SVI-II Instruc Man.book - Fagerberg

Glossary
Accuracy
Actuator Type
Algorithm
ATC Air to Close
ATO Air to Open
CALIBrate
Characteristic
In a control valve the 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
travel of the valve independent of rigidity effects at the mechanical limits.
Accuracy is the greatest deviation from the expected position within the normal
travel, expressed as percent of normal travel.
An actuator is a device that transforms an input signal (mainly an electrical
signal) into motion. A HART compliant actuator receives a 4 - 20 mA control
current signal and causes an actuation function. There are many types of
HART actuators; a positioner is type of actuator. A device of type Actuator
may not be connected to a circuit intended for a device of type Transmitter.
An algorithm is a procedure or formula for solving a problem. There are several
algorithms entailed in SVI II AP operation. The SVI II AP has a position
control algorithm that is a modified PID. Other algorithms embedded in SVI II
AP include the STOPS method for calibrating stroke, and the autoTUNE
method for establishing the best parameters for the PID algorithm.
The combination of a single acting actuator and the control valve where the
valve is closed when air pressure is applied to the actuator
The combination of a single acting actuator and the control valve where the
valve is open when air pressure is applied to the actuator
A mode of the positioner in which the user has access to changing the calibration
of stroke, input signal, and tuning parameters.
The positioner input setpoint command can be selectively modified to provide
a desired relationship between setpoint and valve position. In the valve, the
relationship between stroke and Cv is also called valve inherent characteristic.
It is often adjusted by design, to equal percentage, for example. The positioner
characteristic is applied to modify the setpoint to travel relationship of
the actuator. The characteristic of the positioner must be chosen to compliment
the valve. If the valve is equal percentage, the positioner should be set
to linear. If a linear valve is installed the positioner can be set to an equal percentage
characteristic to improve flow control. SVI II AP offers an eleven point
custom characteristic option that can be created and edited in
G-1