National Instruments NI 6238 用户手册

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You can route the signal to measure (F1) to the Gate of a counter. You can 
route a known timebase (Ft) to the Source of the counter. The known 
timebase can be 80MHzTimebase. For signals that might be slower than 
0.02 Hz, use a slower known timebase.

You can configure the counter to measure one period of the gate signal. The 
frequency of F1 is the inverse of the period. Figure 7-11 illustrates this 
method.

Figure 7-11.  Method 1

In this method, you measure several periods of your signal using a known 
timebase. This method is good for low to medium frequency signals.

You can route the signal to measure (F1) to the Gate of a counter. You can 
route a known timebase (Ft) to the Source of the counter. The known 
timebase can be 80MHzTimebase. For signals that might be slower than 
0.02 Hz, use a slower known timebase.

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 7-12 illustrates this method.

F1

Ft

F1

Ft

Gate

Source

1

2

3

…

N

Single Period

Measurement

…

Period of F1 =

N

Ft

Frequency of F1 =

N

Ft

Interval Measured