Operating Instructions

Descriptions of Parameter Settings
Descriptions of Parameter Settings
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Fig. 92: KP Proportional Gain (P), Ti Integral Time (I), Td Differential Time (D), S Calculation
Concept of PID control:
Proportional gain (P):
The output is proportional to input. With only a proportional gain control, there is always a steady-state error.
Integral time (I):
The controller output is proportional to the integral of the controller input. When an automatic control system is in a
steady state and a steady-state error occurs, the system is called a System with Steady-state Error. To eliminate
the steady-state error, add an “integral part” to the controller. The integral time controls the relation between the
integral part and the error. The integral part increases over time even if the error is small. It gradually increases the
controller output to eliminate the error until it is zero. This stabilizes the system without a steady-state error by
using proportional gain control and integral time control.
Differential control (D):
The controller output is proportional to the differential of the controller input. During elimination of the error,
oscillation or instability may occur. Use the differential control to suppress these effects by acting before the error.
That is, when the error is near 0, the differential control should be 0. Use proportional gain (P) and differential
control (D) to improve the system state during PID adjustment.
Using PID control in a constant pressure pump feedback application:
Set the application’s constant pressure value (bar) to be the set point of PID control. The pressure sensor sends
the actual value as the PID feedback value. After comparing the PID set point and PID feedback, an error displays.
The PID controller calculates the output by using proportional gain (P), integral time (I) and differential time (D) to
control the pump. It controls the drive to use a different pump speed and achieves constant pressure control by
using a 4 to 20 mA signal corresponding to 0 to 10 bar as feedback to the drive.