QE 108 Course Book
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QE108: ELECTRICITY Electrical Measurements Laboratory Report Name : Reg. No: Group No: Year : Session 1: Experiment 1 Permanent Magnet Moving Coil Galvanometer Construction DATE: OBJECTIVE: To study the construction and principle of operation of a Permanent Magnet Moving Coil (PMMC) Galvanometer APPARATUS: Opened PMMC galvanometer RELATED KNOWLEDGE Derive an expression relating the deflection (θ ) of the indicator of a PMMC and the current (i ) flowing through it. r N θ S X Figure 1: Galvanometer Principle LABORATORY WORK: i. Observe the opened Galvanometer provided and identify the main components. ii. Sketch the Galvanometer indicating all the major components. iii. Briefly describe the function of each component on the same sketch. Figure 2: Sketch of the Galvanometer QE108: Electricity – Laboratory sessions Session 1: Experiment 2 PMMC Galvanometer Applications - I: DC Ammeter DATE: OBJECTIVE: To use the PMMC galvanometer as a DC Ammeter APPARATUS: Note the details of the following apparatus that are provided to you. Moving coil meter Identification number: ......................... Full scale deflection: ............................ Meter resistance: .................................. Wire wound rheostat Rated current: ..................................... Total resistance: .................................. DC power supply: ................. “Eureka wire”(Resistance/meter): ................. RELATED KNOWLEDGE (Complete this before coming to the lab) i. Find the minimum resistance that may be connected across the terminals of the given power supply, if the maximum permissible current that can be drawn from it is 1A. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... ii. Derive an expression for the length of the Eureka wire that has to be connected as a shunt to the above moving coil meter to convert it to an ammeter (0-100 mA). Ifs ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... iii. Calculate Ra , Rb , Rc of universal shunt for converting this galvanometer to a multiple-range ammeter with ranges: (0 − 1mA) (0 − 10mA) and (0 − 100mA) : ............................................................................................ ............................................................................................ ............................................................................................ ............................................................................................ ............................................................................................ ............................................................................................ ............................................................................................ ............................................................................................ QE108: Electricity – Laboratory sessions Session 1: Experiment 2 RELATED WORK (contd.) ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... LABORATORY WORK Part - I: Ammeter PROCEDURE 1. Set the wire to the calculated length and connect it across the moving coil meter. 2. Connect the circuit as shown in Figure E2-1. 3. Set the rheostat to about the mid position and keep it fixed at the same position till the end of the L1 experiment. Figure -1: Construction of a moving coil galvanometer 4. Switch on the circuit and measure the current I 1 . 5. Reconnect the ammeter at an appropriate position to measure the current I 2 . 6. Reconnect the ammeter at an appropriate position to measure the current I 3 . 7. Record the range of uncertainty of the readings I1 I2 + E - I3 A Figure E2-1: Experimental circuit OBSERVATIONS: (a). Range of uncertainty = (b). Galvanometer readings: Observed Current Measured Current ( µA ) I1 I2 I3 Table E2-1 QE108: Electricity – Laboratory sessions Session 1: Experiment 2 CALCULATION: (a). Calculate the multiplication factor of the ammeter ............................................................................................................................................................... ............................................................................................................................................................... ............................................................................................................................................................... (b). Do a specimen calculation to find the actual currents ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. TABULATION: Observed Current Actual Current ( mA) I1 I2 I3 Table E2-2 Part – II: Multiple-Range Ammeter (Universal Shunt) PROCEDURE 1. Observe the values of resistors in the universal shunt provided and compare them with the calculated values 2. Reconnect the circuit in Figure E2-1 to measure the currents up to 10mA and repeat the experiment. OBSERVATION: Observed Current Measured Current ( mA ) I1 I2 I3 Table E2-3 CALCULATION: (a). Calculate the multiplication factor of the ammeter ............................................................................................................................................................... ............................................................................................................................................................... ............................................................................................................................................................... (b)................... Do a specimen calculation to find the actual currents ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ............................................................................................................................................................... QE108: Electricity – Laboratory sessions Session 1: Experiment 2 TABULATION: Observed Current Actual Current ( mA) I1 I2 I3 Table E2-4 DISCUSSION: 1. Calculate the resistance of your ammeter in part-I 2. Explain the loading effects of the ammeter on the current that you are trying to measure. 