Rockwell Automation T7832 ICS Regent+Plus Historian Packages for Winterpret - Manual (Page 15)

Historian Package for W INTERPRET (T7832)
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Figure 9. Process Historian Control Parameters.
Start Contact
The Start contact is a discrete variable name that an
application program may turn on to enable the process
historian to begin recording variable entries. When the Start
contact is turned off, the process historian stops recording.
Typically, ladder logic is used to control the on/off status of the
Start contact to coordinate the recording mode of the process
historian to capture vital process information. Two scenarios
are often used.
1. The Start contact is normally on, placing the process
historian in the record mode. The function block
continuously records a time stamp and values of all
variable entries at the Sample Time defined. As recording
continues the historical buffer becomes full and continues
to rollover, but always remains full with the most recent
data over the duration defined by Period.
When ladder logic detects a critical interlock, it turns off
the Start contact immediately or after a timer delay.
When the Start contact turns off, the process historian
function block stops recording and the historical buffer has
"captured" vital process information before, during and
after the critical interlock.
2. The Start contact is normally off, making the process
historian function block idle and no recording takes place.
Ladder logic turns on the Start contact when a critical
interlock or process condition occurs. This places the
process historian in the record mode and samples are