Encoders Sensors

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ME 586 - Automation

Sensors and Encoders

By

Aaron WilliamsEric Detton

October 4, 2000


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Sensors


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Objectives

Identify commonly used sensor types

Where, how and why they are used

Latest and greatest capabilities

Bottom Line (cost)

Where to go to find out more


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Types of Sensors

List obtained from www.plantautomation.com


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Proximity Sensors

InductiveCapacitive

Ultrasonic

Photoelectric


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Inductive Sensors

How they workCreates a radio frequency field using

an oscillator and a coil. The presence of

a metal object changes the field and the

sensor is able to detect this.

*Picture compliments of Baumer Electric Ltd.


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Inductive Sensors

ApplicationsConveyor on/off switches

Begin machine cycle

Quality control (sense lids, proper alignment,etc.)

Count, determine direction of

motion/rotation, positioning

Anytime you want to sense metal

Motor oil is packaged on thisautomatic filling system. As aone-quart bottle moves downthe conveyor, the containerpasses an inductive proximitysensor located at the fillposition.The label on the bottle has adistinctive design, printed withmetallic inks. The label tells theproximity sensor the bottle is inposition and ready to be filled.


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Inductive Sensors

AdvantagesCan detect metal target even

through non-metallic barriers

Eliminates need for contact

Operate in harsh conditions

Rapid response time

Long life, virtually unlimited operating

cycles.


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Inductive Sensors

LimitationsCan only detect conductive metal

Relatively short range. Usually used for less than 1

sensing distance.

May be affected by metal chips collecting on sensor face.


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Inductive Sensors

Things to be Aware OfSpecified range is for axial approach. If object

approaches from the side, range is decreased.

Range depends of metal type!!!!

St37 ( Fe ) 1

Aluminium foil ( Al ) 1

Nickel chromium ( V2A ) 0.9

Mercury ( Hg ) 0.6

Lead, brass ( Pb, Ms ) 0.5

Aluminium ( solid ) 0.45

Copper ( Cu ) 0.4


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Inductive Sensors

Current SpecificationsRange: up to 40 mm

Switching Frequency: 25 Hz to 3 kHz.

Time delay: < 2msRepeatability error: < 1% of range

Cost: $25 to $250 (typically just under $100)


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Capacitive Sensors


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Capacitive Sensors

How they workUses two plates to form a linear capacitor (hence the

name). The amount of energy that can be stored between

the plates depends on the material between them. When a

material other than air is present, the sensor can detect it.


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Capacitive SensorsApplications

conveyors

robotics

jam protection

positioning

parts detection or controlindexing

bottle cap or can lid detection

counting

broken or damaged tool

detection

liquid level control

volume level control

leak detection

avoid or jam control

semiconductor manufacturing

food processing

missing component detection

bottle filling

bottle detection

thickness monitoring

gaming table chip monitoring

missing unit in shipping carton detection

bin level in silo detection

low paper roll monitoring

As oil pours into this storage tank,a capacitive proximity sensor nearthe top signals the fill valve toclose once the tank reachescapacity. Another sensor near the

bottom alerts the filling system ifthe level of the tank becomes toolow.


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Capacitive Sensors

AdvantagesCan detect just about anything

Can detect liquid targets through non-metallic barriers

(glass, plastic, etc.)

Operate in harsh conditions

Quick response time

Can detect difference of object, not just presence

Long operational life, with virtually unlimited cycles.


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Capacitive Sensors

LimitationsTypically short range (less than 15mm)

Affected by varying temperature, humidity and moisture

conditions

Not as accurate as inductive proximity sensors


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Capacitive Sensors

Things to be Aware OfAgain, range depends upon direction of approach

Range also depends on material

Be sure to check for ambient temperature limits


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Capacitive Sensors

Current SpecificationsRange: typically up to 25 mm (can be as high as

150mm!)

Switching Frequency: up to 200 Hz

Time delay:


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Ultrasonic Sensors


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Ultrasonic Sensors

How they workSends out sound waves above audible frequencies

(ultrasonic), and listens for the return. Uses the time delay,

and the speed of sound in air to determine distance to

object. Also can be used just to see if object is there.


