basics of sensor

7/23/2019 Basics of Sensor

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Table of ContentsIntroduction ............................................................................. 2Sensors ................................................................................... 4Limit Switches ......................................................................... 8International Limit Switches .................................................. 18North American Limit Switches ............................................. 22B!" Sensors ....................................................................... 2#Inducti$e %ro&imit' Sensors Theor' of "(eration .................. 28Inducti$e %ro&imit' Sensor )amil' ......................................... 4*Ca(aciti$e %ro&imit' Sensors Theor' of "(eration ................ +4Ca(aciti$e %ro&imit' Sensor )amil' ....................................... +#,ltrasonic %ro&imit' Sensors Theor' of "(eration ................. +-,ltrasonic %ro&imit' Sensor )amil' ....................................... 8%hotoelectric Sensors Theor' of "(eration ............................ 8*%hotoelectric )amil' of Sensors ............................................ -/Sensor A((lications ............................................................... --!e$iew Answers .................................................................. 1*#)inal &am ........................................................................... 1*82

Introduction0elcome to another course in the ST% 2*** series SiemensTechnical Education Proram desined to (re(are ourdistributors to sell Siemens ner' 3 Automation (roductsmore effecti$el'. This course co$ers Sensors and related(roducts.

,(on com(letion of Sensors 'ou should be able to 5escribe ad$antaes disad$antaes and a((lications oflimit switches (hotoelectric sensors inducti$e sensorsca(aciti$e sensors and ultrasonic sensors 5escribe desin and o(eratin (rinci(les of mechanicallimit switches Identif' com(onents of International and North Americanmechanical limit switches 5escribe desin and o(eratin (rinci(les of inducti$eca(aciti$e ultrasonic and (hotoelectric sensors anddescribe differences and similaritiesA((l' correction factors where a((ro(riate to (ro&imit'

sensors Identif' the $arious scan techni6ues of (hotoelectricsensors Identif' ten cateories of inducti$e sensors and sensors ineach cateor' 5escribe the effects of dielectric constant on ca(aciti$e(ro&imit' sensors


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Identif' en$ironmental influences on ultrasonic sensors Identif' t'(es of ultrasonic sensors that re6uire manualad7ustment can be used with S"N%!" and re6uire theuse of a sinal e$aluator/

5escribe the difference between liht o(erate and dar9o(erate modes of a (hotoelectric sensor 5escribe the use of fiber o(tics and laser technolo' usedin Siemens (hotoelectric sensors Select the t'(e of sensor best suited for a (articulara((lication based on material sensin distance andsensor load re6uirementsThis 9nowlede will hel( 'ou better understand customera((lications. In addition 'ou will be better able to describe(roducts to customers and determine im(ortant differencesbetween (roducts. :ou should com(lete Basics of Electricity

and Basics of Control Components before attem(tinSensors. An understandin of man' of the conce(ts co$ered inBasics of Electricity and Basics of Control Components isre6uired for Sensors.If 'ou are an em(lo'ee of a Siemens ner' 3 Automationauthori;ed distributor fill out the final e&am tear and NC> are reistered trademar9s

of the National )ire %rotection Association ?uinc' =A *22-.%ortions of the National lectrical Code are re(rinted with(ermission from N)%A #*


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"ne t'(e of feedbac9 fre6uentl' needed b' industrial


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Eer' %redictableLon Lifeas' to Install5istanceLimitationsIndustrial and=achines

=achine ToolSenses =etal which co$er the use of electrical e6ui(ment in locationswhere fire or e&(losions due to as flammable li6uidscombustible dust or initable fibers ma' be (ossible.+a3ardous EnvironmentsAlthouh 'ou should ne$er s(ecif' or suest the t'(e oflocation it is im(ortant to understand reulations that a((l' toha;ardous locations. It is the users res(onsibilit' to contactlocal reulator' aencies to define the location as 5i$ision I or IIand to com(l' with all a((licable codes.Divisions 5i$ision I identifies a condition where ha;ardous materials arenormall' (resent in the atmos(here. 5i$ision II identifies

conditions where an atmos(here ma' become ha;ardous asresult of abnormal conditions. This ma' occur if for e&am(le a(i(e containin a ha;ardous chemical beins to lea9.Classes and ,roups a;ardous locations are further defined b' class and rou(.Class I rou(s A throuh 5 are chemical ases or li6uids. ClassII rou(s ) and include flammable dust. Class III is notdi$ided into rou(s. It includes all initable fibers and lints suchas clothin fiber in te&tile mills.Class I Class II Class III,roups A$D,ases andLi;uids

,roups E$,)lamma*leDustIgnita*le)i*ers

A Acet'lene =etallic 5ust !a'onB 'droen ) Carbon 5ust ute

Acetaldeh'de rain 5ustth'lene=eth'l ther

Acetoneasoline=ethanol%ro(ane5rou(rou(rou(C

4-&A#'Selection ,uide


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Pressure Proof These de$ices are used in e&tremel' d'namic (ressurestressin such as the monitorin of (iston or $al$e limit(ositions s(eed monitorin and measurement of h'draulicmotors and $acuum a((lications. The o(eratin $oltae is 1* to/* E5C with loads u( to 2** mA. The o(eratin distance of

de$ices rated u( to #2+/ (si is / mm. These are three


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#aterial Shieldednshielded Sn 8mm9 "perating(oltage


