This week.. Components & Symbols Conductors, Insulators, Semi Conductors Multi-meters & Units of Measure Measuring Potential Difference Measuring Current Calculating Input Power Measuring Resistance
Components & Symbols Identify resistors, capacitors including fixed, variable and electrolytic types, inductors, transformers, diodes, transistors, integrated circuits, crystals, microphones and loudspeakers.
Conductors, Insulators, Semi Conductors First we need to understand Electrons. N – Neutrons– Electrons+ Protons *Copper Atom Atoms have a positively charged centre (nucleus). Orbiting around the centre are neutrons. Neutrons are negatively charged. There are often layers of neutrons like the layers of an onion. The neutrons further away from the centre have less attraction to the centre. These electrons can be made to move from one atom to another by applying Potential difference.
Conductors, Insulators, Semi Conductors What is a conductor? Conductors have a naturally low resistance because of their freely available mobile electrons. Metals are good conductors, some common metals used are; Copper, brass, steel, and nickel.
Conductors, Insulators, Semi Conductors What is a conductor.
Conductors, Insulators, Semi Conductors What is an insulator? Insulators have a naturally high resistance because their electrons are so tightly bound that there are virtually no mobile electrons. Insulators are used to stop current flowing. Examples Wood, rubber, plastics, ceramic, glass, and dry air. Insulators can conduct on their surface, for example when wood becomes wet, or when there is high moisture in the air. Insulators can allow current to flow if the potential difference is too high at its ends.
Conductors, Insulators, Semi Conductors What is an insulator? Potential Difference required to break down insulators InsulatorPD (Volts) Mica500,000 v Oiled Paper400,000 v Glass250,000 v Air30,000 v
Conductors, Insulators, Semi Conductors What is a semi conductor? Somewhere between conductors and insulators. They can act like both. Most commonly silicon is used to make them. Pure silicon is used and mixed with other substances to form two Different types. These are known as “P” and “N” type The “N” type material has the spare electrons, whereas the “P” type material appears to have few electrons. Semi conductors examples are diodes, transistors and IC’s
Multi-meters & Units of Measure Units of Measure TypeUnit Potential difference (Voltage)Volts (V) CurrentAmps (A) PowerWatts (W) ResistanceOhms (Ω) CapacitanceFareds (F) InductanceHenry (h) FrequancyHertz (Hz)
Multi-meters & Units of Measure Units of Measure TypeSN Giga (G)10 9 Mega (M)10 6 kilo (k)10 3 milli (m)10 -3 micro (u or ) 10 -6 nano (n)10 -9 pico (p)10 -12 PSU uses 12v and 10mA To work out Power. 12v times 10mA Press 12 10 3 Answer 120mW
Multi-meters & Units of Measure Multi-meters There are two main type of meters – Analogue and Digital. Both of them have advantages and disadvantages. Analogue – Better at reading a variable measurement where you wish to see the peak value. On a digital display as it is changing it is hard to tell. With the needle movement you can pick out the peak a lot more easily. Digital – Digital meters can have their positive and negative probes connected around the wrong way, where as with an analogue meter this can cause damage.
Multi-meters & Units of Measure Multi-meters DCV – Direct Current Voltage. Resistance Off Switch – Always switch back to OFF after measuring! DCA – Direct Current - Current. Diode / continuity check 1.Voltage 2.Current 3.Resistance
Multi-meters & Units of Measure Multi-meters To make the meter easier to read, each section is broken down into different ranges. You will see in this example Volts is in ranges 1000, 200, 20, 2000m, and 200m Also take note that you can also select whether you are using AC or DC. Its important to remember to select the correct value. When you are going to measure for example the voltage of a PSU output, you should first estimate the maximum voltage and then select the correct upper value. For example a 12v PSU, you should then select 20 on the meter. You can also start on the maximum and switch down the ranges until you can read the value correctly. Never start low and then go up as you could cause damage or get an incorrect reading.
