2.6-4 An ideal ammeter is modeled as a short circuit. A more realistic model of an ammeter is a small resistance. Figure P 2.6-4a shows a circuit with an ammeter that measures the current i_m. In Figure P 2.6-4b the ammeter is replaced by the model of an ideal ammeter, a short circuit. Ideally, there is no voltage across the 1-kΩ resistor and the ammeter measures i_mi = 2 A, the ideal value of i_m. In Figure P 2.6-4c the ammeter is modeled by the resistance R_m. Now the current measured by the ammeter is

As R_m → 0, the ammeter becomes an ideal ammeter and i_m → i_mi = 2 A. When R_m > 0, the ammeter is not ideal and i_m < i_mi. The difference between i_m and i_mi is a measurement error caused by the fact that the ammeter is not ideal.

(a) Express the measurement error that occurs when R_m = 10 Ω as a percent of i_mi.

(b) Determine the maximum value of R_m required to ensure that the measurement error is smaller than 5 percent

Figure P 2.6-4

(a) Express the measurement error that occurs when R_m = 10 Ω as a percent of i_mi.

(b) Determine the maximum value of R_m required to ensure that the measurement error is smaller than 5 percent

To ensure measurement error is less than 5%

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This page last updated on December 29, 2018