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Distance measurement and
controls
Submitted by: Patel Aakash
Academic Supervisor: Dr. Hieu Trinh
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TABLE OF CONTENTS
Sr
NO.
TOPIC PAGE
NO.
1 ABSTRACT 3
2 ACKNOWLEDGEMENT 4
3 INTRODUCTION: OVERVIEW 5
4 OBJECTIVE 5
5 LITERATURE REVIEW 6
6 CURRENT SENSORS 6
7 TECHNOLOGY PROGRESSION 88 REFERENCES 13
Abstract:
The general objective of this project entails developing a sensor system for the purpose of
surveying in civil engineering and many other applications. The projected sensor will
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involve precisely measuring the distance in the vertical direction, over a range of
approximately 100 m.
This sensor will be able to continuously scan and record the vertical displacement of the
body at the same time as it is in operation. There are many sensors industrial approaches
have been considered into for their reasoning behind possible implementation for the
sensor required but the two sensor technologies like fiber optical and ultrasonic best met
the characteristic demands of the sensor, and were examined in further detail.
However, the optical technological approach was be obvious of the two, and was
presented, as the measurement means within the displacement sensor.
Acknowledgements
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I would like to acknowledge the support from my Project Supervisor Dr. Hieu
Minh Trinh who was able to locate hard copy sources of desired material, such as
numerous journal articles that I required for this research project. Without his help the
project would have not progressed forward.
Introduction:
Overview:
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Today there are many technologies advancing quickly in every direction. This in
turn utilises sensors in many forms, from simple detection of objects, to measuring
moving objects, to measuring components of objects, scanning dimensions of multiple
arrays, their displacement from a starting position and the velocity at which they may be
travelling.
Today there are many displacement sensors subsist commercially today. Some
of the more common and known displacement sensors are the recently designed for
farming purpose to enabling the farmers to measure the distance from chopper to the
roots of crops. By this way farmers can cut their crops accurately and maintain
continuity. In regards to an industry manner, sensors are employed throughout automatedworkshops. These sensors can be very sensitive and accurate or cover a great spectrum
still with surprising accuracy. Many forms of technology are utilised in sensors today,
from the old mechanical approach, to electronics involving inductance and capacitance,
to the ever-growing optical fibre field.
Objectives:
The objective of this project involves the investigation of level of land surface from
certain level. In this project I m going to design a project which can be very useful, for
surveying purpose in the field of civil engineering. The traditional method of surveying is
very tedious and time consuming. So the main objective of this project is to develop a
device that makes this work easier.
The device that I m going to develop, can be fit on the base of any vehicle. As the car
move in the field this device will measure the distance to surface from certain level.
And this all data will be recorded as well so that later that data can be stored in computer
and analyse it.
So it is very clear that through this device it would be easier to survey any size of land
with out any panic.
Literature Review
Overview
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There is so many research has been done since the commencement of the project.
So the opening approach to the research is to investigate the commercially exciting
product in the market. It has been discovered that the most familiar sensor technologies
of today involve; fiber optics (lasers - infrared), ultrasonic (acoustic waves),
microwave/radar, mechanics (LDVT, contact devices), and electromagnetic fields (eddy
currents, magnetostrictive).
All the technologies are discussed below in detail. Each technology are discussed
with different concerns like theirs costs, their important properties (rigid, very accurate,
span over great range, small resolution, exceptionally responsive, etc.), possible
interfaces etc. From researching these present technologies and also future technologies
being developed one should be able to put all the information together to propose the
perspective technology and pieces for an appropriate height and speed sensor for the
distance measurement and control.
Current Sensors
Today there is a enormous demand of sensors in every field of engineering and
almost all industries these are found exploiting hundreds of sensors within their factories.
The greatest progressions to date in sensor design are smaller sizes, a higher degree of
ruggedness, and greater capabilities1. As sensors are available in smaller in size and
affordable cost allowed the company to use more and more sensors in their equipments
and machines. where in the past finding an adequate place to mount the sensor device
was a task in its self. Also from this scaling down of sensor sizes, less raw materials are
required in manufacturing, thus a saving can be made in the overall cost of production.
