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Reference Manual

00809-0200-4801, Rev CA

July 2010

6-9

Rosemount 3051S

SPM#_Low_Dynamics_Lim

Lower limit on standard deviation for detecting a Low Dynamics condition

(must be specified as a negative number)

All of these limits are specified as a percent change in the statistical value

from its baseline. If a limit is set to 0 (the default setting) then the

corresponding diagnostic is disabled. For example, if

SPM#_High_Variation_Limit is 0, then SPM# does not detect an increase in

standard deviation.

Figure 6-6 illustrates an example of the standard deviation, with its baseline

value and alert limits. During the monitoring phase, the SPM will continuously

evaluate the standard deviation and compare it against the baseline value. An

alert will be detected if the standard deviation either goes above the upper

alert limit, or below the lower alert limit.

In general, a higher value in any of these limits leads to the SPM diagnostic

being less sensitive, because a greater change in mean or standard deviation

is needed to exceed the limit. A lower value makes the diagnostic more

sensitive, and could potentially lead to false detections.

Figure 6-6. Example Alerts for

Standard Deviation

SPM Operations During operation, the following values are updated for each SPM Block (e.g.

SPM1-SPM4)

SPM#_Baseline_Mean

Baseline Mean (calculated average) of the process variable, determined

during the Learning/Verification process, and representing the normal

operating condition

SPM#_Mean

Current Mean of the process variable

SPM#_Mean_Change

Percent change between the Baseline Mean and the Current Mean

SPM#_Baseline_StDev

Baseline Standard Deviation of the process variable, determined during the

Learning/Verification process, and representing the normal operating

condition

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Emerson 3051S Especificaciones Pagina 87