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Today's automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for information about the CAP program. The following question comes from the CAP study guide, Performance Domain V, Deployment.
An increase in which setting can compensate for a thermowell lag time?
a) rate time
b) reset time
d) filter time
e) none of the above
Thermowell and temperature processes have multiple interacting thermal lags. Rate time cancels a secondary thermal lag that can improve control in a slow temperature process without A/D chatter. Reset time adds another lag that further increases the apparent dead time from multiple lags. A large thermowell lag reduces the allowable gain. A process variable filter adds another lag that further increases the apparent dead time from multiple lags.
The correct answer is A, rate time.
Reference: Greg McMillan, Good Tuning: A Pocket Guide.