没有合适的资源?快使用搜索试试~ 我知道了~
首页Understanding Automotive Electronics 8th - Appendix A
Understanding Automotive Electronics 8th - Appendix A
需积分: 9 14 下载量 3 浏览量
更新于2023-05-26
评论
收藏 1.2MB PDF 举报
Understanding Automotive Electronics 8th Appendix A - The Systems Approach to Control and Instrumentation
资源详情
资源评论
资源推荐
APPENDIX
THE SYSTEMS APPROACH
TO CONTROL AND
INSTRUMENTATION
A
OVERVIEW
This book discusses the application of electronics in automobiles from the standpoint of electronic
systems and subsystems. In a sense , the systems approach to describing automotive electronics is a
way of organizing the subject into its component parts based on functional groups. This appendix will
lay the foundation for this discussion by explaining the concepts of a system and a subsystem and how
such systems function and interact with one another. The means for characterizing the performance of
any system will be explained so that the reader will understand some of the relative benefits and limi-
tations of automotive electronic systems. This appendix will explain, generally, what a system is and,
more precisely, what an electronic system is. In addition, basic concepts of electronic systems that
are applicable to all automotive electronic systems, such as structure (architecture) and quantitative
performance analysis principles, will be discussed. In the general field of electronic systems (including
automotive systems), there are three major categories of function, including control, measurement, and
communication.
Two major classes of electronic systems —analog or continuous time (this appendix) and digital or
discrete time (Appendix B)—will be explained. In most cases, it is theoretically possible to impleme nt
a given electronic system as either an analog or a digital system. The relatively low cost of digital elec-
tronics coupled with the high performance achievable relative to analog electronics has led modern
automotive electronic system designers to choose digital rather than analog realizations for new
systems.
CONCEPT OF A SYSTEM
A system is a collection of components that function together to perform a specific task. Various
systems are encountered in everyday life. It is a common practice to refer to the bones of the human
body as the skeletal system. The collection of highways linking the country’s population centers is
known as the interstate freeway system.
Electronic systems are similar in the sense that they consist of collections of electronic and electrical
parts interconnected in such a way as to perform a specific function. The components of an electronic
system include transistors, diodes, resistors, and capacitors , as well as standard electrical parts such
as switches and connectors, among others. All these components are interconnected with individual
595
wires or with printed circuit boards. In addi tion, many automotive electronic systems incorporate spe-
cialized components known as sensors or actuators that enable the electronic system to interface with the
appropriate automotive mechanical systems. Systems can often be broken down into subsystems. The
subsystems also consist of a number of individual parts.
Any electronic system can be described at various levels of abstraction, from a pictorial description
or a schematic drawing at the lowest level to a block diagram at the highest level. For the purpos es of
this appendix, this higher-level abstraction is preferable. At this level, each functional subsystem is
characterized by inputs, outputs, and the relationship between input and output. Normally, only the
system designer or maintenance technician would be concerned with the detailed schematics and
the internal workings of the system. Furthermo re, the only practical way to cover the vast range of
automotive electronic systems is to limit our discussion to this so-called system level of abstraction
in this appendix. It is important for the reader to realize that there are typically many different circuit
configurations capable of performing a given function.
BLOCK DIAGRAM REPRESENTATION OF A SYSTEM
At the level of abstraction appropriate for the present discussion, a block diagram will represent the
electronic system . Depending on whether a given electronic system application is to (a) control,
(b) measure, or (c) communicate, it will have one of the three block diagram configurations shown
in Fig. A.1. The designer of a system often begins with a block diagram, in which major compo-
nents are represented as blocks.
In block diagram architecture, each functional component or subsystem is represented by an appro-
priately labeled block. The inputs and outputs for each block are identified. In electronic systems, these
input and output variables are electrical signals, except for the system input and system output. One
benefit of this approach is that the subsystem operation can be described by functional relationships
between input and output. There is no need to describe the operation of individual transistors and
components within the blocks at this block diagram level.
In the performance analysis of an existing system or in the design of a new one, the system or
subsystem is represented by a mathematical model that is derived from its physical configuration. Nor-
mally, this model is derived from known models of each of its constituent parts, that is, its basic physics.
Initially, this appendix will consider components, subsystems, and system blocks that can be represented
by a linear mathematical model. Later in this appendix, the treatment of nonlinearities is discussed.
