Unit 314 Electrical and Electronic Measurement Notes PDF

Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Learning outcome 1 What is electrical and electronics measurement? Electrical measurements are the methods, devices and calculations used to measure electrical quantities. Measurement of electrical quantit...

Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Learning outcome 1 What is electrical and electronics measurement? Electrical measurements are the methods, devices and calculations used to measure electrical quantities. Measurement of electrical quantities may be done to measure electrical parameters of a system. Digital Multimeter (DMM) What is a voltmeter and what is it used for? Voltmeter, also known as a voltage meter, is an instrument that measures the voltage or potential difference between two points of an electronic or electrical circuit. Usually, the voltmeter is used for Alternating Current (AC) circuits or Direct Current (DC) circuits. A voltmeter measures how much voltage is passing between two points. It does this by measuring the difference between the positive input of voltage and the negative input of voltage. A voltmeter is usually used to check the power in electrical circuits. Display, where you'll see the results of the measurement. Page 1 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Limitations It gives some extra feature are expensive. This voltmeter is usually very hard to spot transient voltage spikes, etc. The speed of operation is limited due to the digitizing circuit. While we have to use the display depends on the external power source or battery. Digital voltmeters are prone to damage if the voltage is too much increased beyond the limit. It is very to spot the transient voltage spikes. What is an ammeter and what is it used for? Ammeter is a device used to measure either alternating or direct current. We know that ampere is the unit of current. Since this device measures the value in amperes, it's known as ammeter. Ammeters are tools used to measure the current in a circuit. The ammeter is connected in series with the circuit, so that the current to be measured flows directly through the ammeter. The circuit must be broken to correctly insert an ammeter. Page 2 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Limitations (both voltmeter and ammeter) Both can be based on the combination of a resistor and a galvanometer, a device that gives an analogue reading of current. Standard voltmeters and ammeters alter the circuit being measured and are thus limited in accuracy In PMMC, heating and vibrating effects mainly occur. So, find errors or reduce the magnetic strength. An ammeter cannot store data. How a voltmeter and an ammeter are connected in a circuit? What is an Ohmmeter and what is it used for? Ohmmeter, instrument for measuring electrical resistance, which is expressed in ohms. Resistance is measured with the circuit's power turned off. The ohmmeter sends its own current through the unknown resistance and then measures that current to provide a resistance value readout. Page 3 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Ohmmeter Working Principle An ohmmeter operates on the principle of Ohm’s law, which states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. An ohmmeter applies a known voltage across the component under test and measures the resulting current to measure resistance. The ohmmeter can calculate the resistance value based on the applied voltage and measured current by applying Ohm’s law. an ohmmeter cannot function properly if some unknown current also flows through the component. The circuit cannot be active. Ammeter–voltmeter method for measuring resistance The ammeter-voltmeter method is a technique used to measure the resistance of an electrical component. It involves using an ammeter and a voltmeter in a circuit with the component whose resistance is to be measured. Here are the steps to follow: 1. Disconnect the power source from the circuit. 2. Connect the ammeter in series with the component whose resistance is to be measured. 3. Connect the voltmeter in parallel with the component. 4. Reconnect the power source to the circuit. 5. Read the current on the ammeter and the voltage on the voltmeter. 6. Use Ohm’s Law (R = V/I) to calculate the resistance of the component, where R is the resistance, V is the voltage across the component, and I is the current through the component. Page 4 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds What is an oscilloscope and what is it used for? Oscilloscopes (or scopes) test and display voltage signals as waveforms, visual representations of the variation of voltage over time. The signals are plotted on a graph, which shows how the signal changes. The vertical (Y) access represents the voltage measurement and the horizontal (X) axis represents time. An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time. Page 5 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Limitation Bandwidth: The bandwidth of an oscilloscope is the range of frequencies