30
Manual Supplement
00809-0200-4853, Rev AB
Rosemount 3051S Series Pressure Transmitter
November 2017
Rosemount 3051S Series Pressure Transmitter
This process needs to be repeated for each impulse line plugging condition that needs to be detected.
For DP measurements, this should be done for both the high side and the low side impulse line.
Optionally, you may also wish to do this for both sides plugged. For GP/AP measurements, this process
would be done only for the single impulse line.
Upper and lower detection limits are chosen based on the degree of standard deviation change that was
observed when the impulse lines were plugged. These limits should be less than the observed change in
standard deviation, but more than changes in standard deviation that happen under normal process
conditions. A lower detection limit will result in a plug being detected earlier and more often, but could
also lead to false detections. A higher detection limit will reduce the likelihood of false detections, but
also increase the probability that an impulse line plug will not be detected.
A good “rule of thumb” is to set the detection limit to half of the observed change in standard deviation,
but no less than 20 percent.
6.23 Advanced PIL configuration
PIL provides the ability for advanced users to fine-tune some of the algorithm settings.
PLINE_RELEARN_THRESHOLD
This adjusts the limit at which the PIL will automatically relearn new baseline values if the process mean
changes. By default, this threshold is:
Two inches of water for DP Range 1 (-25 to 25 inH
2
O) sensors
Five inches of water for DP Range 2 (-250 to 250 inH
2
O) sensors
One percent of Upper Range Limit for all other sensors
When PLINE_RELEARN_THRESHOLD is at 0 (default) the above values are used for the relearn threshold.
When a positive number is entered here, this value (in % of Upper Range Limit) overrides the default
relearn threshold values. For example, if the sensor is type DP Range 3 (-1000 to 1000 inH
2
O), and
PLINE_RELEARN_THRESHOLD is set to 1%, then PIL will relearn if the mean changes by more than 10
inH
2
O.
PLINE_AUTO_RELEARN
This can be used to turn off the automatic relearning. If set to “Disabled”, the PIL will not go back into
learning mode, even if there is a large mean change. In most cases, this parameter should be kept at
“Enabled” because without this check, a large change in a flow rate could also cause a change in the
standard deviation, triggering a false detection.
PLINE_LEARN_LENGTH
The length of time over which mean and standard deviation are calculated during the learning and
verification phases. Default is five minutes. Allowable range is 1-60 minutes. If the process has a periodic
change in the mean over time (e.g. a slow oscillation), a longer learning cycle may provide a better
baseline.
PLINE_DETECT_LENGTH
The length of time over which mean and standard deviation are calculated during the detection phase.
Default is one minute. Allowable range is 1-60 minutes. This value should not be longer than the PLINE
learning cycle. A shorter value will in general allow a plugged impulse line to be detected more quickly.
However, if the process has a dominant cycling or oscillation, this parameter should be set to longer than
the period of oscillation.
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