Engineering Science - Information and Energy Control Systems

HNC Yr1 Science Assignment 4 Steve Goddard

Contents

Topic PageHow Electrical Signal Convey Information 2

How Electrical Systems Control Energy Flow 6Demonstration Of System Operation 8

Bibliography 12

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Engineering Science - Assignment 4

Information and Energy Control Systems

How Electrical Signals Convey Information

1. Describe the following methods used by electrical signals to convey information:

1.1 Frequency Modulation

Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) wave by varying the instantaneous frequency of the wave. This scheme can be used with analogue or digital data.

In analogue FM, the frequency of the AC signal wave, also called the carrier, varies in a continuous manner. Thus, there are infinitely many possible carrier frequencies.

In digital FM, the carrier frequency shifts abruptly, rather than varying continuously. The number of possible carrier frequency states is usually a power of 2. If there are only two possible frequency states, the mode is called frequency-shift keying (FSK). In more complex modes, there can be four, eight, or more different frequency states. Each specific carrier frequency represents a specific digital input data state.

1.2 Modulation Amplitude

Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. The instantaneous amplitude (overall signal power) varies depending on the instantaneous amplitude of the modulating data.In AM, the carrier itself does not fluctuate in amplitude. Instead, the modulating data appears in the form of signal components at frequencies slightly higher and lower than that of the carrier. These components are called sidebands. The lower sideband (LSB) appears at frequencies below the carrier frequency; the upper sideband (USB) appears at frequencies above the carrier frequency. The LSB and USB are essentially "mirror images" of each other in a graph of signal amplitude versus frequency, as shown in the picture below. The sideband power accounts for the variations in the overall amplitude of the signal.

When a carrier is amplitude-modulated with a pure sine wave, up to 1/3 (33 percent) of the overall signal power is contained in the sidebands. The other 2/3 of the signal power is contained in the carrier, which does not contribute to the transfer of data. With a complex modulating signal such as voice, video, or music, the sidebands generally contain 20 to 25 percent of the overall signal power; thus the carrier consumes 75 to 80 percent of the power. This makes AM an inefficient mode. If an attempt is made to increase the modulating data input amplitude beyond these limits, the signal will become distorted, and will occupy a much greater

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bandwidth than it should. This is called over modulation, and can result in interference to signals on nearby frequencies.

1.3 Morse Code

Morse code is a character encoding for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a given message. The short and long elements can be formed by sounds, marks or pulses, in on off keying and are commonly known as "dots" and "dashes" or "dits" and "dahs".Morse code can be transmitted in a number of ways: originally as electrical pulses along a telegraph wire, but also as an audio tone, a radio signal with short and long tones, or as a mechanical or visual signal (e.g. a flashing light) using devices like an Aldis lamp or a heliograph. Morse code is transmitted using just two states (on and off) so it was an early form of a digital code. However,

it is technically not binary, as the pause lengths are required to decode the information.

1.4 ASCII Code

ASCII specifies a correspondence between digital bit patterns and character symbols This allows digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language. The ASCII character encoding or a compatible extension is used on nearly all common computers, especially personal computers and workstations. The preferred MIME name for this encoding is "US-ASCII".ASCII is, strictly, a seven-bit code, meaning it uses patterns of seven binary digits (a range of 0 to 127 decimal) to represent each character. When ASCII was introduced, many computers used eight-bit bytes (groups of bits), also called octets, as the native data type. In seven-bit ASCII encoding, the eighth bit was commonly used as a parity bit for error checking on communication lines or for other device-specific functions. Machines that did not use parity checking typically set the eighth bit to 0.Except for a few of the ASCII control characters that prescribe some elementary line-oriented formatting, ASCII does not define any mechanism for describing the structure or appearance of text within a document. Other schemes, such as markup languages, address page and document layout and formatting.