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Ultrasonic SensorsDifferent TypesUltrasonic proximity sensor withanalog output stage

Both current and voltage outputs from thesensor are proportional to the distance ofthe sensor from the target. This allowssimple non-contact measurement


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Ultrasonic SensorsDifferent TypesUltrasonic retro-reflective sensor A fixed machine part is used here as a

reflector. The time difference between theemission and the reception of an ultrasonicsignal (known as propagation time) istherefore fixed and known. When an objectcomes within this sensing distance the

output is activated


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Ultrasonic SensorsDifferent TypesUltrasonic through beam sensor These sensors are ideal for applications in

which objects follow each other in quicksuccession. They are also recommendedwhen high switching frequencies arerequired, up to 200 Hz


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Ultrasonic Sensors

AdvantagesCan detect more types of objects than other three types of

sensors (pretty much anything)

Very good for telling distances

Longer range than capacitive and inductive sensors

Can operate in harsh conditions

Quick response time

Long operational life, with virtually unlimited cycles.


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Ultrasonic Sensors

LimitationsHave a dead zone close to the face of the sensor cant

detect very close objects

Cant detect very small objects (detectable size depends on

wavelength) (except for really high tech ones0.076mm!)

Speed depends on material (cotton, sponge, etc. require slower

frequencies)

Smooth surfaced objects must be aligned correctly or echowont return to sensor


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Ultrasonic Sensors

Current SpecificationsRange: 50mm to 11.3m

Sampling Frequency: up to 2 kHz (usually about

120 Hz or less, depending on distance and material)

Maximum Target Speed: up to 400 in/sec

Time delay: 0.5 ms

Repeatability: 0.1% of range

Cost: $75several hundred (typically just over

$100)


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Photoelectric Sensors


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Photoelectric SensorsHow they work

A photoelectric proximity switch is one in which the light source andlight sensor are housed in the same unit. The sensor picks up the pulse

of the LED (light emitting diode), which is usually in either the infraredor visible light range, as it reflects off of the object being sensed.


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Photoelectric SensorsThru-Beam A source unit in one location sends a light beam to a

detector unit in another location. An object is detectedwhen it passes between the source unit and the detector

unit, interrupting the light beam.

Reflex The source and detector are housed in one package and(Retro- placed on the same side of the target objects path.Reflective) When the object passes by, the source signal is reflected

back to the detector by a retro-reflector.

Diffuse The source and detector are housed in one package andReflective placed on the same side of the target objects path. When

the object passes by, the source signal is reflected backto the detector off the target object itself.

Background This is a special type of diffuse reflective sensor thatRejection includes two detectors. This arrangement allows the

sensor to detect targets reliably within a defined range,and to ignore objects just outside of this range. Unlike astandard diffuse reflective sensor, color or reflectivity has

minimal effect on the sensing range.


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Photoelectric SensorsApplications (just a few)Material Handling A sensor can ensure that products move alonga conveyor line in an orderly manner. The sensor will stop theoperation if a jam occurs. And items can be counted as they movedown the line.

Packaging Sensors can verify that containers are filled properly,

labeled properly and have tamper-proof seals in place.

Machine operation Sensors can watch to verify that a machine isoperating properly, materials are present and tooling is notbroken.

Paper Industry Sensors can detect web flaws, web splice, clearweb and paper presence, while maintaining high web speeds.

In this cookie kitchen, fiber opticphotoelectric sensors are placed in a hotoven. As long as the sensors detectmotion as the trays of cookies move by,

the oven stays on. If the conveyor stops,the sensors will detect light or dark for toolong, and the output device will shut downthe oven.


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AdvantagesMuch greater sensing range

Can tell how far away the object is

Fast response timeTypically very accurate (considering sensing range)


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Limitations

Dont function well in contaminant environments

Sometimes too powerful (Excess Gain)

Reliability depends on object being sensed (can be toodark, too transparent, etc.)

More expensive

Require more power to operate


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Current Specifications

Range: up to 130m (typically between 0.5 and

10m)

Switching Frequency: up to 1 kHz (typically 20

60 Hz)

Time delay: as low as 0.5 ms (typically 8-50 ms)

Accuracy: as good as 0.5mm or less

Cost: very low end - $50, typical - $125-150, verysophisticated = very expensive


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Sensors Summary

Who Sells Them? (Thomas Register lists 120+ vendors)

Rockwell Automation Cutler-Hammer, Sensor Div.

