Distant Measurement Final Report

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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

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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.

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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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