Description
VPs in a redundant subsystem can be calibrated as a pair or independently. The
same commands are used to perform either calibration.
If you want to calibrate the VPs independently, the FX-455 easiest method is to pull one of
the VPs out of the mounting unit. In this case, calibration is the same as for a non
redundant VP (see Section 25-6). When a VP is calibrated and the Backup is not in
service, and the RDNDNT flflag is set, a warming message is printed to inform the
operator that he is calibrating only one VP of the pair.
In any case, only the Primary VP or a pair can be calibrated. If you attempt to
calibrate with the terminal FX-455 connected to the Backup VP, the VP will print a message
stating that the request is refused.
brand | Product Name | Product model | Order No |
EMERSON | modular | FX-455 | nothing |
Place of Origin | Marketable land | Imported or not | defects liability period |
Europe and America | Nationwide and overseas | yes | a year |
Place of shipment | Delivery method | How to use | Applicable industries |
Xiamen | Shunfeng Express | Commissioning and installation | Power Plant Steel Plant Cement Plant Shipboard Papermaking |
Service advantages | Foreign import, goods preparation and supply | Reasonable price and reliable quality | Pictures are for reference only |
Product features | Primary source of goods, supply by model | After sales guarantee | Chen 1810693-7731 |
If you request a calibration of the FX-455 Primary VP, and the Backup VP is also in service,
the Backup is calibrated unconditionally. During calibration, the Primary disables
the redundancy software state machine so failovers are eliminated.
The message packet exchange between the Primary and Backup VPs includes
command/status bits related to calibration. The following table lists those
commands and descriptions.
In normal, local, and calibrate modes the Valve Positioner is always controlling
valve position. The PI routine runs unconditionally every 10 msec. Typically, it will
execute the PI equation as described below. The FX-455 PI routine has some conditionally
executed parts to handle seating and backseating.
Seating and backseating are important features of valve position control. The
purpose of seating is to ensure that the hydraulic system is forcing the valve closed
and admitting no steam into the turbine. Backseating is desirable because it can
affect effificiency, and because, for certain valve assemblies, a leakoff into other
steam systems are designed, assuming the valve is fully backseated.
The demand position from the Controller to the Valve Positioner is designed for a
range of -5% to 105% and resolution exceeding 13 bits. Seating is in effect when
the position demand is equal to or less than a programmable value, typically 0%,
and actual position feedback is less than 5%. When seating is in effect, the output
is driven to the maximum possible value in the direction that closes the valve. A
timer is started. After 10 seconds, the output is reduced to 50% of the maximum
value in the direction that closes the valve. A similar limit and function is provided
for backseating.
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