3. Briefly explain why a simple shunt arrangement cannot be used in place of an universal shunt. ...................................................................................................................................................................... ...................................................................................................................................................................... ...................................................................................................................................................................... ...................................................................................................................................................................... ...................................................................................................................................................................... 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QE108: Electricity – Laboratory sessions Session 1: Experiment 3 PMMC Galvanometer Applications - II: DC Voltmeter DATE: OBJECTIVE: To use the PMMC galvanometer as a DC Voltmeter APPARATUS: Note the details of the following apparatus that are provided to you. Moving coil meter Identification number: ......................... Full scale deflection: ............................ Meter resistance: .................................. Wire wound rheostat Rated current: ..................................... Total resistance: .................................. DC power supply: ................. Carbon resistors: Colour code..........................Value:................... RELATED KNOWLEDGE (Complete this before coming to the lab) Calculate the value of the resistor to be connected to convert this galvanometer to a DC voltmeter of full scale reading of 2.5 V. ..................................................................................... V Rs Vm , Rm ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... LABORATORY WORK PROCEDURE 1. Choose suitable resistors to get the above-calculated value and connect them in series with the moving coil meter. 2. Connect the circuit as shown in Figure E3-1 with the voltmeter between terminals 1 and 2. 3. Switch on the circuit and measure the voltage. 4. Connect the voltmeter between terminals 1 and 3 and measure the voltage. 5. Connect the voltmeter between terminals 2 and 3 and measure the voltage. 6. Record the range of uncertainty of the readings. 2 1 E V Figure E3-1: Experimental circuit QE108: Electricity – Laboratory sessions Session 1: Experiment 3 OBSERVATIONS: (a). Range of uncertainty = (b). Galvanometer readings: Observed Point Measured Current ( mA) 1 2 3 Table E3-1 CALCULATION: (a). Calculate the multiplication factor of the voltmeter ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ (b). Do a specimen calculation to find the voltage for readings in Table L3-1 ............................................................................................................................................................ .................................................................................................................. .......................................... ............................................................................................................................................................ TABULATION: Observed Point Actual Voltage ( mV ) 1 2 3 Table L3-2 DISCUSSION: 1. Calculate the resistance of your voltmeter 2. How does the insertion of the voltmeter affect the voltage that you are trying to measure? Justify your answer ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... ................................................................................. .................................................................................... QE108: Electricity – Laboratory sessions Session 2: Experiment 1 PMMC Galvanometer Applications – III: Ohmmeter DATE: OBJECTIVE: § To construct an ohmmeter with the given moving coil meter § To measure resistance using the constructed Ohmmeter APPARATUS: Identify the following apparatus and note the details § Moving coil meter o Identification number: o Full scale deflection with shunt (Ifs): § Wire wound rheostat o Rated current: o Total resistance: § DC power supply: (2 V) § Standard Resistor: § Carbon resistors: § Capacitor § Diode RELATED KNOWLEDGE (Complete this before coming to the lab) Consider the circuit given in Figure E4-1. Let the full-scale deflection of the meter be I fs . Zero adjusting resistor Rz is adjusted to give full scale deflection when terminals x and y are short circuited. When a known resistance Rk is inserted between the terminals A and B, with Rz kept unchanged the current is I k . When an unknown resistance RX is inserted between the terminals A and B, the current is I x . Prove that: RX = Rk ⋅ I k (I fs − I x ) ⋅ I x (I fs − I k ) ....................................................................... ....................................................................... ....................................................................... ....................................................................... ....................................................................... ....................................................................... ....................................................................... ....................................................................... Figure E4-1 ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ................ ....................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... QE108: Electricity – Laboratory sessions Session 2: Experiment 1 LABORATORY WORK Part A: Ohmmeter Construction PROCEDURE § Connect the circuit as in Figure E 4-1. § With rheostat R at the maximum setting, short circuit terminals A and B. § Now adjust RZ to give full-scale deflection I fs on the meter. § Insert standard resistance Rk between the terminals A and B and measure the current I k . OBSERVATIONS: Measured current (I k ) : ......................... SPECIMEN CALCULATION: Do a specimen calculation to find RX for a given value of I x = 1,2...10 mA. .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ ............................................................................ TABULATION: RX ( Ω ) I x (mA) 1 2 3 4 5 6 7 8 9 10 Table E4-1 RESULTS: (a). Mark a suitable scale for the constructed Ohmmeter Figure E 4-2: Ohmmeter Scale (b). Plot Rx Vs I x (attach a separate graph sheet) – Figure E4-3 QE108: Electricity – Laboratory sessions Session 2: Experiment 1 Part B: Ohmmeter Measurements PROCEDURE: § Measure the resistance of components shown in Table L4-2 using the above Ohmmeter § Connect the unknown resistance to be measured ( R X 2 ) between the § terminals A and B and measure the corresponding current I 2 Find the corresponding resistance value using Figure L4-3. OBSERVATIONS: Components Nominal Value (Ω) Ix ( mA) Observed Value (Ω) R1 R2 R3 R1 R2 R3 R1 R3 R2 R1 R2 R3 Table E4-2 DISCUSSION: § For one of your measurements estimate the possible reading error on the milliampere scale and hence estimate the corresponding reading error on the ohm scale (use the graph) § If the measured values of the resistors are different from nominal values give possible reasons. QE108: Electricity – Laboratory sessions Session 2: Experiment 2 Multimeter Applications DATE: OBJECTIVE: § To learn how to use multimeter for measuring Resistance, DC voltages and AC voltages § To learn how to use multimeter for checking connectivity § To learn how to check diodes and transistors and identify pins using multimeter APPARATUS: Identify the following details of the analogue multimeter provided § Analogue Multimeter o Type: o DC resistance: o AC resistance: LABORATORY WORK: PROCEDURE: Part A: Measurements (a). Resistance: § § § § Study the range selector switch, terminals, and marking on the meter. Select two resistors having nominal values respectively. Set the multimeter range selector to suitable positions and measure their resistance. Also note down the error due to uncertainty of the scale. Measure the resistance between your left and right hands and also note down the error due to uncertainty of the scale. (b). DC Voltage: § § § § § Set the meter to the highest DC voltage range. Measure the voltage of the given battery or DC power supply, using the multimeter. Roughly calculate the expected voltage reading if the range is lowered by one step. If the calculated value does not exceed the full scale deflection, lower the range by one step and measure the voltage. Repeat from step (3) until you get the maximum possible deflection. (c). AC Voltage: § Set the meter to highest AC voltage range § Repeat from step (2) to (5) in DC voltage procedure with the ac power supply. OBSERVATIONS: (a). Resistance Resistance to be measured Multimeter Range Measured Value (Ω ) 100 Ω 1 kΩ Hand to Hand QE108: Electricity – Laboratory sessions Table E5-1 Error due to uncertainty Session 2: Experiment 2 (b). DC Voltage Multimeter Range Measured Value (V) Error due to uncertainty Table E6-2 (c). AC Voltage Multimeter Range Measured Value (V) Error due to uncertainty Table E6-3 PROCEDURE: § § § Part B: Connectivity checking Set the multimeter to the lowest Ohm range Apply the probes to the terminals where connectivity is to be checked Observe the indicator and determine the connectivity OBSERVATION: Show the connections of the switch in Figure E6-1(a) and (b), when it is in position 1 and position 2 respectively. POSITION 1 POSITION 2 Figure E6-1: Connection diagram of the switch Part C: Identifying Diode and Transistor Pins Note: When an Analogue multimeter is set to Ohm range, the ‘Black’ (COM) probe of the multimeter has a ‘+’ polarity with respect to the ‘Red’ ( +) probe. However, in digital multimeters the ‘Black’ (COM) probe of the multimeter has a ‘-’ polarity with respect to the ‘Red’ ( +) probe. PROCEDURE (a). Diode: § Mark the two pins of the diode as Pin 1 and Pin2. § Connect ‘Black’ probe of the multimeter to Pin 1 and ‘Red’ probe to Pin 2 and observe the connectivity § Connect ‘Black’ probe of the multimeter to Pin 2 and ‘Red’ probe to Pin 1 and observe the connectivity (b). Transistor: § Mark the pins of the transistor as Pin 1, Pin 2 and Pin 3. § Connect the ‘Red’ probe of the multimeter on Pin 1. § Connect the ‘Black’ probe of the multimeter to the other two pins in turn and observe connectivity § Repeat from step 2 with ‘Red’ probe on Pin 2 and then