Chapter 7
Counters
X Series User Manual
7-14
ni.com
Yo
u
can config
u
re the co
u
nter to meas
u
re one period of the gate signal. The
freq
u
ency of
fx
is the inverse of the period. Fig
u
re 7-12 ill
u
strates this
method.
Figure 7-12.
Low Frequency with One Counter
High Frequency with Two Counters
For high freq
u
ency meas
u
rements with two co
u
nters, yo
u
meas
u
re one
p
u
lse of a known width
u
sing yo
u
r signal and derive the freq
u
ency of yo
u
r
signal from the res
u
lt.
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.
In this method, yo
u
ro
u
te a p
u
lse of known d
u
ration (
T
) to the Gate of a
co
u
nter. Yo
u
can generate the p
u
lse
u
sing a second co
u
nter. Yo
u
also can
generate the p
u
lse externally and connect it to a PFI or RTSI terminal. Yo
u
only need to
u
se one co
u
nter if yo
u
generate the p
u
lse externally.
Ro
u
te the signal to meas
u
re (
fx
) to the So
u
rce of the co
u
nter. Config
u
re the
co
u
nter for a single p
u
lse-width meas
u
rement. If yo
u
meas
u
re the width of
p
u
lse
T
to be
N
periods of
fx
, the freq
u
ency of
fx
is
N
/
T
.
fx
fk
G
a
te
S
o
u
rce
1
2
3
…
N
S
ingle Period
Me
asu
rement
…
Period of
fx
=
N
Freq
u
ency of
fx
=
N
Interv
a
l Me
asu
red
fk
fk
fk
fx
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