that it can accurately measure. If the signal of interest has frequencies outside of the oscilloscope's bandwidth, it will be distorted or not displayed at all. Sample rate: The sample rate is the number of times per second that the oscilloscope samples the input signal. A higher sample rate allows the oscilloscope to capture more detail in the signal, but it also requires more memory and processing power. Resolution: The resolution of an oscilloscope is the smallest change in the input signal that it can detect. A higher resolution allows the oscilloscope to measure more accurate values for the signal What is a spectrum analyser and what is it used for? A spectrum analyser is a device that measures and displays signal amplitude (strength) as it varies by frequency within its frequency range (spectrum). The frequency appears on the horizontal (X) axis, and the amplitude is displayed on the vertical (Y) axis. Page 6 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds “Just what is a spectrum and why would we want to analyze it?” Our normal frame of reference is time. We note when certain events occur. This includes electrical events. We can use an oscilloscope to view the instantaneous value of a particular electrical event (or some other event converted to volts through an appropriate transducer) as a function of time. In other words, we use the oscilloscope to view the waveform of a signal in the time domain. Fourier theory tells us any time domain electrical phenomenon is made up of one or more sine waves of appropriate frequency, amplitude, and phase. In other words, we can transform a time-domain signal into its frequency-domain equivalent. Measurements in the frequency domain tell us how much energy is present at each particular frequency. With proper filtering, a waveform such as shown can be decomposed into separate sinusoidal waves, or spectral components, which we can then evaluate independently. Page 7 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Time Domain vs. Frequency Domain https://www.youtube.com/watch?v=I2T3OYNqhyA FFT (Fast Fourier Transform) tutorial that demonstrate the decomposition of a given waveform into frequency domain. This technique helps us to identity the harmonic which might be undesirable. Check this out. https://www.youtube.com/watch?v=zKKGA30bHG0 Limitation of spectrum analyser FFT analyzer cannot work in higher RF frequencies due to limitations on sampling rate of ADC (Analog to Digital Converter). More it will have limitations on bandwidth supported by the spectrum analyzer. Page 8 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds How to generate signals? Signal generators are oscillators, which generate sine waves useful in measuring the response of loudspeakers, amplifiers, microphones, transducers, and acoustic systems; standard signal generators, which generate sine waves over a wide range of output power https://www.youtube.com/watch?v=TILPLvZ-QSs Function generators can generate sine, square, triangle, ramp, and pulse waveforms at a voltage-controllable frequency. https://www.youtube.com/watch?v=mLKPwWGBtIw Signal generators and function generators Signal generators only generate a Sine wave, have limited Frequency stability, no capability of phase looking with the external source, and frequency is controlled by frequency range controller. Page 9 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds On the other hand, function generators generates various waveforms like sine, square, sawtooth, triangular. It generates simple repetitive waveforms of varying magnitudes and frequencies. It uses a signal generator circuit and an electronic oscillator to generate signals, which act as stimuli for testing and designing purposes. What is a logic probe? Logic probes are inexpensive handheld probes that are used to analyze the logic states (high/true: logic 1 or low/false: logic 0) of digital signals. They are used by electrical and electronics engineers to verify or debug their hardware circuit designs. Using a Logic Probe https://www.youtube.com/watch?v=PbFqZk9Pyfg logic pulser is a very effective tool for inspecting and repairing logic circuits. It can directly inject a signal into the logic circuits Page 10 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Using a Logic Pulser https://www.youtube.com/watch?v=Zw4cqM3K_pY Insulation resistance test Insulation resistance tester Insulation testers use a high voltage, low current DC charge to measure the resistance within wires and motor windings to identify current leakage and faulty or damaged insulation, which can lead to arc faults, blown circuits, and risk of electrical shock or fire. What is the minimum value of insulation resistance allowed by bs7671? 1 MΩ By reference to Table 61 of BS 7671, Regulation 612.3. 