At2 H 04 Proximity Selection

DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY PROXIMITY SENSORS == Selection ==

The following items should be considered in selecting a proximity sensor for a given application and control system. 

Sensing range



Sensor mounting



Electrical / Wiring System



Switching Frequency



Dimension



Connection

1. Sensing Range



Nominal sensing Distance (Sn) The rated operating distance for which the sensor is designed. It does not take into account any variations (manufacturing tolerances, temperature, voltage, etc..)



Real Sensing Distance (Sr) The real sensing distance is measured at the rated voltage (Un) and rated ambient temperature (Tn). 0.9 Sn ≤ Sr ≤ 1.1 Sn

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AT2-222 – Sensors & Fiber Optic Technology

Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY



Useable Sensing Distance (Su) The useable sensing distance is measured at the limits of the permissible variations of the ambient temperature (Ta) and the supply voltage (Ub). 0.9 Sr ≤ Su ≤ 1.1 Sr



Assured Operating Distance (Sa) This is the operating zone of the sensor and corresponds to the area in which detection of the standard metal target is certain, whatever the variations in voltage or temperature. 0 ≤ Sa ≤ 0.81 Sr

Assured Operating Distance

Sn Sa = 0.81Sn Target Assured operating distance

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Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY Hysterisis

Drop-out point Pick-up point

H Sensing distance

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AT2-222 – Sensors & Fiber Optic Technology

Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

1.1. Factors Affecting Sensing Range

1.1.1. Target Size

The ideal target should have two sides equal to the diameter of the sensor or three times the nominal sensing range, whichever is greater. The target should be approximately 1mm thick.

Bigger the target, better the sensing range.

Examples:

1.

Sensor diameter: Sn: 3 x Sn:

18mm 5mm 15mm ( < diameter)

Therefore, target should be 18x18x1mm

2.

Sensor diameter: Sn: 3 x Sn:

18mm 8mm 24mm ( > diameter)

Therefore, target should be 24x24x1mm

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AT2-222 – Sensors & Fiber Optic Technology

Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

1.1.2.Target Material

Material

Approximate Reduction Factor

Mild Steel

1.00

Aluminum Foil

1.00

Stainless Steel

0.85

Aluminum

0.40

Copper

0.30

Brass

0.3

The sensing range is better with material that contains more ferrous components.

2. Sensor Mounting

2.1. Flush (or shielded) Mountable

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Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

2.2. Non-Flush (or unshielded) Mountable

Lateral Actuation

Axial Actuation

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY 3. Electrical / Wiring System



Wire types:

DC type (10…58V)

AC type (20…264V)

2-wire 3-wire 4-wire

2-wire 3-wire 4-wire

AC/DC type 2-wire

3.1. - Connection to the load:

3.1.1.2-wire sensors



Load = PLC Input Interface

+ 24V

I0,12

Output (with current)

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- 0V

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY



Load = Relay

Power supply module

+ 24V

-0V

A1 -KA1 A2

3.1.1.1. Residual/leakage current In the “OFF” state (i.e. when no target is present), there is a small leakage current (mA) flowing through the load. According to the specification of certain PLC, this amount is enough to generate a false signal (i.e. no target, but signal received)

(+) (-) Load mA

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Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY Comparison between limit switch & proximity sensor :

+24V dc

-0V dc

Mechanical Limit Switch

Current (mA) Load

0 S1

Proximity Sensor

Current (mA) Load

7 S1

3.1.1.2. Voltage drop (2-wire sensors) In the “ON” state (i.e. when target is present), there is a voltage drop across the sensor (some volts). Sometimes the voltage drop is important that the remaining voltage is not enough to activate the load.

(+) Vd (-) Load

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY Comparison between limit switch & proximity sensor :

+24V dc

-0V dc

Mechanical Limit Switch Load S1 24 Voltage (V) Proximity Sensor Load S1 20 Voltage (V)

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

3.1.1.3.Wiring to PLC TSX 17-20



A sensor connected to channel number 21 – I 0,21 (details for color coding refer to the data sheet delivered with the sensor)

24V DC Inputs

0.25A

0V 24V

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

21

2-wire proximity sensor

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

3.1.2.3-wire sensors (DC type)

3.1.2.1.PNP (or Current Sourcing or Positive-Switching)

BN

(+)

BK

Load

(-)

BU

3.1.2.2.NPN (or Current Sinking or Negative-Switching)

BN

(+) Load

BK

(-)

BU

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY



Load = relay (PNP) BN BU Power supply module

+ 24V BK -0V

A1 KA1 A2



Load = PLC (input negatif logic)

+ 24V BN BK I0,12 BU

PLC

- 0V

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY



Load = PLC (input positif logic)

+ 24V BN

PLC BK I0,12

BU

- 0V

3.1.2.3.Wiring to PLC TSX 17-20



A sensor connected to channel number 21 – I 0,9 (details for color coding refer to the data sheet delivered with the sensor)

24V DC Inputs

0.25A

0V 24V

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

21

3-wires proximity sensor PNP

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Chap. 4 – Proximity Sensors : Selection

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY 4. Switching Frequency

Switching frequency is the rate at which a sensor can turn on and off per second and is measured in Hertz (Hz).

The spacing between targets should be twice the width of the target. The width of the target should be equal to or greater than the diameter of the sensor face.

D

2xD

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY 5. Dimension The sensor dimension(size) to be selected depends on the space constraint.

6. Connection

Three types of connection: 

Pre-wired with specific length provided by the manufacturer.



Female connector. 



To purchase the male connector with specific length provided by the manufacturer.

Screw 

To use our own wire. We are not limited by any specific length.

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AT2-222 – Sensors & Fiber Optic Technology

Chap. 4 – Proximity Sensors : Selection

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