National Instruments NI 6612 User Manual

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Chapter 3 Counters
Large Range with 2 Counters
This measurement method requires two counters: Counter N and Counter M.
For this measurement method, Counter N creates a pulse equal to T1 periods of the
signal-to-measure. The device routes this pulse to Counter M. Counter M measures the duration
of this pulse by counting the number of cycles (T2) of the timebase.
The device returns T2 and T1 to DAQmx. DAQmx reads these value, and uses the known
frequency of the timebase (f
k
) to calculate the frequency (f
x
) of the signal-to-measure as:
Figure 3-18. Frequency Measurement: Large Range of Frequencies with Two Counters
With N as the integer that divides down the input signal (f
x
), which can be configured in
CI.Freq.Div, the maximum error and maximum frequency error for this method are given by:
f
x
f
k
T1
T2
------
×=
Source Out
Counter N
Source
Gate
Counter M
Counter N Out
Interval
to Measure
0123 … T1
012
…
T2
Signal to
Measure (f )
Counter
Timebase (f )
x
k
Signal to Measure (f )
Counter Timebase (f )
x
k
Maximum Error (%)
f
x
Nf
k
f
x
–×
------------------------= 100%×
Maximum Frequency Error (Hz) f
x
f
x
Nf
k
f
x
–×
------------------------×=

National Instruments NI 6612 Specifications

General

Brand	National Instruments
Model	NI 6612
Category	Computer Hardware
Language	English