CN0326: FAQ

Q:

Dear Sir,

We are excited to see pH monitor with Temperature compensation application and would like to know more on this as below

1) This has reference to the configuration available in the evaluation kit Ref EVAL-CN0326-PMDZ Board

2) We understand from your Description for pH application following are important

     ....Guarding, shielding, high insulation resistance standoffs, and other  such standard picoamp methods must be used to minimize leakage at the  high impedance input of the AD8603 buffer...

3) But in the Evaluation Board we do not see any High Insulation resistance StandOff , nor any shield available?. We  see in EVAL-CN0326-PMDZ Board, AD8603 IC pin 3 is directly soldered to PCB and pH probe input is connected to this point. We wish to know wheather PCB impedance is acceptable by doing so for this application?

4) We are unable to find uC firmware C source code for this pH application for this kit? Can we get the same?

5) What modification need to be done for pt 100 RTD?

Thanks

V.Gowrishankar

ELICO LTD

A:

Hi Gowrishankar,

Below are the answers to your inquires.

3. High insulation resistance standoff and shielding will vary depending on the environment where the kit will be used.  It is highly recommended to use High insulation resistance standoff if this kit will be integrated or will be surrounded with high voltage circuits.  And a proper shielding should be applied for applications where RF noise is highly observed in the area.

For detail discussion about shielding and guarding, please refer to this link.

AD8603 can be directly connected to the input of the pH probe as long as a proper guarding/static shielding is observed.  Due to the low frequency operating range of the circuit (<500Hz), the performance of the board would not be highly affected by the PCB impedance. It is highly affected by the input bias current of the buffer due to the high input impedance of the  pH probe sensor.  The circuit note for this kit gives us the overall performance of the board.  It includes the system noise and offset generated base from the PCB design of the kit.

4.  The software use for this kit is a labview and uses System Demonstration Platform (EVAL-SDP-CB1Z)

and SDP PMOD Interposer Board (SDP-PMD-IB1Z) to evaluate the kit using the evaluation software included in the kit. You can evaluate this kit using other microcontroller  via its pmod pin (pin J2) which makes this board more flexible to use.

5.  The RTD resistance value of the included evaluation software can be varied according to the application needed.  The RTD should be connected properly in the kit since this creates current path to the 5kohms resistor (R2) that generates the voltage reference to the ADC.

Regards,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by elico:

Dear Erbe,

Thank you for your clarifications. we are unable to find SOURCE CODE of pH application software. Is it possible to share the same? our idea is to use this EVAL-CN0326-PMDZ module with our micro controller + display as a standalone pH meter. therefore we require pH processing algorithm for this module                                                       

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by JFitzger:

Hi Elico,

Unfortunately the evaluation software was designed in LabVIEW, so we won't be able to provide processor code specific to this application.

Here are some AD7793 driver links:

AD7793 - Microcontroller No-OS Driver    [Analog Devices Wiki]

AD7793 IIO Low Power Sigma-Delta ADC Linux Driver    [Analog Devices Wiki]

You might be more interested in this direct download:

http://wiki.analog.com/_media/resources/tools-software/uc-drivers/renesas/ad7793_generic.zip

James

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by ADIApproved:

I think you are looking for:

http://wiki.analog.com/resources/tools-software/uc-drivers/renesas/ad7793

http://wiki.analog.com/resources/tools-software/linux-drivers/iio-adc/ad7793

It's not specific for that Pmod - but is for the same converter.

-Robin

Q:

Dear Erbe,

Actually what we require is pH equations for both pH CAL and pH READ from the ADC data. This is available in LabWIEW software. We are interested to write C code for our uC for the pH equations.

Regards,

Gowrishankar V.

A:

Hi Gowrishankar,

Under section 3.3 found form the link below is a good reference to implement in C code the equations for pH calibration.

Link:

http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Analytical%20Documents/LIQ_MAN_6033_Theory_Practice_pH_Measurement.pdf

Regards,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by erbe:

H  Prabhu.S,

Thank you for having an interest with CN0326 Evla Board.

you should use the latest version 2.0.0 found for your study.

the source code for CN0326 Evaluation Software will be sent over to your email address.

The software we develop for CN0326 Evaluation board is for evaluation purposes only.

