The Dynamic Baseline Signature Function captures a signature of
the following valve package variables: position versus time;
supply pressure; differential pressure; and actuator exhaust
pressure.
These variables are captured in ambient process conditions.
The dynamic signature can be captured after a break-in period,
which is defined by the end user from 2 cycles to “n” cycles.
However, the nth cycle must be executed within 50 days of
commissioning the device. Once this dynamic baseline signature
is captured, you have an accurate snapshot of real-time valve
package performance for future comparison to maintenance
signatures.
During the last operation, an alarm was triggered due to a
parameter falling outside the configured allowable hysteresis.
Looking at the information below, note how quickly the suspect
parameter is located. One of the most useful functions of the
latest generation of software diagnostic tools is the intelligent
filtering and presentation of key information.
Figure 4. Run Times
Note that the air pressure dropped from 93.9 to 89.9. The lower instrument air decreased the
torque output, resulting in a slower breaking time off the seat. Conversely, it took less time to
break from open to close as the spring toque will increase with less pressure.
Dynamic conditions that can change the torque requirements of a valve are one of the many
primary reasons why engineering firms and end users demand a safety margin when sizing
actuators for a specified valve. Unlike a trunion-mounted ball valve, where the process may have
very little affect on the torque requirements, many process valves such as floating ball, plug and
butterfly are subject to process conditions. Many valve manufacturers offer torque requirements
based on process conditions, but it can be very difficult to test every possible “real-time”
condition in a lab setting.
Don Sanders, Shell Offshore, attending a recent project meeting, stated, “It is very valuable to
know the signature prior to the valve leaving the automated vendor’s shop, and then have the
ability to compare after the device is installed during pre-commissioning and finally when
process conditions are present.”
sors for developing accurate data for
functional alarms. Plus, they employ an
intelligent alarm management system
that helps eliminate nuisance alarms.
Enhanced alarm logic provides more
meaningful alarms when there are relevant changes in process conditions.
Unlike conventional valve positioners, modern control monitors utilize a
Hall Effect sensor to develop a position
feedback signal. This non-contact technology eliminates linkages, levers and
other rotary-to-linear conversions, while
providing highly accurate and repeatable position control and feedback
required for advanced control strategies
and predictive maintenance algorithms.
The use of Hall Effect sensor technology also provides the ability to remote-mount the electronics assembly up to 50
feet away from the remote sensor
assembly mounted to the valve. This feature enables the monitoring and control
of valves in areas of environmental
extremes such as high vibration and or
high/low temperature.
With the aid of an associated software package, service engineers can
calibrate, commission, interrogate and
maintain the intelligent discrete controller from the safety of a remote location. The controller also provides ESD
monitoring and PST capabilities that
are time- and date-stamped and validated in order to increase plant safety and
