Chapter 8
Counters
©
National Instruments Corporation
8-9
Fig
u
re 8-9 shows an example of a b
u
ffered semi-period meas
u
rement.
Figure 8-9.
Buffered Semi-Period Measurement
Note that if yo
u
are
u
sing an external signal as the So
u
rce, at least one
So
u
rce p
u
lse sho
u
ld occ
u
r between each active edge of the Gate signal.
This condition ens
u
res that correct val
u
es are ret
u
rned by the co
u
nter. If this
condition is not met, the co
u
nter ret
u
rns a zero. Refer to the
section for more information.
For information abo
u
t connecting co
u
nter signals, refer to the
section.
Frequency Measurement
Yo
u
can
u
se the co
u
nters to meas
u
re freq
u
ency in several different ways.
Yo
u
can choose one of the following methods depending on yo
u
r
application:
•
Method 1: Measure Low Frequency with One Counter
—In this
method, yo
u
meas
u
re one period of yo
u
r signal
u
sing a known
timebase. This method is good for low freq
u
ency signals.
Yo
u
can ro
u
te the signal to meas
u
re (F1) to the Gate of a co
u
nter. Yo
u
can ro
u
te a known timebase (Ft) to the So
u
rce of the co
u
nter. The
known timebase can be 80MHzTimebase. For signals that might be
slower than 0.02 Hz,
u
se a slower known timebase.
3
1
2
3
1
3
S
OURCE
GATE
Co
u
nter V
a
l
u
e
B
u
ffer
1
3
2
2
1 1
1
3
1
2
0
Co
u
nter Armed
