Have you ever been asked a question on process control that leaves you at a loss for words? Here is your chance to amaze friends and relatives (or at least baffle them) by learning some good concepts and analogies. If you understand the ideas and their significance conveyed in the answers to the following devastating questions, you might just become famous by Friday.
What is loop deadtime? Deadtime is that period of time from the start of a disturbance until the controller makes a correction that arrives at the same point in the loop that the disturbance entered. The controller needs to see the upset, react to it, and send the correction to the right place. To appreciate deadtime, consider when you go to a party and start drinking. The period of time between when you first take a drink and when you first recognize the effect and bypass the next round for coffee is deadtime. As the deadtime approaches zero, the portion of the open-loop error that appears as the closed-loop error approaches zero, and nonlinearities and high process gain (high proof and small body) become unimportant.
What is the open-loop error? Well, if you continued drinking, your state of intoxication would exponentially increase and reach a steady state with you passed out on the floor. The open-loop error is the alcohol concentration at this point. It is the result of having the controller (your mind) in manual or disconnecting it from the loop (your body). A smart party animal knows when to say "when," according to a famous seer.
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