Which is the integrating instrument?

Question

Examoogle · Accepted Answer

Energy meter

Explanation: An integrating instrument is a measuring device that records the total quantity of electricity supplied over a specified period of time. Unlike indicating instruments that show instantaneous values, these meters perform a summation of the physical quantity (e.g., energy) by integrating it with respect to time.

Working Principle: The energy meter operates on the principle of electromagnetic induction. The potential coil (voltage coil) produces a magnetic flux proportional to the voltage, while the current coil produces a flux proportional to the load current; these fluxes induce eddy currents in a rotating aluminum disc, creating a torque proportional to the instantaneous power ($P = VI \cos \phi$). A braking magnet provides a counter-torque, and the disc rotation is geared to a counting mechanism that accumulates the product of power and time, $\int P dt$, effectively measuring total energy in kWh.

Key Formulas: $E = \int_{0}^{T} P dt$ — Represents the accumulation of energy over time $T$.; $T_d \propto \Phi_v \Phi_i \sin(\Delta)$ — Driving torque in an induction-type energy meter.

Key Points: Integrating instruments calculate the time-integral of the measured quantity.; The reading of these instruments depends on both the magnitude of the quantity and the time duration.; Energy meter (kWh meter) and Ampere-hour meter are common examples.; They typically utilize a mechanical counting mechanism or an electronic pulse accumulation circuit.

Advantages: Provides cumulative data over long durations.; Essential for billing and commercial utility management.

Disadvantages: Cannot provide instantaneous readings of parameters.; Subject to mechanical wear (in induction types) over time.

Applications: Domestic and Industrial electricity billing.; Battery state-of-charge estimation (Ampere-hour meters).

Additional Info: Voltmeter, Wattmeter, and Power factor meters are classified as 'Indicating Instruments' because they provide the instantaneous value of the measured quantity at the moment of observation.. An Integrating instrument does not require continuous observation to know the total value.

Answer: C is correct — The energy meter is an integrating instrument that records the total electrical energy consumed over time by calculating the integral of power.

Exam Tip: In exams, remember the mnemonic 'I-I-R': Indicating (Voltmeter), Integrating (Energy meter), Recording (Graphic meter).

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