Automation controls Flashcards
What are the three types of control?
Manual
Remote manual (servo)
Automatic
What are the three types of control systems?
Regulatory
Positional
Programmable
In what type of control system would a finite error exist when operating normally? (speed, voltage, current, temperature)
Regulatory
In what type of control system would the O/P and I/P ideally align under steady state conditions? (steering gear, stabilisers)
Positional
In what type of control system is a laid down sequence of events followed until the cycle is completed or the machine cycle is interrupted? (chilled water & diesel generator start routines)
Programmable
What are the four types of control medium?
Mechanical
Electrical
Pneumatic
Hydraulic
In an open loop system, what is the role of the inlet valve?
Controller
In an open loop system, what is the role of a diesel generator?
System
In an open loop system, what is the role of the input?
Desired value
In an open loop system, what is the role of the output?
Measured value
In an open loop system, what changes will effect output speed?
Fuel pressure
Load change
Wear (long term)
What is added to an open loop system to create a closed loop system?
Feedback
EMD (error measuring device)
Explain feedback?
The relaying of output information back to the input
Explain what an EMD is?
Any device which compares the input value with the output value and produces an error signal
What three things does an electronic governor consist of?
Controller
Electromagnet pickup
Actuator
The error signal is the output of which component of a closed loop system?
Controller
What are the two forms of feedback?
Positive
Negative
Explain positive feedback?
Regenerative
De-stabilising
Used in oscillators
Explain negative feedback?
Non-regenerative
Subtract feedback from input at the EMD
Used in control systems
What systems use negative feedback?
AVR
Steering gear and stabilisers
Cathodic protection
What is it called when the signal in an open or closed loop system changes from one medium to another and gets bigger or smaller?
Gain
What system will always return to its starting point after a disturbance?
Stable
What system will result in oscillations that build until failure after a disturbance?
Unstable
What is a damper?
A device used to reduce sudden changes of motion without affecting the steady state position
What level of damping results in a response which quickly reaches steady state value but oscillates for a significant period of time?
Underdamping
What level of damping has a damping ratio less than 1?
Underdamping
What level of damping is very slow to reach steady state value but does not have any oscillations?
Overdamping
What level of damping has a damping ratio more than 1?
Overdamping
What level of damping will reach the steady state value the fastest without being underdamped?
Critically damping
What level of damping has a damping ratio equal to 1?
Critically damping
What level of damping is fast and has minimum oscillations, resulting in a slightly underdamped system?
Optimally damped
How many oscillations will a optimally damped system go through before entering the acceptance zone?
One and a half
What are the five types of time varying signals?
Sine wave
Impulse
Pulse
Step
Ramp
What are the two types of common lag within a control system?
Process/transfer lag
Distance velocity lag
How is the time constant defined?
The time taken for the output to reach 63% of its final value when a step input is applied
What voltage will a 1st order system reach after one time constant is 10V is applied as the input?
6.3V
How many RC combinations are in a 1st, 2nd and 3rd order system?
1st - 1
2nd - 2
3rd - 3
What are the two basic types of interlocking systems?
Power
Control
In which type of interlocking system is the power source of the hazard interrupted by the switching of a circuit?
Control
In which type of interlocking system is the power source interrupted directly by the opening of the guard?
Power
What are the two types of interlocking switches?
With guard locking
Without guard locking
What are two types of interlocking switches with guard locking?
Unconditional
Conditional
What are two types of interlocking switches without guard locking?
Mechanically actuated
Non-contact actuation
What are three types of mechanically actuated switches?
Tongue operated actuation
Hinge operated actuation
Cam operated actuation
What form of isolation barrier is required in an interlock when it is possible for two sets of contacts to touch each other back to back in the event of a contact weld?
Galvanic isolation
What is a transducer?
A device that converts a signal from one kind (normally physical quantity) into another kind (normally electrical)
What are the four properties of a transducer?
Accuracy
Repeatability
Sensitivity
Response time
Which property is the relationship between the closeness of the output value to the input parameter?
Accuracy
Which property is the variation of the output around an expected value for a constant input?
Repeatability
Which property is how much the output changes for a change in input?