Compact circuitry (has let) brainy sensors pack processing wallop 2. This has been
accomplished due to effective and efficient modeling, and a higher integration in the
electronics of a sensors components into a software package [1]. But still there are some
kinds of sensors that can not be reduced easily. For example, in an inductive sensor its
1 Jim Braun. Guest Commentary The changing world of sensor technology. Design News/02.18.02. pp.
103.2 Dave Edeal, N.C. Cary, Miles Budimir. Electronics Sensors get smarter. Machine Design February 21,
2002. pp. 67-69.
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coil plays an important roll to increase the sensing range and another factor in preventing
the development of smaller sensors is the wire sizes implemented within the sensor
package.
As it is very clear that any kind of physical damage to the sensor; creates a big
problem in machine. Thats why the use of rugged and durable materials within the
sensors facilitates the sensor to bear up physical impact from immediate machinery. The
other engineering design advancement with sensors has been in, increasing the sensing
range to allow users to place the sensor out of harms way of other machines and
applications. These three design advancements have been the main focus of the last few
years and are of major importance along with the cost and reliability of a sensor.
Today there are many types of sensors available in the market that deal with the
detection of displacement. The obtainable methods are; ultrasonic, optoelectronic (laser)
LVDT (linear variable differential transformer), photoelectric (used more for proximity)
and magnetostrictive (electromagnetic involving magnetic fields). Where ultrasonic and
optoelectronic methods are most popular among all these methods for displacement
detection. As they tend to be the leading methods in increased sensing ranges, growing
user confidence and friendlier price tags3 . These two sensors along with the ultrasonic
proximity sensor are anticipated to be much of the US markets growth in sales over the
next five years [3].
Of the sensors of today, the most likely technological approach to be employed
within the displacement sensor seems to be along the lines of either optical fiber or
ultrasonic means. The optical type of sensors seems to fit the characteristic demands as
they can provide unparalleled non-contact displacement measurement of extremely
small targets at reasonably large distances [3]. These sensors also provide accurate
positioning measurements and tend to come in relatively small packages. The only type
of sensor that has similar, if not equal features of the laser displacement sensor is the
ultrasonic linear displacement sensor[3].
3 Brain Totten. Market Update Domestic proximity/linear displacement sensor market swells. Control
Engineering May 2000. pp. 13.
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devices. The two simplest sub-divisions are called intrinsic devices and extrinsic devices
[4]. Intrinsic devices are concerned with the interaction that occurs actually within an
element of the optical fiber itself, while extrinsic devices are concerned with utilising the
optical fiber to couple light, usually to and from the region where the light beam is
influenced by the measurand [4]. Hence, the extrinsic device is what would be required
for the design of the displacement/velocity sensor in question.
Another way of classification is via the measurement method at which the sensor system
measures a particular measurand at a particular location. This is usually achieved with a
point sensor, which is the way most sensors operate [4]. Other methods include:
distributed measurand is determined by the length of the fiber itself; and quasi-
distributed which is somewhat in between the point and distributed methods. The
measurand method for the required sensor in this case is the point scheme.
Figure A Schematic of point sensing [4].
Electromagnetic
There are two major sensor technological processes involving electromagnetic fields.
One is magnetostrictive, which is known as the effect due to mechanical deformation of a
ferromagnetic material that is placed in a magnetic field7 .
The other method utilizes the generation of eddy currents, and is known as
electromagnetic. These two devices based on electromagnetic induction, including
variable impedance, variable reluctance, inductive and eddy current sensors, can
7 H. Kwun, K.A. Bartels. Magnetostrictive sensor technology and its applications. Ultrasonics 36 (1998)
171-178.
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maximize system sensitivity to target movement and minimize sensitivity to all other
effects and variables8 .
