1-19
AMMETER SENSITIVITY
Ammeter sensitivity is the amount of current necessary to cause full scale deflection (maximum
reading) of the ammeter. The smaller the amount of current, the more "sensitive" the ammeter. For
example, an ammeter with a maximum current reading of 1 milliampere would have a sensitivity of
1 milliampere, and be more sensitive than an ammeter with a maximum reading of 1 ampere and a
sensitivity of 1 ampere. Sensitivity can be given for a meter movement, but the term "ammeter
sensitivity" usually refers to the entire ammeter and not just the meter movement. An ammeter consists of
more than just the meter movement.
AMMETER RANGES
If you have a meter movement with a sensitivity of 1 milliampere, you can connect it in series with a
circuit and measure currents up to 1 milliampere. But what do you do to measure currents over 1
milliampere?
To answer this question, look at figure 1-21. In figure 1-21(A), 10 volts are applied to two resistors
in parallel. R1 is a 10-ohm resistor and R2 is a 1.11-ohm resistor. Since voltage in parallel branches is
equal-
Figure 1-21.—Current in a parallel circuit.
In figure 1-21(B), the voltage is increased to 100 volts. Now,