2 indicates that the minimum acceptable value of insulation resistance for a distribution circuit with a distribution board or consumer unit and all its final circuits connected is 1 MΩ. Line – CPC ‘earth’ insulation resistance test Page 11 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds L – N insulation resistance test How to perform an Insulation Resistance Test https://www.youtube.com/watch?v=JWleZaw9790 Page 12 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Current tracer The basic idea is that the tracer detects the magnetic field that surrounds a conductor or trace through which current is flowing. It does not matter if the conductor is insulated. The current tracer is responsive to current over a wide range, typically from 1 mA to 1 A. A prominent indicator lamp resides at the probe tip and its brightness varies with the amount of current. A control can be used to adjust sensitivity. Then, the procedure is to move along a conductor or trace, taking note of the current. An abrupt change signals that a current sink or source has been located. Trouble can arise when there is a fault within an IC, but such difficulties are probably less frequent than nearly-invisible solder bridges that ground out (with varying amounts of resistance) or short adjacent live traces. When this fault has been corrected, operation is frequently restored without wholesale replacement of numerous semiconducting devices. Using a Current Tracer to Find Logic and Ground Shorts https://www.youtube.com/watch?v=Verow5aGL0w Frequency meter When the supply is given to the Weston frequency meter, the current starts flowing into the coil A and B. The perpendicular magnetic field set up in the coils because of the current. The magnitude of the field depends on the current passes through the coils. The magnetic field of both the coil A and coil B acts on the soft iron and the magnetic needle. The position of the needle depends on the relative magnitude of the magnetic field acts on it. Page 13 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Frequency Measurement https://www.youtube.com/watch?v=eIcyFo-nxNc https://www.youtube.com/watch?v=foGhjGu-FUg AC Bridges The AC Bridges are the alternating current electrical circuits used to find or measure the unknown resistance, inductance, and capacitance. These are basically measuring instruments similar to DC Bridges Formula Above two equations represent the basic equations for the balance of an ac bridge. Equation 𝑍1 𝑍4 = 𝑍2 𝑍3. Page 14 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds What is a virtual instrument? A virtual instrument is simply a software that recreates the sounds of a musical instrument with a computer. https://www.virtualmusicalinstruments.com/ Use some spectrum analyzers apps to view the frequencies. https://www.electronics-notes.com/audio-files/square-wave-audio-300Hz.mp3 Waveform types There are many different types of waveform that are seen in electronic circuits. Each type of waveform has its own characteristics and is seen in different places. The different types of electronic waveform or signal are used in different areas. Sine waves are seen in many RF circuits, whereas square waves are seen in many logic applications and ramps, sawtooth waveforms where a voltage or current may linearly ramp up to a given voltage before resetting. Each type has its own characteristics. Sine wave: Sine waves (and not sign waves as has been seen in some cases) are signals that oscillate smoothly either side of a central value - normally zero volts. Sine waves can be expressed as the sine of the angle where there are 360° for each cycle or 2π radians. The sine wave follows the amplitude for any given point can be calculated using V sin(ω.t) where V is the peak voltage, ω is the angular velocity and t is the time. Simulation link (Sine Wave generator) https://www.falstad.com/circuit/e-sine.html Page 15 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Square wave: Square waves switch between two values. Square waves have the same amount of time in each state - they are square waves after all. Simulation link (Square Wave generator) https://www.falstad.com/circuit/e-555square.html Triangular waveform: A triangular waveform rises and then falls. The most common form of triangular waveform rises and then falls at the same rate, although it is possible for the rise and fall rates to be different if required. The rise and fall are linear lines and the transition between rise and fall is near instantaneous. Simulation link (Triangular Waveform generator) https://www.falstad.com/circuit/e-triangle.html Sawtooth (ramp) waveform: A sawtooth or ramp waveform is one which rises to its final value and then falls away with a near vertical drop. This gives a positive ramp waveform. It is also possible to have a negative ramp where the signal slowly falls from a maximum to the low value and then rises with a near vertical slope to the maximum value again. Page 16 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Ramp signals were widely used for analogue televisions where the spot scanned from one side of the screen to the other and then flew back to the beginning again. A ramp voltage was used to steadily move the spot across the screen and then the swift fall would return it to the start of the scan again. There are many