Power Measurement How to Measure Power
94 Agilent 8163A/B, 8164A/B, and 8166A/B User’s Guide, Fourth Edition
How to Set the Averaging Time
NOTE For a Dual Power Sensor, you cannot set the averaging time of the
slave channel, channel 2, directly. By default, the averaging time of the
slave channel, channel 2, is the same value as that for the master
channel, channel 1. See Table 8 on page 101 for more details.
This is the length of time over which a signal is averaged. Longer
averaging times increase the accuracy and improve the noise rejection.
Longer averaging times also decrease sensitivity.
For averaging times of 1 second or less, a new measurement is shown
at the end of each averaging time. This is drawn in Figure 52. A new
measurement is shown on the display at each x.
With modules designed for the HP 8153A Lightwave Multimeter, for
averaging times of more than 1 second, the displayed power is given by
the formula:
Where,
P
new
is the new displayed result,
P
old
is the previously displayed result,
Sample is the value read by the hardware,
T
avg
is the averaging time, as set by the user, and
T
sample
is the time the hardware takes to make a reading.
If the measurement condition change (for example, a range change in
automatic ranging), P
old
is reset and the averaging starts again. This is
why the display update seems faster in automatic ranging.
To set the averaging time to 1 second:
−50 dBm 19.999 nW −47.000 dBm 0.001 nw −90.000 dBm
−60 dBm 1.9999 nW −57.000 dBm 0.1 pW −100.000 dBm
−70 dBm 199.99 pW −67.000 dBm 0.01 pW −110.000 dBm
Table 7 Upper Power Limits and Resolution for Various Power Ranges
[RANGE] Upper Power Limit Resolution
Figure 52 Measurements with Tavg ≤ 1 second
xxxxxxxx
T
avg
P
new
P
old
1
T
sample
T
avg
------ ------------–
èø
æö
Sample
T
sample
T
avg
------- -----------
èø
æö
+=
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