final without hamdy and getting started

Documentation
Hardware
Introduction
--------------------------------------------------------Control systems
Control Strategies
PLC History
Mechanical system
--------------------------------------------------------Motor Types
AC Motor
DC Motor
Stepper Motor
Sensors and actuators
-------------------------------------------------------Introduction
Sensor types
How do I choose the right sensor
Application and Testing
-------------------------------------------------------Stepper Motor approach
Dc motor approach

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Embedded system
Simulated system
Alarms
Pic microcontrollers

PIC18
PIC18F452
Peripherals used
INTERRUPTS
Timer0
A2D
UART

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Introduction
------------------------------------------------------Systems concepts
------------------------------------------------------Human machine interface
------------------------------------------------------Hardware Solutions
------------------------------------------------------Remote terminal Unit
Supervisory Station
Operational philosophy
Communication infrastructures and methods
SCADA Architecture
------------------------------------------------------First Generation: "Monolithic"

Second Generation: "Distributed"
Third Generation: "Networked"
Trends in SCADA
------------------------------------------------------Security Issues
------------------------------------------------------S/W Requirements
------------------------------------------------------Program Components
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Software

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DataBase
SQL server 2005
Introdunction
ADO.net
Introduction
ADO.net Overview

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Connection

1


Introduction
Control systems apply artificial means to change the behavior of a system. The
type of control problem often determines the type of control system that can be used. Each
controller will be designed to meet a specific objective. The major types of control are :

• Continuous - The values to be controlled change smoothly. e.g. the speed of a car.
• Logical - The value to be controlled are easily described as on-off. e.g. the car
motor is on-off. NOTE: all systems are continuous but they can be treated as
logical for simplicity.
e.g. “When I do this, that always happens!” For example, when the power
is turned on, the press closes!
• Linear - Can be described with a simple differential equation. This is the preferred
starting point for simplicity, and a common approximation for real world
problems.
e.g. A car can be driving around a track and can pass same the same spot at

a constant velocity. But, the longer the car runs, the mass decreases, and
it travels faster, but requires less gas, etc. Basically, the math gets
CONTROL
CONTINUOUS DISCRETE
LINEAR NON_LINEAR CONDITIONAL SEQUENTIAL
e.g. PID
e.g. MRAC
e.g. FUZZY LOGIC
BOOLEAN
TEMPORAL
e.g. TIMERS
e.g. COUNTERS
EVENT BASED
EXPERT SYSTEMS
tougher, and the problem becomes non-linear.
e.g. We are driving the perfect car with no friction, with no drag, and can
predict how it will work perfectly.

2


• Non-Linear - Not Linear. This is how the world works and the mathematics
become much more complex.
e.g. As rocket approaches sun, gravity increases, so control must change.
• Sequential - A logical controller that will keep track of time and previous events.
The difference between these control systems can be emphasized by considering a
simple elevator. An elevator is a car that travels between floors, stopping at precise
heights. There are certain logical constraints used for safety and convenience. The points
below emphasize different types of control problems in the elevator.
Logical:

1. The elevator must move towards a floor when a button is pushed.
2. The elevator must open a door when it is at a floor.
3. It must have the door closed before it moves.
etc.
Linear:
1. If the desired position changes to a new value, accelerate quickly
towards the new position.
2. As the elevator approaches the correct position, slow down.
Non-linear:
1 Accelerate slowly to start.
2. Decelerate as you approach the final position.
3. Allow faster motion while moving.
4. Compensate for cable stretch, and changing spring constant, etc.
Logical and sequential control is preferred for system design. These systems are
more stable, and often lower cost. Most continuous systems can be controlled logically.
But, some times we will encounter a system that must be controlled continuously. When
this occurs the control system design becomes more demanding. When improperly controlled,
continuous systems may be unstable and become dangerous.
When a system is well behaved we say it is self regulating. These systems don’t
need to be closely monitored, and we use open loop control. An open loop controller will
set a desired position for a system, but no sensors are used to verify the position. When a
system must be constantly monitored and the control output adjusted we say it is closed
loop. A cruise control in a car is an excellent example. This will monitor the actual speed
of a car, and adjust the speed to meet a set target speed.
Many control technologies are available for control. Early control systems relied
upon mechanisms and electronics to build controlled. Most modern controllers use a complc
puter to achieve control. The most flexible of these controllers is the PLC (Programmable
Logic Controller).

