Rockwell Automation 1336T PLC Comm. Adapter, Series B, FRN 2.xx-3.xx - Manual (Page 245)

9–3
Publication 1336 FORCE–5.13 –– September, 1998
By using the trend parameters, you can monitor up to four
parameters (trend 1 through trend 4). When trending is enabled or
running, data points, or samples, are taken and stored in a circular
buffer for the parameter linked to the Trend Input parameter. The
PLC Communications Adapter Board continues to take data points
until it either reaches a trigger point or a trigger is forced. A number
of data points, called post samples, are then taken once the trend is
triggered.
When complete, the data in the circular buffer is copied and ordered
(from oldest to newest) in a secondary buffer. This buffer is then
available for viewing as long as power is applied, until another
trigger condition occurs (continuous mode), a BRAM recall/initialize
is executed, or the system is reset.
Within this process, you determine:
•
the parameter(s) you want to monitor
•
the rate at which you want the data sampled
•
the trigger point
•
the number of samples taken after the trigger point has been
reached
•
whether you want a single trend to be performed or continuous
trending
The trending operation has four associated states:
When a trend is
in this state:
Then:
Stopped
No data samples are being taken and Trend
Output contains the data samples that have
been taken for the previous trend.
Running
The trigger condition has not been reached and
data samples are being taken at the specified
rate. Trend Input contains the data samples
from the current trend, and Trend Output
contains the data samples from the previous
trend.
Tripped Trigger
The trigger condition has become true and the
post samples are being taken.
Forced Trigger
The trigger condition was forced to be true so
that the post samples could be taken.
Understanding How
Trending Works