Exam 3

Question 1

What are the 2 criteria for good control?

Answer 1

1) Overdamped response
2) 1/4 amp decay
3) Able to withstand a disturbance

Question 2

What is the difference between open loop and closed loop tuning method?

Answer 2

Closed loop: take longer to get initial tuning parameters as the gain needs to be adjusted until the system oscillates but fine tuning takes less time

Open loop: initial tuning takes less time but fine tuning takes longer

Question 3

What are the characteristics of flow control and how do you tune it?

Answer 3

Flow control is a noisy process with a fast response rate. PI control is used with low gains (0.5) and high reset action

Question 4

What are the characteristics of gas pressure control and how do you tune it?

Answer 4

Very fast and stable first order processes. PI control is used with gains from 10 to 50

Question 5

What are the characteristics of level control and how do you tune it?

Answer 5

Acts like a dominant integrating process. Uses P-only control with Ti: 10-30

Question 6

What are the characteristics of temperature control and how do you tune it?

Answer 6

Mass heat balances are slow and nonlinear. Uses PID control and IMC and Z/N open loop method for tuning.

Question 7

Explain how to test whether a control loop is working properly or not

Answer 7

Perform a series of bump tests checking for consistency

Question 8

When checking a loop with a series of bump tests an operator notices that the system is performing inconsistently. What could be the source of these inconsistencies?

Answer 8

1) Engineering problems
2) Valve sticking
3) Deadband in the valve

Question 9

What are the 3 types of damped responses?

Answer 9

1) Overdamped: systems performs slow and offset exists but no overshoot
2) Underdamped: decay ratio is less than 100% but overshoot exists
3) Critically damped: fastest response with no overshoot