Section 7. Installation
236
• One more way to view sub-scans is that they are a convenient (and only) way
to put a loop around a set of measurements. SubScan() / NextSubScan
specifies a timed loop for so many times around a set of measurements that
can be driven by the task sequencer.
7.8.12.3 Measurement Rate: 601 to 2000 Hz
To measure at rates greater than 600 Hz, VoltSE() is switched into burst mode by
placing a dash (-) before the channel number and placing alternate arguments in
other parameters. Alternate arguments are described in the table Parameters for
Analog Burst Mode
(p. 237). In burst mode, VoltSE() dwells on a single channel
and measures it at rates up to 2000 Hz, as demonstrated in the CRBasic example
Measuring VoltSE() at 2000 Hz
. The example program has an 86% duty cycle.
That is, it makes measurements over only the leading 86% of the scan. Note that
burst mode places all measurements for a given burst in a single variable array
and stores the array in a single (but very long!) record in the data table. The exact
sampling interval is calculated as,
Tsample = 1.085069 * INT((SettleUSEC / 1.085069) + 0.5
where SettleUSEC is the sample interval (µs) entered in the SettlingTime parameter
of the analog input instruction.
Table 36. Measuring VoltSE() at 2000 Hz
PipeLineMode'<<<<Pipeline mode ensures precise timing of measurements.
Public BurstSE(1735)
DataTable(BurstSETable,1,-1)
Sample(1735,BurstSE(),FP2)
EndTable
BeginProg
Scan(1,Sec,10,0)
'Measurement speed and count are set within VoltSE()
VoltSe(BurstSE(),1735,mV2_5,-1,False,500,0,1.0,0)
CallTable BurstSETable
NextScan
EndProg
Many variations of the burst program are possible. Multiple channels can be
measured, but one channel burst is completed before the next begins. Caution
dictates that a specific configuration be thoroughly tested before deployment.
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