Rockwell-automation DeviceLogix System User Manual Instrukcja Użytkownika Pobierz pdf (Strona 27)

Publication RA-UM003B-EN-P - February 2010 27

Navigate the Function Block Editor Interface Chapter 2

The PID equation controls the process by sending an output to the

actuator device. The greater the error between the setpoint and

process variable input, the greater the output will be. An additional

value (feedforward or bias) can be added to the control output as an

offset. The PID result (control variable) drives the process variable

toward the setpoint.

The PID function block monitors and controls the process loop for

analog process parameters such as pressure, temperature, flow rate,

and fluid level. Features of the PID function block include:

• PID equations expressed in Dependent Gains (ISA standard)

• Input scaling in engineering units

• Zero-crossing deadband

• Derivative term acts on PV

• Direct or reverse acting control

•Output alarms

• Output limiting with anti-reset windup

• Manual mode (with bumpless transfer)

• Feedforward or output biasing

The PID function block uses the following equation with dependent

gains:

Where:

is Control Gain

is Reset Term

is Rate Term

SP is Set Point

PV is Process Variable

E is (SP-PV) or (PV-SP)

CV is Output Control Variable

Δt is Loop Update Time

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Rockwell-automation DeviceLogix System User Manual Instrukcja Użytkownika Strona 27