Instrumentation and Control Systems 685 Figure 5. Ingold sterilizable pHprobe. (Courtesy ofIngold Electrodes, Inc, wilmington, 9.0 WATER PURITY Water purity is often very important in biochemical processes. One of the best methods to detect the presence of salts or other electrolytic material is to measure its resistivity. Conductivity or resistivity probes are capable of measuring conductivities as high as 20, 000 microsiemens per centimeter and resistivities as high as 20 megohms per centimeter
Instrumentation and Control Systems 685 Figure 5. Ingold sterilizable pH probe. (Courtesy ofIngo[d E[ectrodes, Inc., Wi[mington, Mass.) 9.0 WATER PURITY Water purity is often very important in biochemical processes. One of the best methods to detect the presence of salts or other electrolytic materials is to measure its resistivity .Conductivity or resistivity probes are capable of measuring conductivities as high as 20,000 microsiemens per centimeter and resistivities as high as 20 megoluns per centimeter
686 Fermentation and Biochemical Engineering Handbook 10.0 TEMPERATURE Precise temperature control and profiling are key factors in promoting biomass growth and controlling yield. Temperature is one of the more traditional measurements in bioreactors so there is quite a variety of Filled thermal systems, Fig. 6, are among the more traditional tempera ture measuring devices. Their operating principle is to take advantage of the coefficient of thermal expansion of a sealed fluid to transduce temperature into pressure or movement. This has the advantage of requiring essentially no power and therefore is very popular in mechanical or pneumatic control loops. Although the trend in control is toward digital electronic, pneumatic and mechanical systems are still very popular in areas where solvent or other combustible gases may be present and therefore represent a potential safety hazard. The primary constraint in these types of systems is that the receiver (indicator, recorder, controller )must be in close proximity to the sensor Figure 6. Filled thermal system assembly for temperature measurement. (Courtesy of th Foxboro Co., Foxboro, Mass.)
686 Fermentation and Biochemical Engineering Handbook 10.0 TEMPERATURE Precise temperature control and profiling are key factors in promoting biomass growth and controlling yield. Temperature is one of the more traditional measurements in bioreactors so there is quite a variety of techniques. Filled thermal systems, Fig. 6, are among the more traditional temperature measuring devices. Their operating principle is to take advantage of the coefficient of thermal expansion of a sealed fluid to transduce temperature into pressure or movement. This has the advantage of requiring essentially no power and therefore is very popular in mechanical or pneumatic control loops. Although the trend in control is toward digital electronic, pneumatic and mechanical systems are still very popular in areas where solvent or other combustible gases may be present and therefore represent a potential safety hazard. The primary constraint in these types of systems is that the receiver (indicator, recorder, controller) must be in close proximity to the sensor. Figure 6. Filled thennal system assembly for temperature measurement. (Courtesy of the Foxboro Co., Foxboro, Mass.)