TURCK, Inc. Electro Corp.

SICK, Inc. Stedham Electronics Corp.

Baumer Electric Ltd. Advance Controls, Inc.

Balluff, Inc.

Altech Corp.

Southern Controls, Inc.

Fargo Controls, Inc.
http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=1&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=5&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=1&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=20&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=2&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=23&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=4&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=24&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=6&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=11&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=14&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=18&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=18&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=14&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=11&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=6&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=24&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=4&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=23&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=2&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=20&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=1&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=5&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=5&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=5&pn=0041559&state=&pdm=http://www6.thomasregister.com/ss/.1326977296/TPdcompany.cgi?&index=Product&search=sensors&seq=1&pn=0041559&state=&pdm=


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Sensors Summary

Where to Find out More?

www.theproductfinder.com/sensors/sensor.htm

(good source for info about how they work and lists of vendors)

www.ch.cutler-hammer.com/training/slfstudy/sensors/welcome.htm

(excellent website for more technical information about various types of sensor

and their applications)

http://www.thomasregister.com/

(great source for finding vendors of a specific type of sensor)
http://www.theproductfinder.com/sensors/sensor.htmhttp://www.ch.cutler-hammer.com/training/slfstudy/sensors/welcome.htmhttp://www.thomasregister.com/http://www.thomasregister.com/http://www.ch.cutler-hammer.com/training/slfstudy/sensors/welcome.htmhttp://www.ch.cutler-hammer.com/training/slfstudy/sensors/welcome.htmhttp://www.ch.cutler-hammer.com/training/slfstudy/sensors/welcome.htmhttp://www.theproductfinder.com/sensors/sensor.htm


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Encoders


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Objectives

Present background and function of encoders

Discuss where, when, and why encoders are used

Introduce types, models, and current technology of encoders

Delineate benefits and limitations

Cite references and locations of further information


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BackgroundA vast number of sensor products exist to detect all types of

events. There are sensors to detect the presence of objects, thespeed, the size, the structure, the color, the exact dimensions, the

location, etc. Once the detection occurs, there is also a wide variety

of ways a sensor can communicate, or convert, this information.

Analog-to-digital conversion begins with sampling, or

measuring the amplitude of the analog waveform at equally spaced

discrete instants of time.


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As the signal is sampled theamplitude at each interval is

quantized, and the values are mapped

into a series of binary digits, or bits.

The information is then transmitted

as a digital signal to the receiver,

where it is decoded and the analog

signal reconstituted.


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In order for a sampled signal

to be stored or transmitted in digital

form, each sampled amplitude must

be converted to one of a finite number

of possible values, or levels. For ease

in conversion to binary form, the

number of levels is usually a power of

2--that is, 8, 16, 32, 64, 128, 256, andso on, depending on the degree of

precision required. In the figure, an

analog waveform is shown being

quantized on an 8-level scale (0through 7).

28

=256


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Encoder exampleAn absolute optical encoder has 8rings, 8 LED sensors, and 8 bit resolution. If the output

pattern is 10010110, what is the shafts angular position?

Ring Angle (deg) Pattern Value (deg)1 180 1 180

2 90 0

3 45 0

4 22.5 1 22.5

5 11.25 06 5.625 1 5.6257 2.8125 1 2.8125

8 1.40625 0

Angular Position = 180 + 22.5 + 5.625 + 2.8125

Total = 210.94


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Methods of Encoding

Absolute

A wise man once said,Encoding is to

convert an analog signal to a digital

signal

-Ed Red-

Incremental


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Absolute EncodersThe term absolute defines the

type of information that isrelayed to the processor. There

are only two options available

here, either absolute or

incremental.

The absolute encoder differs from the

incremental encoder in that each angular

location is represented by a different

digital word.


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Absolute EncodersIn the case of the incremental encoder, it is only possible

to know your location relative to another location. The absolute

encoder solves this problem by making each

angular position unique. (An image of an

absolute encoder disk is shown to the right.)