Sensitivity
Which property is the output considered to be equal to the input when 67% of the original error has been corrected?
Response time
What effect does a thermocouple use?
Seebeck
What does CJCU stand for?
Cold junction compensating unit
What does RTD stand for?
Resistance temperature detector
What would the fundamental interval of PT100 RTD be if the resistance at 100 degrees is 138.5 ohms?
38.5
In a negative temperature coefficient resistor, what will happen to the resistance as the temperature increases?
Non-linear decrease
In a positive temperature coefficient, what will happen to the resistance as the temperature increases?
Non-linear increase
What is Poisson’s ratio?
The lateral contraction divided by the longitudinal extension when a material is stretched
What is a strain gauge fitted to on the propeller shafts of ships and submarines?
Brushless torsionmeter
What directly measures linear or angular displacements?
Potentiometer
What does LVDT stand for?
Linear variable differential transformer
What three elements does a LVDT consist of?
One primary winding
Two identical secondary windings connected in series opposition
A moveable ferromagnetic armature
What is linvar used for?
To measure angular displacement
For positional feedback
What are the two types of proximity sensor?
Capacitance
Ultrasound
What are the two types of tachogenerator?
AC
DC
In a DC tachogenerator, what happens when speed is increased?
DC voltage level increases
In a DC tachogenerator, how can we reduce ripple?
Low pass filter
In an AC tachogenerator, a rise in what would be undesirable?
Frequency
When using differential pressure to determine flow rates, what is used to create the difference in pressure in a pipe?
Orifice plate
What type of flow transducer gives an output relative to flow dependant on the differential pressure developed across a constriction placed in a tube?
Orifice plate flow transducer
What would cause a decrease in the number of pulses generated by a phonic wheel transducer?
A decrease in shaft rotation speed
What are the four types of float operated devices?
Float
Spiral
Wire
Reed switching
What are the two types of pressure operated devices?
Strain gauge
Differential pressure
How can ships roll be compensated for when using capacitive tank level transducers to measure tank levels?
Use two or more level transducers
What are the three basic components of an ultra sonic level detector?
Transducer/receiver
Comparator and detector circuit
Solid state output
What would happen to the sensing range of an ultra sonic level detector if the frequency is increased?
The range would decrease
What two devices can be used for high and low level alarms?
Strain gauge
Float switch
What happens to the resistance of a LDR when the intensity of light is increased?
Resistance decreases non-linear
What is photoconductivity?
An optical phenomenon where a materials conductivity is increased when light is absorbed by the material
What are the two types of LDR?
Intrinsic (un-doped)
Extrinsic (doped)
What is backlash?
The loss of angular motion when the direction of rotation of a mechanical drive is reversed
What would the maximum angle of the output shaft be if a 10 degree step was applied to the input?
20 degrees
What three types of friction exist in a servo system?
Static
Coulomb
Viscous
Explain static friction?
The initial drag that must be overcome before motion commences
Explain coulomb friction?
Drag of constant magnitude
Explain viscous friction?
Drag directly proportional to velocity
What does the phase advance circuit do in a servo system?
Modifies the error voltage, causing the driving current to reduce before 0o=0i
Which type of servo system stabilisation has the disadvantage of being susceptible to electrical noise?
Phase advance
What is the maximum torque that can be applied to an energised stationary motor without causing spindle rotation?
Holding torque
What is a stepper motor?
A power device that converts DC voltage pulses into proportional mechanical movement of its spindle
What is the anti clockwise unipolar operation of a stepper motor?
ACBDA
What is the anti clockwise half step operation of a stepper motor?
A, AC, C, CB, B, BD, D, DA, A
What are the three types of stepper motor?
Hybrid
Variable reluctance
Permanent magnet
What are the disadvantages of stepper motors?
Limited in velocity by the maximum stepping rate
Limited by available torque
What is the number of steps per second applied to field windings to cause motor rotation?
Stepping rate
What is the maximum torque which can be applied to a motor, running at a given stepping rate, without losing synchronism?
Pull out torque
What is the maximum torque against which a motor will start, at a given pulse rate, and reach synchronism without losing step?
