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Reference Manual

00809-0100-4801, Rev FA

October 2010

Rosemount 3051S Series

7-4

STATISTICAL PROCESS

MONITORING

Introduction Statistical Process Monitoring (SPM) provides a means for early detection of

abnormal situations in a process environment. The technology is based on

the premise that virtually all dynamic processes have a unique noise or

variation signature when operating normally. Changes in these signatures

may signal that a significant change will occur or has occurred in the process,

process equipment, or transmitter installation. For example, the noise source

may be equipment in the process such as a pump or agitator, the natural

variation in the DP value caused by turbulent flow, or a combination of both.

The sensing of the unique signature begins with the combination of the

Rosemount 3051S pressure transmitter and software resident in the

diagnostic electronics to compute statistical parameters that characterize and

quantify the noise or variation. These statistical parameters are the mean,

standard deviation, and coefficient of variation of the input pressure. Filtering

capability is provided to separate slow changes in the process due to setpoint

changes from the process noise or variation of interest. Figure 7-2 shows an

example of how the standard deviation value is affected by changes in noise

level while the mean or average value remains constant. Figure 7-3 shows an

example of how the coefficient of variation is affected by changes in the

standard deviation and mean.

The calculation of the statistical parameters within the device is accomplished

on a parallel software path used to filter and compute the primary output

signal (such as the 4 - 20 mA output). The primary output is not affected in

any way by this additional capability.

Figure 7-2. Changes in process

noise or variability and affect on

statistical parameters

Standard Deviation increases or decreases with changing noise level.

Process Noise

Standard

Deviation

Mean

1 2 ... 103 104 105 106 107 108 109 110 111 112 113 ... 239 240

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