3

- Control Strategies : Open Loop : -

Requirements

Control
plan

Action

Outcome

Plant
system
Disturbance

Feed forward : -

Modification to plan taking account of disturbance

Requirements

Control
plan

Measurements
Measurements
of disturbances
disturbances

of

Action

Plant
system

Outcome

Disturbance

Closed Loop : -

Feedback

Measured
value
Requirements
)set point(

Deviation
)error signal( Control Action Plant
Compare
plan
system
Disturbance

4

Measurement

outcome


Sequential Control : basis of computer operation.
digital systems that have outputs dependent on previous system state .

Combinational Logic

Storage Device

Programmable Computing Control Systems : -

5


Data memory
Input Data

Firmware

Output Data

Program
Control device:
A programmable logic controller (PLC) or programmable controller is a digital
computer used for automation of electromechanical processes, such as control of machinery
on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many
industries and machines, such as packaging and semiconductor machines. Unlike generalpurpose computers, the PLC is designed for multiple inputs and output arrangements,
extended temperature ranges, immunity to electrical noise, and resistance to vibration and
impact. Programs to control machine operation are typically stored in battery-backed or nonvolatile memory. A PLC is an example of a real time system since output results must be

produced in response to input conditions within a bounded time, otherwise unintended
operation will result.

6


History
Origin
The PLC was invented in response to the needs of the American automotive manufacturing
industry. Programmable controllers were initially adopted by the automotive industry where
software revision replaced the re-wiring of hard-wired control panels when production models
changed.
Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles
was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers
and dedicated closed-loop controllers. The process for updating such facilities for the yearly
model change-over was very time consuming and expensive, as the relay systems needed to be
rewired by skilled electricians.
In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a
request for proposal for an electronic replacement for hard-wired relay systems.
The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first
PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the
result. Bedford Associates started a new company dedicated to developing, manufacturing,
selling, and servicing this new product: Modicon, which stood for MOdular DIgital
CONtroller. One of the people who worked on that project was Dick Morley, who is
considered to be the "father" of the PLC. The Modicon brand was sold in 1977 to Gould
Electronics, and later acquired by German Company AEG and then by French Schneider
Electric, the current owner.
One of the very first 084 models built is now on display at Modicon's headquarters in North
Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after
nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its

product range until the 984 made its appearance.The automotive industry is still one of the
largest users of PLCs.
Development
Early PLCs were designed to replace relay logic systems. These PLCs were programmed in
"ladder logic", which strongly resembles a schematic diagram of relay logic. Modern PLCs
can be programmed in a variety of ways, from ladder logic to more traditional programming
languages such as BASIC and C. Another method is State Logic, a very high-level
programming language designed to program PLCs based on state transition diagrams.
Many of the earliest PLCs expressed all decision making logic in simple ladder logic which
appeared similar to electrical schematic diagrams. This program notation was chosen to reduce
training demands for the existing technicians. Other early PLCs used a form of instruction
list programming, based on a stack-based logic solver.
Basic PLC Operation
PLCs consist of input modules or points, a Central Processing Unit (CPU), and output
modules or points. An input accepts avariety of digital or analog signals from various field
devices (sensors) and converts them into a logic signal that can be used by the CPU. The CPU
makes decisions and executes control instructions based on program instructions in memory.
Output modules convert control instructions from the CPU into a digital
or analog signal that can be used to control various field devices (actuators). A programming
device is used to input the desired instructions. These instructions determine what the PLC

7


will do for a specific input. An operator interface device allows process information to be
displayed and new control parameters to be entered.

Pushbuttons (sensors), in this simple example, connected to PLC inputs, can be used to start
and stop a motor connected to a PLC through a motor starter (actuator).

PLC compared with other control systems
PLCs are well-adapted to a range of automation tasks. These are typically industrial processes
in manufacturing where the cost of developing and maintaining the automation system is high
relative to the total cost of the automation, and where changes to the system would be
expected during its operational life. PLCs contain input and output devices compatible with
industrial pilot devices and controls; little electrical design is required, and the design problem
centers on expressing the desired sequence of operations in ladder logic (or function chart)
notation. PLC applications are typically highly customized systems so the cost of a packaged
PLC is low compared to the cost of a specific custom-built controller design. On the other
hand, in the case of mass-produced goods, customized control systems are economic due to
the lower cost of the components, which can be optimally chosen instead of a "generic"
solution, and where the non-recurring engineering charges are spread over thousands or
millions of units.

