Matching the characteristics of the electrode system and the secondary instrument in a pH-meter

Conclusions

The number and type of adjustment elements in a secondary instrument are determined by the required precision and range of measurements with a pH-meter (Table 3).

The information provided in Table 3 refers to universal instruments intended for measuring pH over a wide range of temperatures up to 100°C. In such pH-meters it is advisable to replace the normally existing pH_u adjustment by an α instrument, without any adjustment of parameter S₂₀ under operating conditions, since the error due to ΔS₂₀ in the application of electrode systems does not exceed 0.02 pH.

By reducing the measurement range with respect to both pH values and temperature, it becomes possible to raise the precision of measurements, owing to a reduction in the values of pH_act-pH_bf and of t_s-20, and to use of a minimum number of adjustable elements, thus simplifying the instrument's circuit and raising its reliability.

In developing pH-meters it is necessary in each particular case to establish, by means of a reduction or analytical technique, the required adjustable elements for the operation of a secondary instrument. For raising the precision of universal instruments which operate over wide ranges of pH and temperature, it is necessary to develope electrode systems with a minimum value of E_n.