Each separate location can be represented

by a binary number, determined by thesequence of light transmission or blockage

as you progress inward to the center.


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Absolute Encoders

Contrary to incremental encoders, absolute encoders

supply a clear code (information) in each angular position.This process offers the advantage that even in case of apower failure the actual position will be transmitted to theevaluation electronics. Furthermore, errors of measurement

due to missing pulses and cumulative errors are excluded.The primary advantage of the absolute encoder is

that the position is not lost in the case of power loss ornoise bursts. The largest disadvantage is added complexityand price.


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Absolute EncodersTop of the LineAstroCODER 150

The only programmable absolute encoder that allows the user to

change programs on the fly.

Industry leading 680 second scan time virtually eliminates error,

allowing for faster machine speeds while maximizing

productivity.

Built-in scalable resolution displays user defined units between

16 and 4096.

Includes resolver based transducers enhancing ruggedness whilemaintaining absolute position even after loss of power.

Accepts inputs from one or two transducers providing independent

dual axis control.

Position data available in three user selected forms: Serial Digital, Parallel Digital and Analog

Voltages.

Factory installed Astro data latch reacts to signal from PLC thereby accommodating any

predetermined scan rate. Available with Windows or DOS based start-up software


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Incremental EncodersLike any other position feedback device, the incremental

encoder is used to determine rotary or linear position. The termincremental describes the type of information that the encoder

sends out, being either incremental or absolute.

The encoder provides relative position information. As

rotation or linear translation occurs, the incremental encoder sends

out one pulse for each set incremental distance of travel. These

pulses can be counted to determine the linear or rotary position

relative to another position. Motion is quantified by a certain

number of pulses.


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Incremental EncodersUsually, the incremental encoder will come with three

channels, referred to as A, B, and Z. A and B are placed 90' out of

phase. With these two channels, the

processor determines the distance

traveled by the number of steps, and

the direction traveled by the leading

wave form. The third channel is thereference. Usually the Z channel will have only one pulse per

revolution or per length of the encoder, so it can be used to

determine an actual location, rather than just an incremental

number. These encoders can be either magnetic, optical,contacting, or capacitive.


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Incremental EncodersThe disadvantage of the incremental encoder is that it is

unable to determine its location upon start-up, but this problem canbe overcome by taking the time to do a homing or reference pulse

sequence, and then moving the desired amount of steps from there.

The added expense and setup time of an absolute encoder should

be avoided unless completely necessary.

Another benefit of the

incremental encoder is the large

range of possible sizes and the high

degree of compatibility.


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Incremental Functions: Quadrature

Incremental optical encoders generate two data

signals that are electrically 90 out of phase with each other,as shown below. The term quadraturerefers to this 90phase relationship. Since each full cycle contains fourtransitions, or edges, an encoder that generates 2500cycles/rev, for example, provides 10,000 edges perrevolution.

Q


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Quadrature20+ years ago, the prevalent electronic circuitry of

the day was based on "edge detection". The transitionscoming from the encoder would act as the "trigger" tocause a count. At each transition, the electronics not onlygenerates a count, but also determines direction of travelso that it knows whether to count up or down. This is

done by establishing whether the transition is going highor going low, and what the state of the other signal is.

High

Low


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FROM TO FROM TO

0,1 1,1 0,1 0,01,1 1,0 1,0 1,1

1,0 0,0 1,0 1,1

0,0 0,1 0,0 1,0

QuadratureHowever, modern electronics looks not at transitions, but at changes of state.

Basically, the user's electronics contains a high-speed clock and constantly samples

the states of A and B. When it sees a change, it counts up or down based on thefollowing table, where 0,1 represents the states of A and B, respectively. Instead ofwaiting for a triggering event from the encoder, the electronics generates its owntriggering based on its detection of a state changefrom the encoder. A subtle difference, but critical tothe operation of modern digital circuitry.

Forward

Reverse

Q d P l


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QuadraturePulses(For the interested reader)

Back when people were counting edges, it was often convenient to

have the encoder vendor provide an output that not only identified a specificnumber of edges per cycle (1, 2 or 4), but also gave direction informationdirectly. Pulse output was introduced for this purpose. Pulses differ from squarewaves in 2 important ways:

Pulse widths are of fixed time duration, whereas the width of a square

wave ON state is a function of speed. (The distance between pulses is,of course, a function of position.)