8


For high volume or very simple fixed automation tasks, different techniques are used. For
example, a consumer dishwasher would be controlled by an electromechanical cam
timer costing only a few dollars in production quantities.
A microcontroller-based design would be appropriate where hundreds or thousands of units
will be produced and so the development cost (design of power supplies and input/output
hardware) can be spread over many sales, and where the end-user would not need to alter the
control. Automotive applications are an example; millions of units are built each year, and
very few end-users alter the programming of these controllers. However, some specialty
vehicles such as transit busses economically use PLCs instead of custom-designed controls,
because the volumes are low and the development cost would be uneconomic.
Very complex process control, such as used in the chemical industry, may require algorithms
and performance beyond the capability of even high-performance PLCs. Very high-speed or
precision controls may also require customized solutions; for example, aircraft flight controls.

Programmable controllers are widely used in motion control, positioning control and torque
control. Some manufacturers produce motion control units to be integrated with PLC so
that G-code (involving a CNC machine) can be used to instruct machine movements.
PLCs may include logic for single-variable feedback analog control loop, a "proportional,
integral, derivative" or "PID controller." A PID loop could be used to control the temperature
of a manufacturing process, for example. Historically PLCs were usually configured with only
a few analog control loops; where processes required hundreds or thousands of loops,
a distributed control system (DCS) would instead be used. As PLCs have become more
powerful, the boundary between DCS and PLC applications has become less distinct.
PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually does
not support control algorithms or control loops. As hardware rapidly becomes more powerful
and cheaper, RTUs, PLCs and DCSs are increasingly beginning to overlap in responsibilities,
and many vendors sell RTUs with PLC-like features and vice versa. The industry has
standardized on the IEC 61131-3 functional block language for creating programs to run on
RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated
development environments.
Comparison of PLC with Other Control Systems :C\Cs

Relay systems

Digital Logics

Computers

PLC systems

Price Per
Function

Fairly Low

Low

High

Low

Physical Size

Bulky

Very Compact

Fairly Compact

Very Compact

Operating
Speed

Slow

Very Fast

Fairly Fast

Fast

Noise Immunity

Excellent

Good

Fairly Good

Good

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Advantages of PLCs :
The same, as well as more complex tasks, can be done with
a PLC. Wiring between devices and relay contacts is done in
the PLC program. Hard-wiring, though still required to connect
field devices, is less intensive. Modifying the application and
correcting errors are easier to handle. It is easier to create and
change a program in a PLC than it is to wire and rewire a circuit.
Following are just a few of the advantages of PLCs:
• Smaller physical size than hard-wire solutions.
• Easier and faster to make changes.
• PLCs have integrated diagnostics and override functions.
• Diagnostics are centrally available.
• Applications can be immediately documented.
• Applications can be duplicated faster and less expensively.

Mechanical system
Overview of Motor Types

Motor Types

Industrial motors come in a variety of basic types. These variations are suitable for many
different applications. Naturally, some types of motors are more suited for certain applications
than other motor types are. This document will hopefully give some guidance in selecting
these motors.










AC Motors
DC Motors
Brushless DC Motors
Servo Motors
Brushed DC Servo Motors
Brushless AC Servo Motors
Stepper Motors
Linear Motors

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AC Motors
Advantages








Simple Design
Low Cost
Reliable Operation
Easily Found Replacements
Variety of Mounting Styles
Many Different Environmental Enclosures

Simple Design
The simple design of the AC motor -- simply a series of three windings in the exterior (stator)
section with a simple rotating section (rotor). The changing field caused by the 50 or 60 Hertz
AC line voltage causes the rotor to rotate around the axis of the motor.
The speed of the AC motor depends only on three variables:
1. The fixed number of winding sets (known as poles) built into the motor, which
determines the motor's base speed.
2. The frequency of the AC line voltage. Variable speed drives change this frequency to
change the speed of the motor.
3. The amount of torque loading on the motor, which causes slip.
Low Cost
The AC motor has the advantage of being the lowest cost motor for applications requiring
more than about 1/2 hp (325 watts) of power. This is due to the simple design of the motor.
For this reason, AC motors are overwhelmingly preferred for fixed speed applications in
industrial applications and for commercial and domestic applications where AC line power

11

can be easily attached. Over 90% of all motors are AC induction motors. They are found in air
conditioners, washers, dryers, industrial machinery, fans, blowers, vacuum cleaners, and
many, many other applications.
Disadvantages




Expensive speed control
Inability to operate at low speeds
Poor positioning control

Poor positioning control
Positioning control is expensive and crude. Even a vector drive is very crude when controlling
a standard AC motor. Servo motors are more appropriate for these applications.

