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Sensors
 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.
Tip
Sensors can automatically enter data
into a computer system, removing the
need for a human to manually enter
the data.
They can be very beneficial as it can
increase the accuracy of the data by
removing the possibility of human
error.
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Key Terms
Sensor: a device that records data about
the surrounding physical environment
Input device: a device that allows data to
be entered into a computer system
Analogue: this is the smooth stream of
data that we process on a daily basis
Microprocessor: an integrated circuit used
in monitoring and control technologies
Actuator: this is a type of motor that
controls a mechanism or system
Infrared: a wave of light emitted by an
object that is invisible to the naked human
eye
Microwave: an electromagnetic wave of
energy Piezoresistance: a specific level of
electrical charge that is linked to a specific
level of resistance or pressure
Humidity: the amount of water in the
atmosphere Photoresistor: a light
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Sensors
 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.
Remember
 Control technologies use
sensors to automatically
control elements of a system,
or a whole system, by using
the data from them to trigger
an action or event.
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Sensors
 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 to trigger any
action that needs to be taken.
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Start
Light sensor
takes reading
Analogue data
converted to digital
value
Value sent to
microprocessor
Microprocessor
compares value to
a pre-set range
N
Is value
in range?
Y
Signal sent to
actuator to turn
street light on.
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Sensors
 A real-life example of a control technology in
operation would be an automated street light.
This may include the following stages:
 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-set range.
 If the value is outside the pre-set range,
the microprocessor sends 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.
 We can represent this as a flowchart:
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Start
Light sensor
takes reading
Analogue data
converted to digital
value
Value sent to
microprocessor
Microprocessor
compares value to
a pre-set range
N
Is value
in range?
Y
Signal sent to
actuator to turn
street light on.
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Sensors
 This is an example of a control system at work. It is a control system as an
action, is triggered 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.
 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 then 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.
 There are a range of different sensors that we need to be able to define. We
also need to describe how they are used in monitoring and control
technologies and evaluate using these technologies in our everyday lives.
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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.
 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.
 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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Motion sensors
 Motion sensors are not error proof and
can sometimes cause a false alarm to
sound.
 Motion sensors can be used in lots of
other monitoring and control systems.
These include:
 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 carpark.
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Figure 3.01 - Passive infrared
sensor in a security system.
Click Here
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Task
Find out how passive and active motion sensors
can be combined to create a security system
that is less prone to error.
Motion sensors
 Motion sensors are not error proof and can
sometimes cause a false alarm to sound.
Discussion Point
 By using motion detectors in various ways a
business can be made more environmentally
friendly.
 Using motion sensors, a business can make
sure that lights are only turned on when a
person is working in a room and they can
also make sure that no water is left running.
Why could this be important to a business?
Figure 3.02 - CCTV security
cameras.
Figure 3.03 - A car park
barrier.
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Pressure sensors
 Pressure sensor measures pressure, normally of a
liquid or 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
Figure 3.04 - A nuclear plant.
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.
 Pressure sensors can be used in many different monitoring and control
technologies. These include:
 The vehicle industry. They are used to form part of the safety system of a
vehicle. Pressure sensors are used to monitor the oil and coolant in the
vehicle. They are used to regulate the power given to the engine based on the
pressure placed on the accelerator and brake. The airbag safety system also
uses pressure sensors. The air bags will be triggered to inflate when a high
amount of pressure is applied to certain parts of the vehicle.
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Pressure sensors
 Chemical and nuclear plants. They are used to
monitor and control the flow of gases and liquids in
industrial plants. This means that substances that
are being transported in the plant, or any chemical
reactions that are carried out, are done extremely
safely. This makes sure that a high level of safety is
maintained in the industrial plant at all times.
 Aviation and marine industry. They are used to
monitor and control the atmosphere within an aero
plane or submarine. This is to make sure that the
correct breathing conditions are maintained.
 Touch screens. A touch screen that uses pressure
sensors is built up of multiple layers. When pressure
is applied to the top layer of the screen it is pushed
into the bottom layer of the screen, creating a
connection that generates an electrical signal. This
electrical signal informs the device of the location
where the pressure has been applied to the screen.
