Emerson Rosemount OCX8800A Manual page 183

Manual
00809-0500-4880
OUT reflects the value and status quality of the PV. In Man mode, the OUT status
constant limit is set to indicate that the value is constant, and the OUT status is
Good.
The Uncertain - EU range violation status is always set, and the PV status is set
high or low limited if the sensor limits for conversion are exceeded.
In the STATUS_OPTS parameter, you can select from the following options to
control the status handling:
• BAD if Limited: Sets the OUT status quality to Bad when the value is higher or
lower than the sensor limits.
• Uncertain if Limited: Sets the OUT status quality to Uncertain when the value is
higher or lower than the sensor limits.
• Uncertain if in Manual mode: The status of the output is set to Uncertain when
the mode is set to Manual.
Note
The transmitter must be in Manual or Out of Service mode to set the status
option.
Note
The AI block only supports the BAD if Limited option. Unsupported options are
not grayed out; they appear on the screen in the same manner as supported
options.
8.9.9 Application information
The PID function block is a powerful, flexible control algorithm that is designed to
work in a variety of control strategies.
The PID block is configured differently for different applications. The following
examples describe the use of the PID block for closed-loop control (basic PID
loop), feedforward control, cascade control with master and slave, and complex
cascade control with override.
Closed loop control
To implement basic closed loop control, compute the error difference between
the process variable (PV) and setpoint (SP) values and calculate a control output
signal using a PID (proportional integral derivative) function block.
The proportional control function responds immediately and directly to a change
in the PV or SP. The proportional term GAIN applies a change in the loop output
based on the current magnitude of the error multiplied by a gain value.
The integral control function reduces the process error by moving the output in
the appropriate direction. The integral term RESET applies a correction based on
the magnitude and duration of the error. Set the RESET parameter to zero for
integral only control. To reduce reset action, configure the RESET parameter to be
a large value.
Rosemount OCX8800A
F Fieldbus
™
OUNDATION
December 2022
183