DC Motors
The brushed DC motor is one of the earliest motor designs. Today, it is the motor of choice in
the majority of variable speed and torque control applications.
Advantages





Easy to understand design
Easy to control speed
Easy to control torque
Simple ,cheap drive design

Easy to understand design
The design of the brushed DC motor is quite simple. A permanent magnetic field is created in
the stator by either of two means:
 Permanent magnets
 Electro-magnetic windings
If the field is created by permanent magnets, the motor is said to be a "permanent magnet DC
motor" (PMDC). If created by electromagnetic windings, the motor is often said to be a "shunt
wound DC motor" (SWDC). Today, because of cost-effectiveness and reliability, the PMDC
motor is the motor of choice for applications involving fractional horsepower DC motors, as
well as most applications up to about three horsepower.
At five horsepower and greater, various forms of the shunt wound DC motor are most
commonly used. This is because the electromagnetic windings are more cost effective than
permanent magnets in this power range.

12


Caution: If a DC motor suffers a loss of field (if for example, the field power connections are
broken), the DC motor will immediately begin to accelerate to the top speed which the loading
will allow. This can result in the motor flying apart if the motor is lightly loaded. The possible
loss of field must be accounted for, particularly with shunt wound DC motors.
Opposing the stator field is the armature field, which is generated by a changing
electromagnetic flux coming from windings located on the rotor. The magnetic poles of the
armature field will attempt to line up with the opposite magnetic poles generated by the stator
field. If we stopped the design at this point, the motor would spin until the poles were opposite
one another, settle into place, and then stop -- which would make a pretty useless motor!
However, we are smarter than that. The section of the rotor where the electricity enters the
rotor windings is called the commutator. The electricity is carried between the rotor and the
stator by conductive graphite-copper brushes (mounted on the rotor) which contact rings on

stator. Imagine power is supplied:
The motor rotates toward the pole alignment point. Just as the motor would get to this point,
the brushes jump across a gap in the stator rings. Momentum carries the motor forward over
this gap. When the brushes get to the other side of the gap, they contact the stator rings again
and -- the polarity of the voltage is reversed in this set of rings! The motor begins accelerating
again, this time trying to get to the opposite set of poles. (The momentum has carried the
motor past the original pole alignment point.) This continues as the motor rotates.
In most DC motors, several sets of windings or permanent magnets are present to smooth out
the motion.
Easy to control speed
Controlling the speed of a brushed DC motor is simple. The higher the armature voltage, the
faster the rotation. This relationship is linear to the motor's maximum speed.
The maximum armature voltage which corresponds to a motor's rated speed (these motors are
usually given a rated speed and a maximum speed, such as 1750/2000 rpm) are available in
certain standard voltages, which roughly increase in conjuntion with horsepower. Thus, the
smallest industrial motors are rated 90 VDC and 180 VDC. Larger units are rated at 250 VDC
and sometimes higher.
Specialty motors for use in mobile applications are rated 12, 24, or 48 VDC. Other tiny motors
may be rated 5 VDC.
Most industrial DC motors will operate reliably over a speed range of about 20:1 -- down to
about 5-7% of base speed. This is much better performance than the comparible AC motor.
This is partly due to the simplicity of control, but is also partly due to the fact that most
industrial DC motors are designed with variable speed operation in mind, and have added heat
dissipation features which allow lower operating speeds.
Easy to control torque
In a brushed DC motor, torque control is also simple, since output torque is proportional to
current. If you limit the current, you have just limited the torque which the motor can achieve.
This makes this motor ideal for delicate applications such as textile manufacturing.
Simple, cheap drive design
The result of this design is that variable speed or variable torque electronics are easy to design

and manufacture. Varying the speed of a brushed DC motor requires little more than a large
enough potentiometer. In practice, these have been replaced for all but sub-fractional

13


horsepower applications by the SCR and PWM drives, which offer relatively precisely control
voltage and current. Common DC drives are available at the low end (up to 2 horsepower) for
under US$100 -- and sometimes under US$50 if precision is not important.
Large DC drives are available up to hundreds of horsepower. However, over about 10
horsepower careful consideration should be given to the price/performance tradeoffs with AC
inverter systems, since the AC systems show a price advantage in the larger systems. (But they
may not be capable of the application's performance requirments).
Disadvantages






Expensive to produce
Can’t reliably control at lowest speeds
Physically larger
High maintenance
Dust

A stepper Motor
is a brushless, synchronous electric motor that can divide a full rotation into a large number of
steps. The motor's position can be controlled precisely, without any feedback mechanism (see
Open-loop controller). Stepper motors are similar to switched reluctance motors (which are

very large stepping motors with a reduced pole count, and generally are closed-loop
commutated.)

