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Technology of Fiber-Optic Sensors

Fiber-​optic sen­sors de­tect ob­jects and con­di­tions by di­rec­ting light to a test ob­ject and eva­lua­ting the in­ten­sity chan­ge of the re­tur­ning light. They can de­tect very small ob­jects, are par­ti­cu­larly fle­xi­ble to mount and are ex­tre­mely re­sis­tant in harsh en­vi­ron­ments – even in high tem­pe­ra­tu­res, hu­mi­dity or wet media. 
Definition
Technology Comparison
Fiber-Optic Amplifiers
Fiber-Optic Cables
Functional Principles
Fiber-Optic Heads
Installation
Industries

What Are Fiber-​Optic Sen­sors?

Fiber-​optic sen­sors use the phy­si­cal pro­per­ties of light when trans­mit­ting it via fiber-​optic cable with glass or plas­tic fi­bers to de­tect ob­jects. They con­sist of a fiber-​optic am­pli­fier and fiber-​optic ca­bles with or without op­tics. The fiber-​optic am­pli­fier con­tains the light sour­ce and the re­cei­ving ele­ment as well as the pro­ces­sing unit of the sen­sor. The fiber-​optic ca­bles are only in­ten­ded to trans­mit and re­cei­ve light. Since fiber-​optic ca­bles do not con­tain elec­tro­nic com­po­nents, fiber-​optic sen­sors are par­ti­cu­larly sui­ta­ble for ap­pli­ca­tions in con­fi­ned spa­ces, harsh en­vi­ron­ments or where other sen­sors can­not be used.

   

How Do Fiber-​Optic Sen­sors Work?

Fiber-​optic sen­sors mea­su­re dif­fe­rent light sizes such as wa­ve­length and in­ten­sity in order to de­ri­ve other mea­su­red va­lues from them. In in­dus­trial au­to­ma­tion, the ener­ge­tic prin­ci­ple is often used. The emit­ter, usually an LED light sour­ce, couples light into a fiber-​optic cable. The light exits at the end of the fiber-​optic cable and either hits an ob­ject which re­flects it back (sen­sing/re­flec­tion prin­ci­ple) or it is de­tec­ted di­rectly by a re­cei­ver (through-​beam prin­ci­ple). The re­tur­ned light is then di­rec­ted to the analy­sis mo­du­le, where a pho­to­dio­de mea­su­res the amount of light re­cei­ved. The elec­tro­nics cons­tantly com­pa­re this amount of light with a de­fi­ned th­reshold value and switch the out­put of the sen­sor ac­cor­dingly.

What Are the Ad­van­ta­ges of Fiber-​Optic Sen­sors?

Fle­xi­ble Ins­ta­lla­tion

Fiber-​optic sen­sors are ex­tre­mely com­pact and ideal for ins­ta­lla­tion in con­fi­ned in­dus­trial en­vi­ron­ments. In ad­di­tion, the high fle­xi­bi­lity and low at­te­nua­tion of the fiber-​optic ca­bles also make lar­ger trans­mis­sion dis­tan­ces pos­si­ble.

High Re­lia­bi­lity

Fiber-​optic sen­sors are ex­tre­mely du­ra­ble and en­su­re re­lia­ble per­for­man­ce even under harsh am­bient con­di­tions such as high tem­pe­ra­tu­res, hu­mi­dity and ag­gres­si­ve media such as co­oling lu­bri­cants or clea­ning agents. 

Elec­tro­mag­ne­tic Com­pa­ti­bi­lity

In fiber-​optic ca­bles, sig­nal trans­mis­sion is pu­rely op­ti­cal, which eli­mi­na­tes the cha­llen­ges as­so­cia­ted with EMC for fiber-​optic sen­sors. They are also ex­tre­mely in­sen­si­ti­ve to elec­tro­mag­ne­tic in­ter­fe­ren­ce.

Fiber-Optics vs. Small Photoelectrics: Technology Overview

 
Fiber-​optic cable Small pho­to­elec­trics
Mea­su­re­ment range
 
Am­bient tem­pe­ra­tu­re
 
Moun­ting ef­fort
De­tec­tion of trans­pa­rent ob­jects
 
Small parts de­tec­tion
Fle­xi­bi­lity and cus­to­mi­za­tion
 

What Are Fiber-​Optic Am­pli­fiers?

Fiber-​optic am­pli­fiers, also known as op­ti­cal am­pli­fiers, are com­po­nents that am­plify sig­nals in op­ti­cal com­mu­ni­ca­tion sys­tems and play a key role in fiber-​optic com­mu­ni­ca­tion. Here, they in­crea­se the trans­mis­sion range.