"Quadrature" has no meaning with pulse output; you get FWD pulseson one line, and REV pulses on another. (Or pulses on one line anddirection information on the other.)

Pulse output options were fairly popular at one time, but it's beendwindling for quite a while. With quad decode chips that are available, therequirement has pretty much become obsolete.

A 3 d M h d!?


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Although many companies have attempted to develop a new method of

encoding, time and again they have returned to the absolute and incrementalmethods. Until now.

A new type of encoder is currently being researched by Gurley PrecisionInstruments. A Gurley Virtual AbsoluteTMencoder is absolute in essence or effectwithout being formally recognized as such. (That's what virtualmeans.) In reality,it is neither an incremental encoder, nor an absolute encoder. It is a whole new

kind of encoder based on pseudorandomencoding technology, which has certaindetails of construction similar to an incremental encoder, and certain kinds ofbehavior similar to an absolute encoder. Pseudorandom output codes directlyfrom the disc or scale are not especially useful, so they've invented means fordecoding those signals into a natural binary format you can use like any otherencoder. This decoder (patent pending) stands in place of the quadrature decoder

and up/down counter used with an incremental, so total cost need not be muchmore than an incremental encoder of comparable resolution. Yet it's effectivelyabsolute!

A 3rd Method!?

A 3 d M h d!?


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A 3rd Method!?A Virtual Absolute encoder

uses just cyclic and index tracks, like an

incremental encoder. However, the indextrack is a serial code similar to a bar codeinstead of just a single line. You do notknow position immediately upon start-up,as you do in a conventional absolute, butafter a very short travel, in either direction

and starting from anywhere, you knowexactly where you are. In a rotary VA

encoder, this initializationangle istypically about one degree, depending onthe encoder's line count; in a linear VA

encoder, about 1/2 mm motion is needed.In a sense, from then on the encoder istruly absolute.

A Virtual Absolute Encoder

A 3 d M h d!?


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A 3rd Method!?Advantages of the Virtual Absolute technology are: The initialization distance or angle is a fixed and very small motion, regardless of the

starting position or direction of travel. Just "bump" it to find out where you are.

The encoder contains inherent built-in-test functions not found in any conventionalencoder. It reports not only various encoder malfunctions, but can also help detectsystem problems such as too high a temperature or excessive speed.

The encoder generates the same whole-word information as a conventional absolute,

so it is very easy to interface to computers, PLC's, servo controls, etc.

With its simpler optics, a rotary VA encoder can be smaller than a conventional

absolute of equal resolution. And you can use a linear VA encoder for applications

where a suitable conventional absolute linear would be very hard to find.

Because of its simpler electronics, reduced parts count, and less critical internal

alignments, a VA encoder is inherently more reliable than a conventional absolute.

A VA encoder is usually dramatically less expensive than a conventional absolute.


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Principal Types of Encoders

Rotary (77 Companies)

Linear (42 Companies)

Optical (69 Companies)

Magnetic (17 Companies)

List obtained from www.plantautomation.com


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Rotary Encoders


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Rotary Encoders

How they work

Most actuator systems contain some form of rotary motion.

Often times, it is necessary to accurately locate the rotary position

of that motion. One way of accomplishing this is with a rotary

encoder. This device is used to

convert a pattern on a rotary disc intoan electrical signal which can be

processed to determine angular

position.


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Rotary EncodersRotary encoders can be classified by two different characteristics:

1) technology used to convert rotary position to an electrical

signal

2) type of electrical output

Several technologies are now used to convert rotaryinformation into an electric signal. The original method was

through physical contacts. This created obvious limitations in

speed, resolution, and life expectancy. This led to the evolution of

optical, magnetic, and capacitive techniques. The two mostcommonly used encoders today are the optical encoders and the

magnetic encoders.

R E d


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Rotary EncodersApplications

The rotary encoders are most often mounted to the back of a

motor to determine the shaft position, but they are definitely not

limited to this. They can be mounted to rotary positioning tables,

screw drives, gearheads, machining tools, or any other application

where a rotary actuator exists. Many drives and motion controllerscan process common rotary encoder signals. Since

the range of rotary encoders is so broad, there is one

for almost every application requiring position

feedback.

