Lecture Presentation Chp-4 - Sfsu

surprisesameSemiconductor

Nov 1, 2013 (3 years and 7 months ago)

152 views

CHAPTER 4

Computerized Data
-
Acquisition Systems

Since the late 1950s, computers have been used to monitor, and in

many
cases
to control, the performance of large process plants such
as refineries
and chemical
plants and to acquire data in major
testing programs such as the space program.

These systems were extremely expensive and required highly skilled
personnel to
set them up. In the late
1960s
, lower
-
cost computer
data
-
acquisition systems
became available
for smaller tests, but
since they were still difficult to set up and program,
their use
was
limited.

I
n
the late
1970s,
the simple and reliable Apple
II personal
computer led to inexpensive and simple data
-
acquisition systems
that
could readily
be used for small experiments. Personal
computer systems (mostly using
the Windows
operating system)
are now so capable that they can be used for a
significant fraction
of all engineering
testing.

FIGURE 4.1 Computerized data
-
acquisition system.

Computer Systems for Data Acquisition

The computer systems most commonly used for data acquisition in
experiments
are personal
computers using the
Windows
operating
system. Sampling rates of over
10 million
samples per second are
possible, and more than 3000 separate sensors can be

sampled (although not in the same system at the same time). Several
major
companies supply
software and hardware to make a personal
computer into a
data
-
acquisition system
, and some of the hardware
is available in low
-
cost generic form. Figure
4.2 shows
a board
designed to plug into the interior bus of a personal computer and a

For monitoring and controlling many production systems,
specialized
embedded computers
are used. Probably the most
common embedded computers are those
used for
fuel control in
modern automobiles. However, embedded computer systems are
used in
a wide variety of devices from medical imaging equipment
to assembly
-
line robots.

Data
-
acquisition board with
eight analog input

channels and two analog
output channels also showing
an analog signal connection
box. Manufactured by
National Instruments.

Figure 4.2

Although
some computers used in data acquisition are highly
specialized (the
engine control computer
in an automobile, for
example), the computers normally used
are quite
standard and have
the following components
:



Central processing unit (CPU)


Program (software)


Random access memory (RAM)


Mass storage systems


Display


User input device (keyboard, mouse, etc.)


Printers and plotters



Components of Computer Systems

FIGURE 4.3

Typical computer system.

Digital

input
-
output

(ports or

expansion bus)

Tne

central processing unit
(CPU)

controls all aspects
of computer system
operation and
performs all of the
arithmetic operations (multiplication, addition, etc.).


The CPU
operations follow instructions contained in
the user
-
provided program
. The CPU also
follows
instructions from the computer operating system
programs and from
built in

programs.

While
numbers used in the everyday world are normally
represented in base
10
(decimal
), it
is far more practical in
computers to represent numbers in base 2 (binary).
Information
in
computers is stored in
bi stable
devices called flip
-
flops, which
can
have two
possible states. One state is defined as "on" and is
assigned a numerical value of
1, and
the other state is defined as
"off" and is assigned a numerical value of 0. A
series of
flip
-
flops
are required to represent a number. For example, the binary
number 0101
,, which corresponds to the decimal number
5,
can
be represented in a
computer Using four flip
-
flops. Each of these
flip
-
flops represents a "
bit" of
the number. The left most "1
" in
the binary number 1001 is the most significant
bit
(MSB). The
rightmost "l"
is the least significant bit (LSB). It is common in
computers to break long
binary numbers
up into segments of 8
bits, which are known as bytes.


Representing Numbers in Computer Systems

Find the
8
-
bit
binary
number with the
same value as that
of the decimal
number 92
.


Solution: This problem
can be solved by a series
of divisions by 2:

is zero
for positive
binary numbers

= 9(10
1
) + 2(10
0
)


These same 4 bits can alternatively be used to
represent
numbers from
-
8 to
+7
. The positive
numbers from 0 to7 are represented by the three least
significant bits
, ranging from 0000 to 0111. The
negative numbers from
-
8 to
-
1 are
represented by
the
binary numbers 1000 to 1111, respectively.


For
positive numbers, the
most significant
bit is always
0, while it is always 1 for negative numbers.

To
convert a
negative decimal
integer to 2's
-
complement binary
the following procedure can be followed:


Convert the decimal integer
-
92 to an 8
-
bit 2's
-
complement binary number.

