Micromod Micro-DCI: 53MC5000 Multi-Loop Process Controller FLEXIBLE CONTROL STRATEGIES - Manual (Page 100)

A.1.2 CS2 - ANALOG BACKUP CONTROLLER
The analog backup controller is used in operations where a remote computer normally controls the
final element directly. In this arrangement the controller acts as a control signal selector and as an
automatic backup. As a backup, the controller will assume control of the process in the event of an
indicated computer failure.
Loading CS2 initializes the ANI3 engineering span to 100.0, the CCO0 invert to 1, and C078 to
100.0. The control scheme is shown in block diagram form in Figure A-2. Also provided is Table A-
2, which is a worksheet that shows the CS2 wirelist connections; wirelist datapoints not connected
are left at default. Table A-2 is partitioned by FCS module type applicable to CS2 (those modules
illustrated in Figure 2-1). The datapoint parameters for each module are shown with their default
values.
The following I/O assignments result from loading CS2 (ANI1 is not used):
ANI0 Process Variable
ANI2 Additive Feed Forward Input
ANI3 Control Element Feedback
ANO0 Backup Control Output
ANO1 Computer Control Status
CCI0 Computer Ready
CCI1 Auto Enable
CCO0 Computer Output Diverter
CCO1 Backup Output Diverter
The PCS operates as a standard PID controller when driving the final element. While in backup
and automatic, the controller continually adjusts its output to match the feedback signal from the fi-
nal element. In this way the transfer to on-line is bumpless. As shown below, selection of the com-
puter or backup control signals to the final element is performed by the controller’s CCO modules
in conjunction with blocking diodes. The computer drives the final element when remote operation
is selected at the controller via the R/L push button and the CCI0 contact is closed; otherwise, the
computer’s control signal is diverted and the controller is active. ANO1 indicates whether the com-
puter or the controller is driving the final element (20 mA computer/4 mA controller). Unless the
CCI1 input is closed, the controller is not permitted to operate in automatic control mode.
FCS 53MC5000 Flexible Control Strategies
A-10
412-TXT