Emerson 3051S Spezifikationen PDF herunterladen (Seite 81)

Reference Manual

00809-0200-4801, Rev CA

July 2010

6-3

Rosemount 3051S

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

speed sensing device, such as the Rosemount 3051S Pressure Transmitter,

with software resident in a F

OUNDATION fieldbus Feature Board to compute

statistical parameters that characterize and quantify the noise or variation.

These statistical parameters are the mean and standard deviation 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 6-2 shows an example of how the standard deviation value ()

is affected by changes in noise level while the mean or average value ()

remains constant. The calculation of the statistical parameters within the

device is accomplished on a parallel software path to the path used to filter

and compute the primary output signal (e.g. the pressure measurement used

for control and operations). The primary output is not affected in any way by

this additional capability.

Figure 6-2. Changes in process

noise or variability and affect on

statistical parameters

The device can provide the statistical information to the user in two ways.

First, the statistical parameters can be made available to the host system

directly via Foundation fieldbus communication protocol or FF to other

protocol converters. Once available, the system may make use of these

statistical parameters to indicate or detect a change in process conditions. In

the simplest example, the statistical values may be stored in the DCS

historian. If a process upset or equipment problem occurs, these values can

be examined to determine if changes in the values foreshadowed or indicated

the process upset. The statistical values can then be made available to the

operator directly, or made available to alarm or alert software.

Second, the device has internal software that can be used to baseline the

process noise or signature via a learning process. Once the learning process

is completed, the device itself can detect significant changes in the noise or

variation, and communicate an alarm via PlantWeb alert. Typical applications

are change in fluid composition or equipment related problems.

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Emerson 3051S Spezifikationen Seite 81