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Update:2013-05-13 18:42:59    Author:    Click:[]

Name：stu             Date：2013-01-14 16:48:33
Title： some basic questions
Content： What is a digital control system? What are the characteristics of a digital control system? what are the differences between a digital control system and a normal control system?
Reply： In most modern engineering systems, there is a need to control the evolution with
time  of  one  or  more  of  the  system  variables.  Controllers  are  required  to  ensure
satisfactory transient and steady-state behavior for these engineering systems. To
guarantee  satisfactory  performance  in  the  presence  of  disturbances  and  model
uncertainty, most controllers in use today employ some form of negative feedback.
A sensor is needed to measure the controlled variable and compare its behavior
to  a  reference  signal.  Control  action  is  based  on  an  error  signal  defined  as  the
difference between the reference and the actual values.
The controller that manipulates the error signal to determine the desired control
action has classically been an analog system, which includes electrical, fluid, pneu-matic, or mechanical components. These systems all have  analog inputs and outputs
(i.e., their input and output signals are defined over a continuous time interval and
have values that are defined over a continuous range of amplitudes). In the past few
decades, analog controllers have often been replaced by digital  controllers whose
inputs and outputs are defined at discrete time instances. The digital controllers are
in the form of digital circuits, digital computers, or microprocessors.
Date：2013-01-16 14:16:51

Name：stu             Date：2013-01-14 16:45:11

Title：

A question in chapter 3

Content：

How to model a digital control system?

Reply：

As in the case of analog control, mathematical models are needed for the analysis
and design of digital control systems. A common configuration for digital control
systems is shown in  Figure 3.1. The configuration includes a digital-to-analog con-verter (DAC), an analog subsystem, and an analog-to-digital converter (ADC). The
DAC converts numbers calculated by a microprocessor or computer into analog
electrical signals that can be amplified and used to control an analog plant. The
analog subsystem includes the plant as well as the amplifiers and actuators neces-sary  to  drive  it.  The  output  of  the  plant  is  periodically  measured  and  converted
to a number that can be fed back to the computer using an ADC. In this chapter,
we develop models for the various components of this digital control configura-tion. Many other configurations that include the same components can be similarly
analyzed.  We  begin  by  developing  models  for  the  ADC  and  DAC,  then  for  thecombination of DAC, analog subsystem, and ADC.

Date：2013-01-14 16:45:34

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