HW#1
CHBE 356: Process Dynamics and Control
Department of Chemical and Biological Engineering, University of British Columbia
Q1 (10 pts)
Figure 1: The liquid receiver.
1. Controlled variables: h
Manipulated variables: Fo
Disturbance variables: Fi
2. Rate of mass accumulation = Rate of mass in - Rate of mass out
If we assume Fi and Fo are mass flow rate then:
dρAh
= Fi − Fo
dt
For constant density and cross-sectional area:
ρA
dh
= Fi − Fo
dt
If we assume Fi and Fo are volumetric flow rate then:
A
dh
= Fi − Fo
dt
3. feedback: measure h, adjust Fo
Feedforward: measure Fi , adjust Fo
Q2 (10 pts)
Both the loops are feedback control loops. The controlled variable is measured to adjust the manipulated
variable. To decide if a controller is feedback or feedforward. Ask yourself the following question: am I measuring the variable that I need to control? If the answer to this question is “Yes”, then you have a feedback
controller. The location of the manipulated variable does not change the type of controller you have. In the
two figures, the same controlled variable (level) is measured and used to determine the percentage opening
of the valve.
Yankai Cao
1
Q3 (10 pts)
Q4 (10 pts)
Q5 (20 pts)
Yankai Cao
2
Yankai Cao
3
Q6 (20 pts)
Q7 (20 pts)
Yankai Cao
4