Figure 1-7.
Error in voltmeter readings
(3) If you double the meter resistance (increase to 4000 ohms), the error
in the voltage reading diminishes to 30 percent (40 volts across R1).
If you
increase the ratio between the meter resistance and load resistance even more by
increasing the meter resistance you obtain a point where the voltmeter error can be
tolerated.
(4) For practical purposes, the voltmeter error can be tolerated when the
voltmeter resistance is ten times as great as the resistance across which the
voltage is measured.
c. Ohmmeter. The ohmmeter is a device that uses a current-actuated meter and
a fixed source of voltage for measurement of resistance (refer to Figure 1-8). It
is used for practical work where simplicity, portability, and ease of operation are
more important than a high degree of precision. There are two types of ohmmeters,
the series type and the shunt type.
The series type has the resistance to be
measured connected in series with the meter movement.
The shunt type has the
resistance to be measured connected in parallel with the meter movement.
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