GE Masoneilan SVI II ESD Installation And Maintenance Manual page 205

DCS
Device Description, DD
Diagnostics
EEPROM
Equal Percentage
Error Messages
Failsafe
Fatal Error
Flash Memory
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Distributed Control System is a generic term for the common control
system architecture that generally performs process control in net-
worked 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 input to the positioner.
The software object installed in the HART
DPI 620 to allow it to communicate and display the custom parame-
ters available in a field device.
The suite of software, and hardware tools that allow SVI II ESD to
monitor its own internal condition and to monitor the control valve
performance and actuator system. Depending on purchased
options 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 perfor-
mance to predict remaining useful service life.
An Electrically Erasable Programmable Read Only Memory. SVI II ESD
has two memories used for permanent storage of data that change
during operation. The micro-controller has EEPROM that perma-
nently 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 pres-
sure in a pipeline as a control valve is opened. It is intended to linear-
ize installed flow versus lift characteristic for improved control.
*
The theoretical curve is y= ae
a 50:1 equal percentage characteristic. However, the theoretical
curve leaves the valve unseated by 2% at 0% input. Actual curve is
corrected to seat the valve at 0%. Corrected curve is Y=(ae
(1-a).
The positioner stores the reasons for errors. Error messages can be
®
read by HART or with local display.
A positioner mode where the valve position is carried to a predeter-
mined safe position. This mode is forced by positioner program in
response to errors. If the errors are cleared then RESET returns the
positioner to the mode prior to the error.
An error which the SVI II ESD program treats as non-recoverable.
Service is required.
A non volatile computer memory. It stores all its data even when
power is off. It performs high speed reads and can be re-written
many times. It is used to store programs and permanent parame-
ters.
Masoneilan SVI II ESD Installation and Maintenance Manual
®
Handheld Communicator
, where a is.02, 1/R, and R=50 for
xln(1⁄a)
) -a)/
xln(1⁄a
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=