Figure 7-11. method 1b – National Instruments Network Device DAQ S User Manual
Page 82
Chapter 7
Counters
7-10
ni.com
You can configure the counter to make K + 1 buffered period
measurements. Recall that the first period measurement in the buffer
should be discarded.
Average the remaining K period measurements to determine the
average period of F1. The frequency of F1 is the inverse of the average
period. Figure 7-11 illustrates this method.
Figure 7-11. Method 1b
•
Method 2: Measure High Frequency with Two Counters—In this
method, you measure one pulse of a known width using your signal
and derive the frequency of your signal from the result. This method is
good for high frequency signals.
In this method, you route a pulse of known duration (T) to the Gate of
a counter. You can generate the pulse using a second counter. You also
can generate the pulse externally and connect it to a PFI or RTSI
terminal. You only need to use one counter if you generate the pulse
externally.
Route the signal to measure (F1) to the Source of the counter.
Configure the counter for a single pulse-width measurement. If you
measure the width of pulse T to be N periods of F1, the frequency of
F1 is N/T.
F1
Ft
F1
Intervals Measured
Gate
Source
Buffered Period
Measurement
Average Period of F1 =
N
1
+ N
2
+ …N
K
K
Frequency of F1 =
N
1
+ N
2
+ …N
K
K
× Ft
Ft
T
1
T
2
… T
K
1
Ft
×
1
2
...N
1
1...
...N
2
… 1...
...N
K