For a block having input x(t) and output y(t) that can be represented by a linear model, the model is
of the form of a differential equation (A.1):
a
o
y + a
1
dy
dt
+ ⋯a
n
d
n
y
dt
n
¼b
o
x + b
1
dx
dt
⋯b
m
d
m
x
dt
m
(A.1)
Typically, n m and such a system block or component is said to be of order n. Analysis of this block is
accomplished by calculating its output y(t) for an arbitrary (but physically realizable) input x(t). The
performance of such a block in an automotive system normally involves finding its response to certain
physically meaningful inputs. Such analysis is explained later in this appendix.
Fig. A.1A depicts the architecture or configuration for a control application electronic system.
In such a system, control of a physical subsystem (called the plant) occurs by regulating some physical
variable (or variables) through an actuator. An actuator is an energy-conversion device having an elec-
trical input and an output of the physical form required to vary the plant (e.g., mechanical energy) as
596 APPENDIX A SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION
required to perform the desired system function. Thus, an actuator has an electrical input and an output
that may be mechanical, pneumatic, hydraulic, chemical, or so forth. The plant being controlled varies
in response to changes in the actuator output. The control is determined by electronic signal processing
based on the measurement of some variable (or variables) by a sensor in relationship to a command
input by the operator of the system (i.e., by the driver in an automotive application). Both sensors
and actuators with automotive applications are explained in Chapter 5.
In an electronic control system, the output of the sensor is always an electrical signal (denoted e
1
in
Fig. A.1A). The input is the desired value of the physical variable in the plant being controlled. The
electronic signal processing generates an output electrical signal (denoted e
2
in Fig. A.1A) that operates
the actuator. The signal processing is designed to achieve the desired control of the plant in relation to
the variable bein g measured by the sensor. The operation of such a control system is described later in
this appendix. At this point, we are interested only in describing the control-system architecture. An
explanation of electronic control is presented later in this appendix with appropriate analytic models
and analysis.
The architecture for electronic measurement (also known as instrumentation) is similar to that for a
control system in the sense that both structures incorporate a sensor and electronic signal processing.
However, instead of an actuator, the measurement architecture incorporates a display device. A disp lay
Command
input
Sensor
Electronic
signal
processing
Electronic
signal
processing
Actuator
Display
Physical
variable
being
measured
Indicated
value of
measurement
Input data
(message)
Output data
(message)
Plant
Sensor
Source Channel
Receiver
Variable being controlled
Control
input
Control application
Measurement application
Communication application
(A)
(B)
(
C
)
e
1
e
1
e
2
e
2
FIG. A.1 Electronic system block diagram variable being controlled. (A) Control system block diagram, (B)
measurement system block diagram, and (C) communication system block diagram.
597APPENDIX A SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION
is an electromechanical or electro-optical device capable of presenting numerical values to the user
(driver). In automotive electronic measurement, the display is sometimes simply a fixed message rather
than a numeric disp lay. Nevertheless , the architecture is as shown in Fig. A.1B. It should be noted that
both control and instrumentation electronic systems use one or more sensors and electronic signal
processing.
Fig. A.1C depicts a block diagram for a communication system. In such a system, data or messages
are sent from a source to a receiver over a communication channel. This particular architecture is
sufficiently general that it can accommodate all communication systems from ordinary car radios to
digital data buses between multiple electronic systems on cars and extravehicular communication.
Communication systems are described in detail in Chapter 9.
ANALOG (CONTINUOUS TIME) SYSTEMS
Modern automotive digita l electronic systems have virtually completely replaced analog systems.
Whereas digital systems are represented by discrete-time mode ls, analog systems are represented
by continuous-time models having a form such as is given in Eq. (A.1). Normally, automotive elec-
tronic systems incorporate components (e.g., sensors and actuators) that are best characterized by
continuous-time models. Typically, only the electronic portion is best characterized by discrete-time
models. Furthermore, even the digital electronics can be represented by an equivalent continuous-time
model, which can be converted to a discrete-time equivalent readily. Consequently, this discussion
begins with a brief overview of linear continuous-time system theory. The discrete-time system theory
is reviewed in Appendix B.
