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Inductive Sensor Technology

In­duc­tive sen­sors are ideal for contact­less de­tec­tion and po­si­tion mo­ni­to­ring of me­tal­lic ob­jects. They de­tect me­tal­lic parts des­pite conta­mi­na­tion such as dust and mois­ture and are in­sen­si­tive to vi­bra­tions.
Mode of Operation
Correction Factor 1
Installation Situations
weproTec
Overview Inductive Sensors
Difference from Optical Sensors

How In­duc­tive Sen­sors Work

In­duc­tive sen­sors de­tect me­tal­lic ob­jects contact­less­ly and mea­sure the dis­tance bet­ween the sen­sor and the ob­ject to be mea­su­red by elec­tro­ma­gne­tic in­duc­tion. To do this, a cur­rent is conduc­ted through a coil, crea­ting an elec­tro­ma­gne­tic field around the coil. If an elec­tri­cal­ly conduc­tive ob­ject such as steel or alu­mi­num ap­proaches the ma­gne­tic field, this is chan­ged. The in­duc­tive sen­sor re­co­gnizes the change in the ma­gne­tic field and eva­luates it to de­ter­mine whe­ther there is a me­tal­lic ob­ject in the vi­ci­ni­ty.
 

Va­rious Swit­ching Out­puts

A si­gnal is present on the di­gi­tal swit­ching out­put as soon as the sen­sor has de­tec­ted an elec­tri­cal­ly conduc­tive ob­ject. The dis­tance can be out­put via an ana­log out­put as a pro­por­tio­nal vol­tage si­gnal – ei­ther as a cur­rent value of 4 mA…20 mA or as a vol­tage value of 0 V…10 V. In the case of in­duc­tive sen­sors with an IO-​Link in­ter­face, the swit­ching out­puts (NPN, PNP or push-​pull) can be confi­gu­red as nor­mal­ly clo­sed or nor­mal­ly open contacts as well as the swit­ching dis­tances.

Swit­ching Dis­tances with In­duc­tive Sen­sors

The swit­ching dis­tance is the dis­tance at which a stan­dard tar­get, which is ap­proa­ching the sen­sing face of an in­duc­tive sen­sor, trig­gers a si­gnal change. The stan­dard tar­get is a groun­ded, square plate made of steel with a thi­ck­ness of d = 1 mm. If an ob­ject moves away from the sen­sing face, the sen­sor re­mains swit­ched on lon­ger. In contrast, the sen­sor switches soo­ner if the ob­ject moves to­wards the sen­sing face. The dif­fe­rence bet­ween the switch-​on and switch-​off point as a per­cen­tage re­la­tive to the swit­ching dis­tance is cal­led swit­ching hys­te­re­sis. The swit­ching dis­tance is fur­ther sub­di­vi­ded into the va­riables no­mi­nal swit­ching dis­tance (Sn), real swit­ching dis­tance (Sr), useable swit­ching dis­tance (Su) and wor­king dis­tance (Sa).

Cor­rec­tion Fac­tor 1

In­fluence of Dif­ferent Ma­te­rials on the Swit­ching Dis­tance

The cor­rec­tion fac­tor of an in­duc­tive sen­sor re­fers to the spe­ci­fied swit­ching dis­tance for an ob­ject made of steel (EN 60947-5-2). If an ob­ject made of ano­ther ma­te­rial needs to be de­tec­ted, the swit­ching dis­tance has to be ad­jus­ted by an amount equal to the spe­ci­fied cor­rec­tion fac­tor. In­duc­tive sen­sors with cor­rec­tion fac­tor 1 have the same swit­ching dis­tance for all me­tals. The cor­rec­tion fac­tor 1 is of great im­por­tance in ap­pli­ca­tions where the ma­te­rial of the ob­ject to be de­tec­ted can vary. For in­duc­tive sen­sors, the cor­rec­tion fac­tor is spe­ci­fied in the data sheet.

Swit­ching Fre­quen­cy for In­duc­tive Sen­sors

The swit­ching fre­quen­cy cor­res­ponds to the maxi­mum pos­sible num­ber of swit­ching ope­ra­tions per se­cond if the dis­tance bet­ween the ob­jects to be de­tec­ted is equal to the size of the in­di­vi­dual ob­ject in Hertz (Hz), i.e. with a pulse duty fac­tor of 1:2.

Ins­tal­la­tion Si­tua­tions of In­duc­tive Sen­sors

In­duc­tive sen­sors are used in a wide range of ap­pli­ca­tions and en­able re­liable de­tec­tion of the smal­lest parts as well as re­liable de­tec­tion of end po­si­tions. Since the in­duc­tive sen­sors react to elec­tri­cal­ly conduc­tive ob­jects and ma­te­rials, suf­fi­cient dis­tance to me­tal­lic ob­jects must be main­tai­ned du­ring ins­tal­la­tion to avoid unin­ten­tio­nal swit­ching of the sen­sor. The ins­tal­la­tion condi­tions can be found in the data sheet of the re­le­vant sen­sor.