Magnetostrictive sensors are another type of displacement sensor; however they
implement the use of magnets and magnetic fields. The basis of magnetostrictive
measurement is time, where the sensor measures the time it takes for a sonic pulse to
travel a desired distance. The position (displacement) is measured by simply the time it
takes for the sonic wave to travel from the position magnet to the pickup, multiplied by
the speed of sound in the waveguide material9. This is a similar approach to the time-of-
flight technique employed by ultrasonic sensors. The resolution of the measurement is
high, due to the sensors ability to sense extremely small slices of sonic-wave travel
time [9]. This type of technology however is more suitable in detecting time-varying
stresses or strains in ferromagnetic materials, which concerns microscopic displacement
within the materials themselves [7].
Eddy current sensor devices are based on electromagnetic induction, and have
been used to determine true position measurement within many applications, for over 35
years. This true position measurement sensing system enables the detection of the target,
as well as determining the targets exact position relative to the calibrated measuring
range of the sensor. The sensor provides a continual response to the variation in
movement of the target via either an analog voltage, current, or digital signal. Such
applications include: displacement, vibration, thickness, alignment, dimensioning, and
part sorting [8]. It can be noted however, that all of these can be classified as variations on
displacement because in each case the parameter being measured is the distance from the
target to the sensor. The only difference is in the interpretation and implementation of
the displacement data [8].
Some of the eddy current sensors most notable features are: being inherently immune to
noise, performing fast, and obtaining accurate measurements in inhospitable
environments [8]. They have been found to be very important in the automotive industry,
8 Scott D. Welsby, Tim Hitz. True Position Measurement with Eddy Current Technology. Sensors
Magazine, November. 1997.9 Blake Doney. Flow Monitoring Exploring Area/Velocity Flowmeters. Water Engineering &
Management November 1999. pp. 11-12.
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especially in the automation of arc welding. These sensors have risen over many other
attempted sensors for the task, such as vision and laser sensors. Unlike these sensors the
electromagnetic sensor is unaffected by the arc light, fumes and the associated spatter. In
this particular case, the sensor had to follow a tracking system designed for sheet metal
arc welding, where the sensor worked excellently, with a tracking accuracy of around
0.2 mm. The output voltage was set at a maximum of 10V for the operation.
This sensor can function in a couple of ways depending on whether the target material
being dealt with is a nonmagnetic conductive material or whether it is a ferromagnetic
material. The following paragraphs describe how the sensor operates with regards to
both manners. When a nonmagnetic conductive target material is placed into the coil
field, eddy currents become induce in the targets surface. These currents generate a
secondary magnetic field, including a secondary voltage in the sensor coil. The result is a
decrease in the coils inductive reactance (the coil-target interaction is similar to the field
interaction between windings of a transformer). Eddy current sensors operate most
efficiently at high-oscillation frequencies. This type of system is also known as variable
impedance because of the significance of the impedance variations in defining its
complex nature [8].
Ultrasonic
Ultrasonic (US) sensors service the market by providing a cost effective sensing method
with unique properties not possessed by other sensing technologies. By using a wide
variety of ultrasonic transducers and several different frequency ranges, an ultrasonic
sensor can be designed to solve many application problems that are cost prohibitive or
that simply cannot be solved by other sensor technologies10. There are many advantages,
some unique, in utilising the sensing technology of ultrasonics:
10 Ultrasonic Technology: An Overview. Ultrasonic Sensors from Migatron. [Online], Available:
http://www.migatron.com/overview.htm
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Measures and detects distances to moving objects;
Impervious to target materials, surface and colour;
Solid-state units have virtually unlimited, maintenance-free lifespan;
Detects small objects over long operating distances;
Resistant to external disturbances such as vibration, infrared radiation, ambient noise and
EMI radiation; and
Sensors are not affected by dust, dirt or high moisture environments. [10]
Traditional method of surveying:
Brief introduction:
Surveys of land are conducted to assure a range of needs and as a outcomes the
equipment and methods vary from one method to another method.
There are three main types of survey:
Mapping surveys
Geodetic surveys
Property surveys
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Mapping survey:
It is done to spot the location of the earth features. Once the size, shape and location of
these features are determined they can be represented on maps.
Natural features shown on maps may include drainage features such as lakes, ponds,
river, and shape of hills, vegetation and submerged lands, some items made by human
being like buildings, bridges, towers and roads.
