Chapter 7
Counters
©
National Instruments
7-15
X Series User Manual
Fig
u
re 7-13 ill
u
strates this method. Another option is to meas
u
re the width
of a known period instead of a known p
u
lse.
Figure 7-13.
High Frequency with Two Counters
Large Range of Frequencies with Two Counters
By
u
sing two co
u
nters, yo
u
can acc
u
rately meas
u
re a signal that might be
high or low freq
u
ency. This techniq
u
e is called reciprocal freq
u
ency
meas
u
rement. When meas
u
ring a large range of freq
u
encies with
two co
u
nters, yo
u
generate a long p
u
lse
u
sing the signal to meas
u
re. Yo
u
then meas
u
re the long p
u
lse with a known timebase. The X Series device
can meas
u
re this long p
u
lse more acc
u
rately than the faster inp
u
t signal.
Note
Co
u
nter 0 is always paired with Co
u
nter 1. Co
u
nter 2 is always paired with
Co
u
nter 3.
Yo
u
can ro
u
te the signal to meas
u
re to the So
u
rce inp
u
t of Co
u
nter 0, as
shown in Fig
u
re 7-14. Ass
u
me this signal to meas
u
re has freq
u
ency
fx
.
NI-DAQmx a
u
tomatically config
u
res Co
u
nter 0 to generate a single p
u
lse
that is the width of
N
periods of the so
u
rce inp
u
t signal.
P
u
l
s
e
fx
P
u
l
s
e
fx
G
a
te
S
o
u
rce
1 2 …
N
P
u
l
s
e-Width
Me
asu
rement
T
=
N
fx
Freq
u
ency of
fx
=
T
Width of
P
u
l
s
e
N
Width of P
u
l
s
e (
T
)
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