WEG CFW-11 Series, Руководство по программированию

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20-1
20
PID Regulator [46]
20 PID REGULATOR [46]
20.1 DESCRIPTION AND DEFINITIONS
The CFW-11 has the special function PID REGULATOR, which can be used to control a closed loop process.
This function places a proportional, integral and derivative regulator, superposed to the normal CFW-11 speed
control. Refer to the block diagram in the
Figure 20.1 on page 20-2 .
The process control is done by means of the motor speed variation, keeping the value of the process variable
(the one to be controlled) at the desired value.
Application examples: the control of flow or pressure in a piping, of the temperature in a furnace or in a
greenhouse, or of the chemicals dosage in tanks.
In order to define the terms used by a PID control, we are going to use a simple example.
An electro-pump is used in a water pumping system where the pressure in the pump output pipe has to be
controlled. A pressure transducer is installed in the pipe and supplies an analog
feedback signal to the CFW-11,
which is proportional to the water pressure. This signal is called the process variable , and can be visualized
at the parameter P0040. A setpoint is programmed in the CFW-11 via the keypad (HMI) (P0525) or adjusted
through an analog input (as a 0 to 10 V or 4 to 20 mA signal). The setpoint is the desired water pressure value
that the pump is supposed to produce, regardless of the consumption variations at the pump output at any time.
The CFW-11 will compare the setpoint with the process variable and control the motor speed trying to eliminate
any error and keeping the process variable equal to the setpoint. The setting of the P, I and D gains determines
how fast the inverter will respond to eliminate this error.