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Rotary Encoders

Current SpecificationsMeasurement range of up to 360Contactless : no wear, no friction, high reliabilityMagnetic : high mechanical ruggednessTemperature range from -40C to +85CProvides absolute position

Accuracy range of 1 to 0.05Digital or analog outputLow costBuilt-in self-test

R t E d


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Rotary EncodersTop of the LineMicroE Systems G1400

FEATURESMiniature Sensor Package

Line Counts from 82K to 2.68B CPR

Safe Transmissive Design

Broad Alignment Tolerances

APPLICATIONSServo Track Writers

Head/Media Testers

Precision Stage Feedback

Grating Period: 5 m

Resolution from 76.6 rad to 2.37 nanoradians

Signal Period: 2.5 m

Power Supply: VDC +/- 5% @100 mA, 12 VDC +/- 5% @1 mA

Speed: 1714 rpm

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Linear Encoders

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Linear EncodersHow they work

This device is used to convert

linear position information into an

electrical output signal. The linear

encoder consists of a linear tape scale

made up of glass or steel, a light source(e.g. LED, laser), and a photoreceptor.

The light source, photoreceptor, and

additional scale are usually housed together. This housing either

surrounds the tape scale in through beam encoders or resides on

one side of the tape scale in reflective linear encoders.

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Linear Encoders

Light is projected through or off the tape scale and isdetected by the photoreceptor. The fixed scale modulates the light

as the receptor and light source progress. The

receptor detects these modulations and

converts the input into an electrical outputusually in the form of a quadrature signal

(shown here). The two channels are always

90' out of phase. The direction of the motion

can be determined by the leading channel.

The output is the same as that of the

incremental encoder.

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Linear EncodersTop of the Line - GEL 221 Linear Scale IP66 - motor technology

Features

Magnetic sensing principle

Corrosion resistant 12 mm measuring rod Easy mounting and adjustment

0.01 mm resolution (w/ external edge-evaluation)

200kHz maximum output frequency

Temperature range 0...+70C or -20...+85C

Supply voltage 5VDC5% or 10...35VDC IP66 protection

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Optical Encoders

Optical Encoders


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Optical EncodersHow they work

This feedback device is used to detect rotary or linear position and convert it to

an electrical output. A light source, usually either an LED or a laser, is projected throughthin slits in a rotary disc for rotary encoders, or a thin tape scale for linear. The LED is

adequate for most applications, although the laser has found niches in several high

precision, high resolution applications.

The disk and tape can either be made of

covered glass with thin etchings in the

cover, or thin metal with etchingsthrough it. Each has appropriate

applications. As light is transmitted, a

photo receptor on the opposite side of

the disc or tape detects the light and

converts it to an electrical output.

Different optical encoders can create a

wide range of signals, (e.g. silicon cell,

analog, sinusoidal).

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Optical Encoders

Optical encoders offer a higher resolution

and accuracy than all other encoders. Somecan offer in excess of 1 million counts per

Revolution (cpr). Often times the best way

to decide what feedback device you should use for

your application is to determine what type of

information your controller, PLC, smart drive, or otherprocessor that you are using is capable of processing

without too much trouble. Frequently many types of

feedback will fit your needs, but only a couple will be

simple to integrate. Due of the different signal options

and versatility of the optical encoder, this is a very

popular position feedback device.

Advantages

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Optical EncodersPos. /Description

1 Circlip

2 Washer

3 Spacer

4 Ball bearing

5 Housing

6 LED support

7 LED8 Spacer ring

9 Codewheel

10 Stator disk

11 Printed circuit

12 Cover13 Ribbon cable

14 Connector

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Optical EncodersTop of the Line - S5S single-ended optical shaft encoder

The S5S single-ended optical shaft encoder is a non-contacting rotary to digital converter.

Useful for position feedback or manual interface, the encoder converts real-time shaft

angle, speed, and direction into TTL-compatible quadrature outputs with or without index.The encoder utilizes an unbreakable mylar disk, metal shaft & bushing, LED light source,

and monolithic electronics. It may operate from a single +5VDC supply.