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2. Describe the inherent function of the following electrical components used within an information system:

2.1 Transducers

A transducer is a device that converts energy from one form into corresponding variations in another, most commonly electrical form. Measurement or input transducers use a range of physical, chemical or biological effects to achieve transduction and they are aimed for high sensitivity and a small amount of disturbance. On the opposite side, output transducers are designed to achieve an end result. Occasionally, a transducer can be referred to as a sensor, which is incorrect as a sensor does not transform energy it either changes by sensing and input which it then passes onto another device. Examples of transducer include:

pH probes Linear motors Rotary motors Microphone Loudspeaker Light Bulb LCD Display

Within Westland Helicopters, certain departments have to use and take readings from transducers on aircraft. These include:

Thermocouples Strain Gauges Accelerometers

2.2 Amplifiers

An amplifier is a device that is there to control amounts of energy or ‘amplify’ an energy source. Amplification is done by using gain within the component. Gain is generally calculated by the ratio or the output power to the input power and is measured in decibels (dB’s). There are many types of amplifiers on the market today ranging from audio amplifiers which started out as vacuum tubes (value) which proved very efficient in high power applications to today’s class D amplifiers which are no bigger than a pea. Video amplifiers also play a significant part in today’s technological advancements. These all vary on bandwidth depending on what signal is being processed whether it be SDTV (480i) to HDTV (1080p).

2.3 Digital to Analogue converters

A digital to analogue converter (DAC) is a device that is used for converting a digital (usually binary) code to an analogue signal (current, voltage or electric charge). Digital to analogue converters are the link between the abstract digital world and the analogue real life. They are built up with a network of resistors, simple switches and current sources or capacitors may implement the conversion.

There are a number of common DAC applications. These include:

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CD Players – converts the digital music to music which you hear. PC Sound cards – converts digital sounds into analogue which can be

heard Digital music Players – converts digital music files into music which you

hear Computer monitors – converts a digital video signal into analogue so you

can see it on a monitor

There are also a number of different digital to analogue converters available. Some of the most common ones are:

Pulse Width Modulator – This is the simplest digital to analogue converter and it works by a stable current or voltage being switched into a low pass analogue filter with the duration determined by the digital input.

Binary Weighted – This type of digital to analogue converter contains one resistor and a current source for each part connected to a summing point. These precise voltages or currents total up to the correct output value. This method is the quickest, but it is the least accurate.

R2R Ladder – This is a binary weighted digital to analogue converter which uses a repeating structure of resistors with values of R and 2R. This is a more accurate converter but it is slower than most others.

Thermometer Coded – This contains an equal resistor or current source segment for each possible output. This is the faster and most accurate digital to analogue converter but because of this, it is the most expensive to produce.

Segmented – This combines the thermometer coded DAC for the most significant bits and the binary weighted DAC for the least significant bits. Due to this, it is both accurate and quick, but a cheaper price to produce.

2.4 Oscillators

An oscillator is a device that produces a repetitive electronic signal. (Sine wave or square wave). A low frequency oscillator generates an AC waveform between 0.1Hz and 10Hz. A voltage controlled oscillator is specifically designed to be controlled by a voltage input. This means that the frequency of oscillation varies with an applied DC voltage, while modulating signals may be fed into the VCO to generate frequency modulation, phase modulation and pulse-width modulation.

3. Explain the meaning of the following terms and discuss their significance within an electrical system:

3.1 Signal

Electronic signals fall into two categories, analogue and digital. Both types of signal have been used from the earliest days of electrical communication. Analogue systems came around first with the telephone, whereas digital systems first appeared when telegraph systems introduced the Morse code.

In analogue systems the information or data is given as an electrical signal that varies in direct proportion to the information or data. It follows that the variation must be continuous and, between the limits of operation of the system, the variation can have any value from an infinite number of values. Such variation is associated with the production of sound (as in the telephone) in radio receivers or vision in television sets.

An analogue system in its most basic form has an input electrical signal that is either a voltage or a current varying directly in proportion to the input information. The input information is converted into the electrical signal by a transducer.

