Modes; Forward Path; Function Diagram Of Ao Function Block - GE FVP110 Maintenance Manual

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The AO function block performs bi-directional signal handling (Figure 58): transfer of the
valve control signal to the transducer block (forward path) and feedback of the valve
position signal from the transducer block to the upstream block (backward path).

Modes

The target mode for the AO function block can be set from five block modes: RCas, Cas,
Auto, Man, and O/S. Regardless of the target mode, the AO block automatically enters
the IMan or LO mode when a specified condition is met (such as when another function
block enters a specific status) depending on the parameter settings.

Forward Path

The following describes the signal input from the upstream block to the AO block and then
passed to the transducer block. The upstream block is typically the PID controller block,
and the control signal from the PID block is input as the source of computing the setpoint
SP for the AO block.
The path for computing the SP differs depending on the mode: In Cas mode, CAS_IN is
used for SP. In RCas mode, RCAS_IN is used for SP. If the value of CAS_IN or
RCAS_IN, whichever is used, is greater than SP_HI_LIM (high limit) or less than
SP_LO_LIM (low limit), the internal SP is set to the respective limits. Also, if the rate of
change in the value of CAS_IN or RCAS_IN, whichever is used, is greater than
SP_RATE_UP (rate-of increase limit) in the increasing direction, or than SP_RATE_DN
(rate-of-decrease limit) in the decreasing direction, the change in internal SP is limited by
the corresponding rate-of-change limit setting.
In RCas, Cas or Auto mode, the SP value is used for the AO block's output OUT, whose
value is then passed to the transducer block via channel 1.
Figure 58 Function Diagram of AO Function Block
FVP 110 Fieldbus Valve Positioner Manual
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