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Chapter 3
Monitoring and control- I
Learningobjectives
By the endof this chapter, you willbe able to:
m identify a range of different sensors
describe how sensors are used in monitoring and control technologies
evaluate usingmonitoringand control technologies in everyday life
w
Chapter 3: Monitoring and control
3.01Sensors • The sensorwill constantly monitorthe surroundingenvironment
• The data readings from the sensorwill normally beanalogue. Therefore, they will be converted to a digitalsignal for a computer system to process. This is donebyan analogue to digital converter
• The digital signal is then sent to a microprocessor. Themicroprocessor processes the value and compares it to
a pre-set value or range of values
• If the value is outside the acceptable range, themicroprocessor will send a signal to an actuator to
trigger any action that needs to be taken.
A real-life example of a control technology in operationwould be an automated street light. This may include thefollowingstages:
• A light sensor will constantly monitorthe level of lightpresent in the surroundingenvironment.
• The analogue data from the readingwill be converted to
a digital value by an analogue to digital converter.
• The digital signal is sent to a microprocessor and themicroprocessor will compare thevalue to a pre-set range.
• If the value is outside the pre-set range, themicroprocessor sends a signal to an actuator that willtrigger the action to turn the street light on or off.
• The whole process will then be repeated.
We can represent this as a flowchart:
Sensor: a device that records data about the surroundingphysical 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 processon a daily basis
Microprocessor: an integrated circuit used in monitoringandcontrol technologies
Actuator: this is a type of motor that controls a mechanism orsystem
Infrared: a wave of light emitted by an object that is invisibleto the naked human eye
Microwave: an electromagnetic wave of energy
Piezoresistance: a specific level of electrical charge that islinked to a specific level of resistance or pressure
Humidity: the amount of water in the atmosphere
Photoresistor: a light controlled resistor
A sensor is an input device that records data about thesurroundingphysical environment. The sensor inputs thisdata into a computer system to be processed. Once thedata has been processed, if necessary, an output can betriggered as a response.
©TIP
StartSensorscan automatically enter data into a computer system,
removingthe needfor a human tomanually enterthedata.They canbeverybeneficial asitcan increase the accuracy ofthedata by removingthe possibility ofhumanerror.
Light sensor takesreading
Usingsensors can also be very beneficial in environments
that could be harmful and dangerous for a human, forexample in a nuclear plant to detect radiation levels, orinside an active volcano to detect changes in activity.
Monitoring and control technologies make use of manydifferent sensors. Monitoring technologies use sensors to
monitor an environment, often collecting data about the
environment.
Analogue data convertedto digital value
Value sent tomicroprocessor
Q Microprocessor comparesvalue to a pre-set range
RememberControl technologies use sensors to automatically controlelements of a system,or a wholesystem, by usingthedata from them to trigger an action or event.
Is value inrange?
Signal sent to actuator toturn street light on/off
The basic concept behind most monitoringand controlsystems is very similar. They will normally go through thefollowingsteps:
i— N Y
Cambridge International AS and A level IT
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 thesystem as a result of the monitoringthat is taking place. A
monitoringsystem outputs results in a different way. Rather
than an action being triggered, the results of the readingstaken from the monitoringcan beoutput in the form of
graphs or charts.This allows the readings to be comparedand any patterns ortrends to be identified. This information
can then be used to inform any future decision making.
Monitoringsystems can be used in scientific experiments.
The experiments are often left to run for periods of time,
with a monitoring system taking readings at regularintervals. The readings are then output and can beanalysed. This kind of technology removes then need for a
human to regularly take the readings. This means that thereadings can be taken over longperiods of time and can
often be more accurate if taken by a system.
There are a range of different sensors that we need to beable to define. We also need to describe how they are
used in monitoringand control technologies and evaluateusing these technologies in our everyday lives.
Motion sensors are not error proof and can sometimescause a false alarm to sound.
mFigure 3.01- Passive infrared sensor in a security system.
TASK
Find out how passive and active motion sensors can becombined to create a security system that is less proneto error.
Motion sensorsA motion sensor detects movement. It can do this eitherpassively or actively. A passive motion sensor readsthe energy in its surroundingenvironment and detectschanges caused by movement. An active motion sensor
emits energy into thesurroundingenvironment to
detect any movement. An example of a passive motion
sensor is a passive infrared sensor. This is a sensor thatdetects the presence of infrared energy if it appears in its
surrounding environment. An example of an active motionsensor is a microwave sensor. This is a sensor that emits
microwaves and detects the changes in the reflection it
receives back when bouncingoff nearby objects.
