Chapter 8
Counters
8-12
ni.com
Fig
u
re 8-12 ill
u
strates this method. Another option wo
u
ld be to
meas
u
re the width of a known period instead of a known p
u
lse.
Figure 8-12.
Method 2
•
Method 3: Measure Large Range of Frequencies Using 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. In this method, 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 USB-621
x
device can meas
u
re this long
p
u
lse more acc
u
rately than the faster inp
u
t signal.
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 8-13. Ass
u
me this signal to meas
u
re has freq
u
ency
F1. Config
u
re 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
F1
P
u
l
s
e
F1
G
a
te
S
o
u
rce
1 2 …
N
P
u
l
s
e-Width
Me
asu
rement
T =
N
F1
Freq
u
ency of F1 =
T
Width of
P
u
l
s
e
N
Width of P
u
l
s
e (T)
