Rockwell Automation 1336T PLC Comm. Adapter, Series B, FRN 2.xx-3.xx - Manual (Page 250)

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Publication 1336 FORCE–5.13 –– September, 1998
Each trend can also be set up as a one–shot or continuous trigger
buffer. When you set up a trend as one–shot, the trend returns to the
stopped state after all post samples have been taken. Even though
the trend is stopped, the sampled data continues to be written to the
Trend Output parameter.
When you set up a trend as continuous, the trend operation continues
after the post samples have been taken. When a new trigger
condition occurs, the previous data samples are overwritten.
To set the buffer type:
1. Select the Trend Continuous Trigger parameter for the
appropriate trend (parameter number 460, 470, 480, or 490).
2. Select 0 if you want to perform a one–shot operation or 1 if you
want the trending to be continuous.
You can change the buffer type while the trend is active.
For a continuous trend, when the trigger condition becomes true and
after the post samples are gathered, there is a period of time when
samples are not being taken. Trending uses this time period to do
some internal housekeeping.
At times, you may want to force a trigger condition. The trend
operation will start taking post samples even though the programmed
trigger condition has not been met.
To force a trigger condition:
1. Select the Trend Select parameter for the appropriate trend
(parameter number 461, 471, 481, or 491).
2. Select a value of 2 to force the trigger.
3. When all post samples are gathered, the Trend Select parameter is
changed to Disable (for one–shot) or Enable (for continuous).
By using cascading trends, you can collect more than 500 data
points. A cascading trend refers to the method of having one trend
set to trigger when another trend either triggers or is forced. The
second trend then starts collecting data points as soon as the first
trend finishes collecting its post samples.
Setting the Buffer Type
Forcing a Trigger
Condition
Using Cascading Trends