Sensors are input devices that record data about the surrounding environment. There are many different types of sensors that are used in monitoring and control technologies, including motion sensors, pressure sensors, moisture/humidity sensors, temperature sensors, and light sensors. Sensors work by collecting analog data, converting it to digital signals, and sending the data to a microprocessor for processing. The microprocessor then compares the sensor readings to preset values and can trigger an output or action if the readings are outside acceptable ranges. Common applications of sensors include security systems, scientific experiments, manufacturing processes, and home appliances.

1. Chapter 3
Monitoring and Control
Cambridge International AS and A Level IT
Anjan Mahanta
anjan.mahanta@satreephuketipc.com

2. Learning Objectives
● Identify a range of different sensors
● Describe how sensors are used in monitoring and control
technologies
● Evaluate using monitoring and control technologies in
everyday life
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3. SENSORS
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4. SENSORS
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● A sensor is an input device that records data about the
surrounding physical environment.
● The sensor inputs this data into a computer system to be
processed.
● Once the data has been processed, if necessary, an output
can be triggered as a response.

5. SENSORS
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6. SENSORS
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● Using sensors can also be very beneficial in environments that could be harmful
and dangerous for a human, for example in a nuclear plant to detect radiation
levels, or inside an active volcano to detect changes in activity.
● Monitoring and control technologies make use of many different sensors.
● Monitoring technologies use sensors to monitor an environment, often
collecting data about the environment.

7. SENSORS
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● The basic concept behind most monitoring and control systems is very similar.
They will normally go through the following steps:
● The sensor will constantly monitor the surrounding environment
● The data readings from the sensor will normally be analogue. Therefore, they will
be converted to a digital signal for a computer system to process. This is done
by an analogue to digital converter
● The digital signal is then sent to a microprocessor. The microprocessor
processes the value and compares it to a pre-set value or range of values
● If the value is outside the acceptable range, the microprocessor will send a
signal to an actuator t o trigger any action that needs to be taken.

8. EXAMPLE
● A light sensor will constantly monitor the level of light present in the
surrounding environment.
● The analogue data from the reading will be converted to a digital value by an
analogue to digital converter.
● The digital signal is sent to a microprocessor and the microprocessor will
compare the value to a pre-setrange.
● If the value is outside the pre-set range, the microprocessors ends a signal to
an actuator that will trigger the action to turn the street light on or off.
● The whole process will then be repeated.
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9. FLOWCHART
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10. SENSORS
● This is an example of a control system at work. It is a control system as an
action is to control an element of the system as a result of the monitoring that
is taking place. A monitoring system outputs results in a different way.
● Rather than an action being triggered, the results of the readings taken from
the monitoring can be output in the form of graphs or charts.
● This allows the readings to be compared and any patterns or trends to be
identified.
● This information can then be used to inform any future decision making.
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11. SENSORS
● Monitoring systems can be used in scientific experiments. The experiments are
often left to run for periods of time, with a monitoring system taking readings at
regular intervals.
● The readings are then output and can be analysed. This kind of technology
removes the need for a human to regularly take the readings.
● This means that the readings can be taken over long periods of time and can
often be more accurate if taken by a system.
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12. MOTION SENSORS
● A motion sensor detects movement. It can do this either passively or actively.
● A passive motion sensor reads the energy in its surrounding environment and
detects changes caused by movement.
● An active motion sensor emits energy into the surrounding environment to detect
any movement.
● An example of a passive motion sensor is a passive infrared sensor. This is a
sensor that detects the presence of infrared energy if it appears in its surrounding
environment. An example of an active motion sensor is a microwave sensor.
● This is a sensor that emits microwaves and detects the changes in the reflection it
receives back when bouncing off nearby objects.
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13. PASSIVE INFRARED SENSORS
● Passive infrared sensors are commonly used in
security systems. These sensors are normally
wall mounted in the corner of a room. As an
intruder walks in front of a sensor, the sensor
detects the infrared energy emitted by the
intruder.
● The detection of infrared energy by the sensor
can then trigger an alarm to sound.
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14. ACTIVE INFRARED SENSORS
● Active motion sensors can also be used in
security systems.
● A microwave sensor continuously emits
microwaves into a room.
● As an intruder walks through the microwaves,
they will be reflected back much more quickly
to the sensor and it will detect the change.
● This change in reflection of the microwaves can
then cause an alarm to sound.
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15. USE OF MOTION SENSORS
● CCTV systems, to manoeuvre the camera
to the direction of motion that is detected
● Opening and closing automatic doors
● Automatically turning lights on or off in a
room when a person enters or leaves
● Automatically turning water taps on or off
● Automated barriers in a car park.
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16. Discussion
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17. PRESSURE SENSORS
● A pressure sensor measures pressure, normally of a liquid or a gas. The
measure of pressure is based upon the force it takes to stop a liquid or gas
from expanding.
● Most modern pressure sensors use a principal called piezoresistance. In
piezoresistance, a specific level of pressure is linked to a specific level of
charge through a substance.
● If a change in the level of charge is detected, this is interpreted as a change in
pressure.
● Pressure sensors can be used in things such as pipes to measure the flow of
liquid or gas through them, to make sure they do not flow too quickly.
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18. PRESSURE SENSORS
● Pressure sensors can be used in many different monitoring and control
technologies. These include:
● The Vehicle Industry
● Chemical and nuclear plants
● Aviation and marine industry
● Touch screens
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19. DISCUSSION
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20. MOISTURE & HUMIDITY SENSORS
● Humidity sensors monitor and measure the humidity that is in the air.
● To monitor the humidity they measure both the moisture and temperature in
the air.
● The percentage of moisture present in the air at a certain temperature is
expressed as the level of humidity. Humidity sensors normally use capacitive
measurement.
● This type of measurement uses two electrical conductors that have a
non-conductive film separating them.
● Moisture collects on the film and changes the level of voltage between the
electrical conductors.
● The measurement of the change in voltage is converted into a measurement of
humidity. 20

21. MOISTURE & HUMIDITY SENSORS
● Humidity sensors can be used both in the home and the workplace to monitor
and control humidity levels, including:
● Wine cellars
● Meteorological stations
● Controlling allergies
● Manufacturing
● Agriculture and farming
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22. TEMPERATURE SENSORS
Temperature sensors monitor and measure the temperature of an environment.
They do this by measuring how much heat is present. Temperature sensors are
used in a great number of control systems, many of them in our home appliances.
These include:
● Washing machine and dishwasher
● Dryer
● Refrigerator and freezer
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23. TEMPERATURE SENSORS
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24. LIGHT SENSORS
● Light sensors monitor and measure light. There are different types of light sensor
and they measure light in different ways.
● The most common type of light sensor is a photoresistor. This type of light
sensor will change its resistance when light shines on and is normally used to
measure the intensity of light.
● This is important in devices such as digital cameras or street lights. The camera
can adjust the level of flash needed depending on the level of light currently
detected by the light sensor.
● A street light can detect when it gets dark enough to need to switch the light on.
● Light sensors can be used in many different devices including barcode scanners,
display screens, automated lighting systems and smartphones. 24

25. TASK
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26. TASK
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