diagrama de un amperímetro que posea simultáneamente las tres escalas 0-200mA, 0-300 mA y 0-400 mA?

Answer 1

Diagram of an ammeter that has 0-200, 0-300 and 0-400 ma scales?

Basically the meter has a certain (usually very small) full-scale current, and higher current scales are provided by switching suitable values of resistance in parallel with the meter. These shunt resistors carry most of the current I being measured. Say the meter has a 100 microamp full-scale movement, and a resistance of 1000 ohms. Then its full-scale voltage E is 0.1 v. The shunt resistors will be approximately E/I, or 0.5, 0.3333 and 0.25 ohms for I = 200, 300 and 400 ma full-scale current. I say approximately, because theoretically one should account for the current in the meter. The exact values for the shunts would be values that provide 0.5, 0.3333 and 0.25 ohms when in parallel with the 1000 ohms of the meter, but the approximate values are only in error by between 0.025% and 0.05%.