7232019 Sorting Out Sensors _ Sensors Content From Machine Design

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Jun 26 2015

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Sorting Out Sensors

Here are some simple guidelines for selecting proximity capacitance and

photoelectric sensors for machine-automation applications

Andrew Waugh AutomationDirect | Machine Design

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Proximity capacitance and photoelectric sensors play an important role in the robust

control of industrial machines To select the proper sensor for a given job engineers

HOME gt TECHNOLOGIES gt SENSORS gt SORTING OUT SENSORS

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should start with a clear understanding of the application requirements sensor

specifications and installation demands Herersquos a look at the importance of factors like

sensing distance environmental effects connectivity concerns and mounting options

Proximity capacitive and photoelectric sensors are available in a variety of form factors

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Sensing Basics

All sensor applications have certain specific needs and a good place to start when

selecting a sensor is to review basic sensor selection criteria Users need to determine

bull Targets the sensor must detect

bull Objects and backgrounds the sensor must not detect

bull The best sensing technology for detecting only the targets

bull Available mounting space and restraints

bull Sensor form factor

bull Electrical requirements

bull Cabling requirements

bull Mounting requirements (see Sensor Mounting Considerations)

Engineers must first understand and identify targets and backgrounds Targets are the

objects parts ink marks or empty spaces the sensor must detect Backgrounds are

everything else that should not be detected and sometimes take the same form as the

aforementioned targets For example the target could be a brown cardboard box

traveling on a conveyor while the background might be an empty space or a worker

walking next to the conveyor

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Next select the best type of sensor that detects the target while ignoring the background

The installation environment and other constraints may affect this decision

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7232019 Sorting Out Sensors _ Sensors Content From Machine Design

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Key differences in sensing technology drive selection as engineers must consider what is

sensed and how it is being sensed Sensing distance and environmental effects also help

determine the final choice of sensor

Proximity Sensors

Inductive proximity sensors generate a magnetic field from an inductive coil which is

disturbed when a ferrous target is present Standard inductive sensors only detect ferrous

objects but they do so consistently and repeatably with little interference from ambient

elements Unfortunately these sensors only detect metal and some metals such as

stainless steel reduce sensing distance

This inductive proximity switch detects the position of an access gate and isnrsquot affected by environmental

conditions

Proximity sensors have sensing ranges from lt1 to 120 mm with longer ranges requiring

Design EngineeringEssentials

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Equipment

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larger sensors For example sensors with a sensing range of 2 to 25 mm are supplied in 8

to 30 mm diameter housings respectively

Photoelectric Sensors

Photoelectric sensors use light to detect objects They emit and receive light at certain

wavelengths infrared visible red or laser light The emitter and receiver may be in one

housing (common in diffuse and retroreflective configurations) or in two separate

housings (common in through-beam configurations) Photoelectric sensing is quite

versatile as these sensors can detect very small objects made of many different material

types at considerable distances

However photoelectric sensors can be influenced by ambient conditions and many

require programming during installation to optimize operation These sensors are the

most sensitive to dirt and debris which can cause false triggers by interfering with the

operation of the emitter and receiver

The Essentials of Mechanical Systems

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7232019 Sorting Out Sensors _ Sensors Content From Machine Design

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With up to four meter sensing distance this rectangular polarized reflective photoelectric sensor is a reliable

option for sensing parts on a conveyor

On the other hand photoelectric sensors have the broadest sensing range With laser light

they can detect objects just a few microns thick A photoelectric laser sensor can also be

configured to detect a target whether positioned close to or far from the target due to thepower of a focused laser beam Less-expensive infrared and visible red photoelectric

sensors have sensing ranges from 100 mm with diffuse beam and up to 50 m with

through-beam

Capacitive Sensors

Capacitive sensors essentially look for the dielectric or density in a sensing area They can

detect almost any object but fare better with high-density objects Capacitive sensors are

ideal for sensing levels of liquids or bulk dry materials The switching threshold can beadjusted to ldquotune outrdquo items that should not be detectedmdasha plastic tank wall or a

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 712

cardboard box for example These sensors can be influenced by ambient materials and

have a relatively small sensing range

Capacitive sensors generally have sensing ranges less than 60 mm although this distance

is strongly influenced by the targetrsquos dielectric value

Proper adjustment of this capacitive sensor provides reliable liquid level detection in this chemical dispense

application

Connection Options

Sensors commonly connect to controllers such as PLCs or PLC-based PACs Electrically

most modern sensors use low-voltage dc control power typically 24 V dc 120 V ac is also

available Discrete sensors primarily provide solid-state positive-to-negative (PNP) or

negative-to-positive (NPN) switching outputs and analog sensors commonly have 0- to

