Time-interval measurements
Measuring time intervals with an oscilloscope can be compared to measuring
the length of a board with a ruler. However, the signal, unlike the board, is
not directly accessible to the senses. Using an oscilloscope is like taking a
photograph of the board, then determining the board’s dimensions by
measuring the photograph. The oscilloscope captures a record of the input
signal, which is called the waveform. This waveform is not a perfect replica
of the input signal, just as the photograph is not an undistorted replica of the
board. This section examines the distortions introduced by the vertical
channels, the probes, and connecting cables, and it shows how these
distortions affect the accuracy of time-interval measurements.
Errors introduced by the vertical channels of the oscilloscope and by the
probe can be divided into the following categories:
•
dc errors. These include offset level error, gain error, vertical
non-linearity, and vertical resolution limits.
•
Dynamic response errors.
In general, the errors from the transient response of the vertical channels and
probes are more significant than those from dc level errors in the vertical
channels, especially for fast-slewing edges.
Measurements
Time-interval measurements
13–30
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