Regards,

Erbe

Q:

Dear Sir,

I am working with "EVAL-CN0326-PMDZ REV.A" evaluation board for pH measuring application. While searching for CN0326 Evaluation LabWIEW Software, i found that there are three different version of the software could you please what difference is there between each version. Is it possible to get source code for latest version for studying the working flow, CAL and pH measurement math function.

Regards,

Prabhu.S

A:

Hi Prabhu,

Attached is a source code of the latest Evaluation Software V2.0.0

Note: We gladly give out the source code of the software to expidite the user's development tiem but we'e not steup to support any modification to the code.

Regards,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Thanks for the quick response and support.

Regards,

Prabhu.S

Q:

Dear sir/madam,

Currently we want to use the CN0326 chip for integrating pH and temperature indications in a controller, using a regular pH electrode and a pT100 temperature sensor. For a while I am testing the chip for precise temperature indications (pH indications work quite fine), but here a problem is occuring in terms of precision. I have been testing some configurations for the AD7793 registers but I'm not sure which setting is the best.

Currently the configuration of the AD7793 is the following:

IOUT1 current = 1 mA

Biasing= Bias AIN1

Gain = 2

Reference voltage = external reference

Channel = AIN2

Continuous measuring.

This configuration results in a standard deviation of 0.16 Degrees celsius (N=70). Is this the expected precision for a pT100, do I need a different configuration?

Kind regards,

Mark

A:

Hi Mark,

thank you for considering CN0326 as part of your system.

i currently not seeing any issue with the configuration you write in the ADC register.

The issue with the precision would somehow be related to the precision of the DAC current source of AD7793, which shows a 5% initial tolerance at 25degC.  But from the result you have just shown, a deviation of 0.16degC is still acceptable.  If the source of error is correct, we can compute for the error introduce by the current source which gives us a result of +/-0.5616uA or +/-0.05%.

Please let me know if there is anything else you want to verify.

Regards,

Erbe

Q:

Hi can you please provide EVAL-CN0326-PMDZ PMOD J2 pin breakout for use with an arduino microcontroller, the reference note doesn't include it. Thanks

A:

Hi Vincent,

You can certainly use the EVAL-CN0326-PMDZ PMOD header with an Arduino controller.  You will need to follow the pin definition on the schematics of the EVAL-CN0326-PMDZ.

 

 

Also ensure that the all the digital timing for the AD7793 is followed, that can be found in the datasheet of the ADC.  Hope this is helpful.

Brandon

Q:

Hellp Brandon,

I would like to consider using CN0326 to monitor the pH in two bio-reactors. I am pretty new to ADI device and LabView thus I might need many help from you. Here I got some questions:

1. To set up my pH monitor system, what components I need to prepare? I have a two-channel pH meter (Orion Dual Star pH/ISE Bechtop) and LabView software installed. I think I need a Data Acquisition Device (DAQ) from National Instrument between my pH meter and laptop. Then I found CN0326 have a well-developed LabView program, so I am interested in it. Should I connect CN0326 with my pH meter and DAQ? Is CN0326 compatible with NI DAQ (e.g. NI USB-6501 module)

2. Can CN0326 monitor pH over time? e.g. I need to record pH value every 10 min. It is even better if I can see the diagram of pH change with LabView.

3. Can CN0326 monitor pH in two reactors at the same time? e.g. my pH meter has two channels with two probes.

4. How many parts I should purchase? There are three components in CN0326, right? Should I buy all of them?

5. What does the sample products mean? How should I choose them?

A:

Hi Tianyu,

Let me try to help.

The EVAL-CN0326-PMDZ is a complete pH front end front analog to digital.  It will allow you to plug in a pH sensor and a temperature sensor for measurements.  The board is designed as a demonstration/rapid prototyping board, so that you can get up and running quickly.

So all you'll need to do is get the "EVAL-CN0326-PMDZ", "SPD-PMDZ-IB1Z", and the "EVAL-SDP-CB1Z".  The combination of those 3 boards and the Labview software we have written is all you will need to get up and started.

So you don't need any National Instruments DAQ boards.

There is a nice user guide written which will explain how to set up the boards, and use the software. (CN-0326 Software User Guide [Analog Devices Wiki] )

Samples are only needed if you want to try and create your own board, so don't worry about that right now.