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Discussion Point
Pressure sensors
are used extensively
in industrial plants.
How would safety
change within the
plant if pressure
sensors could not be
used and why does
this make them
important?
Task
Find out how
pressure sensors
are used in traffic
control systems.
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Moisture and humidity sensors
 Meteorological stations. They are used to help monitor
and predict weather conditions by measuring humidity
levels.
 Controlling allergies. An atmosphere that is high in
humidity can encourage the growth of bacteria and
mould. This can trigger allergies. Humidity sensors can
be used to monitor and control the level of humidity in a
room.
 Manufacturing. In the manufacturing of many products
the level of moisture in the atmosphere is very important.
If humidity is too high or too low it could adversely affect
the product.
 Agriculture and farming. Humidity and moisture sensors
can be used to grow and farm crops in the best conditions
possible. By monitoring and controlling the conditions in
which the crops are grown, the most perfect conditions
can be created, producing the best crops. The level of
moisture in the soil can be kept constant to help the crops
grow.
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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. A
temperature sensor is used in a washing
machine and a dishwasher to measure
the temperature of the water.
A microprocessor in the washing machine
or dishwasher will receive the data sent
by the temperature sensor and can trigger
an action to heat up or cool down the
water if necessary.
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Temperature sensors
 Dryer. A temperature sensor is used in a
dryer to measure the temperature of the
hot air flowing into the dryer. A
microprocessor in the dryer will receive
the data sent by the temperature sensor
and can trigger an action to heat up or
cool down the air if necessary.
 Refrigerator and freezer. A temperature
sensor is used in a refrigerator or freezer
to measure the ambient temperature
inside. A microprocessor in the
refrigerator or freezer will receive the
data sent by the temperature sensor and
can trigger an action to heat up or cool
down the air if necessary.
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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
photo-resistor. This type of light sensor will
change its resistance when light shines on and
is normally used to measure the intensity of
Figure 3.06 - A digital camera.
light.
 This is important in devices such as digital
Task
cameras or street lights. The camera can adjust
the level of flash needed depending on the level Research at least
of light currently detected by the light sensor.
two other types of
 A street light can detect when it gets dark
sensor and explain
enough to need to switch the light on.
now they can be
 Light sensors can be used in many different
used in a monitoring
devices 'eluding barcode scanners, display
screens, automated lighting systems and
and control system.
smartphones.
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Sensors & their uses
 Sensors are used in a wide variety of monitoring
and control systems. These systems are part of
our everyday lives, from helping us cross the road
safely, to making sure our clothes are washed
properly.
 The use of sensors in computer systems can benefit
us greatly. This remove the need for a human to
monitor and measure an environment as this can be
done continuously by the sensor. This can leave us
to get on with other tasks that we to complete. It can
also mean that the monitoring and measuring is more accurate.
 For a human to complete a repeated action, e.g. taking a reading over and
over for long periods of time,
 This can be very arduous and it may prove difficult to maintain accuracy. A
computer system that has a sensor that can perform this role is able to run
for long periods of time, with a high level of accuracy. This level of accuracy
can make a system more reliable than one operated by humans.
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 By using a sensor or a number of sensors in a
monitoring or control system, multiple readings can
be taken in quick succession. It would require people
to perform the same function, and so these people
can be made available to perform other tasks.
 The computer system will make decisions based on
Remember
the data it is given. It will act logically on these
 A computer system
decisions in the way it has been programmed.
using sensors can
 This can be beneficial as the decisions made and
operate 24 hours a
actions taken will be consistent. If a human performed
day, 365 days a
the same decision-making process, external factors
year, meaning that
may affect the decision they make, e.g. how tired they
monitoring can be
are. This could cause inconsistency in the decisiondone on a continual
making process and actions taken.
basis.
 This can sometimes be a disadvantage and a
 It can also remove
the possibility of
computer system may not be able to react to an
human error in the
unexpected event that a human would be able to
measurements.
assess and make a decision about.
