Quiz on PID Control
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1. If the set point is constant `(\frac{dSP(t)}{dt}=0)` which of the following is equivalent to `\frac{de(t)}{dt}`?
A. `-\frac{dPV}{dt}`
- Correct. `\frac{de(t)}{dt} = \frac{dSP(t)}{dt} - \frac{dPV(t)}{dt} = - \frac{dPV(t)}{dt}`
B. `\frac{dPV}{dt}`
- Incorrect. `\frac{de(t)}{dt} = \frac{dSP(t)}{dt} - \frac{dPV(t)}{dt} = - \frac{dPV(t)}{dt}`
C. `\frac{dSP}{dt}`
- Incorrect. `\frac{de(t)}{dt} = \frac{dSP(t)}{dt} - \frac{dPV(t)}{dt} = - \frac{dPV(t)}{dt}`
D. 0
- Incorrect. `\frac{de(t)}{dt} = \frac{dSP(t)}{dt} - \frac{dPV(t)}{dt} = - \frac{dPV(t)}{dt}`
2. What is the advantage of using the replacement for `\frac{de(t)}{dt}` from question 1?
A. It is a simple reformulation with no particular advantage
- Incorrect. It removes derivative kicks, removing unnecessary stress on valves
B. Removing derivative kicks has the effect of significantly improving the overall operation of the system
- Incorrect. The change to remove derivative kicks usually has little impact on the overall performance of the system, but can harm a valve or similar part that the actuator acts on
C. It will reduce potential wear/stress on valves by removing derivative kicks
- Correct. A derivative kick typically sends the actuator to an upper or lower limit for one controller cycle. It typically has little effect on the process but can wear out a valve or other equipment.
D. It simplifies the equation.
- Incorrect. It removes derivative kicks when there are set point changes, removing unnecessary stress on valves or other actuators.
3. What are the simple tuning correlations (IMC with `\theta_p=0`)? Try to recall this without referencing the page. Choose from the options below.
A. `K_c = K_p`, `tau_I = \tau_p`, `\tau_D = 0`
- Incorrect. Correct answer is b
B. `K_c = \frac{1}{K_p}`, `\tau_I = \tau_p`, `tau_D = 0`
- Correct. Correct
C. `K_c = \frac{1}{K_p}`, `\tau_I = 0`, `\tau_D = \tau_p`
- Incorrect. Correct answer is b
D. `K_c = K_p`, `\tau_I = 0`, `\tau_D = \tau_p`
- Incorrect. Correct answer is b
4. What is the value of the derivative filter constant `\alpha` with moderate tuning and negligible dead time `\theta_p`?
A. 0
- Incorrect. The value approaches `\frac{\tau_p^2}{\tau_p^2}` which is 1.
B. -1
- Incorrect. The value approaches `\frac{\tau_p^2}{\tau_p^2}` which is 1.
C. `\tau_p`
- Incorrect. The value approaches `\frac{\tau_p^2}{\tau_p^2}` which is 1.
D. 1
- Correct. The value approaches `\frac{\tau_p^2}{\tau_p^2}`