FeaturesSmall size

Low cost

Positive finger-latching connector

2-channel quadrature,

TTL squarewave outputs 3rd channel index option

Tracks from 0 to 100,000 cycles/secBall bearing option tracks to 10,000 RPM

-40 to +100C operating temperature

Magnetic Encoders


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Magnetic Encoders

Magnetic Encoders


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Magnetic Encoders

This device is used to convert position information into an electrical

output that can be interpreted by a system controller. The two main components

of a magnetic encoder are the read

head and the magnetic disc. The

read head contains a magneto resistive

sensor, which is basically an inductor that

detects changes in the magnetic flux.The disc is magnetically coded. The

magnetic code is interpreted by the

sensor as a series of on and off states.

One magnetic code is interpreted as a 0 bit

value and the next as a 1 bit value. Throughthis combination the magnetic encoder is

able to transmit pulses representing

incremental rotary motion.

How they work

Magnetic Encoders


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Magnetic EncodersAdvantages

The magnetic encoder offers good resolution

can operate in a wide variety of conditions

requires low power for operation

Disadvantages

they cannot achieve very high speeds

Magnetic Encoders


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Magnetic Encoders

Pos. /Description1 DC-Micromotor

2 Terminals

3 End cap

4 Housing

5 Magnet disk

6 Hall sensor

7 Printed circuit

8 Isolation

9 Cover

10 Ribbon cable

11 Connector


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Who Sells Them? (Thomas Register lists 100+ vendors)

>ACC

>ATS

>AVG Automation

>Astrosystems Automation

>Balluff Inc

>Baumer Electric Ltd.>Computer Conversions Corp.

>Dynamics Reseach Corp.

>Eastern Air Devices

>Globetron Electronics

>Gurley Precision Instruments

>MicroE

>Motor Technology UK Limited

>NC Servo Technology

>Omron Electronic Inc.

>Ormec Systems Corp.

>Parvex Inc.

>Quin Systems Ltd.

>Southern Power Inc

>Space Age Control Inc

>Stegmann Inc.

>U.S. Digital Corporation

http://acc-services.com/http://pro.wanadoo.fr/com-mkt/ats.htmhttp://www.avg.net/http://www.astrosystems.com/http://www.balluff.com/http://www.baumerelectric.com/http://www.computerconversions.com/http://www.drc.com/main/bus_area/encoder/intro.htmhttp://www.eadmotors.com/http://www.globetron.com/http://www.gurley.com/http://www.micro-e.com/http://www.motec.co.uk/http://www.ncservo.com/http://www.oei.omron.com/http://www.ormec.com/http://www.parvex.com/http://www.quin.co.uk/http://www.southernpower.com/http://www.spaceagecontrol.com/http://www.stegmann.com/http://www.usdigital.com/http://www.usdigital.com/http://www.stegmann.com/http://www.spaceagecontrol.com/http://www.southernpower.com/http://www.quin.co.uk/http://www.parvex.com/http://www.ormec.com/http://www.oei.omron.com/http://www.ncservo.com/http://www.motec.co.uk/http://www.micro-e.com/http://www.gurley.com/http://www.globetron.com/http://www.eadmotors.com/http://www.drc.com/main/bus_area/encoder/intro.htmhttp://www.computerconversions.com/http://www.baumerelectric.com/http://www.balluff.com/http://www.astrosystems.com/http://www.avg.net/http://pro.wanadoo.fr/com-mkt/ats.htmhttp://acc-services.com/


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www.theproductfinder.com/sensors/sensor.htm

(good source for info about how they work and lists of vendors)

http://www.gpi-encoders.com/

(excellent website for more technical information about various types of

encoders and their applications. Also source of VA encoders.)

http://www.microesys.com/

(source of several leading encoders)

http://www.thomasregister.com/

(great source for finding vendors of a specific type of sensor)

Glossary of Encoder Nomenclature
http://www.theproductfinder.com/sensors/sensor.htmhttp://www.thomasregister.com/http://www.thomasregister.com/http://www.theproductfinder.com/sensors/sensor.htm


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ACCURACY is a measure of how close the output is to where it should be. It is usuallyexpressed in units of distance, such as 30 arc seconds or 0.0001 inch. If it's expressedas a percent, make sure to state whether it's a percent of full scale (not usually meaningfulwith a rotary encoder) or a percent of nominal resolution.

