Department of Electronics Engineering – UoP
Control System: Sample problems
Engr. Cezar N. Velasco Jr.
1. A variable resistor, called a potentiomer, the resistance is varied
by moving a wiper arm control solutions along a fixed resistance.
The resistance from A to C is fixed, but the resistance from B to C
varies with the position of the wiper arm. If it takes 10 turns to
move the wiper arm from A to C, draw a block diagram of the
potentiometer showing the input variable, the output variable, and
(inside the block) the gain, which is a constant and is the amount
by which the input is multiplied to obtain the output.
Answer:
5 turns yields 50 V. Therefore K =
50 𝑉𝑜𝑙𝑡𝑠
5 𝑥 2𝑝𝑖 𝑟𝑎𝑑
= 1.59
K- Constant
2. A temperature control system operates by sensing the difference between the thermostat setting and the actual
temperature and then opening a fuel valve an amount proportional to this difference. Draw a functional closed-loop
block diagram and identifying the input and output transducers, the controller, and the plant. Further, identify the input
and output signals of all subsystems.
Desired Temp
Temp diff
+
Voltage Diff
Actual Temp
3
Thermostat
-
Fuel flow
Amplifier and
valves
Heater
3. An aircraft's attitude varies in roll, pitch, and yaw as defined in Figure. Draw a functional block diagram for a closedloop system that stabilizes the roll as follows: The system measures the actual roll angle with a gyro and compares the
actual roll angle with the desired roll angle. The ailerons respond to the roll angle error by undergoing an angular
deflection. The aircraft responds to this angular deflection, producing a roll angle rate. Identify the input and output
transducers, the controller, and the plant. Further, identify the nature of each signal.
Department of Electronics Engineering – UoP
Control System: Sample problems
Engr. Cezar N. Velasco Jr.
Desired
Roll angle
input voltage
Pilot
controls
+
-
Error signal
Position
Aileron
Position
Control
Roll rate
Aircraft
dynamics
Roll angle
Integrate
Gyro voltage
Gyro
4. Assignment:
Many processes operate on rolled material that moves from a supply reel to a take-up reel. Typically, these systems,
called winders, control the material so that it travels at a constant velocity. Besides velocity, complex winders also
control tension, compensate for roll inertia while accelerating or decelerating, and regulate acceleration due to sudden
changes. A winder is shown in Figure 1.3. The force transducer measures tension; the winder pulls against the nip rolls,
which provide an opposing force; and the bridle provides slip. In order to compensate for changes in speed, the material
is looped around a dancer. The loop prevents rapid changes from causing excessive slack or damaging the material. If
the dancer position is sensed by a potentiometer or other device, speed variations due to buildup on the take-up reel or
other causes can be controlled by comparing the potentiometer voltage to the commanded speed. The system then
corrects the speed and resets the dancer to the desired position. Draw a functional block diagram for the speed control
system, showing each component and signal.