Rockwell Automation FactoryTalk Historian SE 3.0 H2H Interface User Guide - Manual (Page 72)

Startup Command File
66
.BAT .INI Description
the interface; the second occurrence defines
the second scan class, and so on. Historian
Points are associated with a particular scan
class via the Location4 Historian Point
attribute. For example, all Historian Points
that have Location4 set to 1 will receive input
values at the frequency defined by the first
scan class. Similarly, all points that have
Location4 set to 2 will receive input values at
the frequency specified by the second scan
class, and so on.
Two scan classes are defined in the following
example:
/f=00:01:00,00:00:05
/f=00:00:07
or, equivalently:
/f=60,5 /f=7
The first scan class has a scanning frequency
of 1 minute with an offset of 5 seconds, and
the second scan class has a scanning
frequency of 7 seconds. When an offset is
specified, the scans occur at discrete
moments in time according to the formula:
scan times = (reference time) + n(frequency)
+ offset
where n is an integer and the reference time
is midnight on the day that the interface was
started. In the above example, frequency is
60 seconds and offset is 5 seconds for the
first scan class. This means that if the
interface was started at 05:06:06, the first
scan would be at 05:07:05, the second scan
would be at 05:08:05, and so on. Since no
offset is specified for the second scan class,
the absolute scan times are undefined.
The definition of a scan class does not
guarantee that the associated points will be
scanned at the given frequency. If the
interface is under a large load, then some
scans may occur late or be skipped entirely.
See the section “Performance Summaries” in
the UniInt Interface User Manual.doc for more
information on skipped or missed scans.
Sub-second Scan Classes
Sub-second scan classes can be defined on
the command-line, such as
/f=0.5 /f=00:00:00.1
where the scanning frequency associated
with the first scan class is 0.5 seconds and
the scanning frequency associated with the
second scan class is 0.1 of a second.
Similarly, sub-second scan classes with sub-
second offsets can be defined, such as
/f=0.5,0.2 /f=1,0
Wall Clock Scheduling
Scan classes that strictly adhere to wall clock
scheduling are now possible. This feature is
available for interfaces that run on Windows.