LINEAR SYSTEM THEORY: CONTINUOUS TIME
The performance of a continuous-time block (i.e., component/system) is found from the solution to the
differential equation (A.1) for a specific input. One straightforward method of solving this equation is
to take the Lapla ce transform of each term. The Laplace transform (also denoted xsðÞ¼L xtðÞ½) of the
input is denoted x( s) and is defined as following the linear integral transform of its time-domain
representation:
xsðÞ¼
ð
∞
o
e
st
xtðÞdt + xtðÞj
t¼0
(A.2)
where s ¼σ + jω ¼ complex frequency
and where
j ¼
ffiffiffiffiffiffiffi
1
p
(A.3)
Similarly, the Laplace transform of the block output is denoted y(s) and is given by
ysðÞ¼
ð
∞
o
e
st
ytðÞdt + ytðÞj
t¼0
(A.4)
where t ¼0
means the limit as t !0 from the left. This restrict ion on x(t) allows the Laplace transform
to be taken with a discontinuity in x(t)att ¼0 (e.g., step input).
598 APPENDIX A SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION
The differential equation model for a given continuous-time block includes time derivatives of the
input and output. The Laplace transf orm of the time derivative of order m of a variable (e.g., the input)
is given by
ð
∞
o
e
st
d
m
x
dt
m
dt ¼s
m
xsðÞ m ¼1, 2,… (A.5)
For any practical application of the Laplace transform, the initial conditions for both input and output
are zero,
xtðÞj
t¼o
¼0, ytðÞj
t¼o
¼0
the Laplace transform of the differential equation (Eq. A.1) for the block yields
a
0
+ a
1
s + a
2
s
2
… a
n
s
n
ysðÞ¼b
0
+ b
1
s + ⋯b
m
s
m
½xsðÞ (A.6)
It is conventional for the purpos e of conducting analysis for continuous-time systems to define the
transfer function (H(s)) for each block (Eq. A.7):
HsðÞ¼
ysðÞ
xsðÞ
¼
b
0
+ b
1
s + ⋯b
m
s
m
a
0
+ a
1
s + ⋯a
n
s
n
(A.7)
The transfer-function concept is highly useful for continuous-time linear system analysis since the
transfer function for any such system made up of a cascade connection of K blocks (e.g., as depicted
in Fig. A.2) is the produc t of the transfer functions of the individual blocks.
Denoting the transfer function of the kth block H
k
(s) and for the complete system H(s), the latter is
given by
HsðÞ¼
Y
K
k¼1
H
k
sðÞ (A.8)
An alternat e, highly useful, formulation of the transfer function is based on the roots of equations
formed from its numerator and denominator polynomials. The roots z
j
of the numerator polynomial
(P
N
(s)) are the m solutions to the equation:
P
N
sðÞ¼b
0
+ b
1
s + ⋯b
m
s
m
¼0 (A.9)
where P
N
z
j
¼0 j ¼1,2, …,m.
The roots z
j
are cal led the zeros of the transfer function. Similarly, the roots p
i
of the denominator
polynomial (P
D
(s)) are the n solutions to the Eq. (A.10):
P
D
sðÞ¼a
0
+ a
1
s + ⋯a
n
s
n
¼0 (A.10)
Block 1 Block 2 Block k Block K
y
x
K
x
k
x
2
x
1
FIG. A.2 System cascade connection block diagram.
599APPENDIX A SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION
剩余44页未读,继续阅读
frank_technologies
- 粉丝: 13
- 资源: 92
上传资源 快速赚钱
- 我的内容管理 收起
- 我的资源 快来上传第一个资源
- 我的收益 登录查看自己的收益
- 我的积分 登录查看自己的积分
- 我的C币 登录后查看C币余额
- 我的收藏
- 我的下载
- 下载帮助
会员权益专享
最新资源
- zigbee-cluster-library-specification
- JSBSim Reference Manual
- c++校园超市商品信息管理系统课程设计说明书(含源代码) (2).pdf
- 建筑供配电系统相关课件.pptx
- 企业管理规章制度及管理模式.doc
- vb打开摄像头.doc
- 云计算-可信计算中认证协议改进方案.pdf
- [详细完整版]单片机编程4.ppt
- c语言常用算法.pdf
- c++经典程序代码大全.pdf
- 单片机数字时钟资料.doc
- 11项目管理前沿1.0.pptx
- 基于ssm的“魅力”繁峙宣传网站的设计与实现论文.doc
- 智慧交通综合解决方案.pptx
- 建筑防潮设计-PowerPointPresentati.pptx
- SPC统计过程控制程序.pptx
资源上传下载、课程学习等过程中有任何疑问或建议,欢迎提出宝贵意见哦~我们会及时处理!
点击此处反馈
安全验证
文档复制为VIP权益,开通VIP直接复制
信息提交成功
评论0