Masoneilan SVI II AP Installation and Maintenance ... - GE Energy

DCS
Device Description,
DD
Diagnostics
Double Acting
EEPROM
Equal Percentage
Error Messages
Distributed Control System is a generic term for the common
control system architecture that generally performs process
control in networked computers and interacts with field devices
through rack mounted I⁄O cards. A positioner is usually connected
to a DCS output card which controls the 4- 20mA current
to the positioner.
The software object installed in the HART Handheld Communicator
handheld to allow it to communicate and display the custom
parameters available in a field device.
The suite of software, and hardware tools that allow an SVI II
AP to monitors its own internal condition and to monitor the performance
of the control valve and actuator system. Depending
on options purchased the diagnostics can evaluate number of
valve strokes, total accumulated valve stem travel, step
response times with graphs, input to position relationships.
Often system performance signatures are obtained and
retained to compare as-built with future performance to predict
remaining useful service life.
An actuator is double acting when it has pressure applied to
both sides of the piston. A positioner is factory assembled and
calibrated as a double acting that has two pressure outputs one
that increases and one that decreases with increasing position
setpoint. The SVI II AP positioner can be single acting or double
acting.
An Electrically Erasable Programmable Read Only Memory.
SVI II AP has two memories that are used for permanent storage
of data that changes during operation. The micro-controller
has EEPROM which permanently stores changing information
such as number of actuator cycles and totalized valve travel.
The program is stored in flash memory and can be upgraded.
A valve characteristic designed to compensate for the loss of
pressure in a pipeline as a control valve is opened. It is
intended to linearize the installed flow versus lift characteristic
for improved control.
*The theoretical curve is y= ae xln(1⁄a) , where a is.02, 1/R, and
R=50 for a 50:1 equal percentage characteristic. However, the
theoretical curve leaves the valve unseated by 2% at 0% input.
The actual curve, shown here, is corrected to seat the valve at
0%. The corrected curve is Y=(ae xln(1⁄a ) -a)/(1-a).
The positioner stores the reasons for errors. The error messages
can be read by HART or with the local display.
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