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SYSTEMS AND CONTROL B. M Thabethe 4th TERM Electrical and Electronics Hydraulics and Pneumatics Combining Systems Work to be covered this term: Electrical and electronic systems Pneumatics and Hydraulics Pascal’s law and MA Combining systems Electrcal and electronics to understand how electrical circuits, including those with switches, can be used to achieve functional results; to use electrical switches to control devices; to analyse the performance of an electric system in order to check if it is working effectively to design, use and interconnect simple electrical and electronic systems Electrical systems Involve the use of circuits Outcomes for today to understand what is electricity and how it works to understand how electrical circuits, including those with switches, can be used to achieve functional results; to use electrical switches to control devices; to know that systems have inputs, processes and outputs, and to recognise these in products they have made to understand the importance of feedback and how it can be used to ensure the correct functioning of an electrical or electronic system to analyse the performance of an electric system in order to check if it is working effectively to design, use and interconnect simple electrical and electronic systems Electricity But what is electricity? Where does it come from? How does it work? Before we understand all that, we need to know a little bit about atoms and their structure. Conduction of electricity Conductors Semi-conductors Insulators silver copper gold aluminum iron steel brass bronze mercury graphite dirty water concrete glass rubber oil asphalt fiberglass porcelain ceramic quartz (dry) cotton (dry) paper (dry) wood plastic air diamond pure water ATOMS All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles making up an atom are the proton, the neutron and the electron. Electrons spin around the center, or nucleus, of atoms, in the same way the moon spins around the earth. The nucleus is made up of neutrons and protons. Electrons contain a negative charge, protons a positive charge. Neutrons are neutral -- they have neither a positive nor a negative charge. Atoms There are many different kinds of atoms, one for each type of element. An atom is a single part that makes up an element. There are 118 different known elements that make up every thing! Some elements like oxygen we breathe are essential to life. Each atom has a specific number of electrons, protons and neutrons. But no matter how many particles an atom has, the number of neutrons usually needs to be the same as the number of protons. If the numbers are the same, the atom is called balanced, and it is very stable. If not, the atom is considered to be unstable. Quick look at the periodic table So, if an atom had six protons, it should also have six electrons. The element with six protons and six electrons is called …….. Carbon is found in abundance in the sun, stars, comets, atmospheres of most planets, and the food we eat. Coal is made of carbon; so are diamonds. Moving electrons from one atom to another! Electrons can be made to move from one atom to another. When those electrons move between the atoms, a current of electricity is created. The electrons move from one atom to another in a "flow" - called the “bucket brigade method” This method is similar to the fire fighter's bucket brigades in olden times. Moving electrons and circuits Electrons with a negative charge, can't "jump" through the air to a positively charged atom. They have to wait until there is a link or bridge between the negative area and the positive area. We usually call this bridge a "circuit." When a bridge is created, the electrons begin moving quickly. Depending on the resistance of the material making up the bridge, they try to get across as fast as they can. Electric systems How do we construct a circuit? What are the principal parts to be found in every circuit? What happens to bring about the action of electric circuit? – the principal activity involves electric charge – when we arrange for electric charge to move in a pre-determined way, we achieve an electric current. - to produce this effect, we require to enlist the aid of an e.m.f. (electromotive force) Electric systems George Ohm related e.m.f. to the current in his simple law – Ohm’s law, which states: the ratio of voltage to current is constant, provided other physical factors such as temperature remain unchanged; meaning, the amount of current in a circuit is directly proportional to voltage across the circuit, and is inversely proportional to the resistance of the circuit By applying Ohm’s Law we can find out about resistance which is an important physical property associated with all circuits; Ohm’s Law A conductor has a resistance of 1 Ω (ohm) if a potential difference (pd) of 1 V (volt) across its ends causes a current of 1 A (ampère) to flow through it. V R I Current refers to the movement of charges In an electrical circuit electrons move from the negative pole to the positive. If you connected the positive pole of an electrical source to the negative pole, you create a circuit. Current (I) The number of electrons we are willing to let across the circuit at one time is called "current". We measure current using amperes, or "Amps". One AMP is defined as: 18 6 . 25 10 625,000,000,000,000,000,000 electrons moving across your circuit every second! Q I t Since no one wants to remember such a big number, that big number is called a "coulomb," after the scientist Charles A Coulomb who helped discover what a current of electricity is. One coulomb (C) is defined as the amount of charge (Q) that passes a point in a conductor in one second (s) when the current in the conductor is one ampère: Q = It Symbol Meaning Unit Q Charge moving in conductor C (coulomb) I Current in conductor A (ampère) t Time during which current passes a point in a conductor s (seconds) Task 1. How long will it take a charge of 80C to pass a point in a conductor if the current flowing is 2A? 2. What is the charge in coulomb that subsists in a circuit while a current of 2A flows through it for 2mins? Voltage (V) The amount of charge between the sides of the circuit is called "voltage” or potential difference (p.d.) Voltage is the measure of electrical "push" ready to motivate electrons to move through a conductor. We measure Voltage in Volts. The word volt was named after another scientist, Alexander