© National Instruments
|
7-15
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 time-base. The frequency measured will be
fx
=
fk
* (
T
1/
T
2).
Figure 7-15.
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.
Figure 7-16.
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
Summary of Contents for DAQ X NI 634 Series
Page 1: ...PXIe 6349...
