Micromod Micro-DCI: 53SL5100B Single Loop Controller - Manual (Page 43)

53SL5100B Single-Loop Controller
INSTRUCTION MANUAL
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5 SINGLE LOOP (PID) CONTROLLER
5.1 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 correction,
which is applied as an output signal to the final control element (e.g., valve) in the loop. The final control
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.
Figure 5-1. Standard Feedback Control Loop
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 calibrated
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.
 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).