# [SEN0169] Voltage values from pH Meter v1.1 seem off

greg.diehl.gtd 2019-01-04 07:55:13 4093 Views3 Replies
I recently purchased the SEN0169 that has the pH meter v1.1 board. When I connect the pH sensor to the PCB and power it with 5v, the voltage readings from the Output pin (A) seem to be off as I can't calculate proper pH values.

Here are the voltage values I'm getting using pH buffer solutions

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``````pH Buffer           Voltage Reading
4.0                       1.77v
6.86                    1.993v
9.18                    2.17v``````

Here are the voltage readings when the BNC connector is shorted or when no sensor is connected to it
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``````Shorted BNC connector                              2.00v
Nothing connected to BNC connector      4.32v``````
Is the board bad? How can I check the pH sensor directly?

Any help would be greatly appreciated

Greg
2019-01-04 15:56:43 Using the equation in my code the pH values are correct now.

What confused me was I tried the Arduino sample code posted at https://www.dfrobot.com/wiki/index.php/ ... KU:SEN0169 and was getting incorrect values.

Once I replaced:
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``pHValue = 3.5*voltage+Offset;``
With this line:
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``pHValue = (((12.95 * voltage) + (-18.92)) + Offset);``
The pH values appeared properly.

Greg
greg.diehl.gtd
2019-01-04 11:23:22 The voltage you got seems OK with the buffer pH, please calibrate the sensor and output pH value to see if they are good to use. robert.chen
2019-01-04 09:05:05 Given the pH sensor values should be linear, I plotted two values and came up with this equation

y=mx + b

y = 12.95x + (-18.92)

The above equation when supplied with the voltages (x) I mentioned previously will output the pH values (y) I'm expecting.

I'm going to put it in code and retry with the sensor.

Greg
greg.diehl.gtd