Reference Manual
00809-0200-4801, Rev CA
July 2010
6-27
Rosemount 3051S
Detection sensitivities are specified as a percent change in the standard
deviation from the baseline value. Note from Figure 6-21 that a higher
detection limit (% change) actually corresponds to a lower sensitivity, because
a greater change in the process dynamics is required to trigger a plugged
impulse line alert. Likewise, a lower detection limit corresponds to a higher
sensitivity.
In PIL, the Detection Sensitivity is determined by 3 parameters:
PLINE_Sensitivity, PLINE_Detect_Sensitivity, and
PLINE_Single_Detect_Sensitivity.
The PLINE_Sensitivity parameter provides the means to set a basic
detection sensitivity (Figure 6-21). It can be set to the values: High, Medium
(default), or Low. Each value has a corresponding upper and lower limit
shown in the table Table 6-3. Note that setting the basic sensitivity affects
both the upper and the lower detection limits.
So, for example, if the PLINE_Sensitivity is set to High, then a plugged
impulse line will be detected if the standard deviation either increases by
more than 40% above its baseline value, or decreases more than 60% below
its baseline value.
NOTE:
For GP/AP sensors, the PIL does not check for an increase in standard
deviation, and a plugged impulse line is detected only if the standard
deviation goes below the lower limit. For DP sensors, the PIL checks for both
an increase and a decrease in standard deviation.
The upper and lower detection limits can be set to custom values, using the
parameters:
PLINE_Detect_Sensitivity
Adjusts the Lower detection limit. If this value is 0 (default), the Lower limit is
determined by PLINE_Sensitivity. If this value is greater than 0, then it
overrides the basic sensitivity value. This value can be set in the range 0 –
100%
PLINE_Single_Detect_Sensitivity
Adjusts the Upper detection limit. If this value is 0 (default), the Upper limit is
determined by PLINE_Sensitivity. If this value is greater than 0, then it
overrides the basic sensitivity value. This value can be set in the range 0 –
10000% (For software revisions 1.11.x or earlier, the allowable range for this
parameter is 0-100%).
Determining the
Detection Sensitivity
Determining what values to configure for the upper and lower detection limits
can be done by configuring SPM to monitor and trend the standard deviation,
and then looking at how the standard deviation changes when impulse line
plug is simulated, by closing the transmitter root valves or manifold valves.
Table 6-3. Basic PIL Detection Sensitivities
PLINE_Sensitivity Value Upper Standard Deviation Limit Lower Standard Deviation Limit
High 40% 60%
Medium 70% 70%
Low 100% 80%
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