Micromod Micro-DCI: 53MC5000 Multi-Loop Process Controller Instruction Manual - Manual (Page 252)

13.0 CS22 - TWO LOOP OVERRIDE
CONTROLLER
13.1 CS22 - TWO LOOP OVERRIDE CONTROLLER
The Two Loop Override Controller provides two standard PID controllers that function as two inter-
dependent variables, Primary and Limiting, to control a single final element (e.g., valve). Neither
variable may exceed a safe limit. The outputs of both PIDs are fed into a high/low selector that de-
termines which output will drive the final element. The output of the selector is fed back to the Pri-
mary Variable Loop and the Limiting Variable Loop, holding the unselected loop near the active
control output range. The default operation for this control strategy is as a high limit (low selector)
Two Loop Override Controller. As a high limit (low selector) override controller, the lowest output
value is selected to drive the final element via AO0.
After CS22 is started, to configure it for low
limit (high selector) Two Loop Override Controller operation, configure datapoints C088 to 1.0,
C089 to 2.0, and B202 to 102. As a low limit (high selector) Two Loop Override Controller, the
highest output is selected to drive the final control element. A typical low-resolution display high
limit (low selector) Two Loop Override Controller process application is illustrated in Figure 13-1.
In this application the valve is normally adjusted in response to Primary Variable (flow) distur-
bances unless the Limiting Variable (pressure) Loop has the lowest output (assumes reverse ac-
tion between the pressure process variable and the loop output). When this happens, the valve is
closed to reduce pressure. Pressure is the Limiting Variable because it is the more critical value.
Ensure the controller is capable of supporting more than one control loop by comparing the model
number of the controller (found on the controller tag) with the model number breakdown provided
in Section 1.
Figure 13-1. Typical CS22 Two Loop Override Controller Application
FT
AI1 - REMOTE SETPOINT PRIMARY
AI3 - REMOTE SETPOINT LIMITING
DI0 - REMOTE ENABLE PRIMARY
(CLOSED CONTACT)
DI1 - REMOTE ENABLE LIMITING
(CLOSED CONTACT)
AI2 - LIMITING
VARIABLE LOOP
AI0 - PRIMARY
VARIABLE LOOP
DO0 - PROCESS ALARMS PRIMARY
DO1 - PROCESS ALARMS LIMITING
AO1 - OVERRIDE STATUS
AO0 - CONTROL
OUTPUT LIMITING
VALVE
PT
Section 13. CS22 - Two Loop Override Controller
13-1