Multi-meters & Units of Measure Multi-meters Some multimeters may require you to switch where the probes are put to carry out different measurements. For example when measuring Current this meter requires the positive probe is moved to the middle socket. Measuring current is basically the same as voltage in that you should select the highest value first on the meter and work your way down to get a more accurate reading. Nearly all meters use internal batteries, make sure you switch off the meter after use.
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - Please look at page 15 Worksheet 9 in the Intermediate book. 1.Turn on your Simple DC Circuit. 2.Switch on your Multi Meter and set it for use on 3v. 3.Place the probes across G and A 4.Make a note of the voltage
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - 1.Now place the probes in parallel to R1 2.Make a note of the voltage. R1
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - 1.Now place the probes at points D and C 2.Make a note of the voltage. R1
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - 1.Disconnect the wire X 2.Place probes at B and C when the circuit is off. Does the bulb light when you take your measurement? Remember to switch off your meter.
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - Results. Now add up values you measured. 1.Potential Difference across bulb 2.Potential Difference across R1 This should equal the measurement you took across Points D & C. (across battery) * If you are out by more than a few milli volts recheck your work.
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - Results. In a series circuit like this one the current flows through each component in turn. The potential difference across the battery is divided between the components in the circuit. The potential difference across each of those components depends on its resistance but if you add the all together it should be the same as the value across the battery. The potential difference across B and C when the circuit is off may be slightly higher than that across the battery when the circuit is switched on. This is because the potential difference drops slightly when current is flowing through the circuit.
Measuring Potential Difference Paul M0PFX A B C D E F G Y X + - Key Points. Potential difference causes current to flow. Potential difference is measured across (or ‘in parallel with’) components In a series circuit, the potential difference supplied by the battery will always be divided between the components in the circuit. A voltmeter has its own very high internal resistance, so it only draws a tiny amount of current in making the meter operate.
Measuring Current Paul M0PFX A B C D E F G Y X + - Please look at page 16 (worksheet 10). Measuring current is done in amps. Current is the flow of electrons around a circuit. Before we start you need to switch your multimeter to measure current, this may require changing the probe socket over. When measuring current your meter is at its most sensitive. Ensure you are careful or you could damage your meter.
Measuring Current Paul M0PFX A B C D E F G Y X + - Measuring current is done in series to the circuit. This means all current in the circuit is being measured as passes through the meter. The meter has a very low internal resistance so it has little effect on the current flowing through the circuit. In a series circuit it will measure the same at all parts of the circuit. If the meter is taken out of the circuit during the measurement, no current will flow as the circuit will have been broken.
Measuring Current Paul M0PFX A B C D E F G Y X + - On your Simple DC circuit make sure the X wire is not connected. 1.Set the meter to measure DC Amps. 2.Set the level to a high measurement e.g. 10amps, remember to change the probe socket. 3.Double check the range setting and then place the Red (+) probe onto pin C, and the Black (-) probe onto pin B 4.Current should be now flowing and the bulb should light. At this range you should not be able to make out a reading. 5.Once you confirmed that only a small current is flowing, switch to a lower range e.g. 1amp. Switch down lower if needed. Then make a note of the reading.
Measuring Current Paul M0PFX A B C D E F G Y X + - Extra. (optional) If you are in any doubt that the same current is flowing through all parts of the series circuit, try breaking the circuit between the bulb and resister. (Points F and G). Then short B and C using wire X. You can now place the meter between F and G and you should get the same reading you measured between C and B.
Measuring Current Paul M0PFX A B C D E F G Y X + - Summary. 1.Current flow through complete circuits 2.Current is measured in series with the circuit 3.You can measure the current anywhere in the series circuit and it will be the same. 4.An ammeter has a very low series resistance, so it doesn’t alter the current that it is trying to measure. That is why the bulb did light when you measured the current between B and C there was very little opposition to the current flowing through the meter.
