# Explanation of Digital Controller | Real Time System | BSc.CSIT Sixth Semester

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## Explanation of Digital Controller with example, Real Time System Notes | Sixth Semester, BSc.CSIT | Tribhuvan University (TU)

Digital Controller
They are the simplest and the most deterministic real-time applications. They also have the most stringent timing requirements. Many real-time systems are embedded in sensors and actuators and function as digital controllers. Figure below shows such a system. The term plant in the block diagram refers to a controlled system, for example, an engine, a brake, an aircraft, a patient. The state of the plant is monitored by sensors and can be changed by actuators. The real-time (computing) system estimates from the sensor readings, the current state of the plant and computes a control output based on the difference between the current state and the desired state (called reference input in the figure). We call this computation the control-law computation of the controller. The output thus generated activates the actuators, which bring the plant closer to the desired state. A simple example: As an example, we consider an analog single-input/single-output PID (Proportional, Integral, and Derivative) controller. This simple kind of controller is commonly used in practice. The analog sensor reading y(t) gives the measured state of the plant at time t. Let e(t) = r (t) − y(t) denote the difference between the desired state r (t) and the measured state y(t) at time t . The output u(t) of the controller consists of three terms: a term that is proportional to e(t), a term that is proportional to the integral of e(t) and a term that is proportional to the derivative of e(t).

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