Mapping surveys collect data in one of two ways, either the use of aerial photography or
by ground measurement techniques. Ground based methods traditionally involve the
measuring of angles and distances. And the equipment used to accomplish this work are
chains, steel tapes and theodolite. These all equipments are used to measure distance and
angles as well.
Geodetic surveys:
The highly stable, ground reference monuments established by geodetic surveys serve as
a frame work for geographic and land information systems.
Traditionally geodetic surveys have been divided into two types, horizontal and vertical.
Horizontal surveys establish geodetic latitudes and longitudes of monuments with
references to mathematical surfaces. This measurement is made on the surface of the
earth computations are performed in a coordinate system referenced to the ellipsoid.
Vertical surveys establish heights of positions for a network of monuments often referred
to as a bench marks. Depending on accuracy requirements, vertical surveys have been
traditionally run by either differential leveling or trigonometric leveling. 11
11 http://www.sco.wisc.edu/surveying/methods_tools.php
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Property surveys:
A property survey describes, maps, and locates land ownership boundaries and corners,
features and improvements. Property surveys must be performed by a Professional Land
Surveyor who has been licensed by the Wisconsin Department of Regulation and
Licensing. The surveyor assumes the roles of historian, law scholar, investigator and
interpreter. The surveyor researches the property's history to correctly interpret its deed or
legal description.
So from the description of all these methods we can assume that how tedious and
complicated are they. And the biggest disadvantage of traditional surveying is it takes lot
of time to finish the entire work. And to perform this surveying task it needs at least 2
qualified engineers and a helper on the ground all the time.
Thats why the main purpose of this project is to design and implement such a device
which can be very useful for this application like it will be very accurate, user friendly
and fast. So using this device it would be possible to finish this task in just few hours.
And to operate this device there is no need of qualified person on the field.
Project strategy
Up till now laser based measuring instrument was fairly popular in industries to measure
the highly accurate distance. In this device with laser; the distance are determined by
calculating the time of flight of a laser pulses from the device to target and back to the
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device. And using this time of transmission and reflection it can be easy to calculate
distance between device and target. As we know that laser based technology provides
highly accurate and reliable results. But it increases the complexity of circuit and cost as
well.
At the end of all research, I have made up my mind and I am going to design a circuit for
this specific application using an economical light-emitting diode instead of laser diode,
to generate light pulses.
This instrument consists of LED, pre biasing circuit and a firing circuit.
In the design of circuit we use only LED and firing circuit which enables the LED to emit
light pulses but I am going to add one another circuit which is pre biasing circuit which
will make the application more accurate. A pre biasing circuit will provide a reverse bias
signal to the LED to resist light pulse emitting before the firing circuit provides an
enough current signal.
LED generates light pulses which are used to determine distance and ranging
information, which will be very useful in civil ranging application.
To compete the instrument with laser technology, in my project I am going to make use
of LED with firing circuit and pre biasing circuit. By this way it would be possible to
achieve result like laser distance measurement device and at very low cost.
Firing Circuit
There are various ways to design firing circuit. It can be designed using different types of
transistors like MOSFET, avalanche transistor. So the firing circuit can be implemented
as MOSFET based, Avalanche transistor based and discrete transistor pair firing circuit.
The optional pre biasing technique for an LED firing circuit revealed here to improves
the initial rate of rise in the current applied through the LED in a distance measurement.
And ultimately it improves the sharpness of the leading age of produced light pulse. And
by using the pre biasing circuit coupled with the firing circuit we can achieve a very rapid
rise time pulses just like a laser diode.
As the requirement of our project application in the field of civil engineering, arranging
instrument to measure a distance to target can integrate the LED, the firing circuit and the
pre biasing circuits are reveled here.
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The device which I am going to design has a transmit circuit section for generating a light
pulses of acknowledged wave length. A firing circuit generates a drive pulse of short
duration and high pick power to drive the LED. This device also has a receive circuit
section for detecting a reflection of light pulses from the target, and a ranging section for
calculating a distance from the ranging device to the target.
Transmitting section:
The figure given below illustrates the block diagram of transmitting section.
The circuits that I have designed to fire the LED are shown below.