Calculating Input Power The rate in which energy is used by an electrical system is called the input power, i.e. the power going into the system. The ‘system’ could be a single device such as a bulb, or a piece of equipment with many circuits. An amateur transmitter perhaps. In the Foundation level you would have come across that Power (W) is found by multiplying the Potential Difference (V) by the Current (I). Its important when doing these calculations to take care with the units of measure. e.g. 10mA x 12v is 0.01A x 12v. If you slip up here you will get the wrong answer.
Calculating Input Power Paul M0PFX A B C D E F G Y X + - Please look at page 20 (worksheet 12) 1.Turn on the Simple DC Circuit by connecting the X wire to C. 2.Place the voltmeter on the suitable low range. 3.Measure the potential difference across the bulb.
Calculating Input Power Paul M0PFX A B C D E F G Y X + - Please look at page 20 (worksheet 12) 1.Turn on the Simple DC Circuit by connecting the X wire to C. 2.Place the voltmeter on the suitable low range. 3.Measure the potential difference across the bulb. 4.Turn the circuit off by opening wire X. 5.Set the Ammeter to a suitable range 6.Check the polarity and measure the current flowing through the whole circuit (bulb will light when you connect the meter)
Calculating Input Power Paul M0PFX A B C D E F G Y X + - Multiply the current (amps) by the potential difference (volts). If necessary, convert the units first. The result will be the input power to the bulb in watts. The power should be in the region of 0.25 watts.
Calculating Input Power Example You can calculate the fuse to fit using the equations for input power. Amps = Watts / Volts An amateur’s station mains power supply unit is labelled as consuming 500 watts of power…. 500 / 230 = 2.17A Mains fuses come in 3,5, and 13 amps, so you should fit the lowest fuse with the rating higher than the current required. In this case a 3 amp fuse would be suitable.
Calculating Input Power Summary. Input power is the energy supplied to the circuit Input power of the bulb is the rate at which energy is supplied to the bulb. Output power is always less than input power Power (watts) = Volts x Amps Current passing through a resistor results in a transfer of electrical energy to heat energy in the resistor.
Measuring Resistance Page 23 worksheet 14. There are 3 ways to measure resistance. 1.Reading the colour codes, which you would have done when making the Simple DC Circuit 2.Calculate the resistance using a formula (to come later) 3.Measure the resistance using a multi meter.
Measuring Resistance Colour Code First Band gives Value Second Band gives Value Third Band gives multiplier for factor of 10 Fourth Band is the tolerance. Brown = 1, Black = 0, and Orange = 3 10 x 1000 = 10kohm with tolerance of 5% (Gold)
Measuring Resistance Brown = 1, Black = 0, and Orange = 3 10 x 1000 = 10kohm with tolerance of 5% (Gold) Tolerance. Tolerance tells you the actual value of the resistor could be plus or minus the value the colours tell you. In the above example it could be anything from 9.5kohm to 10.5kohm due to the tolerance being 5% which is 500ohm
Measuring Resistance Turn on your multimeter to measure Resistance. 1.Place the probes at either end of the resistor. (it doesn’t matter which way around). 2.Make a note of the resistor. 3.Check the colour code and see if it matches within the tolerance.
Measuring Resistance Measuring resisters in series. 1.Take some drawing pins and place them in the arrangement as shown on the right. 2.Solder two resistors between the pins as shown 3.Take the multimeter and measure the resistance. The result should be the sum of the two resistors.
Measuring Resistance Measuring resisters in series. 1.Take some drawing pins and place them in the arrangement as shown on the right. 2.Solder two resistors between the pins as shown 3.Take the multimeter and measure the resistance. The result should be half the value of the resistors. e.g. if both resistors are 200ohm, the value should measure 100ohms.
Measuring Resistance Summary 1.Resistance is measured in Ohms. 2.Resistor values can be read by using the resistor colour code. 3.Resistance can be measured using an ohmmeter 4.An ohmmeter has an internal battery and must be zeroed before use 5.Resistor values connected in series are added together 6.Two resistors of the same value connected in parallel have a total value of half of one of them.
Next Week Technical Basics and Components Part 2 Diode and Transistors..