Chapter 7
Counters
©
National Instruments
7-17
X Series User Manual
primary co
u
nter co
u
nts the internal time-base of a known freq
u
ency (
fk
).
S
u
ppose T1 is the n
u
mber of ticks of the
u
nknown signal co
u
nted between
sample clocks and T2 is the n
u
mber of ticks co
u
nted of the known
time-base. The freq
u
ency meas
u
red 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 freq
u
ency meas
u
rement
ret
u
rns the freq
u
ency of the p
u
lse j
u
st before the sample clock. This single
meas
u
rement is a single freq
u
ency meas
u
rement and is not an average
between clocks.
Figure 7-16.
Sample Clocked Buffered Frequency Measurement (Non-Averaging)
With sample clocked freq
u
ency meas
u
rements, ens
u
re that the freq
u
ency to
meas
u
re is twice as fast as the sample clock to prevent a meas
u
rement
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
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