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AS


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+H The ma&imum sensin rane of an inducti$e (ro&imit'sensor desinated for reater rated distance is

mm.H inducti$e (ro&imit' sensors detect allmetals without a reduction factor.54

Ca(aciti$e %ro&imit' SensorsTheor' of "(erationCa(aciti$e (ro&imit' sensors are similar to inducti$e (ro&imit'sensors. The main difference between the two t'(es is thatca(aciti$e (ro&imit' sensors (roduce an electrostatic fieldinstead of an electromanetic field. Ca(aciti$e (ro&imit'switches will sense metal as well as nonmetallic materials suchas (a(er lass li6uids and cloth.The sensin surface of a ca(aciti$e sensor is formed b' two

concentricall' sha(ed metal electrodes of an unwoundca(acitor. 0hen an ob7ect nears the sensin surface it entersthe electrostatic field of the electrodes and chanes theca(acitance in an oscillator circuit. As a result the oscillatorbeins oscillatin. The trier circuit reads the oscillatorsam(litude and when it reaches a s(ecific le$el the out(ut stateof the sensor chanes. As the taret mo$es awa' from thesensor the oscillators am(litude decreases switchin thesensor out(ut bac9 to its oriinal state.++Standard Target and Standard tarets are s(ecified for each ca(aciti$e sensor. The

Dielectric Constant standard taret is usuall' defined as metal andor water.Ca(aciti$e sensors de(end on the dielectric constant of thetaret. The larer the dielectric number of a material the easier itis to detect. The followin ra(h shows the relationshi( of thedielectric constant of a taret and the sensors abilit' to detectthe material based on the rated sensin distance GS rH.The followin table shows the dielectric constants of somematerials. If for e&am(le a ca(aciti$e sensor has a ratedsensin distance of 1* mm and the taret is alcohol theeffecti$e sensin distance GSrH is a((ro&imatel' 8+Q of therated distance or 8.+ mm.

#aterial DielectricConstant#aterial DielectricConstantAlcohol 2+.8 %ol'amide +Araldite /. %ol'eth'lene 2./Ba9elite /. %ol'(ro(lene 2./lass + %ol'st'rene /=ica %ol'$in'l Chloride 2.-ard !ubber 4 %orcelain 4.4


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%a(er


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%ac9H=etal Shielded + 1*


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the sensor the blind ;one is from to 8* cm. An ob7ect (lacedin the blind ;one will (roduce an unstable out(ut.'ange Definition The time inter$al between the transmitted sinal and the echois directl' (ro(ortional to the distance between the ob7ect andsensor. The o(eratin rane can be ad7usted in terms of its

width and (osition within the sensin rane. The u((er limit canbe ad7usted on all sensors. The lower limit can be ad7usted onl'with certain $ersions. "b7ects be'ond the u((er limit do not(roduce a chane at the out(ut of the sensor. This is 9nown as@blan9in out the bac9round ."n some sensors a bloc9in rane also e&ists. This is betweenthe lower limit and the blind ;one. An ob7ect in the bloc9inrane (re$ents identification of a taret in the o(eratin rane.There is a sinal out(ut assined to both the o(eratin raneand the out(ut rane.1

'adiation Pattern The radiation (attern of an ultrasonic sensor consists of a maincone and se$eral neihborin cones. The a((ro&imate anle ofthe main cone is +R.)ree ?ones )ree ;ones must be maintained around the sensor to allow forneihborin cones. The followin e&am(les show the free areare6uired for different situations.Parallel Sensors In the first e&am(le two sonar sensors with the same sensinrane ha$e been mounted (arallel to each other. The tarets are$ertical to the sound cone. The distance between the sensors isdetermined b' the sensin rane. )or e&am(le if the sensinrane of the sensors is cm the' must be located at least

1+ cm a(art.XTa r ge t Ta r ge t

Sensing'ange8C#948C#9


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that mutual interferance does not occur.X

Sensing'ange8C#948C#9


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rane. The o(eratin rane is ad7usted for the reflector. The(ulses are bounced off the reflector and the echo (ulses arereturned to the sensor. 0hen a taret bloc9s the echo (ulsesthe out(ut is acti$ated. T'(icall' used in a((lications where thetaret is not a ood sound absorber.

Thru$Beam #ode Thru


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/H The a((ro&imate anle of the main sound cone of anultrasonic (ro&imit' sensor is derees.4H The free ;one between two (arallel ultrasonic sensorswith a rated sensin rane of 2*


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se(arate transducer. The' are confiured with a normall' o(enGN"H normall' closed GNCH or analo out(ut. These sensors ha$ea cubic sha(e G88 & + & /* mmH. The sensors o(erate on 18

basics of sensor

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