Chapter 3: Testing Performance
To test time measurement accuracy
3–18
13
Set t
he From Edge # control to 1 with Direction Rising and Threshold Middle. Set the
To Edge # control to 2 with Direction Rising and Threshold Middle. Click OK.
See Figure 3-12.
Figure 3-12
Measurement Settings for Time Interval Measurement
14 Verify the period is 25 ns ± 43 ps, minimum 24.957 ns and maximum 25.043 ns.
Record the minimum and maximum readings in the Performance Test Record.
15 Change the signal generator frequency to 100 MHz (10 ns period).
16 Select horizontal from the setup menu. Set the position to –11 ns.
17 Clear measurement statistics by pressing the Clear Display button on the front panel.
18 The delta time reading should be 10 ns ± 43 ps, minimum 9.957 ns and maximum
10.043 ns. Record the minimum and maximum readings in the Performance Test
Record.
19 Change the signal generator frequency to 20 MHz (50 ns period).
20 Select horizontal from the setup menu. Set the scale to 100 ns/div, position to –11 ns.
21 Clear measurement statistics by pressing the Clear Display button on the front panel.
For Valid Statistical Data
In equivalent time mode, measurement specifications are valid with sixteen or more acquisitions
averaged. Statistics accumulated before the required number of averaged acquisitions may show the
oscilloscope to fail the specification. This is particularly true for minimum and maximum in this case since
they are set by measurements taken with the fewest averages.
If the procedure above is followed exactly, the required number of acquisitions are averaged before
statistics are turned on. Therefore, if you clear and restart measurements, averaging and statistics are
restarted simultaneously and the result is erroneous data collected from the early averages.
If in doubt about the statistical data, after #Avg is complete select Clear Measurements or Clear All from
the Measure tool bar, then repeat the custom measurement again. This restarts the statistics without
restarting averaging and the result is valid statistical data.
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