on Pin 3. QE108: Electricity – Laboratory sessions Session 2: Experiment 2 OBSERVATIONS: (a). Diode: Pin 1 Pin 2 Connectivity Black Red Red Black Table E6-4 (mark with ‘ ü’ or ‘û’) (b). Transistor: Pin 1 Pin 2 Red Red Black Black û û (mark with ‘ ü’ or ‘û’) û û û Black Connectivity Black Red Red û Pin 3 Black Black Red Red Table E6-5 RESULTS: (a). Diode: Identify the Pins of the diode P Pin N Pin Figure L6-2 (b). Transistor: (i). Identify the type of the transistor (Tick the correct answer) BASE P BASE N BASE P N Figure L6-3 P N BASE (ii). The Base of the transistor is Pin DISCUSSION: Briefly explain, how to identify the collector and emitter pins of the transistor. QE108: Electricity – Laboratory sessions Session 3: Experiment 1 Ammeter Voltmeter Method of Measuring Resistance DATE: OBJECTIVE: § To measure resistance using voltmeter ammeter method § Analyse the effects of voltmeter and ammeter position on accuracy APPARATUS: Identify the following apparatus and note the details § Ammeter (Moving coil meter with current shunt) (A) o Identification number: o Full scale deflection with shunt ( I fs ): 100 mA o Multiplication factor: o Total resistance of Ammeter ( RA ): § Voltmeter (Moving coil meter with voltage shunt) (V) o Identification number: o Full scale deflection with shunt (V fs ): 1 V o Multiplication factor: o Total resistance of Voltmeter ( RV ): § Wire wound rheostat o Rated current: o Total resistance: § Standard resistance box (R) o Resistance range: o Resolution: o Voltage rating: o Current rating: § DC power supply: (5 V) RELATED KNOWLEDGE (Complete this before coming to the lab) Consider the circuit given in Figure E3.1-1 and find the value of R for which the percentage errors in both methods are equal. E V RV R E R A V V R A RA (b) (a) RA Figure E3.1-1 ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ....................................................................... QE108: Electricity – Laboratory sessions Session 3: Experiment 1 .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. ............................................................................ .................................................................. LABORATORY WORK PROCEDURE § Connect the circuit as in Figure E3-1 (a). § Set the Resistance box to § Set the rheostat to at the minimum setting. § Switch on the power § While ensuring the Ammeter reading (Im) not to exceed Ifs, adjust the rheostat to bring the voltmeter reading (Vm) to a clearly readable value [e.g. 0.6 V]. § Observe Vm and Im. § Switch off the supply. § Connect the circuit as in Figure E3-1 (b) and repeat from step 3 to 8. § Repeat from step 2 with R increased in steps of , until . OBSERVATIONS: Actual value of resistance R (Ω ) 5 7 9 11 13 15 17 19 21 23 25 Method 1 Vm (V) I m (mA) Method 2 Vm (V) I m (mA) Table E3.1-1 SPECIMEN CALCULATION: Do a specimen calculation to find the value of R and percentage error using Method 1: ................................................................... Method 2: ................................................................. ................................................................... ................................................................. ................................................................... ................................................................. ................................................................... ................................................................. ................................................................... ................................................................. ................................................................... ................................................................. ................................................................... ................................................................. QE108: Electricity – Laboratory sessions Session 3: Experiment 1 TABULATION Actual value of resistance R (Ω ) 5 7 9 11 13 15 17 19 21 23 25 Method 1 Measured R ( Ω ) Error % Method 2 Measured R ( Ω ) Error % Table E3.1-2 Plot the Error % in method 1 and method 2 Vs actual value of R. CALCULATIONS: (a). Find the value of R for the Error % in both methods to be equal (use graph) (b).Calculate the value of R for the Error % in both methods to be equal ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... ..................................................................... DISCUSSION: For one of your measurements estimate the possible reading error of the resistance due to the uncertainty in ammeter reading QE108: Electricity – Laboratory sessions Session 3: Experiment 2 Megohm Meter (Megger) DATE: OBJECTIVE: § To learn how to use the “Megger” Insulation tester to measure the resistance of various insulations § To measure the insulation resistance of a wiring system APPARATUS: Identify the following apparatus and note the details § “Megger” insulation tester: (500 V/ 1000 M , Hand driven type) RELATED KNOWLEDGE (Complete this before coming to the l ab) Draw the internal circuitry of a Megohm meter and briefly explain its operation .................................................................................. .................................................... ............................ .................................................................................. ................................................................................ .................................................................................. ................................................................................ .................................................................................. ................................................................................ .................................................................................. ................................................................................ .................................................................................. ................................................................................ .................................................................................. ................................................................................ Figure E3.2-1: Internal Circuitry of a Megger LABORATORY WORK Part A: Resistance of Insulation Materials PROCEDURE § Measure the insulation resistance of the materials provided. § Measure the insulation resistance between o Phase-Neutral o Phase-Insulating cover o Neutral-Insulating cover of the service wire provided. § Measure the insulation resistance between o Primary-Secondary winding o Primary-Earth o Secondary-Earth terminals of the each transformer provided and identify the faulty windings (if any) QE108: Electricity – Laboratory sessions Session 3: Experiment 2 OBSERVATIONS: (a). Resistance of insulation materials Material Insulation Resistance / (M Ω ) Thin metal Thick metal Plastic Thin Hardboard Thick Hardboard Table E3.2-1 (b). Resistance of the service wire Terminals Insulation Resistance / (M Ω ) Phase-Neutral Phase-Insulating cover Neutra-Insulating cover Table E3.2-2 (c). Resistance of the single-phase transformers Terminals Insulation Resistance / (M Ω ) Transformer 1 Transformer 2 Primary-Secondary Primary-Earth Secondary-Earth Table E3.2-3 Part B: Test on a Wiring System PROCEDURE § Identify each sub circuit and draw the wiring diagram by checking electricity § Switch off the supply voltage, put all lamps in the holder and close all the switches, so that the wiring is electrically connected together. In the case of the plug circuit L and N terminals should be short-circuited. § Measure the insulation resistance of each sub circuit to earth. § Remove all lamps and close the switches, so that the phase and neutral wires are disconne cted from each other. § Measure the insulation resistance between the phase conductor and the neutral for each sub circuit. § Measure the insulation resistance of the complete wiring system OBSERVATIONS Figure 3.2-2: House Wiring Diagram QE108: Electricity – Laboratory sessions Session 3: Experiment 2 Resistance between phase-neutral and phase-earth. Sub circuit Resistance / (M Ω ) Phase and Earth 1 2 3 Phase and Neutral Table E3.2-4 Insulation resistance of the complete wiring system § § Phase and earth:........................ Phase and Neutral: .................... CALCULATIONS AND RESULTS: (a). Calculate the total insulation resistance and leakage current between phase and earth at normal voltage (b). Calculate the total insulation resistance and leakage current between phase and neutral at normal voltage .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. .......................................................................... .................................................................................. ........................................................... .................................................................................. DISCUSSION: § § § Check whether the resistance values that you observed agree with IEE wiring regulations (refer note available) What is the use of having a ring supply Explain uses of Megger QE108: Electricity – Laboratory sessions Session 4: Experiment 1 Wheatstone Bridge DATE: OBJECTIVE: § To measure the cold resistance of a tungsten filament lamp APPARATUS: Identify the following apparatus and note the details § Moving coil galvanometer o Identification number: o Full scale deflection with shunt (Ifs): § Galvanometer shunt § Decade (Standard) resistance box (R) o Resistance range: o Resolution: o Voltage rating: o Current rating: § Carbon resistors to be used as ratio arms: § DC power supply: (2 V) § Tungsten filament lamp: § Switch RELATED KNOWLEDGE (Complete this before coming to the lab) Considering the circuit shown in Figure E4-1 and starting from the basic equations, show that L = P R at the balance condition of the bridge. Q P Q S R G L SW1 2V Figure E4-1 ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... ........................................................................ ....................................................................... QE108: Electricity – Laboratory sessions Session 4: Experiment 1 LABORATORY WORK PROCEDURE § Connect the circuit as shown in Figure L8-1. § Adjust the galvanometer shunt to get the lowest galvanometer sensitivity § Switch the power on § Bring the galvanometer to zero by adjusting R § Increase the sensitivity of the galvanometer to the next level. § Repeat from step 4 until the sensitivity of the galvanometer is set to the highest level. § Observe the value of R § Switch off the supply. § Interchange arm resistors P and Q and repeat from step 2. OBSERVATIONS: (a). Resistance Test No. P (Ω) Q (Ω) R (Ω) 1. 2 (P and Q interchanged) Table L8-1 CALCULATIONS AND RESULTS: Calculate the cold resistance of the filament lamp. DISCUSSION 1. Explain in detail, the reason for interchanging the ratio arm resistors P and Q and taking the average value of R (Derive any equations used) QE108: Electricity – Laboratory sessions