In the con­text of in­dus­trial au­to­ma­tion, fiber-​optic am­pli­fiers are sen­sors that use fiber-​optics such as glass fi­bers or plas­tic fiber-​optics to mea­su­re va­rious phy­si­cal va­ria­bles such as pres­su­re, tem­pe­ra­tu­re, ex­pan­sion and the pre­sen­ce or po­si­tion of ob­jects. They uti­li­ze the abi­lity of fiber-​optics to trans­mit light, de­tec­ting chan­ges in the spec­trum or amount of light.


What Does Multi Unit Mean?

A sen­sor net­work, also known as a multi unit, con­sists of se­ve­ral sen­sors that can com­mu­ni­ca­te di­rectly with each other. The sen­sors do not in­ter­fe­re with each other, even if they are close to each other or op­po­si­te each other and ins­pec­ting the same ob­ject. This enables ef­fi­cient coor­di­na­tion and co­lla­bo­ra­tion bet­ween the sen­sors. In ad­di­tion, the sen­sor net­work mi­ni­mi­zes the need for ca­bling, as only one cable is re­qui­red for the con­nec­tion to the IO-​Link mas­ter. The sig­nal le­vels and swit­ching chan­nels of all con­nec­ted sen­sors are trans­mit­ted via the IO-​Link pro­cess data, a con­nec­tion cable and a port on the IO-​Link mas­ter. This op­ti­mi­zes data trans­fer and sig­ni­fi­cantly re­du­ces ca­bling and ins­ta­lla­tion ef­fort.

What Is the Align­ment Mode?

Fiber-​optic ca­bles must be alig­ned pre­ci­sely to the tar­get for re­lia­ble ob­ject de­tec­tion. Es­pe­cially when using the through-​beam prin­ci­ple, the emit­ter and re­cei­ver should be po­si­tio­ned axially as clo­sely as pos­si­ble to each other. Since the am­pli­fier or analy­sis mo­du­le is often ins­ta­lled in the con­trol ca­bi­net or outsi­de the field of vi­sion, the setup is often based on the ope­ra­tor’s view and as­sess­ment. The align­ment mode vi­sua­li­zes the sig­nal strength by pul­sing the trans­mit­ting light. Si­mi­lar to par­king sen­sors in the car, the pulse fre­quency in­crea­ses the stron­ger the sig­nal re­cei­ved. The sen­sor head is ad­jus­ted in its angle and axis until the op­ti­mal align­ment with the ma­xi­mum sig­nal is achie­ved. This enables ef­fi­cient and pre­ci­se setup even with grea­ter dis­tan­ces bet­ween the emit­ter and re­cei­ver.

What do you need a DIN rail adap­ter for?

The am­pli­fier unit is usually moun­ted on stan­dar­di­zed DIN rails. Ins­ta­lla­tion is tool-​free by simply and quickly snap­ping the am­pli­fiers onto the rail. When using the multi-​unit mode, se­ve­ral fiber-​optic am­pli­fiers can be arran­ged next to each other in the con­trol ca­bi­net in a space-​saving and non-​slip man­ner.

What Are the Ad­van­ta­ges of Dif­fe­rent Light Sour­ces?

De­pen­ding on the spe­ci­fic re­qui­re­ments of the ap­pli­ca­tion, wen­glor fiber-​optic sen­sors use red, blue, pink or in­fra­red light.

  • Red LEDs (633 nm) offer high pro­cess sta­bi­lity, even with very bright or white test ob­jects.

  • Blue LEDs (455 nm) are par­ti­cu­larly sui­ta­ble for pre­ci­se mea­su­re­ments on glo­wing, glossy or dark sur­fa­ces, as they pe­ne­tra­te less deeply into the test ob­ject.

  • In pink light mode, red and blue LEDs are ac­ti­va­ted si­mul­ta­neo­usly to in­crea­se light out­put and im­pro­ve the range of the sen­sors.

  • In­fra­red light (over 750 nm) is in­vi­si­ble to the human eye, pre­ven­ting vi­sual dis­trac­tions and ma­ni­pu­la­tion – ideal for mo­ving sen­sors on robot grip­pers or au­to­no­mous vehi­cles. It also enables a grea­ter range due to its higher power.

What Are Fiber-​Optic Ca­bles?