Passive infrared sensors are commonly used in securitysystems. These sensors are normally wall mounted in thecorner of a room. As an intruder walks in front of a sensor,the sensor detects the infrared energy emitted by theintruder. The detection of infrared energy by the sensorcan 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 throughthe microwaves, they will be reflected back much more
quickly to the sensor and it will detect the change. Thischange in reflection of the microwaves can then cause an
alarm to sound.
Motion sensors can be used in lots of other monitoringand control systems. These include:
• CCTV systems, to manoeuvre the camera to the directionof motion that is detected
• openingand closing automatic doors
• automaticaltyturninglightsonoroffin a room when a
person enters or leaves
• automatically turningwater taps on or off
• automated barriers in a car park.
m ma
' V
Figure 3.02 - CCTV security cameras.
Chapter 3: Monitoring and control
H.i• Chemical and nuclear plants. They are used to monitor
and control the flow of gases and liquids in industrialplants. This means that substances that are beingtransported in the plant, or any chemical reactions thatare carried out, are done extremely safely. This makessure that a high level of safety is maintained in theindustrial plant at all times.
• Aviation and marine industry. They are used to monitor
and control the atmosphere within an aeroplaneor submarine. This isto make sure that thecorrect
breathingconditions are maintained.
• Touch screens. A touch screen that uses pressuresensors 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,creatinga connectionthat generates an electrical signal. This electrical signalinforms the device of the location where the pressure
has been applied to the screen.
r
Figure 3.03 - A car park barrier.
DISCUSSION POINT
By usingmotion detectors in various ways a business can
be made more environmentally friendly. Usingmotion
sensors, a business can make sure that lights are only
turned on when a person is workingin a room and they can
also make sure that no water is left running. Why could this
be important to a business?
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 themimportant?
Pressure sensorsA pressure sensor measures pressure, normally of a liquidor 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 calledpiezoresistance. 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.
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 usedto 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 highamount of pressure is applied to certain parts of thevehicle.
TASK
Find out how pressure sensors are used in traffic controlsystems.
S\
Figure 3.04 -A nuclear plant.
Cambridge International AS and A level IT
• Agriculture and farming. Humidity and moisture
sensors can be used to grow and farm crops in the bestconditions possible. By monitoring and controllingtheconditions in which the crops are grown, the most
perfect conditions can be created, producingthe bestcrops. The level of moisture in the soil can be keptconstant to help the crops grow.
Temperature sensorsTemperature sensors monitor and measure thetemperature of an environment. They do this bymeasuring how much heat is present. Temperaturesensors are used in a great number of controlsystems, many of them in our home appliances. Theseinclude:
Figure 3.05 - A submarine cockpit.
Moisture and humidity sensorsHumidity sensors monitor and measure the humiditythat is in the air. To monitor the humidity they measure
both the moisture and temperature in the air. Thepercentage 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 conductorsthat have a non-conductive film separating them.Moisture collects on the film and changes the levelof voltage between the electrical conductors. Themeasurement of the change in voltage is converted into a
measurement of humidity.
Humidity sensors can be used both in the home andthe workplace to monitor and control humidity levels,including:
• Wine cellars. The humidity level in the atmosphere ofa wine cellar is very important.Too much or too littlehumidity can cause the wine to spoil. The humidity levelneeds to be kept at a constant and correct level in orderto keep the wine at its best.
• Meteorological stations. They are used to help monitor
and predict weather conditions by measuringhumiditylevels.
• Controllingallergies. An atmosphere that is high inhumidity can encourage the growth of bacteria andmould.This can trigger allergies. Humidity sensors canbe used to monitor and control the level of humidity ina room.
• Manufacturing. In themanufacturingof many productsthe level of moisture in the atmosphere is very
important. If humidity is too high or too low it couldadversely affect the product.
• Washing machine and dishwasher. A temperature
sensor is used in a washingmachine and a dishwasherto measure the temperature of the water. A
microprocessor in the washingmachine or dishwasherwill receive the data sent by the temperature sensor andcan trigger an action to heat up or cool down the water
if necessary.