14


How Stepper Motors Work

Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and
electromagnets on the stationary portion that surrounds the motor, called the stator. Figure 1
illustrates one complete rotation of a stepper motor. At position 1, we can see that the rotor is
beginning at the upper electromagnet, which is currently active (has voltage applied to it). To
move the rotor clockwise (CW), the upper electromagnet is deactivated and the right
electromagnet is activated, causing the rotor to move 90 degrees CW, aligning itself with the
active magnet. This process is repeated in the same manner at the south and west
electromagnets until we once again reach the starting position.
Open-loop versus closed-loop commutation
Steppers are generally commutated open loop, ie. the driver has no feedback on where the
rotor actually is. Stepper motor systems must thus generally be over engineered, especially if
the load inertia is high, or there is widely varying load, so that there is no possibility that the
motor will lose steps. This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an oversized but relatively
cheap stepper.
A new development in stepper control is to incorporate a rotor position feedback (eg. an
encoder or resolver), so that the commutation can be made optimal for torque generation
according to actual rotor position. This turns the stepper motor into a high pole count
brushless servo motor, with exceptional low speed torque and position resolution. An advance
on this technique is to normally run the motor in open loop mode, and only enter closed loop
mode if the rotor position error becomes too large -- this will allow the system to avoid
hunting or oscillating, a common servo problem.

15


Stepper motor drive circuits
Stepper motor performance is strongly dependent on the drive circuit. Torque curves may be
extended to greater speeds if the stator poles can be reversed more quickly, the limiting factor
being the winding inductance. To overcome the inductance and switch the windings quickly,
one must increase the drive voltage. This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
Applications
Computer-controlled stepper motors are one of the most versatile forms of positioning
systems. They are typically digitally controlled as part of an open loop system, and are simpler
and more rugged than closed loop servo systems.
Industrial applications are in high speed pick and place equipment and multi-axis machine
CNC machines often directly driving lead screws or ballscrews. In the field of lasers and
optics they are frequently used in precision positioning equipment such as linear actuators,
linear stages, rotation stages, goniometers, and mirror mounts. Other uses are in packaging
machinery, and positioning of valve pilot stages for fluid control systems.

Digital Encoders
A digital optical encoder is a device that converts
motion into a sequence of digital pulses. By
counting a single bit or by decoding a set of bits,
the pulses can be converted to relative or absolute
position measurements. Encoders have both linear
and rotary configurations, but the most common
type is rotary. Rotary encoders are manufactured
in two basic forms: the absolute encoder where a
unique digital word corresponds to each rotational

position of the shaft, and the incremental encoder,
which produces digital pulses as the shaft rotates,
allowing measurement of relative position of
shaft. Most rotary encoders are composed of a
glass or plastic code disk with a photographically deposited radial pattern organized in tracks.
As radial lines in each track interrupt the beam between a photoemitter-detector pair, digital
pulses are produced.
Absolute encoder
The optical disk of the absolute encoder is designed to produce a digital word that
distinguishes N distinct positions of the shaft. For example, if there are 8 tracks, the encoder is
capable of producing 256 distinct positions or an angular resolution of 1.406 (360/256)
degrees. The most common types of numerical encoding used in the absolute encoder are gray
and binary codes. To illustrate the acion of an absolute encoder, the gray code and natural
binary code dsisk track patterns for a simple 4-track (4-bit) encoder are illustrated in Fig 2 and
3. The linear patterns and associated timing diagrams are what the photodetectors sense as the
code disk circular tracks rotate with the shaft.

16


Sensors and actuators
INTRODUCTION
Sensors allow a PLC to detect the state of a process. Logical sensors can only
detect a state that is either true or false. Examples of physical phenomena that are typically
detected are listed below.
• inductive proximity - is a metal object nearby?
• capacitive proximity - is a dielectric object nearby?
• optical presence - is an object breaking a light beam or reflecting light?

17

• mechanical contact - is an object touching a switch?
The language of PLCs consists of a commonly used set
of terms; many of which are unique to PLCs. In order to
understand the ideas and concepts of PLCs, an understanding
of these terms is necessary.
Sensor:
A sensor is a device that converts a physical condition into an
electrical signal for use by the PLC. Sensors are connected to
the input of a PLC. A pushbutton is one example of a sensor
that is connected to the PLC input. An electrical signal is sent
from the pushbutton to the PLC indicating the condition (open/
closed) of the pushbutton contacts.

