Mr Stevenson's Computer Science Classroom

Control - M Brooke

Topic 7 - Control - Student Booklet

Control

By M Brooke

Centralized control systems

Key Terms

Control systems
Microprocessor
Sensor
Input devices
Processor
Output transducer
Feedback

A computer control system is like many other systems and is made up of three parts:

7.1.1 Discuss a range of control systems.

Centralised control systems use a computer/processor/microchip to control the movement of an object. Control systems exist in all areas of life such as:

Automatic doors, heating systems, taxi meters, elevators, washing machines, process control, device drivers, domestic robots, GPS systems, traffic lights,

7.1.2 Outline the uses of microprocessors and sensor input in control systems.

The role of microprocessors in control

The role of computers in control have several advantages and disadvantages.

Pros

Computers can respond very rapidly to change.
Systems can run 24 hours a day, 365 days a year.
Control systems can operate in places that humans would find dangerous or awkward.
Outputs are consistent and error free.
Computers can process data quickly and machines can operate faster than humans.

Cons

The software for the control system is specialist and may cost a lot of money to develop
If the computer malfunctions the system will not work
If there is a power cut the system will not work
The computer can’t react to unexpected events like a human could. It can only respond in the way it has been programmed to.
It can cause some concern if total control for a system and the decisions are handed over to a computer.

The role of sensors in control

Sensors are used to measure physical quantities such as temperature, light, pressure, sound, and humidity. They send signals to the processor. For example:

A security alarm system may have an infrared sensor which sends a signal when the beam is broken.
A heat sensitive sensor in the corner of a room may detect the presence of a person.
Temperature sensors could be used to control the heating in a large building.
Magnetic sensors are used to detect metal and can be placed in roads to monitor traffic flow.

Other physical quantities that can be transmitted directly to the computer's processor include:

rainfall/water levels
radiation level
pH level
oxygen level

Analogue to digital conversion

Data such as pressure, light and temperature is analogue data. Analogue data is continuously changing data. Computers can only work with digital data. In order to convert analogue to digital data discrete points on the analog signal must be sampled. The more samples you take the more accurate the digital representation. This is known as a sample rate.

An example of sample rates is 44100Hz sample rate that sound engineers use to digitise analogue sound. This means there are 44100 samples every second. At this rate the digitised sound is indistinguishable from the original when played back. The example below show discreet samples on a basic sound wave.

^[1]Note the sample take place over equal amounts of time and the corresponding sample allows the signal to be digitised. If we decreased the time intervals then the digitised signal would more closely approximate the original signal. The more samples you take per second means a better quality digitised signal but requires a lot more storage.

An interface box or analogue to digital converter (ADC) is needed to convert the analogue data from the sensors into digital data the computer can process.

The picture below show the analogue to digital unit (ADC) which converts the analogue data from sensors to digital data which is then transmitted through a USB cable to the computer.

Once the data is in the computer it is easier to analyse and represent using graphs. ^[2]

7.1.3 Evaluate different input devices for the collection of data in specified situations.

SENSOR

Heat

MEASURES

Temperature

Water vapour in the air

Radiation

Light levels

Acid/Alkali levels

Pressue

Levels of smoke in air

Sound level

Angle of tilt

Detects contact

USES

Central heating systems

Greenhouse, swimming pools

Security alarm systems

Security lights.

Environmental monitoring.

Automatic doors, alarm systems

Fire alarm systems.

Alarm systems, voice controlled electronics, noise pollution monitoring

windows in alarm systems, aircraft

Robots

IMAGE

Humidity

Infra-red

Light

Pressure

Smoke

Sound

Tilt

Touch

7.1.4 Explain the relationship between a sensor, the processor and an output transducer.

A control system typically comprises of a computer or microprocessor, a control program which handles data from sensors and sends signals to output devices and an interface box to convert signals between the sensors and the processor.

The output devices tend to be actuators which can control real world events.

Some examples of actuators are shown below:

ACTUATOR

Light bulb or LED

WHAT IT CAN DO

Creates light

Increases temperature

Decreases temperature

Spins things around

Pushes water / air through pipes

Creates noise

PICTURE

Heater

Cooling Unit

Motor

Pump

Buzzer / Bell / Siren

There are two types of control system:

Open loop system
Feedback system

The first type will only look at the input signal in order to decide what to do. For example a microwave oven will run for the set amount of time and switch off. It will take no account of any other factors such as whether the food is too hot or too cold. You set a light switch to come on at 1900 at night. This light will come on at that time irrespective of whether it is dark outside. Feedback systems are discussed in more details below.

7.1.5 Describe the role of feedback in a control system.

In a feedback system the output of a system affects the input.

