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SEN0169 pH sensor showing wrong values

Unread postPosted:Tue Dec 24, 2019 1:26 pm
by helloenthu
Hi All,
I have bought Analog pH Meter Pro SKU SEN0169.

I have tested with pH buffer solutions 7 and 4.
For pH buffer solutions 7, the output of the sensor is approximately 7.2
For pH buffer solutions 4, the output of the sensor is approximately 2.1

At first, the sensor needs to be calibrated. But for calibration, the pH values from the sensor should be at least +/- 0.2pH
But the values from the sensor is varying a lot.
Kindly help me to solve this.

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Wed Dec 25, 2019 1:29 am
by nana.wang
Hi thank you for your support.
Please help to check steps as below:

Step to Use the pH Meter
Cautions:

1. Please use an external switching power supply,and the voltage as close as possible to the +5.00V. More accurate the voltage, more higher the accuracy!

2. Before the electrode in continuous use every time,you need to calibrate it by the standard solution,in order to obtain more accurate results.The best environment temperature is about 25 ℃,and the pH value is known and reliable,close to the measured value. If you measure the acidic sample, the pH value of the standard solution should be 4.00.If you measure the alkaline sample, the pH value of the standard solution should be 9.18.Subsection calibration, just in order to get a better accuracy.

3. Before the pH electrode measured different solutions, we need to use water to wash it. We recommend using deionized water.

If all done right, please do as follows:

(1)Connect equipments according to the graphic,that is,the pH electrode is connected to the BNC connector on the pH meter board,and then use the connection lines,the pH meter board is connected to the ananlong port 0 of the Arduino controller. When the Arduino controller gets power,you will see the blue LED on board is on.

(2)Upload the sample code to the Arduino controller.

(3)Put the pH electrode into the standard solution whose pH value is 7.00,or directly shorted the input of the BNC connector.Open the serial monitor of the Arduino IDE,you can see the pH value printed on it,and the error does not exceed 0.3. Record the pH value printed,then compared with 7.00, and the difference should be changed into the "Offset" in the sample code. For example,the pH value printed is 6.88,so the difference is 0.12.You should change the "# define Offset 0.00" into "# define Offset 0.12" in your program.

(4)Put the pH electrode into the pH standard solution whose value is 4.00.Then wait about one minute,adjust the gain potential device, let the value stabilise at around 4.00.At this time,the acidic calibration has been completed and you can measure the pH value of an acidic solution. Note:If you want to measure the pH value of other solution,you must wash the pH electrode first!

(5) According to the linear characteristics of pH electrode itself, after the above calibration,you can directly measure the pH value of the alkaline solution, but if you want to get better accuracy, you can recalibrate it. Alkaline calibration use the standard solution whose pH value is 9.18.Also adjust the gain potential device, let the value stabilise at around 9.18. After this calibration, you can measure the pH value of the alkaline solution.

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Wed Dec 25, 2019 4:29 am
by helloenthu
The steps you mentioned are fine. But the problem is my pH electrode gives the output wrong(pH value as 2) when it is put into the solution pH4. So how can I calibrate the sensor? Could you get my point?

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Wed Dec 25, 2019 6:47 am
by helloenthu
Is that indicates sensor damage?

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Thu Dec 26, 2019 1:22 am
by nana.wang
Have you calibrated it when putted the sensor to solution 4 after it taked from the solution 7?

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Thu Dec 26, 2019 10:27 am
by helloenthu
No, Because when I put the sensor into the ph solution 4 it shows 2. So I don't know how to calibrate this. Do I need to adjust the potentiometer?
Can you guide me?

Re: SEN0169 pH sensor showing wrong values

Unread postPosted:Fri Dec 27, 2019 7:26 am
by nana.wang
Hi, could you please read through the wiki via https://wiki.dfrobot.com/Analog_pH_Mete ... KU_SEN0169
It contains full instruction of the calibration.