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TOPIC 2.5- Testing Equipments.pptx
- 1. Know the principlesof basic electrical circuits Outcome :State how instruments are connected into circuits in order to measure electrical quantities. Topic2.5-TestingEquipment's BY: ENGR. MART NIKKI LOU M. MANTILLA, REE, RME
- 2. Calculate powerin abasic electrical circuits Series and parallel. Last session
- 3. State how instrumentsare connected into circuits in order to measure electrical quantities. Voltmeter, ammeter, wattmeter, ohmmeter. This session
- 4. Digital Meters Digital meterstake an input signal and converts it to a series of pulses Digital signals are either on or off Advantages of digital meters • Strong • No moving parts • Accurate • Easy to read Disadvantages of digital meters • Batteries need replacing regularly • Not easy to tell if it is the meter or the circuit that is at fault • Readings may vary
- 5. Analogue Meters Analogue signalsare variable which mean they are changing all the time. Moving Iron Meter (repulsion type) A moving-iron meter is based on the principle that when two magnetic fields oppose each other they deflect or try to move in opposite directions
- 6. Moving Iron Meters Thereare two types of moving iron meters repulsion and attraction which both work in a similar way This type of meter is less commonly used now Advantages • Cheap • Fairly robust •Can be used on a.c and d.c. Disadvantages • Uneven scale • Can be affected by heat • Can be affected by stray magnetic fields • Only accurate at the lower end of the scale
- 7. Moving Coil Meter Acoil iswound on an aluminium frame. I t is supported via a spindle resting in jewelled bearings which enable it to move freely.
- 8. Moving Coil Meter Thismeter is much easier to read because the scale is linear, meaning the accuracy is constant Advantages • Even scale • Accurate • Unaffected by stray magnetic fields Disadvantages • Fragile • Expensive • Only measures d.c.
- 9. Voltmeter • On sitefor general purposes we use a multimeter to test for voltage. • A specific voltage testing device is called a voltmeter. • Voltmeter’s measure the difference in potential between to point on a circuit. • This test instrument must be connected in parallel acrossthe load. • Voltmeters have very high internal resistance to ensure accurate readings.
- 10. Voltmeters Voltmeters measure Voltage Voltmetershave to be connected acrossthe load (In parallel) U Load U The voltmeter isconnected in parallel with the load. The same voltage is dropped across the load and the voltmeter.
- 11. Altering the Rangeof the Voltmeter The problem with connecting a voltmeter into a circuit is that the current issupposed to flow through the load, what happens is that it splits up and some current passes through the voltmeter. The voltmeter needs to have a resistance that is very high, so reducing the current to a negligible amount. T o alter the range of the voltmeter we must connect a resistor in series with the meter, this is called a multiplier. Voltmeters
- 12. Ammeter • On sitefor general purposes we use a multimeterto test for current. • A specific current testing device is called a ammeter. • ammeter’s measure the current that pass through them (current flow). • T histest instrument must be connected in series with the circuit. • Ammeter’s have very low internal resistance to ensure false readings aren’t given.
- 13. Ammeters Ammetersmeasure current In acircuit it is critically important that the ammeter is placed in the correct position. (IN SERIES) T o understand why think back to resistors. In a series circuit the current is constant throughout the circuit. The ammeter is connected in series with the load and we will assume that the instrument has a resistance and so a volt drop when the current flows.
- 14. Increasing the Rangeof the Meter If we want to increase the range of the instrument. Which is sometimes necessary as the current can destroy the sensitive coil in the meter. We have to place a resistor in parallel with the meter. This resistor has a very low value and is called a shunt. We have in effect two resistors in parallel connected to a resistor (the load) that isin serieswith them Ammeters
- 15. Wattmeter • On sitefor general purposes we use a multimeter to test for power . • A specific power testing device is called a wattmeter. • wattmeter’s measure the current and voltage that pass through them and display (apparent) power in watts.
- 16. Wattmeter AMMET ER (SERIES) VOLT METER (PARALLEL) Current coil (SERIES) WATTMETER Potential coil (PARALLEL) InDC circuits you can simply measure voltage and current and using P =Ix V and calculate power. In AC circuits using this method you only calculate APPARENT POWER. This value will be incorrect unless we have unity power factor (1). This isdue to factors within a system such as inductance and capacitance, these factors make he current lead or lag the voltage. We use P =Ix V x cos ø In circuits with any of these two factors we must use a wattmeter to measure power.
- 17. Wattmeter Three meter method Currentcoil Potential coil Meter two Meter three Meter one Neutral
- 18. Meter one Meter two Wattmeter Twometer method
- 19. Ohmmeter • Ohmmeter’s measureimpedance (Z)also known asresistance. • On site for general purposes we use a multimeterto test forimpedance. • A specific impedance testing device iscalled a ohmmeter . • Impedance isdefined asthe total opposition to the flow of alternating current at a specific frequency. • Quite often these types of meters are referred to as LRC metres as the quantify readings from resistance, inductance and capacitance.
- 20. Ohmmeter • You mustconnect the tester at each end of the resistive load or circuit. • T est leads must be zeroed out before the test or tested initially and deducted from the result total.
- 21. State how instrumentsare connected into circuits in order to measure electrical quantities. Voltmeter, ammeter, wattmeter, ohmmeter. Consolidation
- 22.