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Food for Thought: Should a Fork Sensor be Your First Choice?

When it comes to reliability and accuracy, there is no optical sensing mode better than the through-beam photoelectric sensor. Its reliability is a result of the extraordinary levels of excess gain – the measurement of light energy above the level required for normal sensing. The more excess gain, the more tolerant of dirt, moisture and debris accumulating on the sensor.

Excess gain comparison

The accuracy of through-beams results from a tight, well-defined sensing area. This chart shows a comparison between the popular sensing modes.

The sensing area starts with an emitted beam projected onto the receiver. The wider the emitted beam, the easier to align. Once aligned, you now have the effective beam which is basically the size of the emitter and receiver lens. The smaller the lens, the smaller the effective beam. Apertures can also be used to narrow down the effective beam.

Simple detection

A target is detected when it breaks the effective beam. The simple detection principle means these sensors can detect anything, regardless of color, texture, or reflectivity. They are generally used in applications that require a sensing range of 2mm to 100m! The simplicity of their operation and wide range make them a go-to detection solution across industries.

Traditional through-beam sensors consist of two separate pieces which must be separately mounted and wired, and perfectly aligned to work. This can be inconvenient and time consuming. But for those applications that can use an opening from 5mm to 220mm, self-contained through-beam sensors, also called fork sensors, provide the usefulness of traditional through-beams without the trouble of alignment. With the emitter and receiver in one housing, they are automatically aligned and require only half the wiring effort.

Light types

Available in four different light types – red light, pinpoint red light, infrared and laser – they can detect even difficult and tiny parts. Red light and pinpoint red light are used for most applications, while laser light is used for small part detection, as small as 0.08 mm. Infrared improves detection efforts in dirty environments.

Through-beam sensors are a go-to solution for photoelectric applications, but with tough housings, various lighting options, and the ease of installation and alignment, fork sensors should be first on your list of photoelectric sensors to consider.

Photoelectric Methods of Operation

Photoelectric sensors vary in their operating principles and can be used in a variety of ways, depending on the application. They can be used to detect whether an object is present, determine its position, measure level, and more. With so many types, it can be hard to narrow down the right sensor for your application while accounting for any environmental conditions. Below will give a brief overview of the different operating principles used in photoelectric sensors and where they can be best used.

Diffuse

Diffuse sensors are the most basic type of photoelectric sensor as they only require the sensor and the object being detected. The sensor has a built-in emitter and receiver, so as light is sent out from the emitter and reaches an object, the light will then bounce off the object and enter the receiver. This sends a discrete signal that an object is within the sensing range. Due to the reflectivity being target-dependent, diffuse sensors have the shortest range of the three main discrete operating principles. Background suppression sensors work under the same principle but can be taught to ignore objects in the background using triangulation to ensure any light beyond a certain angle does not trigger an output. While diffuse sensors can be affected by the color of the target object, the use of a background suppression sensor can limit the effect color has on reliability. Foreground suppression sensors work in the same manner as background suppression but will ignore anything in the foreground of the taught distance.

diffuse

Retro-reflective

Retro-reflective sensors also have the emitter and receiver in a single housing but require a reflector or reflective tape be mounted opposite the sensor for it to be triggered by the received light. As an object passes in front of the reflector, the sensor no longer receives the light back, thus triggering an output. Due to the nature of the reflector, these sensors can operate over much larger distances than a diffuse sensor. These sensors come with non-polarized or polarizing filters. The polarizing filter allows for the sensor to detect shiny objects and not see it as a reflector and prevents any stray ambient light from triggering the sensor.

retroreflective

Through-beam

Through-beam sensors have a separate body for the emitter and receiver and are placed opposite each other. The output is triggered once the beam has been broken. Due to the separate emitter and receiver, the sensor can operate at the longest range of the aforementioned types. At these long ranges and depending on the light type used, the emitter and receiver can be troublesome to set up compared to the diffuse and retro-reflective.

throughbeam

Distance

The previous three types of photoelectric sensors give discrete outputs stating whether an object is present or not. With photoelectric distance sensors, you can get a continuous readout on the position of the object being measured. There are two main ways the distance of the object is measured, time of flight, which calculates how long it takes the light to return to the receiver, and triangulation, which uses the angle of the incoming reflected light to determine distance. Triangulation is the more accurate option, but time of flight can be more cost-effective while still providing good accuracy.

