BOX 6 How to Confuse!*

“The output of the loop controller is adjusted according to a standard digital Proportional-Integral-Derivative (P-I-D) algorithm, which varies it systematically to maintain the control quantity at or very near its operating point. The Proportional, Integral and Derivative gains can be specified by the user. (They remain shown in all modes, but are only effective in P-I-D). The gains should be set with the SCALE in mind: they actually operate directly on the unscaled—i.e. normalized-error. Both excess set point cascade and output cascade can be generated.

“The three gains of a P-I-D loop must be carefully selected to achieve optimum performance of the controlled feedback loops. Those not familiar with closed-loop control theory are urged to consult the factory for guidance in selecting these values for new applications. When selecting these gains, remember that they apply directly to normalized input and output quantities. If the preceding sentence seems obscure to you, get help.”

* Excerpt from an operating manual for a 250-liter fermenter used in vaccine manufacturing.

SOURCE: Text supplied courtesy D. Stainer.

properly trained to use it, the benefit may be lost. Therefore, another key component of technology transfer is ongoing training.

Workshop participants also discussed a concept paper that presented a comprehensive approach to technology transfer. Among other things, the paper proposed the formation of an international public-sector vaccine consortium. The consortium would help developing countries produce high-quality DTP, DTP-combination, and low-profit, “orphan ”44 vaccines through a stepwise process involving technical training and the establishment of demonstration vaccine


In this context, orphan vaccines are those directed against diseases whose prevalence is very low in industrialized nations but that pose a significant health threat in the developing world.

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