1-5
Figure 1-3.—Dual-trace oscilloscope.
Oscilloscopes have a high input impedance and normally will not load down the circuit under test.
However, oscilloscopes are primarily designed for waveform observation and are typically less accurate
than other pieces of test equipment used to measure dc voltages. A distinct advantage of the oscilloscope
is its ability to monitor the level of ac ripple voltage riding the dc voltage. This feature makes the
oscilloscope an indispensable aid in troubleshooting dc power supplies with excessive ripple caused by
component failure.
Digital Multimeter Method
Most analog voltmeters (that use D’Arsonval meter movements) in common use today are accurate to
approximately 2% of full-scale reading. Most digital multimeters, as shown in figure 1-4, have a high
input impedance and are not likely to disturb the circuit being tested. The digital multimeter in most cases
provides an accuracy of at least 0.1%.
Figure 1-4.—Digital multimeter.
Digital multimeters display the reading numerically. These direct-reading displays, along with
automatic range- and polarity-changing features, eliminate the problem of parallax, reduce error and
tedium, and increase measurement speed. Data from these meters in digital format can also be processed
