Ammeters

Ammeters are used to measure the amount of current flowing in a circuit. The laboratory type of ammeter is connected in series. To reduce the effect of the meter on the performance of the circuit, they are constructed with a very low resistance. A clamp-on type of meter is also available that measures the intensity of the electromagnetic field around a single conductor and converts the field intensity into amperage.

26.6.2.1. Ammeters in Series Circuits

When we calculated the amperage of this circuit in the previous section, we determined that with a i20 V source the current was i2 amps. In a series circuit, the electricity does not have alternative paths to follow. Because all of the amperage flows through all components in the circuit, both ammeters in Figure 26.8 will have a reading of 12 amps.

FIGURE 26.7. Voltmeters in parallel circuits.

FIGURE 26.7. Voltmeters in parallel circuits.

FIGURE 26.8. Ammeters in a series circuit.

26.6.2.2. Ammeters in Parallel Circuits

In parallel circuits, ammeters must also be attached so the current passes through them; but because the electricity has alternative paths, they will measure only the current in the conductor they are inserted into, see Figure 26.9.

Problem: What are the readings for ammeters number 1 and number 2 in Figure 26.9 when the source voltage is 120 V?

Solution: In this example problem, ammeter one is located between the source and the first branch on the circuit; therefore it will measure the total current flow in the circuit. Ammeter two is in the last branch of the circuit, therefore it will only measure the current flowing through that branch on the circuit. In a previous section it was explain that to measure current flow, the source voltage and the total resistance of the circuit must be known. The first step is to determine the total resistance of the circuit.

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The next step is to calculate the total current flow in the circuit.

Ammeter number 1 will have a reading of 120 amps.

FIGURE 26.9. Ammeters in a parallel circuit.

FIGURE 26.9. Ammeters in a parallel circuit.

Ammeter number 2 only will measure the current flow in that branch of the circuit. Ohm's law is used to solve this part of the problem also:

In summary, assuming no resistance in the conductors, in a series circuit the amperage remains the same, and the voltage changes as the resistance changes. In parallel circuits the voltage remains the same, and the amperage changes as the resistances changes in the circuit.

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