Micromod Micro-DCI: 53SL5100A Single Loop Controller - Manual (Page 63)

Single Loop Process Controller Instruction Manual
Single Loop (PID) Controller 55
5.0 Single Loop (PID) Controller
5.1 Single Loop (PID) Controller Operation Overview
In a standard feedback control loop, the Single Loop (PID) Controller functions as the primary processing
unit. When the process is altered due to disturbances (e.g., flow rate changes), the controller gauges this
change from the process variable (PV) feedback signal sent to it by a process measurement instrument
(e.g., flow meter) in the loop.
The controller compares the feedback signal to the setpoint level and calculates the required error correc-
tion, which is applied as an output signal to the final control element (e.g., valve) in the loop. The final con-
trol element responds to alter the process (manipulated variable) toward a predetermined operational
setpoint (SP), which can be set locally at the controller front panel or remotely from another instrument. If
the process variable exceeds tolerable limits of change, the controller activates a signal to an alarm. These
events are illustrated in
Figure 5-1 .
Process variable feedback input (Analog Input) received from the process measurement instrument is
typically 1-5 V dc, 4-20 mA dc. The Single Loop Controller zero and span inputs for this signal are cali-
brated by the factory and should not be altered. The controller is defaulted to display the process variable
input as a percentage value determined by input signal amplitude; however, it can be configured to display
direct units of measurement (e.g., gallons per minute [GPM]).
The setpoint value is received from another device (e.g. Single Loop Controller, PC, host computer, etc.),
or is manually entered at the controller front panel.
It is the difference between the setpoint (SP) and received process variable (PV), augmented by the action
of the tuning constants Proportional Band, Reset Time, and Rate Time, that determines the required output
Figure 5-1. Standard Feedback Control Loop
✎ Procedure
Note To minimize sudden process changes, adjust the local setpoint
value to the original remote setpoint value before switching back to
remote setpoint control (Remote).