Howard P. Isermann Department of Chemical and Biological Engineering
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INTRODUCTION
General Comments

Biosensor is the term used for a whole class of sensors based on biochemical reactions to determine specific compounds. Continual measurements of raw materials and products are important for the control of Biochemical processes. Monitoring of important organic pollutants is also desirable for environmental control. Recently, many biosensors have been developed and provide methods of rapid and continuous measurements of various compounds. A biosensor is generally an immobilized enzyme or cell that is combined with a transducer to monitor a specific change in the microenvironment. The probe tip is immersed in the liquid phase and is in contact with the process either directly or through a membrane. To date, these devices have not seen widespread use because of serious disadvantages. These include:

Microbial sensors are suitable for the industrial process because they may be stable for a long time. Two different types of microbial sensors measure organic compounds.

(This portion of the text was written by Craig Pohan and Matt Armstrong at Rensselaer Polytechnic Institute (c) 1995, The following portion was authored by Urban Jenelten)

Sensors are crucial when it comes to controlability, reliability and last but not least to profitability of a process.

Why are sensors so important?

Sensors provide the connection between the "real" world and the world of process control and computers. The sensors' accuracy determines the overall accuracy and reliability of the control system. The most sophisticated analyzer or computer system with cannot correct for faulty measurements.

Both fed-batch and continuous cultures depend heavily on good sensors and accurate measurement for good performance.

What are the general properties of a good sensor:




Fig 1: Placement of a sensor in a control system

If the sensor and the control unit are a considerable distance apart, the sensor should be equipped with an amplifier


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