Fiber-​optic ca­bles are optic fi­bers con­sis­ting of a light-​conducting core and a jac­ket, each ha­ving a dif­fe­rent re­frac­ti­ve index. In this pro­cess, the light is trans­por­ted th­rough the core with vir­tually no los­ses due to total re­flec­tion on the jac­ket. When exiting the fiber-​optic cable, the light is scat­te­red at an aper­tu­re angle of ap­pro­xi­ma­tely 60 de­grees.
 

What Is the Re­frac­ti­ve Index?

The re­frac­ti­ve index des­cri­bes how much light rays chan­ge di­rec­tion when they enter from one me­dium to another. It is de­fi­ned by the ratio of the light ve­lo­city in the va­cuum c to the light ve­lo­city in the con­si­de­red me­dium v. The re­frac­ti­ve index n is di­men­sion­less and va­ries de­pen­ding on fac­tors such as the tem­pe­ra­tu­re and wa­ve­length of the light.

The fo­llo­wing phy­si­cal for­mu­la is used to de­ter­mi­ne the re­frac­ti­ve index:
 
n = v/c

What Is an Aper­tu­re Angle?

The aper­tu­re angle re­fers to the angle at which light exits the op­ti­cal fiber. A large aper­tu­re angle of­fers the ad­van­ta­ge that it enables re­lia­ble de­tec­tion of even he­te­ro­ge­neo­us ob­jects at a short dis­tan­ce. It is also easy to hand­le, as the orien­ta­tion of the de­vi­ce is not im­por­tant. Ho­we­ver, the light out­put quickly spreads over a large area, re­du­cing the range as the light does not stay fo­cu­sed.

To con­trol this wide aper­tu­re angle, len­ses are used that focus or co­lli­ma­te the light as re­qui­red. This enables the de­tec­tion of very small ob­jects or sig­ni­fi­cantly in­crea­ses the range of the fiber-​optic ca­bles.

Op­ti­cal Fi­bers in Com­pa­ri­son

Plas­tic fiber-​optic ca­bles are ideal for ob­ject de­tec­tion in ap­pli­ca­tions re­qui­ring little space. Glass fiber-​optic ca­bles, on the other hand, prove them­sel­ves in de­man­ding am­bient con­di­tions with high tem­pe­ra­tu­res and offer che­mi­cal re­sis­tan­ce. These and other ad­van­ta­ges of these ma­te­rials open up nu­me­rous ap­pli­ca­tion pos­si­bi­li­ties to meet a wide range of re­qui­re­ments.

Glass Fiber-​Optic Ca­bles

Trans­mis­sion of vi­si­ble light and in­fra­red light
To­le­rant to ex­tre­me tem­pe­ra­tu­re ran­ges
Sui­ta­ble for co­rro­si­ve or wet in­dus­trial en­vi­ron­ments
Par­ti­cu­larly low at­te­nua­tion in the area of the in­fra­red light
Risk of brea­ka­ge due to ex­ces­si­ve or re­pea­ted ben­ding

Plas­tic Fiber-​Optic Ca­bles

Trans­mis­sion of vi­si­ble light
Less to­le­rant to ex­tre­me tem­pe­ra­tu­re ran­ges
Not sui­ta­ble for co­rro­si­ve or wet in­dus­trial en­vi­ron­ments
Par­ti­cu­larly low at­te­nua­tion in the vi­si­ble light area
Re­peat bends pos­si­ble due to high fle­xi­bi­lity

Pa­ra­llel Fi­bers

With this type of re­flec­tion, the fi­bers run pa­ra­llel to each other to trans­mit light sig­nals. This fiber arran­ge­ment is avai­la­ble as both plas­tic and glass fiber-​optics and is used in most stan­dard ap­pli­ca­tions.


 

Coa­xial Fi­bers

The coa­xial re­flec­tion type is a high-​precision mea­su­re­ment method con­sis­ting of a core (emit­ter) and a su­rroun­ding area (re­cei­ver). With this type, the di­rec­tion of entry of the test ob­ject into the mea­su­ring range is irre­le­vant for the po­si­tion of the fiber-​optic sen­sor.

 

Mixed Fi­bers

The mixed re­flec­tion type re­fers to a fiber-​optic struc­tu­re in which many trans­mit­ting and re­cei­ving fi­bers are arran­ged without se­pa­ra­tion. The po­si­tion and dis­tan­ce of the fiber-​optic cable to the ob­ject are less re­le­vant here. The image area is very small or not pre­sent.