In these both the circuits its been calculated that this LED can consistently operate with
a 40 amp current pulse through it. The LED is driven by a firing circuit over its
appropriate current but the thing that we need to keep in mind that LED must be driven
within its proper temperature so as to maintain long time. While this particular LED is
also rated as having a 40 nanosecond rise time.
FIG
As shown in first circuit diagram I have used SCR based firing circuit for this application.
And GA301 SCR is been utilized in this circuit here C1 is a high voltage capacitor to fire
the LED. The anode of SCR is coupled through resister to high voltage supply line. And
the cathode is been grounded. And gate of SCR is connected to trigger pulse of the
device. Now in LED, the cathode is connected to capacitor that is connected high voltage
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Firing Circuit
Pre biasing circuit
Trigger
Pulse
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supply through resister, and the anode is connected to ground. And one more bypass
resister connected through the cathode of LED to ground.
Circuit-1 Firing Circuit Using SCR
Circuit operation:
When SCR is off, the capacitor which is connected to cathode of LED charges up to the
high voltage from high voltage supply line and by this time The LED is not conducting.
When we activate the trigger pulse connected to the gate of SCR then SCR conducts fromits anode to cathode and discharge the capacitor through SCR. The discharge current of
capacitor flows through SCR and it provides a forward current to LED which causes the
optical output pulses.
As this is the simple circuits of LED firing circuit I havent consider the pre biasing
circuit.
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Another firing circuit designed in PSpice circuit design software is shown below. The
circuits-2 illustrates the transistor based firing circuit. Here two transistors one is NPN
and the other is PNP with LED configured as a SCR. Here I have used ZTX951 PNP
transistor and ZTX851 NPN transistor, as they are widely used in various applications
and easily available.
Circuit Description
Here PNP transistor has its base connected to an emitter through resister and base is also
coupled to a collector of NPN transistor. The emitter is coupled to high voltage supply
line. The collector of transistor is connected to base of NPN transistor and ground
through resister. A high voltage capacitor is coupled to high voltage supply line and
emitter of PNP transistor. And on the other side a cathode of LED is connected to
capacitor and anode is connected to ground.
Circuit operation
When both transistors are not conducting, a high voltage capacitor charges to the supply
voltage through resister and by this time LED is not active. But when we apply a trigger
pulse to a base of NPN transistor which effectively applies a ground potential to the base
of PNP transistor, so activating PNP transistor. Now capacitor discharges its stored
charge through emitter and collector of PNP transistor to ground through resistor and
through the emitter and collector of NPN transistor as well. Here when capacitor
discharges, LED receives a forward current and produces a optical output pulses.
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Circuit -2 Transistors Based Firing Circuit
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MOSFET based firing circuit
The operation of this MOSFET based firing circuit is almost similar to other two types of
firing circuit.
Receiving section:
In the receiving part when the pulse of light (generated by firing circuit) falls on target
and it reflects back to the receiving section.
In estimating distance to the target the range finder determines the lights complete time of
flight, it means the total time from light pulse generation to light pulse received by
receiving section.
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The receiving section comprises following parts to perform the operation:
Detector
Delay circuit
Comparators
Logic circuit
Range circuit
In the receiving section the reflected light is detected by a detector. The detector
generates an analog signal representing the detected light.
Now the analog signal is fed to simple threshold detection circuit, which is formed from
some form of comparator circuit.
Description of block diagram:
Here comparator-2 is coupled to a threshold and comparator-1 is coupled to incoming
analog signal.
The comparator output is fed to the delay circuit and this delayed output is fed to the first
comparator. Here the positive and negative terminals are connected to delayed signal and
original signal consequently.
And the second comparator is fed the original analog signal on its positive terminal and
threshold voltage on its negative terminal.
Now the total scenario is something like this; the first comparator has its two inputs
which are delayed and original analog signal. While the second comparator has its two
inputs connected with analog signal and threshold signal. Here second comparator
generates output when received analog signal exceed the threshold voltage.
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And the first comparator generates output pulse when original analog signal crosses the
delayed analog signal. The delay is been set in such a way that the cross over occur at
approximately 70% of the analog pulse amplitude.