Pull in torque
What is the maximum switching rate at which a motor will remain in synchronism while the switching rate is gradually increased?
Pull out rate
What is the maximum switching rate at which a loaded motor can start, stop and reverse without losing steps?
Pull in rate
What is the range of switching rates between pull in and pull out curves, in which a motor will run in synchronism but cannot start or reverse?
Slew range
What are the advantages of a stepper motor?
Easily controlled by computers since winding currents are switched on or off
Speed of rotation can be controlled by setting the time between successive steps
Direction of rotation is controlled by the winding excitation sequence
Rotor position is controlled and monitored by counting the number of steps so feedback of position is not required
If the motor is left energised once a target position is reached, the rotor will resist movement
No brushes or slip rings on the rotor therefore very reliable
What are the two types of rotary encoder?
Absolute
Incremental
Which type of encoder maintains position information when power is removed from the system, meaning that the position of the encoder is available immediately on applying power?
Absolute
Which type of encoder accurately records change in position but does not power up with a fixed relationship between encoder state and physical shaft position?
Incremental
What are the three types of absolute rotary encoders?
Mechanical
Optical
Magnetic
What is the equation for step angle?
360/rotor teeth x stator phases
What is the equation for half step angle?
Step angle/2
What is the equation for distance travelled?
Step angle x number of pulses / 360
How far do 4-20 mA loops work?
3km
The ability for 4-20 mA loops to work over long distances is a function of what law?
Ohms
How many components make up a 4-20 mA loop?
5
What is the least amount of 4-20 mA tank level sensors required to give continuous level output and high and low level alarms?
1
What are the five components of a 4-20 mA loop?
Sensor
Transmitter
Power source
Loop
Reciever
What are the two main errors that occur when converting between analogue and digital?
Quantisation
Sampling
What error is caused when there is an insufficient number of samples to accurately represent the source signal?
Sampling error
What error is caused when there is an insufficient number of bits to accurately represent the source signal?
Quantisation error
Which D-A converter only requires two sized resistors?
R2R
What are the components of a microcontroller?
ADC
CLOCK
RAM
CPU
ROM
I/O
DAC
What mode of transmission enables two or more communication channels to share the band width?
Broadband
What are the advantages of digital control?
Greater precision
Better repeatability
Greater reliability
Greater accuracy
Ease of change to system operation by software update
What are the three common network configurations?
Star
Bus
Ring
Which network has a central connection point?
Star
Which network has common backbone to connect all devices to?
Bus
Which network can work in a clockwise or anticlockwise direction?
Ring
What are rules to ensure that data transfer is completed correctly
Protocol
What is the useable frequency range of a copper cable?
Bandwidth
What mode of transmission has only one transmitting device and several recievers?
Broadcast
What mode of transmission devotes the entire capacity of the medium to one communication channel?
Baseband
What are the advantages of fibre optics?
Low losses
Lightweight
Intrinsically safe
Non inductive
Small size
Security of data
What are the disadvantages of fibre optics?
Cable is fragile
Cannot be spliced like copper wire
More expensive than copper cable
Special training required for operatives
Whose theorem states that when converting between analogue and digital, the signal must be sampled at a frequency more than twice the signal frequency?
Nyquist/Shannon
In a bus network, at which percent of network loading will performance problems be caused by collisions?
Above 70%
What form of data transmission will require each byte of data to contain a timing signal for the receiver to detect it?
Asynchronous
What is interfacing?
The process of converting one signal type to another
In a bandwidth diagram, what does the 3dB point mark?
Where signal power falls by 50%
What are the two junctions called for a thermocouple?
Hot
Cold
In an RTD, what is measured during temperature changes?
Resistance
What is added to a positional servo system to modify it to include velocity feedback?
Tacho generator
What is the construction of a basic stepper motor?
Four equally spaced windings which are star connected (ACBD)
Soft iron rotor that works on the principle of minimum reluctance
What type of DA converter requires different values of resistor?
Binary weighted ladder
What are the 5 components of a digital communication channel?
Transmitter
Receiver
Transmission medium
Address system
Protocol