other forms of waveform found in electronic circuits, but these are some of the more widely used. Simulation link (Sawtooth Waveform generator) https://www.falstad.com/circuit/e-555saw.html What is a ramp waveform? A ramp waveform that is similar to a sawtooth waveform but different in that it starts at zero level and gradually rises to its peak level and then instantly drops back to zero level to form one cycle. Sine, square, triangular, sawtooth (ramp) https://www.youtube.com/watch?v=2RoIG8DEt_8 Page 17 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds A pulse wave A pulse wave or pulse train is a type of non-sinusoidal waveform that includes square waves (duty cycle of 50%) and similarly periodic but asymmetrical waves (duty cycles other than 50%). Waveform parameters The sine wave follows a sine curve alternating equally either side of a central value. If the sine wave is displayed on an oscilloscope screen, it can be seen that there are several parameters that can be measured and used. The sine wave follows the values of sine over the period of the cycle. As one cycle is equivalent to 360° or 2𝜋 radians, the instantaneous value of sine can be calculated from the angle in degrees or radians, i.e. how far advanced the waveform is in its cycle. Parameters like the phase angle, amplitude, time period and the like can all be seen. The diagram below shows some of the main parameters of interest for the sine waveform including the time period, phase, amplitude and the like. Page 18 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Amplitude: It can be seen that the amplitude varies across the cycle, but two points which can easily be measured are the positive peak identified as +Apeak and the negative peak identified as -Apeak. Often the peak voltage of a sine wave is used as this is the voltage that would be generated if the waveform was fed into a diode rectifier with a smoothing capacitor after it. The capacitor would charge up to the peak voltage and hold this value, assuming there is no load. Another value known as the peak to peak voltage may also be used in some instances and this is just the total voltage between +Apeak and -Apeak, i.e. it is twice +Apeak. Time period: the time period is the period of time between one point on one cycle of the waveform and the corresponding point on the next one. In other words, it is the time for one complete cycle. Normally the most convenient point to take on a sine wave centred about 0V is the place where it crosses the 0V line. It is very easy for logic, or other circuitry to detect the zero crossing point for the positive (or negative) going edge. Phase: The phase of a sine wave can be understood as the horizontal position of a waveform with respect to one cycle. Looking at the diagram below, it can be seen that the instantaneous phase of the waveform with respect to the start is the angle that is angle that is between the start of the waveform and the current position. Page 19 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds This is often depicted on a circle, the being the vertical height as shown. The phase can be measured in degrees or radians and can be assigned the variable θ, or ϕ it is often easier to have the concept of phase difference between two waveforms. Again using the concept of the circle, it is the angle between the positions of the two waveforms when depicted on a circle. When viewed as the phase difference between two sine waves when viewed, for example on an oscilloscope, it can be seen as the difference in the position of the two waveforms. Page 20 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Frequency: Although not directly visible from a waveform like the one shown in the diagram above, the frequency of a sine wave is still very important. Page 21 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Electric current definition: An electric current is a flow of electric charge in a circuit. More specifically, the electric current is the rate of charge flow past a given point in an electric circuit. The charge can be negatively charged electrons or positive charge carriers including protons, positive ions or holes. Page 22 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Conventional current flow: The conventional current flow is from positive to the negative terminal and indicates the direction that positive charges would flow. Electron flow: The electron flow is from negative to positive terminal. Electrons are negatively charged and are therefore attracted to the positive terminal as unlike charges attract. Voltage basics Voltage can be considered as the pressure that forces the charged electrons to flow in an electrical circuit. This flow of electrons is the electrical current that flows If a positive potential is placed on one end of a conductor, then this will attract that negative charges to it because unlike charges attract. The higher the potential attracting the charges, the greater the attraction and the greater the current flow. Page 23 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds In essence, the voltage is the electrical pressure and it is measured in volts which can be represented by the letter V. Normally the letter V is used for volts in an equation like Ohm’s law, but occasionally the letter E may be used - this stands for EMF or electro-motive force. Voltage test points The test point is a way to determine if the cable is energized. The voltage test point is not intended for actual voltage measurements or phasing operations and has no direct connection to the conductor. It uses an impedance capacitance tap and only voltage indicating instruments designed for this application to establish the presence of voltage should be used. A voltage reading will indicate the presence of voltage, but a reading of no voltage is not sufficient to establish a de-energized circuit before touching the connector. Other procedures should be implemented to establish a de- energized circuit. Voltage tester https://www.youtube.com/watch?v=uT-OwmLkpx4 Power supply The power supply transformer raises or lowers the voltage as needed. Most devices require stepped down voltage from standard AC outlets, which output 100 to 240 Page 24 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds volts, to a much lower amount. Some transformers, however, will step up the voltage and isolate the incoming and outgoing circuits. What is resistance Resistance is the hindrance to the flow of electrons in material. While a potential difference across the conductor encourages the flow of electrons, resistance discourages it. The rate at which charge flows between two terminals is a combination of these two factors. In this analogy, the water pressure caused but he height of the water is analogous to the voltage, the flow of water is analogous to the current, and the restriction of the water flow caused by the pipe is analogous to the resistance. Page 25 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Electric power definition: Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. It is the rate of doing work. Definition of the watt: The watt is the SI unit of power defining the rate of energy conversion and it is equivalent to one joule per second. The watt can be defined according to the application: Page 26 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Electrical definition of the watt: one watt is the rate at which work is done when a current of one ampere, I of current flows through a network which has an electrical potential difference of one volt, V. W = V I Mechanical definition of the watt: one watt is the rate at which work is done when the velocity of an object is held constant at one metre per second against constant opposing force of one newton. 𝑃𝑜𝑤𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝑃 = 𝑉𝐼 𝐽𝑜𝑢𝑙𝑒 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑤ℎ𝑒𝑟𝑒 𝑉 = 𝐼= 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑆𝑒𝑐𝑜𝑛𝑑 𝐽𝑜𝑢𝑙𝑒 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑃 = 𝑉𝐼 [ × ] 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑆𝑒𝑐𝑜𝑛𝑑 𝐽𝑜𝑢𝑙𝑒 𝑃 = 𝑉𝐼 [ ] 𝑆𝑒𝑐𝑜𝑛𝑑 That is the definition of watt. 1 Joule per 1 second is 1 Watt. Inductance basics Inductance is the ability of an inductor to store energy and it does this in the magnetic field that is created by the flow of electrical current. Energy is required to set up the magnetic field and this energy is released when the field falls. As a result of the magnetic field associated with the current flow, inductors generate an opposing voltage proportional to the rate of change in current in a circuit. Inductance is caused by the magnetic field generated by electric currents flowing within an electrical circuit. Typically coils of wire are used as a coil increases the coupling of the magnetic field and increases the effect. There are two ways in which inductance is used: Self-inductance: Self-inductance is the property of a circuit, often a coil, whereby a change in current causes a change in voltage in that circuit due to the magnetic effect of caused by the current flow. It can be seen that self- inductance applies to a single circuit - in other words it is an inductance, typically within a single coil. This effect is used in single coils or chokes. Page 27 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Mutual-inductance: Mutual inductance is an inductive effect where a change in current in one circuit causes a change in voltage across a second circuit as a result of a magnetic field that links both circuits. This effect is used in transformers. Definition of the Henry: The inductance of a circuit is one Henry (L) if the rate of change of current in a circuit is one ampere per second and this results in an electromotive force of one volt. Direct current: As the circuit is made the current starts to flow. As the current increases to its steady value the magnetic field it produces builds up to its final shape. As this occurs, the magnetic field is changing, so this induces a voltage back into the coil itself, as would be expected according to Lenz's Law. The time constant T in seconds of the