This control is used to apply the temperature coefficient of the measured solution.
9. Offset Control (Probe Corrections)
   • This control is used to apply offset correction to the measured Conductivity (4). If offset correction is not needed, leave this control at 0mS/cm.
10. Measurement Range Radio Buttons
    • This control determines the input measurement range. The two measurement ranges are.
11. Measurement Range Indicator
    • This indicator shows the limits of the chosen input measurement range.
12. System Status String Indicator
    • This indicator displays a message to the user detailing the current state of the software.
13. System Status LED Indicator
    • This indicator displays the current state of the software in the form of an LED. There are four status LED colors.
      Inactive
      Busy
      Error
      Waiting for user action
      
14. Calibrate Button
    • Pressing this button initiates a calibration of the board.
15. Calibration Resistances Controls
    • This control is used to apply the values for the three on board calibration resistances R3, R4, R7. The values for this controls has to be changed only if different calibration resistances are populated on the board.
16. ADG715 register value
    • This read only panel showing the ADG715 register value.
17. AD5934 register address and value
    • This read only panel showing the AD5934 register address and value.
18. SDP Firmware Revision
    • Read only data. After the connection is established with the SDP Board, the basic information for the controller can be found here.

1. Follow the instructions to properly install the software and connect the hardware as described in the previous sections.
2. Open the file named CN0349.exe in the installation directory or the shortcut in the start menu.

1. The software should connect to the board automatically. If the hardware is not recognized by the PC the next window will appear, indicating that the software is waiting for proper hardware connection. If that happens perform the hardware connection procedure described in the previous section. After connecting the hardware the list in the window will populate. Choose the connected hardware and click select.
   
   
   
   
2. Upon success, the System Status String Indicator will display SDP Board Ready to Acquire Data

1. Establish a USB Connection Link.
2. Click the Calibrate System tab.
3. Press the Calibrate Button.
4. A pop-up window will appear indicating that the board is being calibrated. Wait for the calibration to finish.
5. When the calibration is finished a second pop-up window will appear to indicate the end of the measurement. Click the OK button.

1. Establish a USB Connection Link.
2. Choose the appropriate Probe Corrections .
3. Choose the Measurement Range .
4. Click the Measure button .
5. A pop-up window appear to indicate that the board is performing a measurement procedure.
6. When the measurement is finished a second pop-up window will appear to indicate the end of the measurement. Click the OK button to close the pop-up window.
7. After clicking OK the indicators are presenting the measured data.

This section will describe how to use the CN0349 board with platforms other than the SDP-B platform (which will be referred to as the “host”). The host can be a MCU platform, FPGA platform, or PC with USB to I2C converter, or any type of programmable platform which has an I2C interface.

For the detailed specifications of the I2C interface, please check: I2C-bus specification. Notice that the CN0349 board does not support all the features of the I2C-bus specification, and the limitations will be described later.

The EVAL-CN0349-PMDZ evaluation board uses a standard Digilent Pmod 8pin I2C connector interface, J2, to communicate with the host. For the detailed Digilent Pmod interface specification please check: Digilent Pmod Interface Specification

For the customer platform to communicate with the CN0349 board, the I2C communication protocol must be designed carefully. The maximum I2C speed and timing is limited by the ADG715 and the AD5934. Please check the data sheet for the AD5934 and ADG715 for more specific details. The host I2C timing and speed must meet with the requirements of both the ADG715 and AD5934. The maximum I2C clock speed for ADG715 and AD5934 is 400kHz.

When designing the software for the CN0349, there are particular register settings that must be adhered to for the AD5934 and the ADG715. These register settings will effect the input range of the individual components, as well as effect system level parameters such as the calibration and range of the entire system, so it's extremely important to follow the software settings provided below.

• INPUT SIGNAL SETTING
  • AD5934 - Sets the fullscale output of the excitation signals, and the inputs to the internal A/D converter
  • Excitation Voltage and PGA MUST have the following settings in the host software, otherwise the results maybe erroneous:

• SYSTEM CALIBRATION
  • ADG715 - Responsible for the conductivity calibration
  • You MUST have at least one of the following calibration settings in your software. Each calibration will increase the accuracy of the system, and provide better results when measuring in either the High or Low Conductivity Range. Two calibration points per range(High or Low) is recommended, otherwise your results will have a higher error:

• SYSTEM MEASUREMENTS
  • ADG715 - Responsible for the measurement of the conductivity range.
  • It is best to use the range that best describes your unknown conductivity. For example, using the High range, when the conductivity measurement you are trying to obtain should be in the low range will add additional errors to the measurement and reduce accuracy.

There are two allowable measurement ranges for the conductivity cell admittance. If the conductivity cell admittance is out of these ranges, incorrect results may occur.

End of Document