Flush Sen­sors

Flush sen­sors can be moun­ted in elec­tri­cal­ly conduc­tive ma­te­rials wi­thout pro­tru­ding be­cause they have a me­tal­lic ring around the sen­sor head that pro­tects the sen­sor from in­fluences from the sur­roun­ding ma­te­rial. This shiel­ding re­duces the elec­tro­ma­gne­tic field and thus re­duces the swit­ching dis­tance. Flush moun­ting pro­tects the sen­sor from da­mage and pre­vents ob­jects pas­sing by from get­ting caught on the sen­sor. This makes them par­ti­cu­lar­ly sui­table for tight ins­tal­la­tion si­tua­tions.

Semi-​Flush Sen­sors

Sen­sors for semi-​flush ins­tal­la­tion have slight­ly lar­ger swit­ching dis­tances com­pa­red to flush sen­sors. They also have less at­tack sur­face for pas­sing ob­jects com­pa­red to non-​flush sen­sors.

Non-​Flush Sen­sors

In the case of non-​flush sen­sors, the sen­sing face is not en­clo­sed by a me­tal­lic hou­sing. As a re­sult, the ge­ne­ra­ted ma­gne­tic field is not shiel­ded by the hou­sing and a lar­ger field can build up. In­duc­tive sen­sors with non-​flush moun­ting have the lar­gest swit­ching dis­tance, but pro­trude si­gni­fi­cant­ly from the sur­roun­ding sur­face. These sen­sors can only be flush-​mounted in non-​conductive ma­te­rials.

we­pro­Tec and Al­ter­na­tive Fre­quen­cy

we­pro­Tec is the ab­bre­via­tion for wenglor proxi­mi­ty switch techno­lo­gy, a wen­glor tech­no­lo­gy for in­duc­tive sen­sors. In­duc­tive sen­sors with we­pro­Tec can be moun­ted very close next to each other, or op­po­site one ano­ther in the dis­tance range B1 . The sen­sors do not in­fluence each other in this range. This is achie­ved by the sen­sors syn­chro­ni­zing with each other and pul­sed with a time delay.
Al­ter­na­tive fre­quen­cy is a sim­pler form of we­pro­Tec tech­no­lo­gy in which an al­ter­na­tive wor­king fre­quen­cy can be pa­ra­me­te­ri­zed. This means that two sen­sors in the im­me­diate vi­ci­ni­ty do not in­ter­fere with each other if the al­ter­na­tive fre­quen­cy is ac­ti­va­ted for one of them and not for the other. They each work at a dif­ferent fre­quen­cy.

Overview of Inductive Sensors

Inductive Sensors with Standard Switching Distances
In­duc­tive Sen­sors with Stan­dard Swit­ching Dis­tances
Inductive Sensors with Increased Switching Distances
In­duc­tive Sen­sors with In­crea­sed Swit­ching Dis­tances
Inductive Sensors with IO-Link
In­duc­tive Sen­sors with IO-​Link
Inductive Sensors with Full-Metal Housing
In­duc­tive Sen­sors with Full-​Metal Hou­sing
Inductive Sensors with Analog Output
In­duc­tive Sen­sors with Ana­log Out­put
Inductive Sensors Welding Field Resistant with Correction Factor 1
In­duc­tive Sen­sors Wel­ding Field Re­sis­tant with Cor­rec­tion Fac­tor 1
Inductive Sensors with Selective Performance
In­duc­tive Sen­sors with Se­lec­tive Per­for­mance
Inductive Sensors for Extreme Temperature Ranges
In­duc­tive Sen­sors for Ex­treme Tem­pe­ra­ture Ranges
Inductive Ring Sensors
In­duc­tive Ring Sen­sors

Dif­fe­rence Bet­ween In­duc­tive Sen­sors and Pho­toe­lec­tro­nic Sen­sors

Both in­duc­tive and op­ti­cal sen­sors en­able iden­ti­fi­ca­tion so­lu­tions in pro­cess au­to­ma­tion. Dif­ferent func­tio­nal prin­ciples and as­so­cia­ted ad­van­tages en­able a wide va­rie­ty of ap­pli­ca­tions that meet a wide range of re­qui­re­ments.

In­duc­tive Sen­sors

Ob­ject de­tec­tion via elec­tro­ma­gne­tic in­duc­tion
De­tec­tion of elec­tri­cal­ly conduc­tive ob­jects
Me­tal­lic en­vi­ron­ments can cause in­ter­fe­rence
Re­liable ob­ject de­tec­tion at close range

Pho­toe­lec­tro­nic Sen­sors

Ob­ject de­tec­tion via in­fra­red light, red light, blue light or laser light
Material-​independent de­tec­tion of ob­jects
Im­pair­ment due to conta­mi­na­tion, vi­bra­tions or am­bient light
High pre­ci­sion in close range and at long dis­tances
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