2. Sensors
Sensors are devices or
components that detect
and measure physical
properties or
environmental conditions
and convert this
information into electrical
signals or other readable
outputs.
3. Actuators
• Actuators are devices or
components that are
responsible for
converting control
signals or electrical input
into mechanical motion
or action. In essence,
they are the
counterparts to sensors.
4. A typical sensors-based control system
Mechanical/Physical
signal
Sensor
Electrical Signal
Actuator
Performed
action
6. Ultrasonic sensor
• An HC-SR04 ultrasonic distance sensor
actually consists of two ultrasonic
transducers.
• One acts as a transmitter that converts
the electrical signal into 40 KHz
ultrasonic sound pulses. The other acts
as a receiver and listens for the
transmitted pulses.
• This sensor provides excellent non-
contact range detection between 2 cm
to 400 cm (~13 feet) with an accuracy of
3 mm.
7. Ultrasonic sensor
• At first, the trig pin stays high for 10
microseconds and the sensor transmits a 40
kHz signal from the transmitter.
• As the sound is sent, the echo pin becomes
high and stays high until it receives the
ultrasonic signal back.
• When the receiver receives the reflected
ultrasonic sound signal, it immediately
becomes low.
• This generates a pulse on the echo pin
whose width varies from 150 µs to 25 ms
depending on the time taken to receive the
signal.
• The microcontroller calculates the time
difference between the trig pin signal and
echo pin signal.
• The distance of the object or the surface can
be calculated through the following formula:
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 × 𝑇𝑖𝑚𝑒
2
8. Ultrasonic sensor
• The microcontroller calculates the time
difference between the trig pin signal
and echo pin signal.
• The distance of the object or the surface
can be calculated through the following
formula:
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 × 𝑇𝑖𝑚𝑒
2
• If a signal is not received by the receiver,
the echo pin stays high for 38
microseconds, and then goes low.
• This means there is no obstruction in
front of the ultrasonic sensor.
9. Flame sensor
• The IR flame sensor detects flame by detecting
the IR ray from the fire.
• The main detection is performed by the
phototransistor.
• When light between 760 nm to 1100 nm
wavelength range hit the phototransistor, the
resistance of it decreases.
• As a result, voltage across it also decreases.
• The LM393 comparator integrated circuit
compares this voltage with the threshold voltage.
• As the voltage across phototransistor is lower
than the threshold voltage in this situation, the
sensor output goes low.
• On the other hand, when the phototransistor do
not detect any IR ray, its resistance increases.
• Hence more voltage is given to the comparator
circuit.
• As in this case, input voltage is more than the
threshold voltage, the sensor output goes high.
10. Humidity sensor
• The components of the temperature and humidity sensor
module mainly include a humidity-sensitive capacitor and a
conversion circuit.
• The humidity-sensitive capacitor comprises a glass substrate,
a lower electrode, a humidity-sensitive material, and an upper
electrode.
• Humidity-sensitive material is a kind of high molecular
polymer; its dielectric constantly changes with the relative
humidity of the environment. When the environmental
humidity changes, the capacitance of the humidity-sensitive
element changes accordingly.
• When the relative humidity increases, the humidity-sensitive
capacitance increases, and vice versa.
• The conversion circuit of the sensor converts the change in
humidity-sensitive capacitance into a change in voltage, which
corresponds to a relative humidity shift of 0 to 100% RH. The
output of the sensor shows a linear shift of 0 to 1v.
11. Light-dependent resistor
• The LDR sensor contains cadmium sulphide.
• In the dark, it has a resistance of 1 Mega
Ohm and electricity can not pass through
the sensor.
• In presence of light, the resistance
decreases and the electricity can pass
through the sensor.
• From this resistance variance, light intensity
is sensed by LDR.
12. Smoke Detector
• There are three types of smoke detectors:
• Photoelectric detectors
• Ionization detectors
• Dual sensor detectors
1. Photoelectric Detector:
In a photoelectric detector, whenever
smoke enters, it disrupts the path of a
laser. As a result, the sensor triggers the
alarm.
This type of smoke detectors are better
at detecting the slow burning fires.
13. Smoke Detector
2. Ionization Detector:
Ionization detectors use two electrically
charged plates to ionize the air in the
sensor. When smoke enters the detector
it disrupts the flow of ion and triggers
the alarm. laser. As a result, the sensor
triggers the alarm.