Ef­fect of Fiber Dia­me­ter/Bund­le Dia­me­ter

The lar­ger the dia­me­ter of the light-​conducting core, the more light can be trans­por­ted th­rough the cable. This leads to grea­ter ran­ges and im­pro­ved de­tec­tion of deep black ob­jects. For cer­tain fiber-​optic heads, such as fiber-​optic cable bands, more fi­bers and con­se­quently a lar­ger dia­me­ter are the­re­fo­re re­qui­red.

What Does the Ben­ding Ra­dius Say?

The ben­ding ra­dius de­ter­mi­nes how much a cable can be bent without da­ma­ging it or af­fec­ting the sig­nal qua­lity. If a fiber-​optic cable is bent ex­ces­si­vely, there is a risk that the fiber jac­ket in the cable breaks and light es­ca­pes from the fiber core. This can lead not only to in­crea­sed dam­ping, but also to mi­cro­cracks in the fiber core, re­sul­ting in per­ma­nent da­ma­ge. The­re­fo­re, it is im­por­tant to ob­ser­ve the ben­ding ra­dius, es­pe­cially for glass fiber-​optic ca­bles.

What Is the Struc­tu­re of Fiber-​Optic Ca­bles?

Plastic Fiber-Optic Cables

Glass Fiber-Optic Cables

What Types of Jac­kets Are there for Glass Fiber-​Optic Ca­bles?

Plas­tic, PVC

The most cost-​effective va­riant. Sui­ta­ble for stan­dard ap­pli­ca­tions that do not re­qui­re spe­cial re­sis­tan­ce to en­vi­ron­men­tal in­fluen­ces.

Stain­less Steel

Pro­vi­des the highest level of pro­tec­tion against me­cha­ni­cal stress. Less fle­xi­ble ins­ta­lla­tion as lar­ger ben­ding radii are re­qui­red. No pro­tec­tion against gas­ses or li­quids.

Si­li­co­ne

Ma­xi­mum re­sis­tan­ce to ag­gres­si­ve media. Ab­so­lu­tely tight, so fluids and gas­ses can­not pe­ne­tra­te the jac­ket and da­ma­ge the op­ti­cal fi­bers. FDA com­pliant.

What Are the Ope­ra­tio­nal Prin­ci­ples of Fiber-​Optic Sen­sors?

Re­flex Mode

In the case of re­flex mode, the emit­ter and the re­cei­ver are en­clo­sed in a sin­gle hou­sing. The light emit­ted by the emit­ter hits the test ob­ject and is re­tur­ned to the re­cei­ver. The ob­ject is de­tec­ted based on the amount of re­flec­ted light reaching the re­cei­ver of the fiber-​optic cable.

Through-​Beam Mode

The through-​beam model con­sists of an op­po­sing emit­ter and re­cei­ver. As soon as the test ob­ject pas­ses th­rough the space bet­ween the emit­ter and re­cei­ver, the light of the fiber-​optic cable is in­te­rrup­ted. De­tec­tion is then per­for­med by re­du­cing the re­cei­ved light in­ten­sity.

Retro-​Reflex Sen­sor

With the retro-​reflex sen­sor prin­ci­ple, the emit­ter and re­cei­ver are lo­ca­ted in a hou­sing, while on the op­po­si­te side a re­flec­tor is po­si­tio­ned. The test ob­ject is de­tec­ted when the light re­flec­ted back by the re­flec­tor is either com­ple­tely in­te­rrup­ted or re­du­ced. 

Fiber-​Optic Cable Bands

Fiber-​optic cable bands are used to mo­ni­tor areas. In con­trast to spot-​shaped light spots, which only mo­ni­tor the pre­sen­ce of ob­jects within one point, fiber-​optic cable bands de­tect se­ve­ral cen­ti­me­ters. The sen­sor de­tects the ob­ject as soon as the sig­nal is wea­ke­ned or com­ple­tely in­te­rrup­ted.

Com­pa­ri­son of Dy­na­mic Read­just­ment and Jump De­tec­tion

Both dy­na­mic read­just­ment and jump de­tec­tion are sui­ta­ble for re­lia­ble de­tec­tion of ob­jects under chan­ging en­vi­ron­men­tal con­di­tions. In dy­na­mic read­just­ment, a quasi-​fixed th­reshold value is used, whe­reas jump de­tec­tion does not re­qui­re a th­reshold value and only eva­lua­tes sig­nal chan­ges ins­tead.

