Micromod Micro-DCI: 53MC5000 Multi-Loop Process Controller FLEXIBLE CONTROL STRATEGIES - Manual (Page 142)

A.1.7 CS21 - TWO-LOOP CASCADE CONTROLLER
The two-loop cascade controller consists of two standard PID control loops, arranged in a cascade
setup whereby the output of the primary controller, based on its setpoint and process variable, be-
comes the setpoint for the secondary controller.
Loading CS21 initializes the ANI2 engineering span to 100.0, C088 to 1.0, C089 to 1.0, and the dis-
play list sequence to incorporate a second display group (CON1). The control scheme is shown in
block diagram form in Figure A-7. Also provided is Table A-7, which is a worksheet that shows the
CS20 wirelist connections; wirelist datapoints not connected are left at default. Table A-7 is parti-
tioned by FCS module type applicable to CS21 (those modules illustrated in Figures 2-1 and 2-2).
The datapoint parameters for each module are shown with their default values.
The following I/O assignments result from loading CS21:
ANI0 Process Variable Primary
ANI1 Remote Setpoint Primary
ANI2 Process Variable Secondary
ANI3 Additive Feed Forward Secondary
ANO0 Control Output (Secondary)
ANO1 Secondary Setpoint Transmit
CCI0 Cascade Enable
CCI1 Remote Enable Primary
CCO0 Process Alarms Secondary
CCO1 Process Alarms Primary
This control strategy provides bumpless/balanceless transfer between local and cascade control by
forcing the primary output to match the secondary setpoint when the secondary is in local mode.
Proper scaling of the primary output (secondary setpoint) is accomplished using the K1 (C149) and
B1 (C148) parameters of the secondary controller. The current setpoint of the secondary, also
scaled by the same K1 and B1, is reflected in the value of ANO1.
ANI2 is the controlled process variable of the secondary that the output (ANO0) is controlling
through the final element. The secondary also is provided with an additive feed forward signal
(ANI3). Cascade control is not permitted if CCI0 is an open contact. The primary process variable
is supplied by ANI0. If a closed contact is on CCI1, selection of remote setpoint operation is possi-
ble in the primary controller via the R/L push button. The remote setpoint value is derived from
ANI1.
Alarm conditions for both primary and secondary controllers are indicated by a closed contact on
the CCOs. Secondary loop alarms appear at CCO0, and primary loop alarms appear at CCO1.
FCS 53MC5000 Flexible Control Strategies
A–52
417-TXT