Instrumentation and Process Control
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Transcript of Instrumentation and Process Control
Instrumentation and Process Control
• Fermentation systems must be efficiently controlled in order to optimize productivity and product yield, and ensure reproducibility.
• The key physical and chemical parameters involved are largely depend on– a. the bioreactor,– b. its mode of operation– c. microorganism being used.
• They are primarily – aeration, – mixing, – temperature, – pH and – foam control.
Control and maintenance at optimum levels inside the reactor is mediated by sensors (or electrodes), along with compatible control systems and data logging
• Samples can be taken off-line for various analysis, such as – cell counts – determination of DNA, – determination of RNA; – determination of lipids, – determination of specific proteins, – determination of carbohydrates and – other key metabolites and substrates.
There are three main classes of sensor:
1. Sensors which penetrate into the interior of the fermenter, e.g. pH electrodes, dissolved-oxygen electrodes.
2. Sensors which operate on samples which are continuously withdrawn from the fermenter, e.g. exhaust-gas analyzers.
3. Sensors which do not come into contact with the fermentation broth or gases, e.g. tachometers, load cells.
• Internal sensors
– are in or above the fermentation medium ( e.g. pH, oxygen, foam, redox, medium analysis and pressure probes).– should be steam sterilizable and robust.
• Some sensors do not come into direct contact with any internal component of the bioreactor and do not need sterilization; for example, – load cells, – agitator shaft power and speed meters, and – external sensors used to analyze samples regularly withdrawn from
the bioreactor.
• It is also possible to characterize a sensor in relation to its application for process control. These are of three types:-
– 1. In-line sensor.
– 2. On-line sensor.
– 3. Off-line sensor.
Characteristics of ideal sensor or Criteria for selection or evaluation
• When evaluating sensors to use in measurement and control it is important to consider – response time, – gain,– sensitivity, – accuracy, – ease and speed of calibration,– stability, – reliability, – output signal (continuous or discontinuous),– materials of construction, – robustness, – sterilization,– maintenance, – availability to purchase and – cost
The Sensors used in bioprocess fermenter monitoring and control
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