Campbell Scientific CR6 CR6 Measurement and Control System - Page 306

Section 8. Operation • 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 CR6 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. 306) shows the basic code requirements. The DataTime() instruction is a more recent introduction that facilitates time stamping with system time. See Data Table Declarations (p. 518) and CRBasic Editor Help for more information. CRBasic Example 64. Time Stamping with System Time ' 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 Scan(1,Sec,10,0) 'Delay -- in an operational program, delay may be caused by other code Delay(1,500,mSec) 'Measure Value -- can be any analog measurement PanelTemp(Value,0) 'Immediately call SlowSequence to execute CallTable() TriggerSequence(1,0) NextScan 306