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Masoneilan SVI II ESD Installation and Maintenance Manual
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Appendix H. Glossary
Accuracy
In a control valve position is measured between mechanical motion limits in the
valve. These limits can include position variations due to actuator and valve
rigidity. therefore, accuracy is referenced to positions within normal valve travel,
independent of rigidity effects at mechanical limits stops. Accuracy is the great-
est deviation from the expected position within the normal travel, expressed as
normal travel percentage.
Actuator Type
An actuator is a device that transforms an input signal (mainly an electrical sig-
nal) into motion. A HART
®
compliant actuator receives a 4 - 20 mA control cur-
rent signal and causes an actuation function. There are many types of HART
®
actuators; a positioner is a type of actuator. A device of type Actuator can not be
connected to a circuit intended for a device of type Transmitter.
Algorithm
An algorithm is a procedure or formula for solving a problem. There are several
algorithms entailed in SVI II ESD operation. SVI II ESD has a position control algo-
rithm that is a modified PID algorithm. Other embedded algorithms in SVI II ESD
include STOPS method for calibrating stroke, and autoTUNE method for estab-
lishing the best parameters for the PID algorithm.
ATC Air to Close
The combination of a single acting actuator and control valve where the valve is
closed when air pressure is applied to the actuator.
ATO Air to Open
The combination of a single acting actuator and control valve where the valve is
open when air pressure is applied to the actuator.
CALIBrate
A positioner mode of operation in which you have access to changing stroke cal-
ibration, input signal, and tuning parameters.
Summary of Contents for SVI II ESD
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