8//3 2//nd e//xam Flashcards
an element in a mechatronic or measurement system that detects the
magnitude of a physical parameter and changes it into a signal that can be
processed by the system.
sensor
a device that converts physical quantity into an electrical signal element that converts a change in some physical variable into a related
sensors
active element of a sensor
transducer
element that converts a change in some physical variable into a related
change in some other physical variable
transducer
Monitoring and control systems require sensors to measure physical
quantities such as (7) examples
position, distance, force, strain, temperature, vibration,
and acceleration.
used to open or close
connections within circuits
switch
switches responds to ____forces
applied to it
mechanical
- the parts of a switch that
opens and closes circuit
contacts
work as a pair, or a set, with
one moveable contact and
one stationary contact
contacts
the moveable contact in a switch
pole
the stationary contact in a
switch
throw
draw the switch with its parts
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one moveable contact
single pole switch
–two moveable
contacts operating together
double pole switch
– one position in
which each pole closes a set of
contacts or completes a circuit
single-throw switch
–two positions in
which each pole makes contact and
completes a circuit
double throw switch
drawing of the ff:
single pole to triple pole, single throw to double throw (6)
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usually either single break or double break
break
drawing of single break
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drawing of double break
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5 common examples of switch
toggle switch
knife switch
mercury switch
snap-action switch
reed switch
used in lighting
controls
toggle switch
consists of hinged
metal blades and metal clips into
which the blades fit
knife switch
closed by liquid
mercury completing a circuit
between a set of fixed contacts
mercury switch
used for
limit switches
snap-action switch
closes when a
magnetic field is near
reed switch
Sensors that provide information in the form of electrical resistivity of
a material (Flammini and Depari, 2017)
resistive sensors
Electrical Resistance formula (2)
R=pL/A
R= Ri(1+(alphadeltaT))
5 Common Examples of Resistive Sensors
potentiometer
strain gauge
thermistor
light-dependent resistor
resistive gas sensor
–used for position sensing
* Rotary and linear
potentiometer
used for measuring force
strain gauge
– used for measuring
temperature
thermistor
– used for light detection
light dependent resistor
– used for detecting presence/concentration
resistive gas sensor
- detect a change in capacitance when something or someone approaches or touches the sensor
capacitive sensors
- Changes in capacitance cause changes in the ______ properties of a circuit that can be detected
electrical
Capacitance Formula
C=Ea/d
8 Common Applications of Capacitive Sensors
- Flow sensing
- Pressure sensing
- Liquid level detection
- Spacing detection
- Thickness measurement
- Limit switch
- Accelerometers
- Humidity detection
convert light rays into electronic signals
optical sensors
2 points of optical sensors
transmitting point
receivng end
Two points:
1. _______ – emits light
2. _______– receives light emitted by the transmitting point
Transmitting point
Receiving end
Light can travel through or be reflected by the object being measured
and the ___of light received by the receiving end is assessed.
quality
Common Parameters Measured examples
- Temperature
- Pressure
- Flow
- Liquid level
*Displacement - Vibration
- Rotation
- Magnetic fields
- Acceleration
- Force
- Radiation
- pH
*Humidity - Strain
- Velocity
- Electric fields
- Acoustic fields
- Sensors that produce current or
voltage difference when exposed
to temperature changes
Thermoelectric Sensors
formula for thermoelectric sensors (V=)
V=alpha*(T1-T2)
Thermoelectric Sensors takes advantages of
Seebeck effect
When two wires are joined and connected at both ends, a _____ is generated as a response to a difference in temperature across the two points.
potential difference
Another formula for V in thermoelectric sensor
V=(Sm1-Sm2)Th
Measures temperature
difference between two points
thermocouple
a reference temperature at one
junction must be determined to
know the temperature being
measured
thermocouple
Thermocouple Use ____, or ____ temperature detector as basis
thermistor
resistance
For rugged applications
Thermocouple
Thermocouple formula for Vopen-circuit
Vopen-circuit= (Sm1-Sm2)Th - (Sm1-Sm2)Tc
have made a tremendous contribution towards mechanizing and
automating many agricultural and food processing operations
Control Systems
In control systems,
* better ___ and __ are obtained
* can safely and accurately control ___
* well-suited to work with ____systems
accuracy and reliability
equipment
computer-controlled
the controlling device operates
independently of the process
variable it controls
Open-loop Control System
2 Classification of Control Systems
Open-loop Control System
Close-loop Control System
the main characteristic of this
type of system is that an
operator is required to oversee
the operation
Open-loop Control System
An operator must be available
at the appropriate times to start
and stop the system
Open-loop Control System
flowchart of Open-loop Control System
input –> controller –> process –> output
the switching function is done
automatically by devices
sensing the process
variable(s)
Close-loop Control System
uses sensors and feedback
to automatically control
devices
Close-loop Control System
drawing of Close-loop Control System
input –> controller –> process –> output
but with feedback loop attached to switch between input and controller . then putput