This is best explained by taking a real life example.such as a control system that has to maintain a constant level in a water tank.

water level falls too low
sensor detects water level is too low
valve opened to let water in
sensor detects water level is too high
valve opened to let water out

This process will run indefinitely

7.1.6 Discuss the social impacts and ethical considerations associated with the use of embedded systems.

Surveillance

“Surveillance is the use of IT to monitor the actions of people. For example, monitoring may be used to track, record and assess employees’ performance. It can be used to support claims for promotion or to ensure that employees follow the organization’s internet policy appropriately.” IBO ITGS Syllabus

There are several types of surveillance systems such as those that monitor employees in the workplace^[3], students in the classroom^[4], prisoner tagging (see below), secret service surveillance^[5].

Prisoner tagging

Source: BBC News, 2004, “Satellite tracking for criminals.”

http://news.bbc.co.uk/1/hi/uk/3620024.stm [24 July 2005].^[6]

Convicted criminals can be fitted with a tracking belt and electronic transmitter on

their ankles (item 1 in the picture). The Government officials at the control centre (item 4 in

the picture) are able to pinpoint their exact position using a computer (item 5 in the picture)

at any time. These devices enable criminals to live in the community rather than being kept

in prison.

There are several pros and cons related to this

Pros

Government no longer needs to house or feed the prisoner in a prison so there is a cost saving.

Can be safer for the community as people who may not normally be sent to prison can be effectively monitored.

Families who rely on convicted person can continue to live with them and receive financial/emotional support.

There may be improved rehabilitation as offenders are not removed from society and put in a “criminal” environment.

Cons

Risk of devices being removed and prisoners offending.

Does not necessarily prevent any future crimes

System is expensive to set up.

System may not be reliable and there may be areas where the system does not cover.

Extra people are required to monitor and intervene when there are problems.

There may be privacy issues.

The security of the system is important as any hacking would reveal sensitive data.

CCTV

Closed-circuit television (CCTV), also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors.^[7]

Many CCTV units are used for security reasons in private areas. However many CCTV systems exist in public spaces and there are many privacy and security issues surrounding the use of CCTV systems in public spaces. This article^[8] discusses such issues in the wake of the recent Boston bombing incident. it is good to use this as a basis for thinking about whether the pros outweigh the cons.

Improved safety systems

There are many examples of where computer systems are used to improve the safety of systems. On good example is in the car industry where active safety systems are used extensively to protect the driver and passengers. .

Distributed systems

7.1.7 Compare a centrally controlled system with a distributed system.

Key Terms

Centrally controlled system
Distributed system
Autonomous agents

Distributed Computing

A type of computing in which different components and objects comprising an application can be located on different computers connected to a network.^[9]

Pros

Cost

Performance

Scalability

Reliability

Cons

Network bandwidth

Security

Software complexity

Video on distributed control systems:

https://www.youtube.com/watch?t=14&v=Lr8did1fhAc

Climate modelling

http://www.olcf.ornl.gov/titan/

http://www.bbc.co.uk/sn/climateexperiment/

7.1.8 Outline the role of autonomous agents acting within a larger system

http://www.youtube.com/watch?v=uNZJMZ0hi1Y

Now test yourself

https://quizlet.com/122575196/test/embed

Michael Brooke emjbe.net

[1] "An Algorithm for Music: The Discrete Fourier Transform." 2012. 21 Sep. 2015 <http://www.seas.gwu.edu/~simhaweb/alg/lectures/module14/module14.html>

[2] "LogIT Black Box Datalogger | Rapid Online." 2014. 21 Sep. 2015 <http://www.rapidonline.com/Test-Measurement/LogIT-Black-Box-Datalogger-80589>

[3] "Employee Monitoring: How Far is Too Far? - Innovative ..." 2014. 18 Sep. 2015 <http://www.innovativeemployeesolutions.com/articles/employee-monitoring-how-far-is-too-far/>

[4] "Should school children have tracking chips? - Science ..." 2013. 18 Sep. 2015 <http://blogs.discovery.com/inscider/2013/04/should-children-have-tracking-chips.html>

[5] "U.S. Confirms That It Gathers Online Data Overseas - The ..." 2013. 18 Sep. 2015 <http://www.nytimes.com/2013/06/07/us/nsa-verizon-calls.html>

[6] "BBC NEWS | UK | Satellite tracking for criminals." 2004. 18 Sep. 2015 <http://news.bbc.co.uk/2/hi/uk_news/3620024.stm>

[7] "Closed-circuit television - Wikipedia, the free encyclopedia." 2011. 18 Sep. 2015 <https://en.wikipedia.org/wiki/Closed-circuit_television>

[8] "After Boston: The pros and cons of surveillance ... - CNN.com." 2013. 18 Sep. 2015 <http://www.cnn.com/2013/04/26/tech/innovation/security-cameras-boston-bombings/>

[9] "What is distributed computing? A Webopedia Definition." 2002. 21 Sep. 2015 <http://www.webopedia.com/TERM/D/distributed_computing.html>

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