10-V or 4- to 20-mA outputs

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 812

Most sensors require a specific switching type either PNP or NPN However some sensors

can be modified for either type as well as for other options These sensors let

programming switch configuration or wiring of the device determine the switching type

at the time of installation Similar options are available for normally open and closed

switching states

Whether the connection is to the sensor or a photoelectric sensor amplifier a variety of

cabling options are available Prewired cables have the cable molded into the sensor This

usually is the least expensive option and simplifies purchasing Another benefit is the

molded cable works well with small sensors as it permits mounting in tight spaces

However prewired cables are restricted to available lengthsmdashfor the most part

approximately 2 to 5 meters When the sensor fails the cable must be rerun and secured

increasing installation time

Quick-disconnect cables have become an extremely popular choice These cables let

technicians add a cable of any length or material independent of the sensor Onceinstalled changing failed sensors is quick and simple But while quick-disconnect cable

options are plentiful they can add cost and complicate the purchasing process

Quick-disconnect plugs are becoming an industry standard Precut 2- to 15-m length

cables are typically available in axial and right-angle configurations with M8 or M12 size

screw-lock connectors on one end and flying leads at the other end Regardless of the

sensor selected the specified cable must work with the electrical configuration of the

sensor For example M8 and M12 connectors commonly come in 3- and 4-pole

configurations for sensors The number of pins must also be carefully specified

Application Guidelines

When properly specified most sensors can function in a variety of applications However

although there is much overlap in sensor application there are cases where one sensor

technology works better than the others

For example sensing end-of-travel of a pneumatic or motor-driven actuator and sensing

metal objects are common applications for an inductive proximity switch Once a

premium product these simple and robust devices are some of the most commonly used

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 912

today due to more competitive pricing If there is a ferrous target within a close distance

the inductive proximity sensor is the best choice due to its rugged design and minimal

effects from outside influence Common uses include detecting presence of a metal part

conveyor pallet or gear teethmdashor detecting actuator movement and home position

Photoelectric sensors are versatile sensors which work well in a wide range of

applications Common uses include sensing part presence in a fixture or sensing parts on

a conveyor Using the precision of a laser even small printed circuit board components

can be detected It is also possible to measure height of an object from meters away

Detecting print marks on a high-speed labeling machine or counting bottles on a filling

line are common uses for standard photoelectric sensors However placing the sensorunder water or where it may be splashed with oil or process fluid can cause sensing

issues

A key feature of capacitive sensors is the ability to see through paper plastic a nd

cardboard boxes These sensors can also sense liquid presence or detect an object

traveling through a liquid Counting machined brass fittings passing the sensor while

submerged in cutting fluid is feasible with a capacitive sensor but not with other types

This adjustability permits detection of a variety of liquid and solids including water oil

chemicals powders a nd grains

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1012

Tweet

G0

Sensing liquid level through tank walls sight glasses or in a mounting well for both high

and low level are other primary applications for capacitive sensors When mounted

closely enough the capacitive sensor can also detect fill level in boxes or opaque bottles

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Each of these sensing technologies affects sensing range (distance) While a longer

sensing range may seem like a better choice consider the application carefully to

minimize false triggering of a sensor

Andrew Waugh is Safety and Sensor Product Manager at AutomationDirect

Cumming Ga

Please Log In or Register to post comments

Related Articles

Inductive Linear Position Sensor Handles Off-Road Challenges

Sensor Sense RFID for smart position sensing

Sensor Sense Position alignment using vision sensors

Practical Tips for Specifying Sensors

2015 Engineering Compensation Survey Facing New Challenges in a Changing Industry

Search Parts

SHARE 6Recommend

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 712

cardboard box for example These sensors can be influenced by ambient materials and

have a relatively small sensing range

Capacitive sensors generally have sensing ranges less than 60 mm although this distance

is strongly influenced by the targetrsquos dielectric value

Proper adjustment of this capacitive sensor provides reliable liquid level detection in this chemical dispense

application

Connection Options

Sensors commonly connect to controllers such as PLCs or PLC-based PACs Electrically

most modern sensors use low-voltage dc control power typically 24 V dc 120 V ac is also

available Discrete sensors primarily provide solid-state positive-to-negative (PNP) or

negative-to-positive (NPN) switching outputs and analog sensors commonly have 0- to

10-V or 4- to 20-mA outputs

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 812

Most sensors require a specific switching type either PNP or NPN However some sensors

can be modified for either type as well as for other options These sensors let

programming switch configuration or wiring of the device determine the switching type

at the time of installation Similar options are available for normally open and closed

switching states

Whether the connection is to the sensor or a photoelectric sensor amplifier a variety of

cabling options are available Prewired cables have the cable molded into the sensor This

usually is the least expensive option and simplifies purchasing Another benefit is the

molded cable works well with small sensors as it permits mounting in tight spaces

