PH transducer

In order to ensure that the pH in the SO2 scrubber does not fall excessively, leading to gas emission, it is essential to control the addition of sodium hydroxide to the unit. Cascade control systems can be used, where the pH transducer is used to define a set point for a flow control loop. However, variable-speed metering pumps are more commonly used, the speed of the pump being controlled directly by pH. 

S. J. Jang, Electrostrictive Ceramics for Transducer Applications, Ph.D. dissertation. The Pennsylvania State University, University Park, 1979. 

An ultrasonic transducer is installed on the pH probe mount in the acid-alkali treatment module [T-31], This prevents fouling of the electrodes and provides a more closely controlled pH in the effluent discharged to the precipitator. 

In-situ emulsion formation, as proposed by Kamath et al(19), with DAS surfactants may cause higher pressure drops across the core. This is because of the blocking tendency of the emulsion which has lower mobility. This could explain the earlier plugging of the core compared to other runs. Effluent pH and viscosity showed behavior similar to the previous runs. It is worthwhile noting here that such pressure drops were not manifested by face plugging of the core near the entrance. This was confirmed by simultaneously monitoring the pressure at the inlet end of the core as well as the differential pressure across the two pressure taps located about 1 cm. from each end of the core. The inlet end pressure transducer showed reasonably low pressures throughout the run for each experiment. 

Trettnak W., Leiner M.J.P., Wolfbeis O.S., Fibre-optic glucose sensor with a pH optrode as a transducer, Biosensors 1988 4 15. 

The optical sensors are composed of ion-selective carriers (ionophores), pH indicator dyes (chromoionophores), and lipophilic ionic additives dissolved in thin layers of plasticized PVC. Ionophores extract the analyte from the sample solution into the polymer membrane. The extraction process is combined with co-extraction or exchange of a proton in order to maintain electroneutrality within the unpolar polymer membrane. This is optically transduced by a pH indicator dye (chromoionophore)10. 

The pH optical fiber sensor without any pH-sensitive dye was also described70. Porous silica layer made by the sol-gel method was cladded onto optical fibre core and was exploited as the optical transducer. Acid-base properties of silica surface caused that the surface charge of silica changed with pH of the solution. For example saturation of the sol-gel layer with cations leads to an increase of the electron density of the film, hence, the refractive index of the film. Since the surface charge of silica depends on pH, the refractive index of silica film varies also with pH. Thus, changes of... 

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