SW4
In ultimate cycle tuning method, what step is the procedure, "Set Kp to a slightly higher value" ? Give your
answer in ordinal number, i.e. 1st, 2nd, 3rd and so on.
Answer: 6th
A temperature control system operating between 0oC and 30oC with an error of 3oC has a _____ of (3/30) x
100 = 10%.
Answer: percentage deviation
KP/KI is called the _____ TI.
Answer: integral action time
In a tank-water-level control system, its capacitance has the tendency to dampen out _____.
Answer: disturbances/disturbance
In the control of the level of water in a tank, an important attribute of the system is its _____.
Answer: capacitance
The term _____ is used to describe methods used to select the best controller setting to obtain a
particular form of performance.
Answer: tuning
KD/KP is called the _____ TD.
Answer: derivative action time
The term _____ is used to describe the use of digital computers in the control system to calculate the
control signal that is applied to the actuators to control the plant.
Answer: direct digital control
The term _____ is used to describe the use of digital computers in the control system to calculate the control
signal that is applied to the actuators to control the plant.
Answer: direct digital control
There can be a sudden change in controller output on the transition from manual to automatic modes, this
being termed a _____ in the plant operation.
Answer: bump
Decide whether each of these statements is True (T) or False (F).
With a PI process control system tested at start -up using the ultimate cycle method with
the derivative mode turned off and the integral mode set to its lowest setting, the period
of oscillation was found to be 20 minutes with a proportional gain setting of 1.2. The
optimum settings, using the criteria of Ziegler and Nichols, will be:
(i) an integral constant of 0.06 min-1.
(ii) a proportional gain setting of 1.2.
Answer: (i) F (ii) F
In ultimate cycle tuning method, what step is the procedure "Turn off all control modes but proportional" ?
Give your answer in ordinal number, i.e. 1st, 2nd, 3rd and so on.
Answer: 2nd
A steady state error will not occur when there is a change to the set value with a control system operating
in the mode:
Answer: proportional plus integral
The term ____ is used when the amplitude of the response of the system shows oscillations which decay
with time so that the amplitude decreases by a quarter on each oscillation.
Answer: quarter amplitude decay
Any change made at some point A will take some time before its affects are apparent at a point B, the
time delay depending on the distance between A and B and the rate of flow between them. The term
_____ is sometimes used to describe such delays.
Answer: distance-velocity lag
The term _____ is used when the deviation is just quoted as the difference between the measured value
and the set value.
Answer: absolute deviation
_____ are control system components which basically have an input of the error signal, i.e. the difference
between the required value signal and the feedback signal, and an output of a signal to modify the system
output.
Answer: Process controllers
A widely used form of on-off controller is a _____.
Answer: relay
KD is the constant of proportionality in a derivative control and is commonly referred to as the _____ since
it has units of time.
Answer: derivative time
The set-point is compared to the measured value to give the error signal, this being generally termed the
_____.
Answer: deviation
With _____ the change in controller output from the set point value is proportional to the rate of change
with time of the error signal.
Answer: derivative control
SW5
On-off control can be implemented by [a] such as bimetallic strips or relays. with more rapid switching
being achieved with [b], e.g. thyristors or transistors used to control the speed of a motor.
Answer for a: mechanical switches
Answer for b: electronic circuits
KD is the constant of proportionality in a derivative control and is commonly referred to as the _____ since
it has units of time.
Answer: derivative time
_____ effectively hides a disturbance from the control system until its well into the system and needs to
be made as small as possible.
Answer: Dead time
Decide whether each of these statements is True (T) or False (F).
An on-off temperature controller must have:
(i) an error signal input which switches the controller on or off.
(ii) an output signal to switch on or off the correction element.
Answer: (i) F (ii) T
The term _____ is used when an increase in input gives a decrease in output, e.g. an air conditioner
where an increase in the energy input to it results in a decrease temperature.
Answer: reverse action
The term _____ is used for an element that for an increase in its input gives an increase in its output, e.g.
a domestic central heating furnace where an increase in the controlled input to the system results in an
increase in temperature.
Answer: direct action
Decide whether each of these statements is True (T) or False (F).
With a PI process control system tested at start -up using the ultimate cycle method with the derivative
mode turned off and the integral mode set to its lowest setting, the period of oscillation was found to be
20 minutes with a proportional gain setting of 1.2. The optimum settings, using the criteria of Ziegler
and Nichols, will be:
(i) an integral constant of 0.06 min-1.
(ii) a proportional gain setting of 1.2.
Answer: (i) F (ii) F
The _____ is the fractional or percentage deviation that will produce a 100% change in controller
output.
Answer: proportional band
The term _____ is used to describe the use of digital computers in the control system to calculate the
control signal that is applied to the actuators to control the plant.
Answer: direct digital control
In the equation, controller output = Kp x controller input, Kp is a constant called the _____.