However prewired cables are restricted to available lengthsmdashfor the most part

approximately 2 to 5 meters When the sensor fails the cable must be rerun and secured

increasing installation time

Quick-disconnect cables have become an extremely popular choice These cables let

technicians add a cable of any length or material independent of the sensor Onceinstalled changing failed sensors is quick and simple But while quick-disconnect cable

options are plentiful they can add cost and complicate the purchasing process

Quick-disconnect plugs are becoming an industry standard Precut 2- to 15-m length

cables are typically available in axial and right-angle configurations with M8 or M12 size

screw-lock connectors on one end and flying leads at the other end Regardless of the

sensor selected the specified cable must work with the electrical configuration of the

sensor For example M8 and M12 connectors commonly come in 3- and 4-pole

configurations for sensors The number of pins must also be carefully specified

Application Guidelines

When properly specified most sensors can function in a variety of applications However

although there is much overlap in sensor application there are cases where one sensor

technology works better than the others

For example sensing end-of-travel of a pneumatic or motor-driven actuator and sensing

metal objects are common applications for an inductive proximity switch Once a

premium product these simple and robust devices are some of the most commonly used

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 912

today due to more competitive pricing If there is a ferrous target within a close distance

the inductive proximity sensor is the best choice due to its rugged design and minimal

effects from outside influence Common uses include detecting presence of a metal part

conveyor pallet or gear teethmdashor detecting actuator movement and home position

Photoelectric sensors are versatile sensors which work well in a wide range of

applications Common uses include sensing part presence in a fixture or sensing parts on

a conveyor Using the precision of a laser even small printed circuit board components

can be detected It is also possible to measure height of an object from meters away

Detecting print marks on a high-speed labeling machine or counting bottles on a filling

line are common uses for standard photoelectric sensors However placing the sensorunder water or where it may be splashed with oil or process fluid can cause sensing

issues

A key feature of capacitive sensors is the ability to see through paper plastic a nd

cardboard boxes These sensors can also sense liquid presence or detect an object

traveling through a liquid Counting machined brass fittings passing the sensor while

submerged in cutting fluid is feasible with a capacitive sensor but not with other types

This adjustability permits detection of a variety of liquid and solids including water oil

chemicals powders a nd grains

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1012

Tweet

G0

Sensing liquid level through tank walls sight glasses or in a mounting well for both high

and low level are other primary applications for capacitive sensors When mounted

closely enough the capacitive sensor can also detect fill level in boxes or opaque bottles

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Each of these sensing technologies affects sensing range (distance) While a longer

sensing range may seem like a better choice consider the application carefully to

minimize false triggering of a sensor

Andrew Waugh is Safety and Sensor Product Manager at AutomationDirect

Cumming Ga

Please Log In or Register to post comments

Related Articles

Inductive Linear Position Sensor Handles Off-Road Challenges

Sensor Sense RFID for smart position sensing

Sensor Sense Position alignment using vision sensors

Practical Tips for Specifying Sensors

2015 Engineering Compensation Survey Facing New Challenges in a Changing Industry

Search Parts

SHARE 6Recommend

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 812

Most sensors require a specific switching type either PNP or NPN However some sensors

can be modified for either type as well as for other options These sensors let

programming switch configuration or wiring of the device determine the switching type

at the time of installation Similar options are available for normally open and closed

switching states

Whether the connection is to the sensor or a photoelectric sensor amplifier a variety of

cabling options are available Prewired cables have the cable molded into the sensor This

usually is the least expensive option and simplifies purchasing Another benefit is the

molded cable works well with small sensors as it permits mounting in tight spaces

However prewired cables are restricted to available lengthsmdashfor the most part

approximately 2 to 5 meters When the sensor fails the cable must be rerun and secured

increasing installation time

Quick-disconnect cables have become an extremely popular choice These cables let

technicians add a cable of any length or material independent of the sensor Onceinstalled changing failed sensors is quick and simple But while quick-disconnect cable

options are plentiful they can add cost and complicate the purchasing process

Quick-disconnect plugs are becoming an industry standard Precut 2- to 15-m length

cables are typically available in axial and right-angle configurations with M8 or M12 size

screw-lock connectors on one end and flying leads at the other end Regardless of the

sensor selected the specified cable must work with the electrical configuration of the

sensor For example M8 and M12 connectors commonly come in 3- and 4-pole

configurations for sensors The number of pins must also be carefully specified

Application Guidelines

When properly specified most sensors can function in a variety of applications However

although there is much overlap in sensor application there are cases where one sensor

technology works better than the others

For example sensing end-of-travel of a pneumatic or motor-driven actuator and sensing

metal objects are common applications for an inductive proximity switch Once a

premium product these simple and robust devices are some of the most commonly used

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 912

today due to more competitive pricing If there is a ferrous target within a close distance

the inductive proximity sensor is the best choice due to its rugged design and minimal

effects from outside influence Common uses include detecting presence of a metal part

conveyor pallet or gear teethmdashor detecting actuator movement and home position

