New technology dispels notions of costly pH sensors
November 2002Analytical Instrumentation & Environmental Monitoring
Until recently, pH sensors have been considered costly to operate, as the electrode had to be regularly serviced, cleaned, calibrated and even replaced. A new generation automatic measuring point, introduced by instrumentation specialist Endress+Hauser, has changed this perspective by placing pH measurement into a completely new cost range.
TopCal S, an automatic measuring device from Endress+Hauser, consists of a transmitter with complete system control, a simple electropneumatic unit, containers for cleaning and buffer solutions. To complete the fully-equipped measuring point, all that is required is a pH electrode, a measuring cable, the pneumatic assembly and the cost-effective control unit.
Consistent application of intelligent electronics and the smart integration of components in the mechanical systems have made it possible for Endress+Hauser to factor in a substantial reduction in the price of fully automated systems. The greatest savings, however, result from sustained usage of an automatic measuring point. In the scenario of a chemical process where industrial detergents are neutralised and dechromated in a series of four connected basins, two pH measuring points would require manual cleaning twice a day, taking an estimated 80 minutes. Another half an hour a week would be required for calibration. If the transmitters are several meters from the measuring point, as is normally the case, two people would be required for the task, resulting in weekly servicing time per measuring point being 100 minutes for cleaning and 15 minutes for calibration. This means that the purchase and installation costs of the alternative option, namely automatic measuring points, is spent every two and a half years on servicing a comparable manual solution.
Another cost parameter to be taken into consideration results from electrode replacements. The pH value is a significant process parameter in the production of malonic acid anhydride, used in the production of age-resistant PVC, for instance. Measurements are taken in-process at 60-70°C. Normal combination electrodes have a service life of only a few days. After many experiments, Endress+Hauser has developed a compact electrode with double reference and armoured glass - extending maximum service life to four weeks. Alternatively, plants could purchase a fully automatic measuring point with a normal combination electrode. Measurements would, however, be taken at intervals as the electrode is inserted into the process for two minutes every hour and stored in the assembly for the remainder of the time. It does increase electrode service life to six months and significantly increases annual savings.
The very high cost of having to discard a complete batch in industries such as biochemistry means that acquiring high quality instrumentation makes good economic sense, especially against the background of related cost drivers such as poor product quality, reworking and contractual penalties. Endress+Hauser can assist individual clients in selecting the correct measuring option for an application based on the production parameters involved.
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