The output rate of change of an integral controller is dependent on the magnitude of the input.

EO 1.4DESCRIBE the characteristics of the following types of automatic control systems:

c. Integral control

Reset Control (Integral)

Integral control describes a controller in which the output rate of change is dependent on the magnitude of the input. Specifically, a smaller amplitude input causes a slower rate of change of the output. This controller is called an integral controller because it approximates the mathematical function of integration. The integral control method is also known as reset control.

Definition of Integral Control

A device that performs the mathematical function of integration is called an integrator. The mathematical result of integration is called the integral. The integrator provides a linear output with a rate of change that is directly related to the amplitude of the step change input and a constant that specifies the function of integration.

For the example shown in Figure 19, the step change has an amplitude of 10%, and the constant of the integrator causes the output to change 0.2% per second for each 1 % of the input.

The integrator acts to transform the step change into a gradually changing signal. As you can see, the input amplitude is repeated in the output every 5 seconds. As long as the input remains constant at 10%, the output will continue to ramp up every 5 seconds until the integrator saturates.

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Figure 19 Integral Output for a Fixed Input