Light type and environment

With each operating principle, there are three light types used in photoelectric sensors: red light, laser red light, and infrared. Depending on the environmental conditions and application, certain light types will fare better than others. Red light is the standard light type and can be used in most applications. Laser red light is used for more precise detection as it has a smaller light spot. Infrared is used in lower-visibility environments as it can pass through more dirt and dust than the other two types. Although infrared can work better in these dirtier environments, photoelectric sensors should mainly be used where build-up is less likely. Mounting should also be considered as these sensors are usually not as heavy duty as some proximity switches and break/fail more easily.

As you can see, photoelectric sensors have many different methods of operation and flexibility with light type to help in a wide range of applications. When considering using these sensors, it is important to account for the environmental conditions surrounding the sensor, as well as mounting restrictions/positioning, when choosing which is right for your application.

For more information on photoelectric sensors, visit this page for more information.

Imagine the Perfect Photoelectric Sensor

Photoelectric sensors have been around for a long time and have made huge advancements in technology since the 1970’s. We have gone from incandescent bulbs to modulated LED’s in red light, infrared and laser outputs. Today we have multiple sensing modes like through-beam, diffuse, background suppression, retroreflective, luminescence, distance measuring and the list goes on and on. The outputs of the sensors have made leaps from relays to PNP, NPN, PNP/NPN, analog, push/pull, triac, to having timers and counters and now they can communicate on networks.

The ability of the sensor to communicate on a network such as IO-Link is now enabling sensors to be smarter and provide more and more information. The information provided can tell us the health of the sensor, for example, whether it needs re-alignment to provide us better diagnostics information to make troubleshooting faster thus reducing downtimes. In addition, we can now distribute I/O over longer distances and configure just the right amount of IO in the required space on the machine reducing installation time.

IO-Link networks enable quick error free replacement of sensors that have failed or have been damaged. If a sensor fails, the network has the ability to download the operating parameters to the sensor without the need of a programming device.

With all of these advancements in sensor technology why do we still have different sensors for each sensing mode? Why can’t we have one sensor with one part number that would be completely configurable?

BOS21M_Infographic_112917

Just think of the possibilities of a single part number that could be configured for any of the basic sensing modes of through-beam, retroreflective, background suppression and diffuse. To be able to go from 30 or more part numbers to one part would save OEM’s end users a tremendous amount of money in spares. To be able to change the sensing mode on the fly and download the required parameters for a changing process or format change. Even the ability to teach the sensing switch points on the fly, change the hysteresis, have variable counter and time delays. Just imagine the ability to get more advanced diagnostics like stress level (I would like that myself), lifetime, operating hours, LED power and so much more.

Obviously we could not have one sensor part number with all of the different light sources but to have a sensor with a light source that could be completely configurable would be phenomenal. Just think of the applications. Just think outside the box. Just imagine the possibilities. Let us know what your thoughts are.

To learn more about photoelectric sensors, visit www.balluff.com.

Non-Contact Infrared Temperature Sensors with IO-Link – Enabler for Industry 4.0

Automation in Steel-Plants

Modern production requires a very high level of automation. One big benefit of fully automated plants and processes is the reduction of faults and mishaps that may lead to highly expensive downtime. In large steel plants there are hundreds of red hot steel slabs moving around, being processed, milled and manufactured into various products such as wires, coils and bars. Keeping track of these objects is of utmost importance to ensure a smooth and cost efficient production. A blockage or damage of a production line usually leads to an unexpected downtime and it takes hours to be rectified and restart the process.

To meet the challenges of the manufacturing processes in modern steel plants you need to control and monitor automatically material flows. This applies especially the path of the workpieces through the plant (as components of the product to be manufactured) and will be placed also at locations with limited access or hazardous areas within the factory.