Keep in mind this is mostly used for demo/prototyping purposes, so it may not be able to do your 2 channel measurement with this board.  But the knowledge and proof of concept work will greatly reduce the amount of time you spend trying to figure out the analog front end.

The software will track the pH over time, but I'm not sure how many samples are kept in memory for the demonstration.  So for you particular application you may want to change or modify the software to do so.

Hope this clears things up.

Brandon

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by shelley:

Thanks for your prompt reply, Brandon. It is better for me to find a device for 2 channel measurement. I will learn from here! Thanks again!

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Verti:

Dear Brandon,

        So you mean that actually this evaluation board  can not link to any manufacture's PH probe, just use one precise REF+ resistor to simulate the input signal?

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Brandon:

Hi Vertigo,

Not sure why I didn't answer this awhile back, but the board itself can connect to many different pH probe manufacturers.  So long they have a BNC connectable probe and the output range doesn't exceed the input range of the board, you should be ok to use the board with many probes.

I was merely saying that we tested the board using a precision voltage source and resistor, which simulates the typical output of a probe.

Brandon

Q:

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Hi,

In this CN0326-Evaluation Software V2.0.0, i observed temperature compensation is applied in calibration and i didn't observed in run mode(Read_ADC). Is there  temperature compensation is applied in run mode?

Regards,

Prabhu.S

A:

Hi Prabhu.S,

temperature compensation is already being applied when in run mode.

Make sure that the correct value of an RTD was written during the calibration.

Cheers,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Thanks for your reply,

Please explain or mark, where temperature compensation is applied in run mode(Read ADC) in LabView Block Diagram.

Regards,

Prabhu.S

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by erbe:

Hi Prabhu.S,

By checking the functional block under  "Calibrate Solution 1" and  "Calibrate Solution 2", it shows temperature compensation was done before running the system.

Cheers,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Thanks for your reply,

Kindly help me to understand following

1. I am not able to understand where pH electrode slope is getting corrected w.r.t temperature both during CAL & READ? (please indicate with details, which functional block performs this activity?)

Regards,

Prabhu.S

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by erbe:

Hi Prabhu.S,

i just want to clarify that the the temperature compensation was done during the calibration which is under the VI block encircled as shown in the image below. 

Cheers,

Erbe

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Thanks.

I wish to understand during READ MODE for a unknown pH solution what would be pH reading after calibration, when that solution temperature is at 5.0degC and also at 100.0degC?  will pH value is same or different?

Regards,

Prabhu.S

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by erbe:

Hi Prabhu.S, 

The software algorithm only provides temperature compensation during the calibration, which means that it assumes that the temperature of the solution when reading the pH will stay the same as when it was calibrated.  During read mode, when there is a changes in temperature on the  sample solution, a new calibration should be done.

Cheers,

Erbe   

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Thanks for this confirmation.

I am eager to understand, application of your temperature CAL algorithm during READ mode temperature compensation, based on CAL. co-efficient generated during CAL?

This, since ATC probe is connected, during READ mode solution pH has to be measured in my application(with out repeatedly doing CAL) and our room temperature will vary more than 10.0degC on a day.

Regards,

Prabhu.S

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by Prabhu.S:

Dear Erbe,

Awaiting for your reply.

Regards,

Prabhu.S

RE: CN0326: Isolated Low Power pH Monitor with Temperature Compensation by erbe:

Hi Prabhu.S,

The Coefficients for the error and systems that were used in the read mode were derived from general polynomial fit using the Least Square.  Slope points for error coefficient were taken from the ideal pH0 and pH7 and for system coefficients, it was taken from the given table for a specific buffer solution.

The software is therefore needed a bit modification under the read mode to satisfy your requirement in doing a calibration everytime you do a sampling.

Cheers,

Erbe

Q:

Hi

I am going to use some CN0326 with Arduino a as well.

I have a very simple question before ordering: what are the connector used for the temperature probe? I have reread the specification several times, but have not been able to find the information.

Thank your!

Jesper

A:

Hi Jasper,

Thank you for your interest of using CN0326 for your project.

The temperature probe connector that can be used for this project is an RCA type connector.

Cheers,

Erbe