Fixed Swit­ching Point

The most com­mon mode of ope­ra­tion of a sen­sor is based on a fixed swit­ching point. The sen­sor de­ter­mi­nes the th­reshold value or the swit­ching point du­ring the teach-​in pro­cess in ac­cor­dan­ce with a spe­ci­fied teach-​in logic. In nor­mal teach, this co­rres­ponds to 50% of the cu­rrent sig­nal, for exam­ple. If the am­bient con­di­tions and the ob­jects to be de­tec­ted are very cons­tant, the mode of ope­ra­tion with a fixed swit­ching point of­fers the highest in­sen­si­ti­vity to in­ter­fe­ren­ce, as ex­ter­nal in­fluen­ces can­not chan­ge the swit­ching point: If the sig­nal is above the de­fi­ned th­reshold, the out­put is ac­ti­va­ted; if it is below, the out­put re­mains inac­ti­ve. Ho­we­ver, if the sig­nal is al­te­red due to con­ta­mi­na­tion, for exam­ple, this can lead to per­ma­nent mal­fun­ctions.

Dy­na­mic Read­just­ment

The dy­na­mic read­just­ment is par­ti­cu­larly sui­ta­ble for the re­flex mode with sta­tic back­grounds as well as for the through-​beam mode. The non-​switched state should pre­vail, as the th­reshold value is only read­jus­ted in this state. If there is con­ta­mi­na­tion on the fiber-​optic head or on the back­ground, this is com­pen­sa­ted by dy­na­mic ad­just­ment of the th­reshold value.

Jump De­tec­tion

The ab­so­lu­te sig­nal va­lues are irre­le­vant for jump de­tec­tion. Ins­tead, the di­rec­tion of the sig­nal chan­ge (ne­ga­ti­ve, po­si­ti­ve or both di­rec­tions), the mag­ni­tu­de of the chan­ge and the ob­ser­va­tion pe­riod can be in­clu­ded in the eva­lua­tion. This enables the de­tec­tion of highly va­ria­ble ob­jects (e.g. in color or sur­fa­ce fi­nish) on non-​static back­grounds (such as a slowly soi­ling con­ve­yor belt) as well as the de­tec­tion of ob­jects without prior tea­ching (e.g. with chan­ging bat­ches).

Over­view of Fiber-​Optic Heads

An­gled

An­gled sen­sor heads are ideal for tight spa­ces where the op­ti­cal axis and cable outlet must be orien­ted dif­fe­rently. Thanks to the th­read, the sen­sor heads can be ea­sily scre­wed into pre­pa­red holes or fas­te­ned to an angle or plate with two nuts.

L Type

The L type allows easy moun­ting with two screws and of­fers pre­de­fi­ned po­si­tions of the op­ti­cal axes. Exact align­ment is not ne­ces­sary due to the large aper­tu­re angle of the fiber-​optic ca­bles.
 

Flat

Flat sen­sor heads can be ea­sily in­te­gra­ted into the base of the work­pie­ce ca­rrier. The fle­xi­bi­lity of the cable outlet on the sen­sor head allows easy cable rou­ting to the left, right or rear.

Fle­xi­ble

The thin, long metal sen­sor lance can be adap­ted to the spe­ci­fic re­qui­re­ments of the res­pec­ti­ve ap­pli­ca­tion by sim­ple ben­ding.

Fiber-​Optic Cable Bands

Fiber-​optic cable bands in through-​beam mode are ideal for mo­ni­to­ring large areas. Re­flex fiber-​optic cable bands, on the other hand, are par­ti­cu­larly ef­fec­ti­ve for de­tec­ting he­te­ro­ge­neo­us ob­jects and can also be used for mea­su­ring ap­pli­ca­tions th­rough the eva­lua­tion of the re­flec­ted light.

Mi­nia­tu­re

Mi­nia­tu­re sen­sor heads are par­ti­cu­larly sui­ta­ble for ap­pli­ca­tions in the tigh­test of spa­ces.

Th­read

Th­rea­ded sen­sor heads allow for quick and easy ins­ta­lla­tion. They can either be scre­wed di­rectly into pre-​drilled holes or fixed to brac­kets or pla­tes using two nuts.

Smooth

Smooth sen­sor heads are ideal for use in con­fi­ned spa­ces and can be in­ser­ted or glued into pre­fa­bri­ca­ted moun­ting brac­kets.

The Fo­llo­wing Must Be Ob­ser­ved when Ins­ta­lling Fiber-​Optic Sen­sors

To en­su­re re­lia­ble ob­ject de­tec­tion and ac­cu­ra­te mea­su­re­ment data, the fo­llo­wing ins­truc­tions should be ob­ser­ved when ins­ta­lling the sen­sor.

