Rockwell Automation 1336T PLC Comm. Adapter, Series B, FRN 2.xx-3.xx - Manual (Page 249)

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Publication 1336 FORCE–5.13 –– September, 1998
You can specify how often you want the PLC Communications
Adapter Board to take data samples. Data samples may be taken in a
range of 2 milliseconds to 30 seconds, in 2 millisecond increments.
The rate at which the data is sampled and at which the trigger
condition is evaluated is the same up to 20 milliseconds. This
assures that possible trigger conditions are monitored whenever the
sample rate exceeds 20 milliseconds.
To set the data sample rate:
1. Select the Sample Rate parameter for the appropriate trend
(parameter number 458, 468, 478, or 488).
2. Enter the sample rate. The drive rounds this value to the nearest
2 millisecond interval.
You can change the sample rate while the trend is active.
You also need to specify the number of data samples taken once a
trigger condition occurs. You can specify that 0 through 499 post
samples be taken, with one sample reserved for the instance when
the trigger condition becomes true.
Typically, when a trend buffer is set to trigger on a fault, you would
set the post sample parameter to a lower number, such as 20. This
allows you to evaluate the trended parameters data from before the
trigger.
When a trend buffer is set up as a level detector, the post sample
parameter is generally set to a higher value. This allows you to
evaluate what happened after the trigger occurred.
To set the number of post samples:
1. Select the Post Samples parameter for the appropriate trend
(parameter number 459, 469, 479, or 489).
2. Enter the number of data points to be taken after the trigger
condition becomes true.
You can change the number of post samples while the trend is active.
Note: If the trigger condition occurs before the pre–samples can be
taken, the pre–samples may be unreliable. The pre–samples are
valid if the trigger does not occur in less than the pre–sample time
after the trend is enabled and in the continuous mode after a trigger.
You can use the following formula to determine the pre–sample time:
pre–sample time = (500 – Post Samples – 1) * Sample Rate
Adjusting the Data Sample
Rate
Setting the Number of
Post Samples
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