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Chapter 5
Counters
Sample Clocked Buffered Frequency Measurement
Sample clocked buffered point frequency measurements can either be a single frequency
measurement or an average between sample clocks. Use
CI.Freq.EnableAveraging
to set the
behavior. For buffered frequency, the default is True.
A sample clocked buffered frequency measurement with
CI.Freq.EnableAveraging
set to True
uses the embedded counter and a sample clock to perform a frequency measurement. For each
sample clock period, the embedded counter counts the signal to measure (
fx
) and the primary
counter counts the internal time-base of a known frequency (
fk
). Suppose T1 is the number of
ticks of the unknown signal counted between sample clocks and T2 is the number of ticks
counted of the known timebase as shown in Figure 5-15. The frequency measured is:
fx
=
fk
* (T1/T2)
Figure 5-15.
Sample Clocked Buffered Frequency Measurement (Averaging)
When
CI.Freq.EnableAveraging
is set to false, the frequency measurement returns the
frequency of the pulse just before the sample clock. This single measurement is a single
frequency measurement and is not an average between clocks as shown in Figure 5-16.
Figure 5-16.
Sample Clocked Buffered Frequency Measurement (Non-Averaging)
With sample clocked frequency measurements, ensure that the frequency to measure is twice as
fast as the sample clock to prevent a measurement overflow.
G
a
te
(
fx
)
S
o
u
rce
(
fk
)
Sa
mple
Clock
Co
u
nter Armed
S
1
S
2
S3
T1 T2
1 6
T1 T2
1 7
2 10
T1T2
1 7
2 10
1 6
B
u
ffer
1
2
1
6
10
6
G
a
te
S
o
u
rce
Sa
mple
Clock
Co
u
nter Armed
L
a
tched
V
a
l
u
e
s
6
6
4
6
4
6
4
6
6
