Fisher FIELDVUEDVC6200f Instruction Manual page 226

DVC6200f Digital Valve Controller
PID Function Block
February 2017
Shed With No Return Options
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 a remote target mode is identical to
that for Shed With Return Options.
Normal—On failure of a remote 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 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 mode the block was in before changing to one of the remote target
modes. On failure of a remote connection, the block sets the target mode to the retained target mode.
Auto—On failure of a remote connection, the block sets the target mode to Auto, if permitted.
Man—On failure of a remote connection, the block sets the target mode to Man, if permitted.
The user may configure SHED_OPTS [34] 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
If the input status on the PID block is Bad, the mode of the block reverts to Manual. In addition, you can select the
Target to Manual if Bad IN status option to direct the target mode to revert to manual. You can set the status option in
Manual or Out of Service mode only.
Set Point Selection and Limiting
The set point of the PID block is only valid when the block is in Auto, Cas, or RCas. Figure E‐6 illustrates the method for
set point selection. You can configure the SP_HI_LIM [21] and SP_LO_LIM [22] parameters to limit the set point. In
Cascade or Remote Cascade mode, the set point is adjusted by another function block or by a host computer, and the
output is computed based on the set point.
Figure E‐6. PID Function Block Set Point Selection
Operator
Set point
SP HI LIM
SP LO LIM
Auto
Setpoint
Man
Limiting
CAS
B2722
In Automatic mode, the set point is entered manually by the operator, and the output is computed based on the set
point. In Auto mode, you can also adjust the set point limit and the set point rate of change using the SP_RATE_UP
[20] and SP_RATE_DN [19] parameters.
226
SP RATE UP
SP RATE DN
Auto
Rate
Man
Limiting
CAS
Instruction Manual
D103412X012