Unication Messenger m90 Instrukcja Użytkownika Pobierz pdf (Strona 241)

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PID

The PID function uses system feedback to continuously control a dynamic process. The

purpose of PID control is to keep a process running as close as possible to a desired Set

Point.

The M90 can run 4 closed PID loops.

About PID and Process Control

A common type of control is On-Off control. Many heating systems work on this principle.

The heater is off when the temperature is above the Set Point, and turns on when the

temperature is below the Set Point. The lag in the system response time causes the

temperature to overshoot and oscillate around the Set Point.

PID control enables you to minimize overshoot and damp the resulting

oscillations.

PID enables your controller to automatically regulate your process by:

1. Taking the output signal from the process, called the Process Variable (PV),

2. Comparing this output value with the process Set Point. The difference between the

output Process Variable and the Set Point is called the Error signal.

3. Using the Error signal to regulate the controller output signal, called the Control

Variable (CV), to keep the process running at the Set Point. Note that this output

signal may be an analog or time-proportional variable value.

In the figure below, a system is regulated according to temperature.

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