Actuators:
Actuators convert an electrical signal from the PLC into a
physical condition. Actuators are connected to the PLC output.
A motor starter is one example of an actuator that is connected
to the PLC output. Depending on the output PLC signal the
motor starter will either start or stop the motor.

Generally there are 5 steps to determine which switch type is best suited to the
application. This depends on the material properties of the target to be detected.
Step ( 1 ) : Step ( 2 ) : Step ( 3 ) : Step ( 4 ) : Step ( 5 ) : -

type of sensor .
Housing design .
Sensing range (mm)
Electrical data and connections

General specifications

18



Proximity Sensor:
A type of sensing switch that detects the presence or absence of an object without
physical contact.



Inductive Proximity Sensor:-

A type of sensing switch that uses an electromagnetic coil to detect the presence of a
metal object without coming into physical contact with it. Inductive proximity sensors
ignore nonmetallic objects.



Capacitive Proximity Sensor :-

A type of sensing switch that produces an electrostatic field to detect the presence of
metal and nonmetallic objects without coming into contact with them.


Ultrasonic
Sensor
A type of sensing
switch

that uses high frequency sound to detect the presence of an object without coming into
contact with the object.

19


1 THE DESIGN PROCESS
The design of a technical system involves making choices on the basis of criteria (from a list
of requirements),
availability of parts and materials, financial resources, and time. These aspects play a
significant role when designing a measurement system.
Blanchard and Fabrycky (1998) distinguish six major phases of the design process: (a)
conceptual design;
(b) preliminary design; (c) detail design and development;
(d) production/construction; (e) operational use/maintenance;
(f) retirement – see also (Sydenham, 2004). Thus, sensor selection is a crucial activity in the
systems design
process, as it will make a great impact on the production of the measurement instrument and
the performance during its entire lifetime and may even have consequences related
to disposal.
Design methods have evolved over time, from purely intuitive (as in art) to formal
(managerial). The process
of sensor selection is somewhere in between: it is an act of engineering, in which the design is
supported by
advanced tools for simulating system behavior based on scientific knowledge. The basic
attitude is (still) the use ofknow-how contained in the minds of people and acquired.
2 THE REQUIREMENTS
Sensor selection means meeting requirements. Unfortunately, these requirements are often not
known precisely
or in detail, in particular when the designer and the user are different persons. The first task of

the designer is to get as much information as possible about the future applications
of the measurement instrument, all possible conditions of operation, the environmental factors,
and the specifications with respect to quality, physical dimensions, and costs.
The list of demands should be exhaustive. Even when not all items are relevant, they must be
indicated as
such. This will leave more room to the designer, and will minimize the risk of being forced to
start all over
again at a later date. Rework is an expensive process and should be avoided where possible by
reducing errors as
early as possible in the systems engineering life cycle process. The requirements list should be
made in such
a way as to enable unambiguous comparison with the final specifications of the designed
instrument. Once the
designer has a complete idea about the future use of the instrument, the phase of the
conceptual design can
start.
Before thinking about sensors, the measurement principle has to be considered first. For the
instrumentation of
each measurement principle, the designer has a multitude of sensing methods at his or her
disposal. For realization of a particular sensor method, the designer has to choose

20


the optimal sensor type out of a vast collection of sensors offered by numerous sensor
manufacturers
How do I Choose the Right Sensor?
Step 1:
What is the sensing distance required?
The sensing distance is the distance between the tip of the sensor and the object to be sensed.

The selection guide and the specifications table for each sensor family lists the sensing
distances.
Some things to keep in mind are:
A. In many applications, it is beneficial to place the sensor as far as possible from the sensing
object due to temperature concerns. If a sensor is placed too close to a hot temperature source,
the sensor will fail quicker and require more maintenance.
Greater distance may be achieved with extended and triple range sensors. In many
applications, a sensor may not be mountable close to the sensed object. In this case, longer
sensing distances are needed. Extended sensing distance sensors are offered in 8mm to 30mm
dimeters, and triple sensing distance sensors in 8mm and 12mm formats.
In many cases, using an extended distance sensor to get the sensor farther away from the
detected object can be beneficial to the life of the sensor. For example, without an extended
distance sensor you may not be able to place the sensor close enough to the detectable object,
or you may need to buy more expensive high temperature sensors.
Another example would be a mechanical overshoot situation, where mounting the sensor
farther from the detection object may eliminate unneeded contact with the sensor, thereby
extending the life of the sensor.
These are just a few examples, but the benefits of using extended distance sensors are obvious
in many applications. Think of how extended distance sensors could save you time and money
in your application.
B. The material being sensed (i.e. brass, copper, aluminum, steel, etc.) makes a difference in
the type of sensor needed.
Note: If you are sensing a non-metallic object, you must use a capacitive sensor.
The sensing distances specified in this catalog were calculated using FE360 material. Many
materials are more difficult to sense and require a shorter distance from the sensor tip to the
object sensed.
If sensing a material that is difficult to sense, you may consider using our unique stainless
steel sensing technology. This will measure virtually all materials at the specified sensing
distances.

