Measurement Computing UL for NI LabVIEW - Manual (Page 61)

Universal Library Virtual Instruments (VIs) Counter VIs
CFreqIn.VI
Measures the frequency of a signal. This VI can only be used with 9513 counters, and uses internal counters
#5 and #4.
Summary:
Inputs: BoardNum [U32] - The board number assigned when installed with InstaCal. Can
be 0 to 100.
SigSource [U32] - Specifies which signal will be measured
GateInterval [I16] - Gating interval in milliseconds
Outputs: Count [U32] - The raw count is returned here
Freq [U32] - The measured frequency in Hz returned here.
ErrCode [I32] - Error code. See ErrMsg.VI
Arguments:
BoardNum The board number associated with a board when it was installed with InstaCal. The
specified board must have a 9513 counter.
SigSource Specifies the source of the signal from which the frequency will be calculated.
The signal to be measured is routed internally from the source specified by
SigSource to the clock input of counter 5. On boards with more than one 9513
chip, there is more than one counter 5. Which counter 5 is used is also determined
by
SigSource . SigSource can be set to one of the following values:
CTRINPUT1 through CTRINPUT5
GATE1 through GATE4
One 9513
chip:
FREQ1 through FREQ5
Chip 1 used
CTRINPUT1 through CTRINPUT10
GATE 1 through GATE 9 (excluding gate 5)
Two 9513
chips:
FREQ1 through FREQ10
Chip 1 or Chip 2
used
CTRINPUT1 through CTRINPUT20
GATE1 through GATE19 (excluding gates 5, 10 & 15)
Four 9513
chips:
FREQ1 through FREQ20
Chips 1- 4 can
be used
The SigSource value determines which chip is used. CTRINPUT6 through
CTRINPUT10, FREQ6 through FREQ10 and GATE6 through GATE9 indicate
chip 2 will be used. The signal to measure must be present at the chip 2 input
specified by
SigSource . Also, the gating connection from counter 4 output to
counter 5 gate must be made between counters 4 and 5 of this chip (see "Notes" on
page 63). See board-specific information to determine valid values for your board.
GateInterval Specifies the time (in milliseconds) that the counter will be counting. The optimum
GateInterval depends on the frequency of the measured signal. The counter can
count up to 65535.
If the gating interval is too low, then the count will be too low and the resolution of
the frequency measurement will be poor. For example, if the count changes from 1
to 2 the measured frequency doubles.
If the gating interval in too long then the counter will overflow and a FREQOVERRUN
error will occur.
Count The counts reached during the gating interval.
Freq The measured frequency in Hz.
ErrCode Error code returned from the Universal Library. Zero if no error occurred. Use the
ErrMsg VI to convert ErrCode into a readable string.
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