Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 41)

Rockwell Automation Publication 1756-UM005B-EN-P - January 2013 41
Module Features Chapter 3
Table 6 - Notes for Archiving
Note Description
1 Setting the RPI less than the
recommended value If the RPI value is less than the recommended value, archiving still works, but the module performs only a limited number of
archive samples before the RPI expires.
The I.LastUpdateIndex tag contains values from 0…19 to indicate the last sample number.
You need to take this into account and move only some of the values returned by the module.
2 Using the I.RollingTimeStamp tag The RollingTimeStamp tag stores an integer value from 0…32,767 ms that increments each time the module sends new data to
the controller.
In the example used above in
step 2 , the I.RollingTimeStamp increments by 8 each time new data is present.
Ladder logic associated with storing and monitoring archived data can also track the I.RollingTimeStamp tag to determine if the
archive data has changed.
A running history of I.RollingTimeStamp can also be used to verify the age of the data by subtracting the previous
I.RollingTimeStamp value from the current I.RollingTimestamp value. The difference equals either the RPI or the COS update rate
of the module.
3 Using the I.CSTTimestamp tag This value represents the Coordinated System Time available to all modules on the backplane. By using I.CSTTimestamp, you can
get better resolution (± 1 RTS) and can correlate the analog values taken by the 1756-IF4FXOF2F module to other events and
data in your system.
4 Using the module in the local chassis Use archiving only when the module is in the local chassis. Do not use archiving when the module is in a remote chassis.
The high-speed scanning that occurs when archiving applies to only the inputs on the module and not the outputs. The outputs
are updated at the RPI rate.
5 Archiving channel signal data Only channel signal data is archived. General status, fault, and alarms are not included in the archive.
If alarming is important in your application, we recommend that you latch alarm data and examine the information in the I.In
tags for every archive sample to isolate when an incident occurred.
6 Synchronizing the Archiving function You can synchronize the Archiving function across multiple modules in the same local chassis by checking the Synchronize
Module Inputs checkbox on the Input Configuration tab of the Module Properties dialog box.
Synchronizing inputs causes the start of each archive sample period on each module to begin within 100 μs of each other.