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Digital signals have one of a limited number of discrete values. In most applications, the applications have two values which in crude terms could be explained as ON and OFF. These values are usually described as 1 and 0, being the presence and absence of the supply voltage or current. As previously mentioned in question 1.3, the first form of digital signal in common use was that associated with the Morse code.

3.2 Noise

Electronic noise is created by interference and can be a problem in any electronic circuit. Semi-conductor devices can also contribute flicker noise and generation-recombination noise. In electrical circuits random variations in voltage and current are caused by random movement of electrons carrying the current as they are moved around by thermal energy.How electrical Signals Control Energy Flow

4. Describe the following methods used by electrical signals to control energy flow:

4.1 Temperature sensing and control

The most common application of temperature sensing and control is a thermostat. This is a device that is found on virtually every heating system where by the thermostat regulates the temperature to a desired set temperature. This can be achieved by the thermostat switching the heating on and off to regulate this desired temperature set by the operator, thus creating a regulated energy flow.

4.2 Humidity sensing and control

Devices using humidity sensing and control use hermidistats to know when to switch themselves on or off. These work by using the expansion and contraction of certain materials to measure the humidity in an area. This means that the more water molecules that are in the air, the more there will be on the material, and this is what the humidistat will measure.

Examples of devices using humidity sensing and control are dehumidifiers, humidifiers and also air purifiers.

4.3 Speed control of AC and DC machines

Speed control is used in both AC and DC machines. For an AC machine, a universal motor is used instead. It operates single phase AC supplies and accelerates until the output and load torque are equal. In DC machines, a common way of controlling the speed is with a DC motor. It is used with a tacho generator usually, which controls the driven load speed and it is essentially a torque source controller. The speed is controlled by regulating the voltage applied to the motor and all current passes through the voltage regulator.

5. Describe the functions of the following electrical components used within an energy flow control system:

5.1 Relays

A relay is a simple electromechanical switch made up of an electromagnet and a set of contacts.

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Relays are amazingly simple devices. There are four parts in every relay: Electromagnet Armature that can be attracted by the electromagnet Spring Set of electrical contacts

5.2 Thyristors

A thyristor or a Silicone Controlled Rectifier is a solid state semiconductor/junction diode that allows a significant current in one direction and little in the other. The thyristor passes negligible current when reverse biased and when forward biased the current is also negligible until the forward breakdown voltage is exceeded. Generally, thyristors are used when a high current/high voltage application is involved and usually control alternating current. Another use that thyristors serve is the control element for phase angle triggered controllers.

5.3 Triacs

A triac or TRIode for Alternating Current is an electronic component similar to 2 silicon-controlled rectifiers joined in inverse parallel and with the gates connected together. The result of this is a bidirectional electronic switch which can conduct current in either direction when it is triggered. It can be triggered by either a positive or negative current being applied to its gate electrode. Similar to the thyristor, the triac will continue to conduct until the current drops below a set threshold value. Low power triacs are used in a number of applications such as light dimmers, speed controls for electric fans and electric motors and in the computer controlled circuits in many household appliances. To assist in the turning off of a triac, snubber circuits may be used and they can also be used to prevent premature triggering of the triac.

5.4 Transistors

A transistor is a semiconductor that uses a small amount of voltage or current to control a larger change in voltage or current. It is used in a large number of applications including amplification, switching, voltage stabilization, signal modulation and it also can be used as an oscillator. Transistors are split into 2 categories. These categories are bipolar junction transistors (BJTs) and field effect transistors (FETs). Transistors are used in switches, amplifiers and computers.

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Demonstration of System Operation

6. Choose a recognised communication system, e.g. television, radio, RS232, satellite communications, an EFTPOS system, mobile phone to satellite uplink, broadband, etc.

6.1 Evaluate and justify the method used to convey information in your chosen system.

The communication system that I have chosen is broadband.