Step 2:
How much space is available for mounting the sensor?
Have you ever tried using a round sensor or short body version, and not been able to make it
fit? Our rectangular sensors can meet your needs.
The same technology used in a standard round proximity sensor is enclosed in a rectangular
housing. This technology includes sensing distances, electrical protection and switching
frequencies similar to round sensors.
Step 3:

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Is a shielded or unshielded sensor needed?
Shielded and unshielded sensors are also referred to as embeddable and nonembeddable.
Unshielded sensors allow longer sensing distances but shielded sensors allow flush mounting.
Step 4:
Consider environmental placement concerns. Will the sensor be placed underwater, in a hightemperature environment, continually splashed with oil, etc.?
This will determine the type of sensor you may use. In the selection table and in the
specification tables for each sensorfamily, we list the environmental protection degree ratings.
Most of our sensors are rated IEC-IP67 and others are rated IP65 or IP68.
These ratings are defined as:
IP65: Protection from live or moving parts, dust, and protection from water jets from any
direction.
IP67: Protection from live or moving parts, dust, and protection from immersion in water.
IP68: Protection from live or moving parts, dust, and protection from submersion in water
under pressure.
Step 5:
What is the sensor output connected to?
Note: If using AC sensors, please skip this step.
The type of output required must be determined (i.e., NPN, PNP or analog).

Most PLC products will accept either output. If connecting to a solid state
relay, a PNP output is needed.
Step 6a:
Do I need 2, 3, or 4-wire discrete outputs?
This is somewhat determined by what the sensor will be connected to.
Step 6b:
Do I need analog outputs?
This is determined by the sensor application and what the sensor will be connected to. Sensors
with analog outputs produce an output signal approximately proportional to the target
distance.
Step 7:
Determine output connection type.
Do you want an axial cable factory attached to the sensor (pigtail) or a quick disconnect cable?
There are many advantages to using a quick-disconnect cable, such as easier maintenance and
replacement. All proximity sensors will fail in time and using a Q/D (quick-disconnect) cable
allows for simple replacement.
Factory attached axial cables come in a 2 meter length. CD08/CD12 Q/D cables come in 2
meter, 5 meter , and 7 meter lengths.
Extension cables are available in 1 meter and 3 meter lengths to extend the length of the
standard Q/D cables.
Q/D cables are offered in PVC and PUR jackets for meeting the requirements of all
applications. Axial cables typically come with a PVC jacket. PVC is a general purpose
insulation while PUR provides excellent oxidation, oil and ozone resistance. PUR is beneficial
if the cable is exposed to oils or placed in direct sunlight.
There are also advantages to a factory attached axial cable:
Cost: The cable is integrate into the sensor and included in the price. Q/D cables must be
purchased separately.

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Environmental impact: Since the cable is sealed into the sensor, there is less chance of oil,
water or dust penetration into the sensor, which could cause failure.
Multi-Axis Synchronization
In many machine control and automation problems, there are two or more axes of
motion which must be coordinated. The term "multi-axis synchronization" refers to the
motion which requires coordination, and the techniques used to achieve control of the
motion. With today’s increasing automation and machine sophistication, the control
applications have become more demanding, and the control techniques have improved.
This paper reviews some of the basic elements of motion coordination, illustrated with the
requirements of familiar applications. A review of control choices is presented, with
special emphasis on a technique called following. The key concepts and capabilities of
following are explained with the help of a detailed web processing example.
Introduction to Multi-Axis Synchronization
The term "axis of motion" refers to one degree of freedom, or forward and
backward motion along one direction. It may be linear or rotary motion, and may take the
form of a conveyer belt, a rotary knife, or many other types. When two or more axes of
motion are involved on a single machine, that machine is employing multi-axis motion.
The axes may be working independently, or moving together. The need for multi-axis
synchronization arises whenever the axes must move together, and the relationship
between their respective motion is important.
The most familiar example of a multi-axis application requiring synchronization is
that of an X-Y plotter. Here there are two axes, the X direction and the Y direction.
Each may move independently of each other, but if a two dimensional figure is to be
drawn accurately, their motion must be coordinated.
X-Y cutting machine
In many machines, the synchronization requires more than the coordination of
starting and stopping. The position and velocity relationship between the axes will often
be important to the proper operation of the machine. For example, if there are
interlocking moving parts on a machine, position coordination during motion may be required

