CN0326 measurement error

Hi Thuanbkhn,

Thank you for using CN0326 as your reference design.  firstly, I would like to understand further what you are trying to do.  you are currently using CN0326 and want to run CN0326 using SMT32f407 processor.  Then to test this system, you used DC Power Supply (E3632A) from Keysight to provide voltage input from 0-1170mV with an RTD connected in channel 2.  the system (CN0326 + STM32f407) works as expected from what you mentioned above.

Are you using an actual pH probe from Atlas?

when you said that you are getting a results that  is not stable, are you referring to the reading you are measuring from the system (CN0326 + STM32f407) that you are currently evaluating with an actual probe from Atlas connected to channel 1 of the CN0326?

As per checking HI8424, it  is a compact, waterproof, portable pH/mV/temperature meter that is supplied complete with a protective carrying case. 

Are you trying to compare the results you are getting from HI8424 to the system (CN0326 + STM32f407) you have?

(Please take note that HI8424 has a pH resolution about +/-0.01 while CN0326 has about +/-0.0005.)

Cheers,

Erbe

Thanks erbe for the reply.

Exactly, I test KEYSIGHT E3632A , result very well. voltage 0 - 1170mV, step 1mV. ( Channel 1). Channel 2 test resistor result very well. ( 1000 Ohm)

I practically use two pH sensors, including Atlast Scientific sensor pH, pH sensor of HI8424 and standarad solution 4.01, 7.01.

Result unstable is read Channel 1, (mes pH using AD8603 + 1MEG Ohm). However not unstable, and channel 2 ( mes temp equivalent resistor 1000 Ohm, 0.1% relsult exactly.)

HI8424 read result exactly solution standard.

Have a difference test KEYSIGHT E3632A  and sensor pH . 

How to find and  fix error .

Thanks erbe for the reply.

Exactly, I test KEYSIGHT E3632A , result very well. voltage 0 - 1170mV, step 1mV. ( Channel 1). Channel 2 test resistor result very well. ( 1000 Ohm)

I practically use two pH sensors, including Atlast Scientific sensor pH, pH sensor of HI8424 and standarad solution 4.01, 7.01.

Result unstable is read Channel 1, (mes pH using AD8603 + 1MEG Ohm). However not unstable, and channel 2 ( mes temp equivalent resistor 1000 Ohm, 0.1% relsult exactly.)

HI8424 read result exactly solution standard.

Have a difference test KEYSIGHT E3632A  and sensor pH . 

How to find and  fix error .

Hi Thuanbkhn,

have you done any calibration for CN0326 using STM32f407?

if you are doing any calibration, can you share the method your are using?

when you said that the reading is not stable, can you describe that in detail? is it rising and falling irregularly in pH reading?  upto what pH range if it did?

Cheers,

Erbe