These are stronger in detecting fast
flaming fires. However, due to their
design they can be triggered by dust and
steam.
14. Smoke Detector
2. Dual sensor detector:
This type of smoke detectors use both
photoelectric and ionization smoke
detecting mechanism.
15. Actuator
• Actuators are devices or components that are responsible for
converting control signals or electrical input into mechanical
motion or action. In essence, they are the counterparts to
sensors.
• Types of actuator:
a) Hydraulic actuator
b) Pneumatic actuator
c) Electrical actuator
16. Hydraulic
Actuator
• When a large amount of force is
required to operate a valve (for example,
the main steam system valves), hydraulic
actuators are normally used. A typical
piston-type hydraulic actuator is shown in
Below Figure. It consists of a cylinder,
piston, spring, hydraulic supply and return
line, and stem.
• The piston slides vertically inside the
cylinder and separates the cylinder into
two chambers. The upper chamber
contains the spring, and the lower
chamber contains hydraulic oil.
17. Hydraulic
Actuator
• The hydraulic supply and return
line is connected to the lower
chamber and allows hydraulic
fluid to flow to and from the
lower chamber of the actuator.
The stem transmits the motion of
the piston to a valve.
• Initially, with no hydraulic fluid
pressure, the spring force
holds the valve in the closed
position. As fluid enters the
lower chamber, pressure in the
chamber increases.
18. Hydraulic
Actuator
• This pressure results in a force on
the bottom of the piston opposite to
the force caused by the spring. When
the hydraulic force is greater than the
spring force, the piston begins to
move upward, the spring
compresses, and the valve begins to
open.
• As the hydraulic pressure
increases, the valve continues to
open. Conversely, as hydraulic oil
is drained from the cylinder, the
hydraulic force becomes less than
the spring force, the piston moves
downward, and the valve closes.
By regulating amount of oil
supplied or drained from the
actuator, the valve can be
positioned between fully open and
19. Hydraulic
Actuator
• The principles of operation of a
hydraulic actuator are like those
of the pneumatic actuator. Each
uses some motive force to
overcome spring force to move
the valve. Also, hydraulic
actuators can be designed to fail-
open or fail-closed to provide a
fail-safe feature.
20. Hydraulic Actuator
•Advantages
1. Hydraulic actuators are rugged and
suited for high force applications. They
can produce forces 25 times greater than
pneumatic cylinders of equal size. They
also operate in pressures of up to 4,000
psi.
2. A hydraulic actuator can hold force and
torque constant without the pump
supplying more fluid or pressure due to
the incompressibility of fluids.
3. Hydraulic actuators can have their
pumps and motors located a considerable
distance away with minimal loss of power.
•Disadvantages
1. Hydraulics will leak fluid. Like pneumatic
actuators, loss of fluid leads to less
efficiency and cleanliness problems
resulting in potential damage to
surrounding components and areas.
2. Hydraulic actuators require many
complementary parts, including a fluid
reservoir, motor, pump, release valves,
and heat exchangers, along with noise
reduction equipment.
21. Pneumatic
Actuator
• A pneumatic actuator operates
in a way that it converts the
pressurized air applied to it into
displacement. The two major
units of these actuators are piston
and diaphragm. It can be two
types:
• Linear
• Rotary
24. Electrical Actuator
Electrical actuators are devices that convert electrical energy into a mechanical force or
kinetic energy, capable of causing movements in a part of an appliance. They are typically
used to control the movement of valves, pumps, gates, dampers, and other types of
equipment or machinery.
Examples of electrical actuator:
1. DC Motor, AC Motor, Pumps, Stepper Motor, Servo motor, etc.
25. Hydraulic
Actuator
• The principles of operation of a
hydraulic actuator are like those
of the pneumatic actuator. Each
uses some motive force to
overcome spring force to move
the valve. Also, hydraulic
actuators can be designed to fail-
open or fail-closed to provide a
fail-safe feature.
26. Smoke Detector
2. Dual sensor detector:
This type of smoke detectors use both
photoelectric and ionization smoke
detecting mechanism.
27. Smoke Detector
2. Dual sensor detector:
This type of smoke detectors use both
photoelectric and ionization smoke
detecting mechanism.
