AUTOMATED PH-MEASUREMENT BASED ON ONLINE COMPENSATION OF THE SENSOR SLOPE

In this publication a new method of pH-measurement with pH-glas sensor s is described, which offers on-line measurement and compensation of s ensor slope without dismounting the sensor and putting it into buffers . So the frequency of calibration and therefore the maintenance costs may be reduced. By supervision of the slope, measured on-line, it is a lso possible to become aware of defect sensors and to replace them wel l aimed. The new method uses two pH-glas electrodes with different int ernal buffers (for instance pH(i) = 4.6 and 7) and one common referenc e electrode. The sensor slope can be computed from the differential vo ltage between both electrodes. It may be used to create a pH-value bei ng more accurate than conventional pH-values under certain assumptions . In the following report a short review is given about automation of pH-measurement and the new method is described in detail. Special atte ntion is given to error calculation of pH-values due to changes of sen sor parameters and to the possibility for alarming maintenance demand and sensor failure. The report closes with first measurements, a compa ration of theoretical and measured results and a short outlook.