grayson_o
Today, I attached the final pH sensor to the Arduino hydroponic sensor assembly and tested it. The sensor worked exactly as designed right out of the box, which was helpful. The data was returned through the serial monitor exactly as expected, and could be parsed easily by the Python script I already have in place (although I used my MacBook's serial capabilities through the Arduino IDE for this experiment for ease of use).
One issue that I found was that the Energy Lab seems to have no distilled water - the sensor is supposed to be rinsed in distilled water following immersion in a test liquid to prevent accuracy drift, but I was forced to settle for tap water. This is unlikely to damage the sensor, but might over a longer period, so finding distilled water soon will be necessary.
All three components worked as designed and corresponded exactly to the values displayed by the commercial handheld pH and EC meters - the Arduino system is actually more precise, returning values at 3 significant digits rather than the handheld reader's 2. To measure whether or not drift was occurring over time due to water ionization, I set up the system in the water for 16 minutes and plotted the results. The sample size is still too small to say definitively whether or not ionization is occurring, but results look encouraging so far.
Excluding the outlier value in the first reading, both the pH and EC readings remained relatively constant throughout the period that I measured the values. pH fluctuated relatively consistently, remaining in the same range with a small degree of error throughout the experiment, which implies that it was not affected by local ionization.
EC had a slight upward trend, increasing by 0.1 Siemens by the end of the experiment and having a maximum value of 2.89 Siemens (0.17 Siemens above the initial reading). I worry that this is the result of ionization (but if it is, the effects are very slight). To say for sure, a more long-term study must be conducted, and controlled against the handheld EC reader. My data is recorded in the Google spreadsheet https://docs.google.com/spreadsheets/d/1ygsmvdz7_ylkOoCiFEAPgX5vfisa7rl_ZeV5a3XpFBM/edit#gid=0.
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