From the name, broadband essentially means wide bandwidth and because of that a lot more information can be carried. It can also be referred to as data transmission, where multiple pieces of data are sent at the same time and this increases the rate of effective transmission. Broadband, or Active Digital Subscribers Line (ADSL) is a transmission medium network where by packets of information are sent thousands of times a second at set frequencies over an exchange network that gets relayed from the exchange server to your Personal Computer. The speed that the exchange server supplies limit the amount of bandwidth channels that can be used at any one time. This is known as the download limit. This can vary from 1 Mega Bit per Second (mbs) to 10mbs. In the 90’s phone lines could only support audio frequencies as this were their main purpose. As time went on, British Telecom increased the frequencies of its telephone exchanges making way for video frequencies by demand from business users. This eventually became public and virtually every house in the UK has a broadband connection. The future of broadband is being implemented all the time, the trouble is, phone lines can only handle up to a certain frequency before it gets too much, so fibre optic technology is being put into place with speeds starting at 32mbs going all the way up to 40gbs.

6.2 Within your chosen system consider/discuss the following:

6.2.1 Security

Using broadband potentially makes your PC vulnerable to unwanted visitors such as viruses; because of this precautions are deemed necessary. This is because broadband has an ‘always-on’ nature.When signing up for broadband you should look into what security you ISP (internet service provider) will provide you with to protect your PC and any information you have on it. It is also advised that you install your own firewall and virus scanning software packages to further protect your PC.

6.2.2 Encryption

Encryption is used to protect system from outside hackers, software piracy and reverse engineering. In a broadband system, the encryption is obtained using broadband encryption units. These are the key units in the system that protects it from outside interference and they protect both corporate and public backbone networks. They are inserted at the connection between public and corporate networks and they operate on real time data.

Such a product is the r & S SITline which provides encryption for up to 4096 bi-directional channels with a broadband of 16kbs to 155mbps.

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6.2.3 Bandwidth

This depends on the amount of channels and frequency the exchange server allows down the users phone line. The days before broadband, dial up used to run purely on audio frequencies which meant that a slow connection of 20kbs to 50kbs was established. Now, broadband runs on video frequencies well into 8mbs giving a fast connection due to more channels available and a higher frequency rate. Broadband bandwidth is measured in bps (bits per second) and can be bought at different amounts depending on how fast you require your download speed. Such values include 2Mbps, 4Mbps and 10Mbps.

6.2.4 Cost

Broadband can vary in price, if a user would like 8mbs broadband, they can expect to pay up to £40 a month. 2mbs is an average connection speed and will total approximately £20 per month. These prices are of course based on the ISP availability and price that they charge.

Business users on the other hand will either opt for Very high bit Digital Subscriber Line (VDSL) or fibre optics if cost is relative. These services can be expensive but give a very high amount of channels and high frequencies which can be very beneficial with 100 plus users on the internet at one time.

6.2.5 Reliability

The reliability of broadband depends on the broadband entry level cost. A low cost usually does not have a service level agreement, therefore if a fault occurs your connection may be unavailable for part or most of the working day. Also if the ISP is busy you may not get a connection as fast or as quick as you like.Because of this it would be worth thinking about having a backup connection if it fails such as a modem.

7. Investigate and analyse an energy flow control system (e.g. AC & DC machines, heating, lighting, air conditioning, etc.) as follows:

7.1 Draw and appropriately label the general block diagram of an open-loop control system, giving two suitable examples.

Open-loop control systems are kept as simple as possible. An input is applied, a function or process occurs and an output is produced, an operator would have to adjust the input in response of the output. Two good examples of this is a system with a variable switch on a heater and the output of heat and the speed of a car.