The cross over point between the original pulses triggers the logic circuit to generate the
leading edge of time of arrival pulse.
Figure 2 waveforms
Logic circuit
The logic circuit I am going to explain is just a exemplary and not exclusive, it can be
designed in various ways.
Here I have designed this logic circuit diagram using exclusive-or, conventional flip flop
and inverter gates.
So here logic circuit can be divided into three sections.
Detection section
Measurement section
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Spacing section
The detection sections consists inverter and flip flop connected to exclusive-or gates. It
detects the output pulse from second comparator and enables the measurement section.
The measurement section comprises flip flop connected with exclusive-or gate and
inverter. This section is enabled by the detection section and once its been enabled it
generate a time of arrival pulse when the analog signal crosses the delayed analog signal
as shown in wave forms.
23
o Measurement section
o Detection section
o Spacing section
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And the third section is spacing section that consists of two exclusive-or gate, two flip
flops and an inverter. The main function of this section is to ensure that whether the
detection section enables the measurement section. This ensures that the analysis of one
optical pulse is completed before beginning the analysis of the next optical pulse.
Circuit operation:
Here the logic circuit is initialized when the reset input is at logic high. By this way it
will set all the flip flops to logic high. And this set the time of arrival pulse to logic low.
The rising edge of output of second comparator clocks the flip flop of detection section.
And output of this flip flop enables output of first comparator which in turn clocks the
flip flop of measurement section.
Here every time of arrival pulse will be generated when output of second comparator is
high. When the output of second comparator is low at that time their will not be any
generation of time of arrival pulse.
The flip flop in spacing section ensure that this process is occurs correctly. When time of
arrival pulse is generated, it will clock one of the two flip flops then output of one flip
flop when time of arrival pulse E goes low.
Block diagram of entire project:
After designing transmitting section and receiving section, its a time to interface these
sections with microcontroller to display or store its output.
As shown in block diagram both transmitting section and receiving section are directly
connected to the timing section.
Here the timing section note the total time of flight. As transmitting section is connected
with timing section, when the optical pulse generates that time is stock up in the timing
section as a reference time. And when this generated pulse falls on target and reflected
back to receiving section, that time is stored in timing section.
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So by using both times timing section calculates the total time taken by light pulse from
transmitting section to receiving section. And calibrate this time into distance. And these
data are stored in the memory of microcontroller.
For the ease of this application we can use display to read the instant distance on the
field.
Conclusion
From the research and development I can conclude that: it is possible to design a device
for surveying application using LED, and it will be possible to get same accurate result as
laser technology. And this device will be more economic, accurate and user friendly.
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9. 0. References
1. Jim Braun. Guest Commentary The changing world of sensor technology .
Design News/02.18.02. pp. 103.
2. Dave Edeal, N.C. Cary, Miles Budimir. Electronics Sensors get smarter.
Machine Design February 21, 2002. pp. 67-69.
3. Brain Totten. Market Update Domestic proximity/linear displacement sensor
market swells. Control Engineering May 2000. pp. 13.
4. K.T.V. Grattan, Dr. T. Sun. Fiber optic sensor technology: an overview. Sensors
and Actuators 82 (2000) 40-61.
5. O. Toedter, A.W. Koch. A simple laser-based distance measuring device.
Measurement Vol. 20, no. 2, pp. 121-128, 1997.
6. Acuity Research Laser Measuring: Sensors & Scanners.
7. [Online], Available: http://www.acuityresearch.com
8. H. Kwun, K.A. Bartels. Magnetostrictive sensor technology and its applications.
Ultrasonics 36 (1998) 171-178.
9. Scott D. Welsby, Tim Hitz. True Position Measurement with Eddy Current
Technology. Sensors Magazine, November. 1997.
10. Blake Doney. Flow Monitoring Exploring Area/Velocity Flowmeters. Water
Engineering & Management November 1999. pp. 11-12.
11. Ultrasonic Technology: An Overview. Ultrasonic Sensors from Migatron.
12. [Online], Available: http://www.migatron.com/overview.htm
13. http://www.sco.wisc.edu/surveying/methods_tools.php
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