Figure out pH calibration equations & coefficients

[aufdenkampe]

We would like to create an offline spreadsheet for external determination of the YosemiTech pH calibration coefficients, similar to #14.

However, pH requires 6 parameters to convert from measured mV to pH, suggesting a polynomial that almost certainly includes temperature compensation.

pH calibration is unlike those of of conductivity, turbidity and dissolved oxygen, which have two calibration parameters (K = slope; B = intercept) that are easily calculated from a linear regression. We have found offline solutions for those, see #14.

We would like to figure out the equations for those 6 pH calibration coefficients. The following resources have been quite helpful, especially the first:

• pH Meter Calibration Equations, http://www.wetnewf.org/pdfs/ph-meter-calibration.html
• On Calibration of pH Meters, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3933894/
• pH Potential Hydrogen vs. mV Millivolts el. current equivalents, https://www.traditionaloven.com/conversions_of_measures/ph-voltage.html

However, I'm still quite confused and will likely need help from YosemiTech to figure out what they are doing.

[aufdenkampe]

I figured this out, with the help of Mike Tung and the other fine people at YosemiTech! We now have a working Y532-pH-Calibrator.xlsx, shared via commits 486a45bbcadbd7c66b5178244be4e2136f8f7e04 and 5e2d3951c7aba8b91bcb42378d740c656f666241.

See https://github.com/EnviroDIY/YosemitechModbus/tree/master/utilities/CalibrationProtocolSpreadsheet

[aufdenkampe]

Moved to the /extras/calibrator_spreadsheets subdirectory with commit https://github.com/EnviroDIY/YosemitechModbus/commit/4546da7e2fab20498c6181eed89a62574f78b9aa on Sep 19, 2022 (see https://github.com/EnviroDIY/YosemitechModbus/issues/28)