Example 4.3

+92

= 01011100

,invert
all the bits, to obtain

10100011

then add 1 to obtain the final result,

1

10100100

Transistors amplify current
, for example they can be used to amplify the
small output current from a logic IC so that it can operate a lamp, relay or
other high current device. In many circuits a resistor is used to convert the
changing current to a changing voltage, so the transistor is being used to
amplify voltage.

A transistor may be used as a switch (either fully on with maximum
current, or fully off with no current) and as an amplifier (always partly on).


Types of
transistor: Watch @

http://www.youtube.com/watch?v=ZaBLiciesOU

These logic circuits can be built very compact on
a silicon chip
with 1,000,000 transistors per square centimeter
. We can turn
them on and off very rapidly by switching every 0.000000001
seconds. Such logic chips are at the heart of your personal
computer and many other gadgets you use today.

Vacuum tubes were made containing several three
terminal devices called triodes.

http://www.youtube.com/watch?v=e0oUxG0eE9s&feature=related

http://
www.youtube.com/watch?v=CLLcRRBph90&feature=related

http://www.youtube.com/watch?v=
-
GQmtITMdas&feature=related


http://www.google.com/imgres?q=pn+junction&hl=en&sa=X&biw=1024&bih=653&tb
m=isch&prmd=imvnsb&tbnid=3Cdvby5O9KVooM:&imgrefurl=http://sunnywinenergy.c
om/en/AboutSun_02_en.htm&docid=RPDYxAQeqkIzaM&w=465&h=316&ei=AMd2TuKS
B_TYiAKxt9XLBw&zoom=1&iact=rc&dur=503&page=10&tbnh=113&tbnw=166&start=1
31&ndsp=13&ved=1t:429,r:8,s:131&tx=79&ty=52

A

p

n junction

is formed at the boundary
between a

P
-
type

and

N
-
type

semiconductor
created

in a single crystal of
semiconductor by

doping
, for example by

ion
implantation
,
diffusion

of

dopants
, or
by

epitaxy

(growing a layer of crystal doped
with one type of dopant on top of a layer of
crystal doped with another type of dopant). If
two separate pieces of material were used, this
would introduce a

grain boundary

between the
semiconductors which severely inhibits its utility
by

scattering

the electrons and holes.
[
citation
needed
]
.

P

N junctions are elementary "building blocks"
of many

semiconductor electronic devices

such
as

diodes
,

transistors
,

solar cells
,

LEDs
,
and
integrated

circuits
; they are the active sites
where the electronic action of the device takes
place. For example, a common type
of

transistor
, the

bipolar junction transistor
,
consists of two p

n junctions in series, in the
form n

p

n or p

n

p.


Electronic Numerical Integrator and Computer


18,000
vacuum tubes.


Occupied a 30 by 50 foot room


Programming by plugging wires into a patch panel. Very difficult to do, because this style
programming requires intimate
歮owledge
of the computer.


1946:

ENIAC

completed


1.
Vacuum tube

(1939)

2.
Transistor

(invented in 1947, used in IBM 7090 in 1958)

3.
Integrated circuit

or chip (invented in 1959, used in IBM 360 in 1964)

1.
A small wafer of silicon that has been photographically imprinted to contain
a large number of transistors together.

4.
Large
-
scale integration:

microprocessor

(1975)

1.
Entire processing unit on a single chip of silicon

Four generations of computers


Transistors

Old CPU's

Basics of Analog
-
to
-
Digital
Converters



To explain the function of the A"/D converter it is
necessary to describe two
distinct methods
by which
electronic systems process
numerical information:
analog
and digital.


Many everyday electronic devices, such as television
sets and audio amplifiers,
were basically
analog devices
(although they may have some digital components).


Modern computers
, on the other hand, are digital
devices. If we are trying to represent a
value of
5 V in
an analog device, we could, for example, charge a
capacitor to 5 V. In a
digital
device,5
V will
be
represented by
a
digital
code (a
digital
binary
number such
0101), which
is stored on
bistable

flip
-
flops.



The
two
-
light
-
bulb device is a 2
-
bit
A/D
converter.

In general, the
output of an
analog
-
to
-
digital
converter has
2
N

possible
values,

A unipolar
converter can
only respond to analog inputs with the same sign. Examples of
the
input range
are 0 to 5 V or 0 to
-
10 V. Bipolar converters can convert both positive
and
negative analog
inputs, with +5 V or
+10
V being typical input ranges.

Figure 4.6.