The first part of this article series addresses the pH probe and an examination of the different design challenges related to the front-end signal-conditioning circuit, including how to achieve low cost with high precision and reliability in data conversion. Part 2 delves into increasing the accuracy and precision in data processing, discussing calibration techniques such as a general polynomial fit using the least-square method for approximation in scattered predefined data for pH calibration. It will also provide a reference circuit design for a wireless monitoring system.
Understanding the pH Probe
An aqueous solution can fall under acidic, alkaline, or neutral levels. In chemistry, this is measured by a numeric scale, called pH, which stands for power of hydrogen according to the Carlsberg Foundation. This scale is logarithmic and goes from 1 to 14. The pH level can be expressed mathematically as pH = −log (H+). Therefore, if the hydrogen ion concentration is 1.0 × 10−2 moles/liter, then pH = −log (1.0 × 10−2) gives a value of 2.