3-18
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Chapter 3
Counter Input
Figure 3-19.
Frequency Measurement: High Frequency with Two Counters
With the known measurement time (
T
), which can be configured in CI.Freq.MeasTime, the
maximum error and maximum frequency error for this method are given by:
To use the High Frequency with 2 Counters method, configure the following:
•
DAQmx Create channel (CI-Frequency)—Use this VI or function to create the channel.
•
CI.Freq.MeasMeth—Set this property to High Frequency with 2 Counters
Note that this measurement method requires two counters. You can use:
•
Counter 0 paired with Counter 1
•
Counter 2 paired with Counter 3
•
Counter 4 paired with Counter 5
•
Counter 6 paired with Counter 7
P
u
l
s
e
P
u
l
s
e
1
2
…
P
T
S
o
u
rce
O
u
t
Co
u
nter M
S
o
u
rce
G
a
te
Co
u
nter N
S
ign
a
l to
Me
asu
re
S
ign
a
l to
Me
asu
re (f )
Co
u
nter
Time
bas
e (f )
k
x
Maximum Error (%)
1
T f
x
×
-------------
=
100%
×
Maximum Frequency Error (Hz)
1
T
---
=
