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Meters

One of the important things that an engineer should take into consideration is «how much». How much current is this circuit carrying? What is value of voltage in this circuit? What is value of resistance? In fact, to measure the current and the voltage is not difficult at all. One should connect an ammeter or a voltmeter to the circuit and read off the amperes or volts.

The ammeter is used to measure the value of current. When the ammeter is used, the circuit should be opened at one point and the terminals of the meter should be connected to it. One should take into consideration that the positive terminal of the meter is connected to the positive terminal of the source, the negative terminal – to the negative terminal of the source.

Common ammeters for direct current measurements are the ammeters of the magneto-electric system. In an ammeter of this type an armature coil rotates between the poles of a permanent magnet; but the coil turns only through a small angle. The greater the current in the coil, the greater is the force, and therefore, greater the angle of rotation of the armature. The deflection is measured by means of a pointer connected to the armature and the scale of the meter reads directly in amperes.

When the currents to be measured are very small, one should use a galvanometer.

In addition to instruments for measuring current and voltage, there are also devices for measuring electric power and energy. (A. Kovalenko)



Вопросы

  1. One important thing that an engineer should take into consideration

  2. What does ammeter measure?

  3. How is deflection measured?

  4. Common ammeters for direct current measurements are

  5. When the currents to be measured are very small, one should use _____.

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