Volta, who built the word's first battery. You'll remember that we defined energy as the "ability to do work." Well, one volt is defined as the amount of electrical charge needed to make one Coulomb (625,000,000,000,000,000,000 electrons) do one a specific amount of work -- which is labeled one joule. Joule is also named after a scientist, James Prescott Joule. Voltage (V) In scientific terms, it is the specific energy per unit charge, mathematically defined as joules per coulomb. It is analogous to pressure in a fluid system: the force that moves fluid through a pipe, and is measured in the unit of the Volt (V). Resistance (R) We can limit the number of electrons crossing over the "circuit," by letting only a certain number through at a time. And we can make electricity do something for us while they are on their way. For example, we can "make" the electrons "heat" a filament in a bulb, causing it to glow and give off light. When we limit the number of electrons that can cross over our circuit, we say we are giving it "resistance.". We "resist" letting all the electrons through. Copper wire is just one type of bridge we use in circuits. Effects of resistance Before electrons can move far, however, they can collide with one of the atoms along the way. This slows them down or even reverses their direction. As a result, they lose energy to the atoms. This energy appears as heat, and the scattering is a resistance to the current. The 4 constituents of a basic electrical system 1. The source: The function of the source is to provide the energy for the electric system. A source may usually be thought of as a battery or a generator 2. The Load: The function of the load is to absorb the electric energy supplied by the source. Most domestic electric equipment constitutes loads. Common examples include lamps, heaters, kettles, stoves etc. The 4 constituents of a basic electrical system 3. The transmission system: This conducts energy from the source to the load. Typically the transmission system consists of insulated wire. 4. The control apparatus: As the name suggests, its function is to control. The most simple control is a switch which permits the energy to flow or else interrupts the flow. Simple circuit Draw a diagram Systems with increased loads Electrical technology is very complex, thus our e.g. of a simple circuit seldom exists except in battery torches; In this regard we look to systems with an increased number of loads; To handle 2 or more loads we need to be adept at recognizing seriesconnected and parallel-connected loads Series and parallel connected loads Loads are series connected when the same current flow passes through each of them; Loads are connected in parallel when the same potential difference is applied to each of them. Characteristics of Series Connections 1. Current has a single pathway through the circuit. 2. Total resistance is the sum of the individual resistances along the circuit path. 3. The current in the circuit is equal to the voltage supplied by the source divided by the total resistance of the circuit. 4. The total voltage impressed divides among individual devices in the circuit so that the sum of the “voltage drops” across the resistance of each individual device is equal to the total voltage supplied by the source. 5. The voltage drop across each device is proportional to its resistance. Characteristics of Parallel Connections 1. Each device connects the same two points A and B of the circuit. The voltage is therefore the same across each device. 2. The total current in the circuit divides among the parallel branches. The current in each branch is inversely proportional to the resistance of the branch. 3. The total current in the circuit equals the sum of the currents in its parallel branches. 4. As the number of parallel branches is increased, the overall resistance of the circuit is decreased. Use of A-meter and V-meter A-meter is connected in series with the load V-meter is connected in parallel (across) to the load or energy source Digital communication: Binary system Logic gates: AND-gate and OR-gate use circuits to model how these two gates operate; determine the rule governing the operation of these gates; use the computer to simulate how these gates operate; apply what you have learnt to solve a real life situation problem. Boolean addition Boolean addition is equivalent to the OR function and basic rules are: 0+0=0 0+1=1 1+1=1 Boolean Multiplication Boolean multiplication is equivalent to the AND operation and the basic rules are: 0.0=0 0.1=0 1.1=1 Note: The dot (.) implies multiplication. A product term is equal to 1 if only all the variables are 1. A product term is equal to 0 when one or more of the variables are equal to 0. Series and parallel connected controls (switches) A logic gate is one that behaves like a switch, i.e. two position device with on and off states. This is termed a binary device, in which the on state is represented by 1 and the off by state by 0. The OR function Either A or B should happen F = A OR B which in logic terms is represented as: F= A+B NB. (+ not additive function but means OR in logic) The AND function Both A and B should happen; F = A AND B which in logic terms is represented as: F A B Task Ms Dube, being an eager teacher, had planned to demonstrate how simple electronic circuits and devices are used to make an output signal respond to an input signal. In her planning she assumed certain prior knowledge and competency. She was terribly disappointed when her learners didn’t demonstrate the necessary prior knowledge and competency in the following areas: Homework understanding of electrical circuits with more than one output device in the circuit (series and parallel) and represent them using systems diagrams; understanding of how electrical circuits with more than one input or control device will work based on different logic conditions (‘AND’ and ‘OR’ logic) and represent them using circuit diagrams, systems diagrams and truth tables To do: Discuss how you plan a way forward for Ms Dube. In other words, how would you help her teach this section? Power The rate at which energy is delivered to a load / the rate of energy transfer / rate of doing work is called electric power. Electric power can be measured by the product of current and voltage (power = current x voltage). Electric power is measured in watts (W). Thus one watt of power is the result of one ampere of current driven by one volt of force through a circuit.