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

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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.

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• 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.

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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