Instruments and Measurements

Problem 444: A DC ammeter has an internal resistance of 0.1 ohm. A shunt of \(1.010\times10^{-3}\) ohm is connected to the ammeter. What is the multiplier of the set up?

Problem 445: A 1% d'Arsonval meter movement has coil and swamping resistance adding to 200 ohms. The full-scale voltage is 50 mV. Determine the shunt resistance required producing 1 A full scale current meter?

Problem 446: A galvanometer with a 20-ohm coil resistance has a full-scale deflection current of 10 mA. If a 0.02 ohm is placed across the meter to increase its capacity, what is the approximate new full scale current of the meter?

Problem 447: A moving iron meter gives full-scale deflection with 100 V applied across the coil. The coil has 20,000 turns and a resistance of 2.5k\(\Omega\). If this instrument is to be used as an ammeter with a full-scale deflection of 10 A, how many turns are needed?

Problem 448: A moving iron ammeter is wound with 50 turns and gives full-scale deflection with 4 A. If it is desired to extend the full-scale reading to 10 A, how many turns are needed on the same bobbin?

Problem 449: A galvanometer has a coil resistance of 50 ohms and a current sensitivity of 0.001 \(\mu\)A per mm. How much is the voltage across its terminals when the deflection is 15 cm at full scale?

Problem 450: A 0-10 mA galvanometer with a coil resistance of 20 ohms is converted to a 0-50 V voltmeter by using

Problem 451: A certain 50 \(\mu\)A meter movement has a resistance of 90 ohms. What value of series multiplier is needed to make the instrument to read 5 V (maximum).

Problem 452: A voltmeter with an internal resistance of 5000 ohms is calibrated to read 10 volts at full scale. How much series resistance is needed in order to measure 150 volts at full scale?

Problem 453: A 1000 ohms per volt, 2% meter movement has a coil resistance of 200 ohms. Determine the external resistance necessary to provide a full-scale reading of 5 V.

Problem 454: An ammeter rated 5 A, having a resistance of 0.5 \(\Omega\), is to be converted into a 200-V voltmeter by connecting a resistor in series with the ammeter. Calculate the value of this resistance.

Problem 455: A direct current wattmeter with a potential coil connected across the load side of the instrument reads 250 W. If the voltage across the load is rated at 230 V, what is the actual power drawn by the load. The resistance of the potential coil is known to be 1 k\(\Omega\).

Problem 456: The stator of a 440-V, 50-hp shunt motor is tested at 75°C for its insulation resistance between terminals connected together and the ground frame. When a 50,000-ohm voltmeter is connected in series with a 600-V DC source and the insulation resistance, the meter indicates 125 V. Calculate the insulation resistance.

Problem 457: It is desired to measure the resistance of the insulation between the motor winding and the motor frame. A 300-V, 50,000 ohm voltmeter is used in making the measurements. The voltmeter when connected across the source reads 230 V and when connected in series with the insulation, it reads 5 V. Find the insulation resistance.

Problem 458: When a 150 k\(\Omega\) voltmeter is connected across a constant source, it registers 230 V. When one terminal is connected to the core of a cable while the rubber insulation of the cable is connected to the other terminal of the line, the meter registers 15 V. Determine the insulation resistance of the cable.

Problem 459: An unknown voltage is to be measured by means of a 250 V-scale voltmeter having an internal resistance of 10,000 ohms. For safety purposes a 1000 ohms resistor is connected in series with one of the voltmeter terminals. If the meter reads 200 volts, determine the unknown voltage.

Problem 460: Two identical 1000 ohm per volt DC voltmeter are connected in series to measure an unknown supply voltage. The first voltmeter is connected to its 200 V scale while the second voltmeter is connected to its 250 V scale. What is the voltage of the supply if the first voltmeter reads 100 V.

Problem 461: A 20 k\(\Omega\) per volt voltmeter indicated a reading of 250 V on its 300 V scale when used to measure an unknown voltage. If a 50 k\(\Omega\) resistor was connected in series with the instrument during the test, determine the value of the unknown voltage.

Problem 462: A 300-V voltmeter draws 2-mA current for full-scale deflection. This voltmeter is used to measure the voltage across a 50 k\(\Omega\) resistor in series with a 25 k\(\Omega\) resistor. The combination of the resistors is being connected across a 150-V source. What is the voltmeter reading?

Problem 463: The Meralco test of a 10-A wattmeter having a constant of 0.4, the disk makes 40 revolutions in 53.6 seconds. The average volts and amperes during this period of test are 116 volts and 9.4 A. What is the percent accuracy of the meter at this load.