Inductive

Inductiv e S ens ors

Introduction to

Inductive Proximity Switches

Pepperl+Fuchs Kolleg GmbH, Page 1

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Block Diagram

Inductiv e S ens ors

Plastic cover

Epoxy resin LED

Coil

O-ring seal

Cover paste

Ferrite core IC

Support

Housing

Support ring

Printed board

Oscillator

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Comparator

Output amp.

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Physical Basics

Inductiv e S ens ors

M12 R1

Primary circuit: sensor coil

R2

Secondary circuit: target

the alternating electromagnetic field created by the coil induces eddy currents in the target if the target is made of non-ferromagnetic material the alternating electromagnetic field created by the coil induces eddy currents and generates magnetic losses in the target if the target is made of ferromagnetic material the magnetic losses are higher than the losses generated by the eddy currents operating distances vary depending on the target material and are normally shorter than the usable operating distance. They may increase in case of target of thin NE foils. Pepperl+Fuchs Kolleg GmbH, Page 3

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Measurering the "Rated operation distance"

Inductiv e S ens ors

Reference axis

Steel Fe360

operating distance

☞ Test conditions – ambient temperature: 20 °C – Power supply: 24 V DC or 230 V AC – Target: Steel Fe360, square, 1mm thick, length diameter of active area or three times rated operation distance (large operating distance)

☞ High number of tested proximity switches ☞ Pure characteristic value witch disregards manufacturing tolerances as well as temperature or voltage fluctuations Pepperl+Fuchs Kolleg GmbH, Page 4

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Definition of Operation Distances 1 Target Su max.

☞ sr = Effective operating distance

Sr max.

Inductiv e S ens ors

☞ sn = Rated operation distance – single proximity switch – voltage within the operating voltage range – ambient temperature 23 °C + 5 °C

Sn Sr min. Su min.

Su max. + Differential travel Sr max. + Differential travel Sn + Differential travel Sr min. + Differential travel Su min. + Differential travel

Sa

☞ 0.9* sn < sr < 1.1*sn ☞ su = usable operating distance – single proximity switch – voltage between 85% and 110% of rated operating voltage – temperature range -25 °C ... +70 °C

☞ 0.9* sr < su < 1.1*sr ☞ 0.81*sn < sa < 1.12*sn ☞ sa = assured operating distance Pepperl+Fuchs Kolleg GmbH, Page 5

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Reduction Factor

Inductiv e S ens ors

Steel Fe360 (1)

☞ Reduction factor records the reduction of operating distance from the standard target because of the deviating object characteristics

Stainless steel (0.65 ... 0.85) Brass (0.25 ... 0.55) Aluminium (0.2 ... 0.5) Copper (0.15 ... 0.45)

s

☞ Reduction factor is a function of – conductivity – permeability

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Influence of the target characteristics

Inductiv e S ens ors

The area a*b is smaller than the area of the standard target – operating distance decreases

The area a*b is larger than the area of the standard target – no influence

The target is thicker than the standard target – influence is a function of penetration b depth – low penetration depth (small proximity switches) ==> no influence – high penetration depth (big proximity switches) ==> operating distance decreases

The target is thinner than the standard target

a d

– operating distance increases (only for NE metals) Pepperl+Fuchs Kolleg GmbH, Page 7

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Differential travel H

Inductiv e S ens ors

Distance between the operating point when the target approaches the proximity switch and the release point when the target moves away

switch off Direction of movement

switch on

less than 20% of the effective operating distance sr

test conditions: temperature range power supply actuating standard target :

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23°C ( +/- 5°C) rated voltage as already defined

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Inductiv e S ens ors

Frequency of operating cycles (f) number of operating cycles performed by a proximity switch during a specified period of time.

