Study Questions

Apply Your Knowledge

What is the typical accuracy for an industrial thermocouple?


See seek an "order-of-magnitude" estimate

± 10 K

± 1 K


± 0.1 K

± 0.01 K















Which of the following is a source of noise for the measurement of a distillation tray temperature?


Imperfect mixing on the tray.

Oscillations in the liquid flow from the tray above.


Variations in the feed composition.

Electronic interference due to induction from close electrical wires.














We use the first order filter because its conforms to the perfect filter shown below.


















Why do we design a version of the PID controller with a filter on the derivative mode only?



There is no theoretical basis, its purely based on experience.

The design provides zero steady-state offset.


We never design the controller as described.

It reduces excessive variation in the derivative due to high frequency noise without slowing the proportional and integral modes.



























Consider a situation in which the control loop has been functioning well; then, we increase the sensor range from
0-100 to 0-200 C.  What should be changed in the commercial controller?


The commercial controller uses scaled variables


Must repeat the process reaction curve experiment.

Reduce or eliminate the derivative mode.


Increase the scaled controller gain by a factor of 2.

Do not change anything.














For the process below, a heating medium flows through the exchanger coils, and the valve is fail closed.  What is the correct sense for the controller?


The commercial controller uses scaled variables


To answer, must perform the process reaction curve experiment .

Either sense would work OK.


The sense would be Direct               (increase-increase).

The sense would be Reverse            (increase-decrease).






















In the data from a feedback PID control loop below, the poor performance is due to (integral) reset windup.