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Transcript
Chapter - 2 Questions Answer the following questions :Show True or False :1- When connecting shunt resistance Rsh to the meter movement this will increase the range of the current measurement . ( ) 2- When connecting shunt resistance Rsh to the meter movement the sensitivity will decrease. ( ) 3- The clamp-on meter is used only to measure AC current . ( ) 4- The average power in an AC circuit is measured by wattmeter ( ) 5 - To get accuracy of voltage and current measurements select the scale that cause deflection of pointer at mid scale. ( ) 6 - The clamp-on meter is used only to measure DC current without opening the circuit. ( ) 7 - In Wattmeter: a- In wattmeter, current through moving coil is proportional to the voltage across the load and is in phase. ( ) b- Deflecting torque is directly proportional to current and to the strength of the magnetic field. ( ) c- Average value for AC power = Constant value for DC power. ( ) d- Power Factor sin Φ = Watts / Volt x Ampere ( ) 769840177 1 Switching Section Chapter - 2 Questions Complete the following :The clamp-on meter is used only to measure …………………………………… 1. 2- The average power in an AC circuit is measured by ……………………………. 3- To solve the problem of drawback when changing positions of the range in an elementary multi-range ammeter, we can : i- …………………………………………………………………………………… ii- ………………………………………………………………………………….. iii- ………………………………………………………………………………….. 4- The Ammeter is to be protected from high currents, during time of change range because it may cause for the ammeter the following defects : a- ……………………………………………… b- ……………………………………………… c- ……………………………………………… 5- Why a make-before-break switch is used to select the ammeter shunts? ……………………………………………… ……………………………………………… 6 - In Wattmeter: a- The wattmeter uses an ………………………. Movement . b- In measuring power, the wattmeter is connected,so that the load current flow through the…………………… coil. c- In wattmeter, the moving coil is connected ………… the line ……………… with the load. d- In wattmeter, a ……………………… is connected in …………….. with the moving coil. e- In wattmeter, in any given position of the coil ,the deflecting torque is ………………….. to the power e x I f- Wattmeter is used to measure …………….. and …………………. Power. 769840177 2 Switching Section Chapter - 2 Questions Solve the following : 1 ) Assuming that a 50 μA, 2 K Ω movement is available , Design an ammeter that provides the following ranges : 0 –1 ma 0 – 5 ma 0 – 100 ma . ( Calculate the shunt resistance for each range). Range 769840177 Rsh 3 Rm Switching Section Chapter - 2 Questions 2 – A meter movement 50 μA, 2 K Ω coil resistance is usd to construct aytron shunt ammeter. The resistance values are R1=1 Ω , R2 = 10 Ω ,and R3 = 95 Ω A ) Draw the circuit for ranges 1 ma, 10 ma, 100 ma . B ) Calculate : 1- The effective shunt resistance for each range ( RSHE ). 2- The effective meter resistance. ( RME ). 3- The input resistance ( RIN ). 4- Accuracy of the meter on the scales, if the RTH for the circuit under measurements is 40 K Ω. ( RTH = 40 K Ω ) 5- Error for each range. 769840177 4 Switching Section Chapter - 2 Questions Questions : 1 ) a - Supply the main parts on the figure of clamp-on meter and then complete the questions ? : 1 ) The purpose of the moving coil is to ........................................................ ....................................................................................................................................... ....................................................................................................................................... 2 ) The purpose of the spring is to ...................................................................... ....................................................................................................................................... ....................................................................................................................................... 3 ) The purpose of the rectifiers is to ............................................................... ....................................................................................................................................... ....................................................................................................................................... 4 ) The clamp-on meter is used to measure ………………….. with ………….values without ……………… the circuit . 5 ) The clamp on meter consists of : a) …………………………………………………. b) …………………………………………………. c) ………………………………………………….. 769840177 5 Switching Section Chapter - 2 Questions Choose the correct answer :1 ) When measuring current Im = 15 μA it is better to use a ) IFS = 50 μA scale. b ) IFS = 30 μA scale. c ) IFS = 35 μA scale. d ) IFS = 20 μA scale. 2 ) The clamp-on meter is used to measure : a ) Power. b ) D.C. current. c ) A.C. voltage d ) High values A.C. current without opening the circuit. 3 ) To build an ammeter that measures currents greater than the meter movement full-scale value, you use a : a ) 0.001 Ω resistor . b ) Multiplier resistor . c ) Shunt resistor. d ) Voltage divider. 769840177 6 Switching Section