Rockwell Automation T3832 ICS Regent Historian Package for Winterpret - Manual (Page 39)

Historian Package for W INTERPRET (T3832)
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Theory of Operation
Each historian function block is part of an application
program and is executed when the application program is
loaded and running in the Regent. Each time the application
program is scanned, the function block is executed. When the
Regent executes the function block, the operations performed
are determined by the status of the control parameters
defined for the function block. For Sequence of Events
function blocks, the control parameters include a Start
Contact, Clear Contact, a Size Value and a Count Register.
For Process Historian function blocks, the control parameters
include a Start Contact, a Clear Contact, a Sample Time and
a Period.
When the function block is executed, the normal historical
recording operations occur when the Start Contact is on and
the Clear Contact is Off. Specific operations for each type of
historian function block are explained below.
Sequence of Events Function Block
Execution
The Regent executes a sequence of events function block
using the sequence described below.
Start Contact Is On
If the start contact has switched from off to on, the following
occurs:
1. The “Start Contact” event is added to the events buffer.
2. The current state of all event entries are recorded in a last-
state table.
3. No further processing occurs during the scan.
If the start contact was on in the previous scan, the following
occurs:
1. If the clear contact has switched from on to off, the “Clear
Contact” event is added to the event buffer.
2. The present state of each event entry is compared to the
state written in the last-state table. If a change of state is