Detection of Hot Metal

Standard sensors such as inductive or photoelectric devices cannot be used near red hot objects as they either would be damaged by the heat or would be overloaded with the tremendous infrared radiation emitted by the object. However, there is a sensing principle that uses this infrared radiation to detect the hot object and even gives a clue about its temperature.

Non-contact infrared thermometers meet the requirements and are successfully used in this kind of application. (The basics of this technology were discussed in a previous post.) They can be mounted away from the hot object so they are not destroyed by the heat, yet they capture the Infrared emitted as this radiation travels virtually unlimited. Moreover, the wavelength and intensity of the radiation can be evaluated to allow for a pretty accurate temperature reading of the object. Still there are certain parameters to be set or taught to make the device work correctly. As many of these infrared thermometers are placed in hazardous or inaccessible places, a parametrization or adjustment directly at the device is often difficult or even impossible. Therefore, an intelligent interface is required both to monitor and read out data generated by the sensor and – even more important – to download parameters and other data to the sensor.

Technical basics of Infrared Hot-Metal-Detectors

Traditional photoelectric sensors generate a signal and receive in most cases a reflection of this signal. Contrary to this, an infrared sensor does not emit any signal. The physical basics of an infrared sensor is to detect infrared radiation which is emitted by any object.
Each body, with a temperature above absolute zero (-273.15°C or −459.67 °F) emits an
electromagnetic radiation from its surface, which is proportional to its intrinsic
temperature. This radiation is called temperature or heat radiation.

By use of different technologies, such as photodiodes or thermopiles, this radiation can be detected and measured over a long distance.

Key Advantages of Infrared Thermometry

This non-contact, optical-based measuring method offers various advantages over thermometers with direct contact:

Reactionless measurement, i.e. the measured object remains unaffected, making it possible to measure the temperature of very small parts
Very fast measuring frequence
Measurement over long distances is possible, measuring device can be located outside the hazardous area
Very hot temperatures can be measured
Object detection of very hot parts: pyrometers can be used for object detection of very hot parts where conventional optical sensors are limited by the high infrared radiation
Measurement of moving objects is possible
No wear at the measuring point
Non-hazardous measurement of electrically live parts

IO-Link for smarter sensors

IO-Link as sensor interface has been established for nearly all sensor types in the past 10 years. It is a standardized uniform interface for sensors and actuators irrespective of their complexity. They provide consistent communication between devices and the control system/HMI. It also allows for a dynamic change of sensor parameters by the controller or the operator on the HMI thus reducing downtimes for product changeovers. If a device needs to be replaced there is automatic parameter reassignment as soon as the new device has been installed and connected. This too reduces manual intervention and prevents incorrect settings. No special device-proprietary software is needed and wiring is easy, using three wire standard cables without any need for shielding.

Therefore, IO-Link is the ideal interface for a non-contact temperature sensor.

All values and data generated within the temperature sensor can be uploaded to the control system and can be used for condition monitoring and preventive maintenance purposes. As steel plants need to know in-process data to maintain a constant high quality of their products, sensors that provide more data than just a binary signal will generate extra benefit for a reliable, smooth production in the Industry 4.0 realm.

To learn more about this technology visit www.balluff.com.

How Hot is Hot? – The Basics of Infrared Temperature Sensors

Detecting hot objects in industrial applications can be quite challenging. There are a number of technologies available for these applications depending on the temperatures involved and the accuracy required. In this blog we are going to focus on infrared temperature sensors.

Every object with a temperature above absolute zero (-273.15°C or -459.8°F) emits infrared light in proportion to its temperature. The amount and type of radiation enables the temperature of the object to be determined.

In an infrared temperature sensor a lens focuses the thermal radiation emitted by the object on to an infrared detector. The rays are restricted in the IR temperature sensor by a diaphragm, to create a precise measuring spot on the object. Any false radiation is blocked at the lens by a spectral filter. The infrared detector converts radiation into an electrical signal. This is also proportional to the temperature of the target object and is used for signal processing in a digital processor. This electrical signal is the basis for all functions of the temperature sensor.

