Control Systems
Digital Control Loops

Digital Control Loops

What are time constants and where are they found?

The figure below shows the most fundamental feedback digital control system, which is a more complicated version of a purely analog control system. It contains a plant (typically a physical system that we would like to control), a digital controller, an analog to digital converter (A/D), which changes a voltage or current signal into a digital form (number), a digital to analog converter (D/A), which changes a digital signal (number) into a voltage or current signal, an actuator, which implements the control action, and a summing junction that determines the error between the actual and commanded values. The feedback sensor is represented by its own transfer function as well.

Virtually all modern advanced control systems closely follow the figure below.

Hover over the figure for more details.

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Detailed Explanation

The system signals are described in more detail here:

1) Response, R(s) = Y(s) Gsens(s)

2) A/D

3) Error signal, E(z) = X(z)-R(z)

4) Controller, H(z)

5) D/A

6) Actuator.

7) The plant, G(s)

Simulink Example

The figures below show all signals for a simple system - compare the waveforms with a fully analog system: Control System Block Diagram.

Plant - an analog-domain single pole system with 1 rad/s bandwidth.

Controller - a discrete-time proportional controller with gain of 5.

Sensor - an analog-domain single pole system with 10 rad/s bandwidth.

Simulink model and results are shown below.


This page is a modification of a now non-existent page located at:


Version of this article is 10/9/2017.

Proportional Controller Implementation

In MatLab, DSPs, and FPGAs.


Control System Block Diagram

The fundamentals of signal flow.


System Modeling With Transfer Functions

Introduction to dynamic systems.


Fourier Series Demo

It is all sine waves.

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