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HP4402.book : chapter2.fm 28 Wed Apr 23 15:29:05 1997
Power Meter Operation
Setting Averaging
2-28 HP EPM-442A User’s Guide
Setting Averaging
The power meter uses a digital filter to average power readings. The
number of readings averaged can range from 1 to 1024 in binary
progression. This filter is used to reduce noise, obtain the desired
resolution and to reduce the jitter in the measurement results. Increasing
the value of the filter length reduces measurement noise. However, the
time to take the measurement is increased. You can select the filter length
or you can set the power meter to auto filter mode. The default is “AUTO”.
When the auto filter mode is enabled, the power meter automatically sets
the number of readings averaged together to satisfy the filtering
requirements for most power measurements. The number of readings
averaged together depends on the resolution and the power level currently
being measured. Figure 2-5 lists the number of readings averaged for each
range and resolution when the power meter is in auto filter mode and is
set to normal speed mode (refer to the HP EPM-441A/442A Programming
Guide for details of the readings averaged in the other speed modes).
Resolution is a window function and not a channel function. In the case
where a channel is set up in both the upper and lower window and the
resolution settings are different, the highest resolution setting is taken to
calculate the averaging number. For example, if the upper window has a
resolution setting of 2 and is measuring channel A - channel B and the
lower window has a resolution of 4 and is measuring channel A. In this
instance channel A averaging is calculated with a resolution of 4 and
channel B with a resolution of 2.