Example 1

Example 2

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Heating Process

Input Output

Of the switched selection

Of the room temperatur

Brain/ Error Detector Power

SelectorCarburettor

Engine

Gearbox/ Transmission

Speed

Eye


7.2 Draw and appropriately label the general block diagram of a closed-loop control system, giving two suitable examples

A closed look system is where an operator selects the desired output and the system will automatically controls the inputs to achieve the desired output. Two good examples would be air conditioning and an oven which is set to a temperature and will maintain that temperature under normal circumstances. But if the oven door is opened, the oven will detect this and increase the amount of heat released in order to maintain the temperature in the oven.

7.3 Describe the relative advantages and disadvantages of each of these control systems

A feedback controller/signal is the main difference between an open and a closed loop system, so the relative advantages and disadvantages would be around weather it’s a good idea to have this feedback or not. The feedback can for example keep an oven's temperature within acceptable ranges as mentioned above or maintain a car's speed through an uphill climb. Every feedback controller has a different strategy for accomplishing its particular target, but all use some variation on the closed-loop control algorithm, this is – measure a process variable, decide if its value is acceptable, apply a corrective effort as necessary, and repeat the whole operation infinitely.

Error = reference value – measured value signal

Open loop controllers, on the other hand, do not use feedback. They apply a single corrective effort when commanded by the user and assume that the desired results will be achieved. An oven may have a separate open-loop controller that opens and closes the oven doors without verification. The steam supply system may have an emergency shutdown controller that automatically cuts power and vents the lines when a dangerous over-pressure condition is detected.Even feedback controllers must operate in the open-loop mode on occasion. A sensor may fail to generate the feedback signal or an operator may take over the feedback operation to manipulate the controller's output manually.Operator intervention is generally required when a feedback controller proves unable to maintain stable closed-loop control. For example, a particularly aggressive pressure controller may overcompensate for a drop in line pressure. If the controller then overcompensates for its overcompensation, the pressure may end up lower than before, then higher, then even lower, then even higher, etc. The simplest way to terminate such unstable oscillations is to break the loop and regain control manually.There are also many applications where experienced operators can make manual corrections faster than a feedback controller can. Using knowledge of the process' past behavior, operators can manipulate process inputs now to achieve the desired output values later. A feedback controller, on the other hand, must wait until the effects of its latest efforts are measurable before it decides on the next appropriate control action. Predictable processes with long time constants or excessive dead time are particularly suited for open-loop manual control.

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The principal drawback/ disadvantage of open-loop control is accuracy loss. Without feedback, there is no guarantee that the control inputs applied to the process will actually have the desired effect.

7.4 Choose one of your examples of closed-loop control system and give an in-depth analysis as to the function of:

7.4.1 The individual elements

For my chosen closed-loop control system I have chosen the air conditioning. The individual elements of the system involve an input with a comparison element to measure the value against the input, to correct any error there will be a controller and a process which would be a switch from cold to hot air and the fans to pump the air out. This will produce the output, from this a measurement will be taken with a thermostat to determine the new temperature and then the loop continues. For a more visual description se the diagram below:

7.4.2 The system as a whole

Air conditioning units work by measuring the temperature or the air and comparing this to a user defined temperature. The system measures this error and adjusts the temperature output accordingly so that the temperature stays within the defined value. Specifically for air conditioning systems temperature normally vary between 1 or 2 degrees above and below the defined temperature.In perfect circumstances the above will always happen but more than likely there will be external elements that will be influencing the temperature control such as an open window which will make the system think it is colder in the room that it might be therefore it will work harder to increase the temperature and use more energy in doing so.

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Switch

Comparison

InputFan

Temperature Measurement

Output


Bibliography

http://searchnetworking.techtarget.com/ - Frequency modulation

www.wikipedia.org – Various information

www.whatis.com

www.howstuffworks.com

Higher Engineering Science – W Bolton

Class Notes

NC Course Handouts

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http://www.howstuffworks.com/

http://www.whatis.com/

http://www.wikipedia.org/

http://searchnetworking.techtarget.com/

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Engineering Science - Information and Energy Control Systems