Photoelectric sensors are versatile sensors which work well in a wide range of

applications Common uses include sensing part presence in a fixture or sensing parts on

a conveyor Using the precision of a laser even small printed circuit board components

can be detected It is also possible to measure height of an object from meters away

Detecting print marks on a high-speed labeling machine or counting bottles on a filling

line are common uses for standard photoelectric sensors However placing the sensorunder water or where it may be splashed with oil or process fluid can cause sensing

issues

A key feature of capacitive sensors is the ability to see through paper plastic a nd

cardboard boxes These sensors can also sense liquid presence or detect an object

traveling through a liquid Counting machined brass fittings passing the sensor while

submerged in cutting fluid is feasible with a capacitive sensor but not with other types

This adjustability permits detection of a variety of liquid and solids including water oil

chemicals powders a nd grains

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1012

Tweet

G0

Sensing liquid level through tank walls sight glasses or in a mounting well for both high

and low level are other primary applications for capacitive sensors When mounted

closely enough the capacitive sensor can also detect fill level in boxes or opaque bottles

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Each of these sensing technologies affects sensing range (distance) While a longer

sensing range may seem like a better choice consider the application carefully to

minimize false triggering of a sensor

Andrew Waugh is Safety and Sensor Product Manager at AutomationDirect

Cumming Ga

Please Log In or Register to post comments

Related Articles

Inductive Linear Position Sensor Handles Off-Road Challenges

Sensor Sense RFID for smart position sensing

Sensor Sense Position alignment using vision sensors

Practical Tips for Specifying Sensors

2015 Engineering Compensation Survey Facing New Challenges in a Changing Industry

Search Parts

SHARE 6Recommend

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 912

today due to more competitive pricing If there is a ferrous target within a close distance

the inductive proximity sensor is the best choice due to its rugged design and minimal

effects from outside influence Common uses include detecting presence of a metal part

conveyor pallet or gear teethmdashor detecting actuator movement and home position

Photoelectric sensors are versatile sensors which work well in a wide range of

applications Common uses include sensing part presence in a fixture or sensing parts on

a conveyor Using the precision of a laser even small printed circuit board components

can be detected It is also possible to measure height of an object from meters away

Detecting print marks on a high-speed labeling machine or counting bottles on a filling

line are common uses for standard photoelectric sensors However placing the sensorunder water or where it may be splashed with oil or process fluid can cause sensing

issues

A key feature of capacitive sensors is the ability to see through paper plastic a nd

cardboard boxes These sensors can also sense liquid presence or detect an object

traveling through a liquid Counting machined brass fittings passing the sensor while

submerged in cutting fluid is feasible with a capacitive sensor but not with other types

This adjustability permits detection of a variety of liquid and solids including water oil

chemicals powders a nd grains

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1012

Tweet

G0

Sensing liquid level through tank walls sight glasses or in a mounting well for both high

and low level are other primary applications for capacitive sensors When mounted

closely enough the capacitive sensor can also detect fill level in boxes or opaque bottles

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Each of these sensing technologies affects sensing range (distance) While a longer

sensing range may seem like a better choice consider the application carefully to

minimize false triggering of a sensor

Andrew Waugh is Safety and Sensor Product Manager at AutomationDirect

Cumming Ga

Please Log In or Register to post comments

Related Articles

Inductive Linear Position Sensor Handles Off-Road Challenges

Sensor Sense RFID for smart position sensing

Sensor Sense Position alignment using vision sensors

Practical Tips for Specifying Sensors

2015 Engineering Compensation Survey Facing New Challenges in a Changing Industry

Search Parts

SHARE 6Recommend

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1012

Tweet

G0

Sensing liquid level through tank walls sight glasses or in a mounting well for both high

and low level are other primary applications for capacitive sensors When mounted

closely enough the capacitive sensor can also detect fill level in boxes or opaque bottles

Download this article in PDF format

This file type includes high resolution graphics and schematics when applicable

Each of these sensing technologies affects sensing range (distance) While a longer

sensing range may seem like a better choice consider the application carefully to

minimize false triggering of a sensor

Andrew Waugh is Safety and Sensor Product Manager at AutomationDirect

Cumming Ga

Please Log In or Register to post comments

Related Articles

Inductive Linear Position Sensor Handles Off-Road Challenges

Sensor Sense RFID for smart position sensing

Sensor Sense Position alignment using vision sensors

Practical Tips for Specifying Sensors

2015 Engineering Compensation Survey Facing New Challenges in a Changing Industry

Search Parts

SHARE 6Recommend

7232019 Sorting Out Sensors _ Sensors Content From Machine Design

httpslidepdfcomreaderfullsorting-out-sensors-sensors-content-from-machine-design 1112

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