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Pharos University

Pharos University. EE212_ELECTRICAL MEASUREMENT & Interface Prepared By: Dr. Sahar Abd El Moneim Moussa. Ch4_ Moving iron (mi). Moving Iron (MI) The a ttraction type moving iron instrument is shown in figure

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Pharos University

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  1. Pharos University EE212_ELECTRICAL MEASUREMENT & Interface Prepared By: Dr. SaharAbd El MoneimMoussa Dr. SaharAbd El MoneimMoussa

  2. Ch4_ Moving iron (mi) Dr. Sahar Abd El Moneim Moussa

  3. Moving Iron (MI) • The attraction type moving iron instrument is shown in figure • The action of moving iron instrument depends upon the magnetic effect. It can be used for either dc or ac measurements. Dr. Sahar Abd El Moneim Moussa

  4. Due to the attraction of the iron vane, a deflecting torque ( TD) is produced. • At steady state, when the pointer comes to rest at a position calibrated to give the measured value. At this position the control torque should be equal to the deflecting torque and opposing it: Dr. Sahar Abd El Moneim Moussa

  5. Dr. Sahar Abd El Moneim Moussa

  6. Example (1): The inductance of a moving iron ammeter is given by the expression L=(10+5-22) H. where  is the angular deflection in radians from zero position. Determine the angular deflection in radians for a current of 10A if the deflection for a current of 5 A is 30. Also determine the spring constant Solution: It will Solved in the lecture Dr. Sahar Abd El Moneim Moussa

  7. Errors in Moving Iron Instrument • Temperature effect error • Frequency Error (for ac measurement only) • Temperature Effect Error: Dr. SaharAbd El MoneimMoussa

  8. B.Frequency Effect Error: • This equation is dependent on the frequency. • To eliminate the dependence on the frequency, the time constants of the two parallel branches must be equal, Dr. SaharAbd El MoneimMoussa

  9. B.Frequency Effect Error: (cont.) • This equation is dependent on the frequency. Dr. SaharAbd El MoneimMoussa

  10. To eliminate the dependence on the frequency, a capacitor is connected in parallel with the multiplier as shown in figure of magnitude, Dr. SaharAbd El MoneimMoussa

  11. Example (2): An ac voltmeter with maximum scale reading of 50 V has an inductance of 0.09 H and a total resistance of 500 . The magnetizing coil is wound with 50  of copper wire and the reminder in series with it. Find the value of the capacitance that should be placed across the non-inductive series resistance to make the instrument read correctly both on dc as well as on Ac of 50 Hz circuit. Solution: It will Solved in the lecture Dr. Sahar Abd El Moneim Moussa

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