Electrodynamometer Type Instruments

By Prof Sunil Kumar, Electrical Engineering, IEC College, Greater Noida, Uttar Pradesh


Explain the working of a moving iron type instruments. Derive the expression for torque produced


An energy meter revolves 10 revolutions of disc for unit of energy. Find the number of revolutions made by it during an hour when connected across when connected 20A at 210V and 0.8 power factor leading. If energy meter revolves 350 revolutions, find the % error


Explain how following torque are produced in pmmc instrument and attracted type moving iron instruments
1. Deflecting torque
2. Control torque
3. Damping torque



Explain in brief why enegry meter reads enegry while wattmeter does not. An enegry meter has a registration constant of 100rev/kwh if the meter is connected to a load drawing 20A at 230V and 0.8 power factor for 5 hours. Find the number of revolution should be made by it of it is actually made 1800 revolutions. find the % age error and explain it from consumer point of view? 


Briefy discuss the construction and working of a PMMC instrument. Why is the linear scale. How range is extended in moving coil ammeter and voltameter? 


Discuss the construction and working of an electrodynamic wattmeter with the help of diagram? 


A 50A, 230V meter on full load list makes 61 revolution in 37 seconds if the normal disc speed is 500 revolution per kwh find the % age error? 


Explain the working principle of induction type wattmeter with the help of diagram? 


Compare merits and devices of moving iron type instrument and dynameter type instrument which one is superior why? 


Differentiate amongst indicating, recording and integrating type of instruments giving example of each type? 


11. Explain construction and principle of operation of dynamometer instruction. Why is this instrument suitable for both ac and dc measurements? 


Q12. Why shunt is usually used voltmeter and ammeter? A moving coil instrument has a resistance of 5Ω and gives full deflection of 100mv. Show how the instrument may be used to measure:
1. voltage upto 50V
2. current upto 10A 


Q13. A moving coil instrument gives full scale deflection with 15mA. The resistance of coil is 5Ω. It is desired to convert this instrument into an ammeter to read upto 2A. How to acheive it further how to convert this instrument to read upto 30V

    Im = 15mA , Rm = 5Ω 


Q14. Explain the principle of operation of attraction type moving iron instruments and explain how the controlling and damping forces are obtained? 


Q15. A moving coil instrument gives a full scale detection of 20mA. When a potential difference of 50mV is applied. Calculate the series resistance to measure 500V on scale?