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 Sensors are also extremely beneficial for use in
environments that are dangerous to humans.
This means that we can be kept safe yet
dangerous environments can still be monitored.
 Also, computers can process data much more
quickly and respond faster to any necessary
actions than a human, so a dangerous
environment can be monitored and controlled
more effectively.
 There is always a risk involved in using
computer systems in monitoring and control.
The system is electronic and if a power failure
occurs, the system will not operate. If the
system is controlling a crucial process, this
could have a detrimental effect. This could also
happen with a simple system malfunction.
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 A sensor is an input device that records data about the surrounding
physical environment. Sensors are used in monitoring and control
technologies. They monitor the surrounding environment and trigger
any events that need to occur to control a process.
 A monitoring system uses sensors to take readings and mostly
outputs them in graphs and charts, or a simple print out. A control
system uses sensors to take readings and an action can be triggered
if a reading is, for example, outside an acceptable range.
 There are a wide range of sensors used in monitoring and control
systems. These include motion sensors, pressure sensors, moisture
and humidity sensors, temperature sensors and light sensors. There
are a number of other sensors that you may have researched
including sound sensors and gas sensors.
 The use of monitoring and control systems can be very beneficial.
They can keep us safe from the need to monitor dangerous
environments and they can carry out monitoring on a more
continuous basis, as well as having a higher degree of accuracy.
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?
Questions
1. Define the term sensor.
[2]
2. Describe two types of sensor that can be
used in a security system.
[4]
3. Explain two benefits of using sensors to
monitor the environment in a nuclear plant. [4]
4. Evaluate the use of monitoring and control
systems in household appliances.
[6]
5. Explain how a monitoring and control system
could be used to create an environmentally
friendly office building.
[4]
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Answers
1. Any combination of the following [2]:
• An input device that records data about the environment or
surroundings.
• Automatically inputs the data into a computer system to be
processed.
• Can monitor a range of aspects such as light, temperature,
pressure, moisture and humidity.
2. Any two of the following [4]:
• An infrared (motion) sensor can be used ...
• ... monitors infrared energy emitted and can detected an
increase from an intruder.
• A pressure sensor (switch) can be used ...
• ... can sense a change in weight of an intruder entering a
building.
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Answers
3. Any two from the following [4]:
 Sensors can be placed in areas that are dangerous for a
human to enter...
 ... this means that crucial elements of the system, such as
areas of radiation, can be measured and controlled from a
safe distance.
 Sensors can take readings 24/7 ...
 ... this means that humans do not need to be present in the
plant at all time to monitor processes and can just be alerted
to a crisis situation, should one arise.
 Sensor readings will have a higher level of accuracy and
consistency...
 ... in an environment where the accuracy of readings is
paramount due to safety, this is vital.
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Answers
4.
Level of response: Level 3 [5-6 marks]
Candidates will address a range of household appliances and evaluate their use in
terms of monitoring and controls systems. The points raised will be justified. There
will be a reasoned conclusion. The information will be relevant, clear, organised and
presented in a structured and coherent format.
Level 2 [3-4 marks]
Candidates will address a limited range of household appliances and look at their
use in terms of monitoring and controls systems, although development of some of
the points will be limited. There will be a conclusion. For the most part the
information will be relevant and presented in a structured and coherent format.
Level 1 [1-2 marks]
Candidates may only give reference to a single household appliance, with limited
reference to monitoring and control systems. Answers may be simplistic with little or
no relevance.
0 marks for a response with no valid comments.
Possible points:

Increased safety for appliances.

Appliances can be made more efficient.

It may be possible to remotely control devices.
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Answers
5. Any combination of the following [4]:
 Motion sensors could be used to control light systems...
 ... this would mean that lights would turn off
automatically when a room is unused, making it more
energy efficient.
 Temperature sensors could be used to control the air
conditioning system ...
 ... the system could be turned off when the room reaches
the desired temperate and turned back on again when it
falls outside of this, making it more energy efficient.
 Pressure sensors could be used on windows ...
 ... this would detect if a window is open and turn off an
air conditioning system to save energy if it is.