• Dryer. A temperature sensor is used in a dryer to
measure the temperature of the hot air flowing into thedryer. A microprocessor in the dryer will receive the datasent by the temperaturesensor and can trigger an actionto heat up or cool down the air if necessary.
• Refrigerator and freezer. A temperature sensor is usedin a refrigerator or freezer to measure the ambienttemperature inside. A microprocessor in the refrigeratoror freezer will receive the data sent by the temperature
sensor and can trigger an action to heat up or cool downthe air if necessary.
TASK
Can you think of any other appliances in your home thatmay use a temperature sensor as part of a monitoringand control system?
Light sensorsLight 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 aphotoresistor. This type of light sensor will changeits resistance when light shines on and is normally usedto measure the intensity of light. This is important in
Chapter 3: Monitoring and control
can make a system more reliable than one operated byhumans.
By using a sensor or a number of sensors in a monitoringor control system, multiple readings can be taken inquick succession. It would require people to performthe same function, and so these people can be madeavailable to perform other tasks. The computer system
will make decisions based on the data it is given. It willact logically on these decisions in the way it has beenprogrammed. This can be beneficial as the decisionsmade and actions taken will be consistent. If a humanperformed the same decision-making process, externalfactors may affect the decision they make, for examplehow tired they are. This could cause inconsistency inthe decision-making process and actions taken. This cansometimes be a disadvantage and a computer system
may not be able to react to an unexpected event thata human would be able to assess and make a decisionabout.
devices such as digital cameras or street lights. Thecamera can adjust the level of flash needed dependingon 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.
/f
Figure 3.06 - A digital camera.
Q Remember
A computer system usingsensors can operate 24hoursa day,365 days a year, meaning that monitoringcanbedone on a continual basis. It can also remove thepossibility of human error in the measurements.
Light sensors can be used in many different devicesincludingbarcode scanners, display screens, automatedlightingsystems and smartphones.
TASK
Research at least two other types of sensor and explainhow they can be used in a monitoringand controlsystem.
Sensors are also extremely beneficial for use inenvironments that are dangerous to humans. Thismeans that we can be kept safe yet dangerousenvironments can still be monitored. Also, computerscan process data much more quickly and respond fasterto any necessary actions than a human, so a dangerousenvironment can be monitored and controlled moreeffectively.
There is always a risk involved in using computersystems 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 crucialprocess, this could have a detrimental effect. This couldalso happen with a simple system malfunction.
Sensors are used in a wide variety of monitoringand
control systems. These systems are part of our everydaylives, from helping us cross the road safely, to makingsure our clothes are washed properly. The use of sensorsin computer systems can benefit us greatly. This removethe need for a human to monitor and measure an
environment as this can be done continuously by thesensor. This can leave us to get on with other tasks that we
need to complete. It can also mean that the monitoringand measuring is more accurate.
For a human to complete a repeated action, for exampletaking a reading over and over for long periods of time,
can be very arduous and it may prove difficult to maintainaccuracy. A computer system that has a sensor that
can perform this role is able to run for long periods oftime, with a high level of accuracy. This level of accuracy
3.02 Summary
A sensor is an input device that records data about thesurroundingphysical environment. Sensors are used in
monitoringand control technologies. They monitor thesurroundingenvironment and trigger any events that needto occur to control a process.
Cambridge International AS and A level IT
A monitoringsystem uses sensors to take readings andmostly outputs them in graphs and charts, or a simpleprintout. A control system uses sensors to take readingsand an action can be triggered if a reading is, for example,outside an acceptable range.
There are a wide range of sensors used in monitoringand
control systems. These include motion sensors, pressuresensors,moisture and humidity sensors,temperature
sensors and light sensors. There are a number of othersensors that you may have researched includingsoundsensors and gas sensors.
The use of monitoring and control systems can be verybeneficial. They can keep us safe from the need to
monitor dangerous environments and they can carry out
monitoringon a more continuous basis, as well as having ahigher degree of accuracy.
Review questions
1 Define the termsensor. [2]
2 Describe two types of sensor that can be used in a security system. [4]
3 Explain two benefits of usingsensors to monitor the environment in a nuclear
plant. [4]
4 Evaluate the use of monitoringand control systems in householdappliances. [6]
5 Explain how a monitoring and control system could be used to create an environmentally
friendly office building. [4]
D