Answer: gain
The term _____ is used for the values between the on and off values in an on-off control.
Answer: dead band
neutral zone
There can be a sudden change in controller output on the transition from manual to automatic modes, this
being termed a _____ in the plant operation.
Answer: bump
With _____ the change in controller output from the set point value is proportional to the rate of
change with time of the error signal.
Answer: derivative control
The ways in which process controllers react to error changes are termed the _____.
Answer: control laws
control modes
The error signal which persist under steady state conditions is termed the steady state error or the
_____.
Answer: proportional offset
Decide whether each of these statements is True (T) or False (F).
With a PI process control system tested by the process reaction method and the controller output
changed by 10%, the response graph obtained was as shown in the figure below. The optimum settings,
using the criteria of Ziegler and Nichols, will be:
(i) proportional gain constant 7.2.
(ii) integral constant 0.15 min-1.
Answer: (i) T (ii) F
KP/KI is called the _____ TI.
Answer: integral action time
In any control system with feedback, the system cannot respond instantly to any change and thus there
are delays while the system takes time to accommodate the change. Such delays are referred to as
_____.
Answer: dead time
lags
The set-point is compared to the measured value to give the error signal, this being generally termed
the _____.
Answer: deviation
The term ____ is used when the amplitude of the response of the system shows oscillations which decay
with time so that the amplitude decreases by a quarter on each oscillation.
Answer: quarter amplitude decay
SW6
A PLC is a microprocessor-based system that uses a programmable memory to [a] and [b] such as logic,
sequencing, timing, counting and arithmetic in order to control machines and processes and is designed
to be operated by engineers with perhaps a limited knowledge of computers and computing languages.
Answer for a: store instructions
Answer for b: implement functions
The input and output sections are where the processor receives information from [a] and communicate
information to [b].
Answer for a: external devices
Answer for b: external devices
Complete the following statements related to ladder-diagram drawing conventions:
• Electrical devices are shown in their [a].
• A particular device can appear in [b] of a ladder.
Answer for a: normal condition
Answer for b: more than one rung
In Mitsubishi PLCs, the element labeled with the addresses M100, M101, etc, is called ______.
Answer: marker
Select from the given choices the ladder diagram that implements an XOR gate.
Answer:
Decide whether each of these statements is True (T) or False (F).
The figure below shows a ladder diagram for which there is an output from Output 1 when:
(i) there is an input to Input 2 and a momentary input to Input 1.
(ii) there is an input to Input 1 or an input to Input 2.
Answer: (i) T (ii) F
Decide whether each of these statements is True (T) or False (F).
When there is an input to Input 1 in the figure below, the output is switched:
(i) on for the time for which the counter was pre-set.
(ii) off for the time for which the counter was pre-set.
Answer: (i) F (ii) F
The term [a] is used for a control action such as closing contacts of a switch, used as an input to the PLC
while the term [b] is used for a device connected to the output of a PLC, e.g. a motor.
Answer for a: input
Answer for b: output
Decide whether each of these statements is True (T) or False (F).
When there is an input to Input 1 in the figure below:
(i) the counter contacts in the third rung close.
(ii) the counter is ready to start counting the pulses from Input 2.
Answer: (i) F (ii) T
In the ladder-diagram drawing conventions, each rung must start with at least one [a] and must end
with at least one [b].
Answer for a: input
Answer for b: output
In the ladder-diagram drawing conventions, the [a] of the diagram represent the [b] between which
circuits are connected.
Answer for a: vertical lines
Answer for b: power rails
Select from the given choices the ladder diagram that implements a NAND gate.
Answer:
A/An _____ is an element in PLCs that behaves like relays, being able to be switched on or off and, in
turn, switch other devices on or off.
Answer: internal relay
Decide whether each of these statements is True (T) or False (F).
For the ladder diagram shown below, the internal relay:
(i) switches on when there is just an input ot Input 1.
(ii) switches on when there is an input to Input 1 and to Input 2.
Answer: (i) F (ii) T
Select from the given choices the ladder diagram that implements a latch circuit.
Answer:
Select from the given choices the ladder diagram that implements an AND gate.
Answer:
The following are types of optoisolator outputs: [a] are suitable for a.c. and d.c.switching while [b] are
used to control external loads which are connected to the a.c. power supply.
Answer for a: relay outputs
Answer for b: Triac outputs
Decide whether each of these statements is True (T) or False (F).
For the ladder diagram shown below:
(i) the first rung gives the condition required to reset the counter.
(ii) the second rung gives the condition required to generate pulses to be counted.
Answer: (i) T (ii) T
In Siemens PLCs, the element labeled with the addresses 100, M101, etc, is termed ______.
Answer: flag
_____ count down from the pre-set value to zero, i.e. events are subracted from the set value.
Answer: Down-counters
