Tight-Shut And Full-Open Actions; Backward Path; Final_Position_Value - GE FVP110 Maintenance Manual

Tight-shut and Full-open Actions

Tight-shut and Full-open Actions
The tight-shut action decreases the output pressure to a level much lower than the 0%
pressure level for an air-to-open valve (or increases it to a level much higher than the
0% pressure level for an air-to-close valve) when FINAL_VALUE.value is less than
FINAL_VALUE_CUTOFF_LO in order to ensure that the valve is tightly shut off. After
the tight-shut action is activated, when FINAL_VALUE.value becomes greater than
FINAL_VALUE_CUTOFF_LO by 1% or more, the tightshut action turns off.
Conversely, the full-open action increases the output pressure to a level much higher
than the 100% pressure level for an air-to-open valve (or decreases it to a level much
lower than the 100% pressure level for an air-to-close valve) when
FINAL_VALUE.value is larger than FINAL_VALUE_CUTOFF_HI in order to ensure that
the valve is fully open. After the full-open action is activated, when FINAL_VALUE.value
becomes less than FINAL_VALUE_CUTOFF_HI by 1% or more, the fullopen action
turns off.
Although the actual output signal level is changed to a level outside the range during
the period when the tight-shut or full-open action is on, the value of
FINAL_VALUE.value remains as computed and is not affected by these actions.

Backward Path

The following describes the signal input from the device hardware to the transducer
block, which is then passed to other function blocks.

FINAL_POSITION_VALUE

The parameter FINAL_POSITION_VALUE contains a percentage value of the valve
position sent from the position sensor where 0% is the shut-off position as is the case
for FINAL_VALUE.value. When one or more of the following conditions become true,
the data status of FINAL_POSITION_VALUE becomes Bad, which is sent to the
connected AO block and upstream function blocks:
❑
Bad - Out of service: The block is in the O/S mode.
❑
Bad - Sensor failure: The position sensor has failed.
❑
Bad - Device failure: The A/D converter has failed.
❑
Bad - Non specific: The deviation exceeds the limit.
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Transducer Block