to avoid collision. If multiple axes control the orientation of a moving part, the
position and velocity synchronization of the axes will determine how accurately the part is
oriented as it moves. In some cases, a certain velocity or position achieved on one axis
will be the signal to start motion on another axis. In such cases, the accuracy of the
eventual position relationship of the axes will depend on how accurately the position of
first axis is monitored by the second.

The Mechanical Approach to Synchronization
By definition, synchronization of two or more axes requires a definite relationship
between one axis and the others. Before electronic motion control was available, the
traditional approach to this had been largely mechanical, using a central motion source.
Individual axes were driven from this source with gears and drive trains. The gears
determine the speed relationship, and the drive trains deliver the motion to the appropriate
place. Such an approach works well if the desired gear ratio is constant and the drive train
is short and direct. More complex arrangements require more costly mechanics, and the
problems of backlash and mechanical wear become more pronounced.

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If the relationship desired between axes was not constant, but needed to follow a
pattern, mechanical cams were used. The shape of the cam determines the motion pattern
of the cam follower with respect to the motion of the cam driver. If the required shape is
very complex, the cam can be quite difficult to design, and expensive to machine and
produce. Cams are also subject to wear, which directly affects the accuracy and
repeatability of the cam follower motion.
Individual axes were started and stopped using clutches and brakes. These are
required to accelerate and decelerate the load, but as with all mechanics, they suffer the
problem of wear. They also do not allow for precise control of the position relationship
between axes, because the amount of slip during starting and stopping can not be precisely

controlled. Clutches and brakes tend to be rough on the rest of the machinery, because of
the sudden jerk when they are engaged.
Stepper and Servo Motion Control Systems
The availability of electronic motion control has brought solutions to the problems
inherent with the mechanical approach to synchronization. To understand how these
solutions are achieved, it is helpful to review basic electronic motion control systems. One
axis of electronic motion control consists of the motor, the motor drive, and the
controller. The controller accepts motion commands from a host computer or an
internally stored program. These commands are interpreted by the controller to generate
continuously updated position commands (motion profiles) to the drive. The motor drive
controls the current to the motor which will result in the commanded position. In a multiaxis
system, one controller can control several motor and drive combinations.
The motion control system may be a stepper or servo system. Stepper systems
tend to be less expensive than servo systems, but have less speed and power for a given
size of motor. In stepper systems, the drive receives position commands in the form of
low voltage pulses (steps), and adjusts the phase of the current in two sets of motor coils
to align the motor shaft. Each new step received corresponds to an additional increment
of rotation on the shaft. Current is maintained in the motor coils, even when the motor
shaft is in the correct position. Common step motor resolutions range from 200 steps per
revolution (full stepping) to 50,000 steps per revolution (micro-stepping).
Servo systems employ motor shaft position feedback , either from an incremental
encoder or from a resolver. The actual position and velocity derived from the feedback is
compared to that commanded in the motion profile to result in a torque command to the
drive. In servo motors, the phase of the current is adjusted according to the actual
position of the shaft. It is continuously adjusted to produce maximum torque for a given
current amplitude. This process is called commutation, and is done mechanically in
brushed motors, and electronically in brushless motors. The drive controls the amplitude
of the current to the motor in proportion to the torque command. In analog servo
systems, the feedback goes to the controller, and the controller’s output is an analog
torque command. In digital servo systems, the drive accepts steps as the position

commands, and the shaft feedback goes only to the drive. Servo systems must be tuned to
match the load they are moving for the best performance. A properly tuned system results
in powerful and precise positioning of the load.
The choice of motion control system will depend on the particular application. A
dedicated motion control company such as Compumotor can provide any of these
systems, as well as expert technical assistance in the design, implementation, and tuning of
the system.
The Electronic Approach to Synchronization
Programmable stepper and servo motor systems provide a direct replacement to

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