Reference Manual
00809-0100-4801, Rev FA
October 2010
Rosemount 3051S Series
7-8
In the “Monitoring” mode, statistical values of mean, standard deviation, and
coefficient of variation are continuously calculated, with new values available
every second. When using mean and standard deviation as the SPM
variables, the mean value is compared to the baseline mean value. If the
mean has changed by a significant amount, the diagnostic can automatically
return to the “Learning” mode. The diagnostic does this because a significant
change in mean is likely due to a change in process operation and can result
in a significant change in noise level (i.e. standard deviation) as well. If the
mean has not changed, the standard deviation value is compared to the
baseline value. If the standard deviation has changed significantly and
exceeds configured sensitivity thresholds, this may indicate a change has
occurred in the process, equipment, or transmitter installation and a HART
alert or analog alarm is generated.
For DP flow applications where the mean pressure is likely to change due to
changing process operation, the recommended SPM variable for process
diagnostics is the coefficient of variation. Since the coefficient of variation is
the ratio of standard deviation to mean, it represents normalized process
noise values even when the mean is changing. If the coefficient of variation
changes significantly relative to the baseline and exceeds sensitivity
thresholds, the transmitter can generate a HART alert or analog alarm.
NOTE
SPM diagnostic capability in the Rosemount 3051S HART pressure
transmitter calculates and detects significant changes in statistical parameters
derived from the input pressure signal. These statistical parameters relate to
the variability of and the noise signals present in the pressure signal. It is
difficult to predict specifically which noise sources may be present in a given
pressure measurement application, the specific influence of those noise
sources on the statistical parameters, and the expected changes in the noise
sources at any time. Therefore, Rosemount cannot absolutely warrant or
guarantee that SPM will accurately detect each specific condition under all
circumstances.
Assigning Statistical
Values to Outputs
The statistical values of mean, standard deviation, and coefficient of variation
can be made available to other systems or data historians via HART
communication. WirelessHART adaptor, such as the Smart Wireless THUM
can also be used to obtain additional variables. Devices that convert HART
variables to analog 4-20 mA outputs, such as the Rosemount 333 Tri-Loop
can also be used.
Statistical values can be assigned to be 2nd variable, 3rd variable, or 4th
variable. This is accomplished through Variable Mapping. See Figure 7-6.
Device Dashboard
Fast Keys
2, 2, 5, 1
(182 Seiten)
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