Length and Cut­ting

Fiber-​optic ca­bles are avai­la­ble in va­rious lengths. Plas­tic fiber-​optic ca­bles can be cut to size by the cus­to­mer, glass fiber-​optic ca­bles only in­dus­trially, as they must be ground and po­lished after cut­ting. The length has little ef­fect on the de­tec­tion range, but lon­ger fiber-​optic ca­bles let less light th­rough.


Tip: Se­lect a sui­ta­ble glass fiber-​optic cable.

De­tec­tion Range

Due to the large aper­tu­re angle, fiber-​optic ca­bles have only a small de­tec­tion range. Higher de­tec­tion ran­ges can be achie­ved with lar­ger fiber bund­le/core dia­me­ters or with len­ses that focus the light.


Tip: Use fiber-​optic ca­bles pri­ma­rily for short ran­ges and de­tec­tion of small parts.

Ben­ding Ra­dius

Fiber-​optic ca­bles are fle­xi­ble, but mi­ni­mum ben­ding radii must be main­tai­ned to avoid da­ma­ge and light loss. High-​flex plas­tic fiber-​optic ca­bles are sui­ta­ble for tight ben­ding radii or mo­ving ins­ta­lla­tions. The fo­llo­wing ap­plies in ge­ne­ral: Sma­ller dia­me­ters allow sma­ller ben­ding radii.

Tip: Ins­ta­lla­tion of high-​flex fiber-​optic ca­bles.

Tem­pe­ra­tu­re

Plas­tic and glass fiber-​optic ca­bles dif­fer in terms of tem­pe­ra­tu­re re­sis­tan­ce. Above 85 °C, stain­less steel or si­li­co­ne coated glass fiber-​optic ca­bles should be used.

Tip: Thanks to in­di­vi­dual lengths, the analy­sis mo­du­le can also be pla­ced in the con­trol ca­bi­net.

Sen­sor Orien­ta­tion

In re­flex mode, the emit­ter and re­cei­ver should be ins­ta­lled at a 90° angle to the test ob­ject when ap­proa­ching from the side to en­su­re smooth swit­ching on and off.

Tip: A pla­nar orien­ta­tion to the ob­ject leads to an off­set with de­la­yed on and off swit­ching.

Cable with De­di­ca­ted Emit­ter

For fiber-​optic heads with coa­xial light emis­sion and for cer­tain fiber optic cable bands, it is es­sen­tial to en­su­re the co­rrect as­sign­ment of emit­ter on the fiber-​optic head to emit­ter on the am­pli­fier.

Tip: The am­pli­fiers are mar­ked with arrows for this pur­po­se.

Sectors and Industries which Use Fiber-Optic Sensors

In the pro­duc­tion of metal pro­fi­les, the pre­sen­ce and di­men­sions of the ob­jects must be de­tec­ted be­fo­re a clam­ping de­vi­ce se­cu­res them in place. Pro­fi­les can be black, white, chro­me, glossy or matt. Glass fiber-​optic light cur­tains based on the transmitter-​receiver prin­ci­ple are used in con­fi­ned spa­ces, to­gether with a uni­ver­sal re­flex sen­sor. The op­ti­cal fi­bers are arran­ged in a sin­gle line to crea­te a light band. The width is mea­su­red, the li­near sig­nal is out­put pro­por­tio­nal to the glass fiber cover and the co­rrect po­si­tion is de­ter­mi­ned.

¿Qué ob­je­tos no pue­den de­tec­tar de forma óp­ti­ma los sen­so­res de fibra óp­ti­ca?

  • El agua y otros lí­qui­dos trans­pa­ren­tes que ab­sor­ben mucha luz o la re­frac­tan pue­den pro­vo­car me­di­cio­nes im­pre­ci­sas.
  • Los ob­je­tos muy trans­pa­ren­tes, como el vi­drio trans­pa­ren­te, que per­mi­ten que la luz pase com­ple­ta­men­te sin re­fle­jar­la, di­fi­cul­tan la de­tec­ción.
  • Los ob­je­tos de color negro in­ten­so, que ab­sor­ben mucho la luz in­ci­den­te y la re­fle­jan mí­ni­ma­men­te o no la re­fle­jan, di­fi­cul­tan el re­torno de la señal al sen­sor.
  • Los ob­je­tos muy bri­llan­tes que re­fle­jan la luz en di­rec­cio­nes im­pre­de­ci­bles im­pi­den una de­tec­ción de ob­je­tos pre­ci­sa.
     
 

 
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