Campbell CR800 Series, Operator'S Manual

Page: 312 / 598

Section 8. Operation
312
Time-stamp skew is not a problem with most applications because,
• program execution times are usually short, so time stamp skew is only a
few milliseconds. Most measurement requirements allow for a few
milliseconds of skew.
• data processed into averages, maxima, minima, and so forth are
composites of several measurements. Associated time stamps only
reflect the time the last measurement was made and processing
calculations were completed, so the significance of the exact time a
specific sample was measured diminishes.
Applications measuring and storing sample data wherein exact time stamps are
required can be adversely affected by time-stamp skew. Skew can be avoided by
• Making measurements in the scan before time-consuming code.
• Programming the CR800 such that the time stamp reflects the system
time rather than the scan time. When CallTable() is executed from
within the
Scan() / NextScan
construct, as is normally done, the time
stamp reflects scan time. By executing the CallTable() instruction
outside the Scan() / NextScan construct, the time stamp will reflect
system time instead of scan time. CRBasic example Time Stamping
with System Time
(p. 312)
shows the basic code requirements. The
DataTime() instruction is a more recent introduction that facilitates time
stamping with system time. See topics concerning data table
declarations in CRBasic Editor Help for more information.
Time Stamping with System Time
'This program example demonstrates the time stamping of data with system time instead of
'the default use of scan time (time at which a scan started).
'
'Declare Variables
Public value
'Declare data table
DataTable (Test,True,1000)
Sample (1,Value,FP2)
EndTable
SequentialMode
BeginProg