BIT is an abbreviation for Binary digit; it refers to the smallest element of resolution.

CPR can mean either cycles/rev or counts/rev. To avoid confusion, this term should not be

used.

ERROR is the algebraic difference between the indicated value and the true value of theinput.

FREQUENCY RESPONSE is the encoder's electronic speed limit, expressed in kilohertz (1kHz = 1000 Hz = 1000 cycles/sec). For calculations, rotational speed must be in rev/sec(rps = rpm/60); linear speed must be either in/sec or mm/sec, depending on the scale linecount.



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INDEX SIGNAL is a once-per-rev output used to establish a reference or return to a knownstarting position; also called reference, marker, home, or Z

INTERPOLATION involves an electronic technique for increasing the resolution from thenumber of optical cycles on the disc or scale to a higher number of quadrature squarewaves per revolution or per unit length. These square waves can then be quadraturedecoded.

MEASURING STEP is the smallest resolution element; it assumes quadrature decode. (seealso QUANTUM)

PPR (pulses per revolution) Commonly (but mistakenly) used instead of cycles/rev whenreferring to quadrature square wave output.

QUADRATURE refers to the 90-electrical-degree phase relationship between the A and B

channels of incremental encoder output.



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QUADRATURE DECODE (or 4X Decode) refers to the common practice of counting all 4quadrature states (or square wave transitions) per cycle of quadrature square waves.

Thus, an encoder with 1000 cycles/rev, for example, has a resolution of 4000 counts/rev.

QUANTIZATION ERROR is inherent in all digital systems; it reflects the fact that youhave no knowledge of how close you are to a transition. It is commonly accepted asbeing equal to 1/2 bit.

QUANTUM(plural is quanta) = BIT. It is the smallest resolution element. (quanta and bitare more commonly used with absolute encoders; counts/rev or measuring steps aremore common with incremental encoders.)

REPEATABILITY is a measure of how close the output is this time to where it was lasttime, for input motion in the same direction. It's not usually specified explicitly, but it isincluded in the accuracy figure. (As a rule of thumb, the repeatability is generally around

1/10 the accuracy.)



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RESOLUTION is the smallest movement detectable by the encoder. It can be expressed in

either electrical terms per distance (e.g., 3600 counts/rev or 100 pulses/mm) or in units ofdistance (e.g., 0.1 or 0.01 mm).

SLEW SPEED is the maximum allowable speed from mechanical considerations. It isindependent of the maximum speed dictated by frequency response.

Conversion Factors


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Conversion FactorsANGULAR MEASURE

1 revolution = 360 = 21,600 minutes = 1,296,000 seconds 2pi radians (rad)

1 = 60 minutes (min) = 3600 seconds (s) 0.0175 rad

1 min = 60 s = 0.0167 0.291 mrad

1 s = 0.0167 min = 0.000278 4.85 rad

1 rad 57.3; 1 mrad 3.48 min; 1 rad 0.206 s

Sometimes the terms "arcminutes" and "arcseconds" are used to differentiate the units of angle

from the units of time. If the context makes the meaning clear, the "arc" prefix need not be used.

Occasionally, the symbols ' and " are used to indicate arcminutes and arcseconds, respectively.Because they can be confused with feet and inches, they should not be used.

Conversion Factors


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LINEAR MEASURE

1 foot (ft) = 12 inches (in) = 304.8 millimeters (mm)

1 in = 25.4 mm

0.001 in = 25.4 micrometer (m)

1 meter (m) 3.281 ft 39.37 in

1 mm 0.0394 in

1 m 39.37 in

The terms "mil" (= 0.001 in; short for milli-inch) and "micron" (= 1 m) should not

be used.

Conversion Factors

Conversion Factors


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SPEED

1 rev/min (rpm) = 1/60 rev/s (rps)

1 rad/s 57.3 deg/s 0.159 rev/s

1 in/min 0.423 mm/s

1 mm/min 0.000657 in/s

Conversion Factors

Encoders Sensors

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