HP 3562A Operating Manual page 88

AVERAGING IN THE LINEAR RESOLUTION MODE
Why Four Averaging Functions?
Stable averaging weights old and new data records equally to yield the arithmetic mean for
the number of averages selected. It displays the result of each intermediate average (if fast
averaging i s all) and stops the measurement after the selected number of averages have been
calculated. Stable averaging is calculated with the following formula:
Exponential averaging weights new data more than old to maintain a moving average, rather
than the cumulative result provided by stable averaging. It displays the result of each intermedi·
ate average (if fast averaging is all). Exponential averaging continues until the measurement is
paused. The number of averages is still important with exponential averaging because the
weighting of new versus old data is dependent on the number entered with N U M BER AVGS.
As the number of averages increases, new time records are weighted less. Note also that
exponential averaging selects the next highest power of two (e.g., 2, 4, 8, 16) as the exponen·
tial averaging constant. For example, if 25 averages are requested, the measurement uses 32
(25). Exponential averaging is calculated with the following formula:
The analyzer uses stable averaging to acquire the first 2 n averages.
The peak hold function differs from stable and exponential averaging by showing the max·
imum values that occurred at each of the 801 display lines during the measurement period,
rather than the average values. It stops after the selected number of measurements have been
made. The peak hold function is applicable only to frequency domain measurements, with time
averaging off.
The peak continuous function performs the same operation as peak hold except it can·
tinues indefinitely until paused by the user. The peak continuous function is also applicable
only to frequency domain measurements, with time averaging off.
Selecting an averaging type depends on your input data and what you need to learn from the
measurement. For example, exponential averaging may be selected to track a varying input
signal because it weights new data more than old, while the peak continuous function could
be used to monitor and record noise peaks or frequency drift.
1·34
Chaoter 1-Usino the Linear Resolution Mode
A o
=
where Ao
D
'quantity is time record when time averaging is on: power spectrum. frequency
response or correlation when time averaging is off.
where: Ao
On
'quantity is time record when time averaging is on; power spectrum, frequency
response or correlation when time averaging is off.
n
cumulative average
=
o quantity'
=
n number of averages
=
cumUlative average
=
time quantity'
=
n number of averages
=