Introduction
The aim of the unit is to
provide a general background in control theory with details of the construction
and performance of the associated practical equipment over a range of
applications, using an inter-disciplinary approach. Much of the work in this
unit requires a compatible level of supporting mathematics to assist the
candidates to put into practice the various theoretical concepts. It is not
intended that the mathematics is separately examined.
Knowledge requirements
Instructors must ensure that
candidates are able to:
Control principles
222.1 Explain a range of terms
relating to control systems.
Terms: open and closed loop control,
negative and positive feedback, input signal (reference or set value), output
signal (reset value), error signal, signal conditioning, open and closed loop
transfer functions, comparators, offset, control variable
222.2 Define a closed loop
proportional control system as one where the feedback is proportional to the
difference between the input and output signals (error).
222.3 Explain why the closed
loop formed by the feedback always acts to reduce the amplitude of the error
(negative feedback), for the operation of the system to remain stable.
222.4 Describe, with the aid
of blf)Ck diagrams, examples of simple closed loop control systems with
proportional feedback.
Examples: control of position, shaft
speed, temperature, voltage, pressure .
222.5 Explain that in control
systems, sensors are required to sense the level of the input and/or the output
to provide signals proportional to the quantities being measured and also, an
actuator may be required at the output to convert the output signal to a
suitable form to drive the load.
Systems: control of position, shaft
speed, temperature, voltage, pressure
222.6 Explain that closed loop
systems are error actuated and hence the error is never reduced completely to
zero.
Systems: control of position, shaft
speed, temperature, voltage, pressure
Sensors (transducers)
222.7 Describe, with the aid
of diagrams, the construction, the principles of operation, and characteristics
of a range of sensors.
Sensors: diaphragm and bellows types
including capadty , inductive and piezoelectric transducers for pressure
measurement; load cells and strain gauges, including bridges techniques for
measurement of weight; thermistors, thermocouples and resistance - thermometers
for temperature measurement; linear variable differential transformer and
resistance potential divider for linear displacement; digital optical encoders
for rotational displacement; tacho generators and pulse counting techniques with
magnetic induction for measurement of angular velocity; venturi with pressure
transducers, 'turbine meters and doppler frequency shift meters for measurement
of liquid flow
222.8 Select approp.riate sensors/transducers for common applications using manufacturers' or suppliers' data sheets to establish practical specifications and describe the requirements for signal conditioning where appropriate.