Target / no target ratio = 1:2

 This value is a function of the oscillator frequency of the given proximity switch high oscillator frequency (small operating distance) ==> high frequency of operating cycles low oscillator frequency (large operating distance) ==> low frequency of operating cycles

Pepperl+Fuchs Kolleg GmbH, Page 9

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Inductiv e S ens ors

Connection to PLC Wiring

☞ In most applications the proximity switch is directly connected to the input card of a PLC

PLC Input-card

Example: ☞ max. Frequency of operation cycles 5 kHz ==> period = 200 µs ☞ min. input pulse length = 66 µs ☞ Problem: time of the PLC program

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24 VDC

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☞ The PLC-program works with the input information which was read at the "Read-IDI-time" ☞ No changes of input information's will be detected during the "PLC-program time" and "Write ODI-time"

Read IDI Program time

Inductiv e S ens ors

Problem: Program Time

PLC-Program

Write ODI

☞ The output signal of the proximity switch must be longer than the program time

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Inductiv e S ens ors

Cylindrical Housing ☞ Diameter 3 mm ... 30 mm (threaded or unthreaded) ☞ Housing materials – High Grade Stainless Steel 303 – Brass, Nickel Plated or Teflon Coated – Semi-crystalline Polybutylenterephlatate (Crastin) – Crystalline polyphenylenesulphide (Ryton)

☞ Crastin is resistant to abrasion, heat and cold and withstands hydrocarbons, acids and seawater ☞ Ryton is retains form stability up to 200 °C Pepperl+Fuchs Kolleg GmbH, Page 12

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Inductiv e S ens ors

Embeddable/Non-embeddable Mounting

> 3*d > 3*sn

> 3*sn

> 2*sn

d

d >d

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> 3*d

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Inductiv e S ens ors

Advantages/Disadvantages of Embeddable Mounting Advantages

Disadvantages

☞ no mutual influence when the distance between two proximity switches is > diameter/length of sensing face

☞ achieve approx. 60% of the operating distance of prox. switches intended for embeddable mounting or

☞ real "flush" mounting in conductive material ☞ less sensitive than non-embeddable mountable prox. switches to fault inducing influences

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☞ higher volume than prox. switches intended for embeddable mounting

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Inductiv e S ens ors

Quasi Embeddable Mounting ⇒ Proximity switch with increased operation distance (NEB ...) ⇒ Proximity switch for non-embeddable mounting B

⇒ For ferromagnetic materials A = 0.2*d ⇒ For non-ferromagnetic materials A = 0,1*d

d A

⇒ Non-conductive materials A=0 ⇒ Distance between two proximity switches = d

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Inductiv e S ens ors

Problems of Increased Operation Distance Increased operation distance realised by pre-damping the oscillator of inductive proximity switch Current flow decreases due to the pre-damping

5 I/mA

Standard proximity switch

4

3

Increased Operation Distance

2

When the current flow decreases further (e. g. changing ambient temperature, conductive dirt, other magnetic fields, ...) the oscillator may stop oscillating

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SW OFF SW ON

1

s/mm

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Rectangular Housing Screw-On Sensors

Inductiv e S ens ors

Surface Switch

- Mountable on surface - Sensing face upwards or sideways available - Housing material normally PBT

- large front - Operating dist. > 50 mm - Housing material: PBT - Front face: 80x80 mm

VariKont / VariKontM - standard mounting hole arrangement in acc. with 60 947-5 (mech. roller lever limit switches) - Material of the base: PTB or metal - Housing material: PBT - Front face: VariKont: 40x40 mm or 55x55 mm VariKont M: 30x30 mm - Rotatable in 15° steps (VariKontM) or 90° steps VariKont

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Inductiv e S ens ors

Other Types of Housing Ring Type Sensor - Housing looks like a ring and is made of PBT - magnetic field is concentrated in the ring - activated output when the target moves into the ring - with bistabile output available - no reduction factor

Slot Type Sensors - U-shaped housing made of PBT - magnetic field is built up between two coils positioned opposite each other in the sides of the U - activated output when the target enters the slot between the coils - no reduction factor - Entry depth is a function of material

Pepperl+Fuchs Kolleg GmbH, Page 18

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Inductiv e S ens ors

High intensity electromagnetic fields

cylindrical conductor Distance/mm 12.5 25 I / kA B / mT 5 80 40 10 160 80 20 320 160 50 800 400 100 1600 800

50

100

20 40 80 200 400

10 20 40 100 200

Sensors with compensating winding and ferrite cores with a high saturation flux can withstand magnetic fields up to 200 mT Pepperl+Fuchs Kolleg GmbH, Page 19

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Inductiv e S ens ors

NE/FE Switch Advantages

– reduction factor 1 in a standard proximity switch housing

Target: Fe Target: Al

Q

Pre-damping

Target

Inconvenients – difficult to manufacture for small housings

– expensive

Distance

NJ15+U1+2E2-NE/FE

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Inductiv e S ens ors

Electrical Values Power Supply ☞ DC Sensors – Voltage range:

10 VDC ... 30 VDC 10 VDC ... 60 VDC 5 VDC ... 60 VDC

☞ AC Sensors – Voltage range: – Frequency range:

98 VAC ... 253 VAC 48 Hz ... 62 Hz

☞ AC/DC Sensors – Voltage range:

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10 VDC . .. 30 VDC 24 VAC ... 240 VAC

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Important Characteristics

Inductiv e S ens ors

☞ Rated Operational Voltage – Minimum and maximum value of the supply voltage

☞ Rated Operational Current – Maximum load current for continuous operation

☞ Off-State Current – Current that flows across the load when the prox. switch is switched off

☞ No-Load Current – Self current requirement of the proximity switch

☞ Short Time Current – Current which can flows for a short period of time in the on state, without damaging the proximity switch

☞ Voltage Drop – Voltage which is measured across a two wire proximity switch in the on state Pepperl+Fuchs Kolleg GmbH, Page 22

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Inductiv e S ens ors

Short Circuit Protection + 1

Most of the proximity switches are protected with a pulsing protection method If the limiting current is exceeded, the output will be blocked and released periodically

4 3

Load -

IK Iact

Ratio tp / tk approx. 1 / 100 tp tk

Pepperl+Fuchs Kolleg GmbH, Page 23

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Types of Connection 1

Inductiv e S ens ors

Two-wire Sensors (Type Z) "Positive logic" NO/NC (Z2)

NO (Z0) + 24 VDC

+ 24 VDC

BN/3

- 24 VDC

1 2 3 4

BU/4

BU/4

Load

Load

NO/NC (Z2)

NC (Z1) + 24 VDC

BN/3

- 24 VDC

1 2 3 4 Load

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Load

"Negative Logic", NC + 24 VDC

BN/1

BU/2

"Negative logic", NO

BU/2

Load

BN/1

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Load

Reverse Polarity

Inductiv e S ens ors

+ 24 VDC BN/3

BU/4

Protection

Load

Tolerant

+

-

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Standard EN 50227 (NAMUR) 1 mA

Inductive proximity switch type N 2.1 1.8 1.6

1.2 other proximity switches 0.15 Lead breakage

Distance ON OFF

Schematic diagram Switch Amplifier 1k 10 k

Inductiv e S ens ors

Short circuit 6.5

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1k 8V

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New NAMUR Switches mA

Inductiv e S ens ors

Short circuit 6.5

N0 type (normally closed) 2.1 1.8 1.6

1.2

0.15 Lead breakage

Distance ON OFF

☞ Rectangular curve ☞ Switching point will be given by the sensor ☞ N1 type (normally open) also available

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Inductiv e S ens ors

Standard EN 50227 (NAMUR) 2

☞ ☞ ☞ ☞ ☞

Valid for proximity switches and mechanical contacts Analogue or rectangular curve (N0/N1-type) is allowed Switching point between 1.2 ... 2.1 mA Hysteresis = 0.2 mA Lead breakage monitoring: – current less than 50 µA ... 150 µA (typ. 100 µA)

☞ Lead Resistant < 50 Ω (at max. ambient temperature) ☞ Short circuit monitoring: – Switch Amplifier load less than 100 Ω ... 360 Ω

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Types of Connection 2

Inductiv e S ens ors

Three-wire Sensors (Type E) E2

pnp-type

E3 L+ (+24 VDC)

L+ (+24 VDC)

BN/1

BN/1

BK/4

BK/2

BU/3

BU/3

Load

L- (Ground)

E/E0

Output

L- (Ground)

npn-type

E1 L+ (Ground) BN/1 BK/4 BU/3

L+ (Ground) BN/1

Load L- (-24 VDC)

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Load

Load

BK/2 BU/3

Load L- (-24 VDC)

Load Output

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Types of Connection 3

Inductiv e S ens ors

Four-wire Sensors (Type A) A2 (pnp) 1 2 4 3

A (npn) L+ (+24 VDC) Load L- (Ground)

1 2 4 3

L+ (Ground) Load L- (-24 VDC)

☞ Advantage: Two types of output in one housing ☞ Disadvantage: Higher price

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