Fisher FIELDVUEDVC6200f Instruction Manual page 212

DVC6200f Digital Valve Controller
AO Function Block
February 2017
For any shed with no return option, the target mode changes as determined by the option. Therefore, there is no
attempt to restore the connection following failure. The behavior on change to the remote cascade target mode is
identical to that for Shed With Return Options.
Normal—On failure of a remote cascade connection the block sets the target mode to the highest permitted
non‐remote mode. Cas is the highest permitted non‐remote mode and Auto is is the next highest permitted
non‐remote mode. If Cas or Auto are not available, the block will shed by default to Man.
Retained Target—The retained target mode is the previous target mode before it was changed to RCAS or ROUT. On
failure of a remote cascade connection the block sets the target mode to the retained target mode.
Auto—On failure of a remote cascade connection, the block sets the target mode to Auto, if permitted.
Man—On failure of remote cascade connection, the block sets the target mode to Man, if permitted.
The user may configure SHED_OPT [27] so that it calls for a target mode that is not permitted. When doing this, the
mode logic uses the following rules as applied by the remote logic:
D Shed logic never results in a non‐permitted target mode.
D Shed logic never attempts to attain an actual mode of Auto or Cas if that mode is not permitted.
Status Handling
Output or readback fault detection is reflected in the status of PV [7], OUT [9], and BKCAL_OUT [25]. A limited SP [8]
condition is reflected in the BKCAL_OUT [25] status. When simulation is enabled through the SIMULATE [10] attribute,
you can set the value and status for PV [7] and READBACK [16].
When the block is in Cas mode and the CAS_IN [17] input goes bad, the block sheds mode to the next permitted
mode.
Setting the Output
To set the output for the AO block, you must first set the mode to define the manner in which the block determines its
setpoint. In Manual mode the value of the output attribute (OUT [9]) must be set manually by the user, and is
independent of the setpoint. In Automatic mode, OUT [9] is set automatically based on the value specified by the set
point (SP [8]) in engineering units and the I/O Options attribute. In addition, you can limit the SP [8] value and the rate
at which a change in the SP [8] is passed to OUT [9].
In Cascade mode, the cascade input connection (CAS_IN [17]) is used to update the SP [8]. The back calculation
output (BKCAL_OUT [25]) is wired to the back calculation input (BKCAL_IN [27]) of the upstream block that provides
CAS_IN [17]. This provides bumpless transfer on mode changes and windup protection in the upstream block.
Note
You must wire BKCAL_OUT [25] to BKCAL_IN [27] of the upstream block that provides CAS_IN [17]. Otherwise, the AO will not
initialize properly, and the setpoint at CAS_IN [17] will not be passed to OUT [9].
An analog readback value, such as valve position, is shown by the process value (PV [7]) attribute in engineering units.
To support testing, you can enable simulation, which allows you to manually set the channel feedback. There is no
alarm detection in the AO function block.
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Instruction Manual
D103412X012