circuit which will include the inductor value L Henries and the associated circuit resistance, R Ohms can be calculated as L/R. T is the time for the current I amps to rise to 0.63 of its final steady state value of V/R. The energy stored in the magnetic field is 1/2 L I2. Page 28 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds The rise in current when a steady voltage is applied to an inductor When the current is switched off this means that effectively the resistance of the circuit rises suddenly to infinity. This means that the ratio L / R becomes very small and the magnetic field falls very rapidly. This represents a large change in magnetic field and accordingly the inductance tries to keep the current flowing and a back EMF is set up to oppose this arising from the energy stored in the magnetic field. When the back EMF is set up, the very high voltages generated mean that sparks can appear across the switch contact, especially just as the contact is broken. This leads to pitted contacts and wear on any mechanical switches. In electronic circuits this back EMF can destroy semiconductor devices and therefore ways of reducing this back EMF are often employed. Alternating current: For the case of the alternating current passing through an inductor, the same basic principles are used, but as the waveform is repetitive, we tend to look at the way the inductor responds in a slightly different way as it is more convenient. By its very nature, an alternating waveform is changing all of the time. This means that the resulting magnetic field will always be changing, and there will always be an induced back EMF produced. The result of this is that the inductor impedes the flow of the alternating current through it as a result of the inductance. This is in addition to the resistance caused but he Ohmic resistance of the wire. Page 29 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds It means that if the Ohmic resistance of the inductor is low, it will pass direct current, DC with little loss, but it can present a high impedance to any high frequency signal. This characteristic of an inductor can be used in ensuring that any high frequency signals do not pass though the inductor. Logic state The logical sense, true or false, of a given binary signal. A binary signal is a digital signal that has only two valid values. In physical terms the logical sense of a binary signal is determined by the voltage level or current value of the signal, and this in turn is determined by the device technology. 2-level logic. In binary logic the two levels are logical high and logical low, which generally correspond to binary numbers 1 and 0 respectively or truth values true and false respectively. Page 30 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds Distortion refers to any change in an original signal’s shape or characteristics; specifically, in electronics and communications it involves altering waveforms that carry information, such as sound signals or video streams. Distortion in a signal is the alteration or change of the shape or some other characteristic of the waveform. In contrast, noise is an external random signal added to the original signal. It's harder to remove the effects of noise than to remove the effects of distortion This external electrical noise includes lightning and electrical storms, electromagnetic interference from currents in cables, and frequency interference from equipment like radio transmitters. Electrical noise can disrupt circuit operation and potentially damage equipment. Page 31 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds RMS Voltage Graphical Method Whilst the method of calculation is the same for both halves of an AC waveform, for this example we will consider only the positive half cycle. The effective or rms value of a waveform can be found with a reasonable amount of accuracy by taking equally spaced instantaneous values along the waveform. The positive half of the waveform is divided up into any number of “n” equal portions or mid-ordinates and the more mid-ordinates that are drawn along the waveform, the more accurate will be the final result. The width of each mid-ordinate will therefore be no degrees and the height of each mid-ordinate will be equal to the instantaneous value of the waveform at that time along the x-axis of the waveform. Page 32 of 33 Unit 314 Electrical and Electronic Measurement, Testing and Fault Diagnosis City and Guilds RMS Values Oscilloscope Vertical Position and Offset explained https://www.youtube.com/watch?v=-eccL4oLVM4 AC/DC Coupling https://www.youtube.com/watch?v=UJ16QDyfw94 The lower half of the image is symmetrical whereas the upper half is not. That is the offset. The top part of the image shows a DC offset. It actually moves the zero point. The cause could be sometimes a DC voltage is superimposed on the signal and it causes the zero point go up or down. It depends on the voltage which is positive or negative. In this example the upper image shows the signal carrying a positive DC offset. Page 33 of 33