There are a number of factors that need to be taken into account when selecting an infrared temperature sensor.

What is the temperature range of the application?
- The temperature range can vary. Balluff’s BTS infrared sensor, for example, has a range of 250°C to 1,250°C or for those Fahrenheit fans 482°F to 2,282° This temperature range covers a majority of heat treating, steel processing, and other industrial applications.
What is the size of the object or target?
- The target must completely fill the light spot or viewing area of the sensor completely to ensure an accurate reading. The resolution of the optics is a relationship to the distance and the diameter of the spot.

Is the target moving?
- One of the major advantages of an infrared temperature sensor is its ability to detect high temperatures of moving objects with fast response times without contact and from safe distances.
What type of output is required?
- Infrared temperature sensors can have both an analog output of 4-20mA to correspond to the temperature and is robust enough to survive industrial applications and longer run lengths. In addition, some sensors also have a programmable digital output for alarms or go no go signals.
- Smart infrared temperature sensors also have the ability to communicate on networks such as IO-Link. This network enables full parameterization while providing diagnostics and other valuable process information.

Infrared temperature sensors allow you to monitor temperature ranges without contact and with no feedback effect, detect hot objects, and measure temperatures. A variety of setting options and special processing functions enable use in a wide range of applications. The IO-Link interface allows parameterizing of the sensor remotely, e.g. by the host controller.

For more information visit www.balluff.com

The Foundation of Photoelectric Sensors

The foundation of a photoelectric sensor is light! Without the light you have a housing with some electronics in it that makes an interesting object to leave on your desk as a conversation starter. Is all light the same? Does the light source really matter? When do you select one over the other?

Red light or red LED light sources are the most favored as they are easy to set up and confirm that the sensor is working properly since you have a bright light that you can focus on your target. Depending on the lensing the light spot size can vary from a pin point to a spot that can be several centimeters square or round. It is important that you aim the sensor correctly if you have the sensor installed near an operator so as the light is not shining in their eyes as it can be rather irritating.

There are several misconceptions with the laser light. Many think that lasers are the most powerful light and can penetrate anything. Also there is the concern that lasers will cause damage to the human eye. Lasers in photoelectric sensors are typically available as either a Class 1 or Class 2. Class 1 lasers are safe under normal use conditions and are considered to be incapable of damage. Class 2 lasers are more powerful, however it is the normal response of human eye to blink which will limit the exposure time and avoid damage. Class 2 lasers can be hazardous if looked at for extended periods of time. In either case viewing a laser light with a magnifying optic could cause damage.

Lasers provide a consistent light with a small beam diameter (light spot) that provides a perfect solution for small part detection. Although the light beam is small and concentrated, it can be easily interrupted by airborne particles. If there is dust or mist in the environment the light will be scattered making the application less successful than desired. In some cases the sensing distance will be greater with a laser light than with a red light.

Infrared LED’s will produce an invisible, to the human eye, light while being more efficient and generating the most light with the least amount of heat. Infrared light sources are perfect for harsh and contaminated environments where there is oil or dust. Also infrared through-beam sensors are sometimes capable of “seeing through” a package or object which is sometimes preferred to solve an application. The ability to see though an object or dirt makes this light source perfect in very contaminated environments when the contamination builds up on the lens or reflector.

In all cases LED’s are modulated or turned on and off very rapidly. This modulation determines the amount of light a photoelectric sensor can create and prolongs the life of the LED. In addition, the sensor receiver is designed to look for the modulated light at the same frequency to help eliminate ambient light causing the sensors output to false trigger.

We have determined that all light sources are not the same each with their benefits and drawbacks. Selection of the light source really depends on the application as often red lights have been installed in very contaminated applications that required the power of the infrared.

If you are interested in learning more about the basics of photoelectrics request the Photoelectric Handbook or visit www.balluff.us/photoelectric.

Back to the Basics – Photoelectric Light Source

Welcome to the first in a series of getting back to the basic blogs about photoelectric sensors.

All photoelectric sensors require a light source to operate. The light source is integral to the sensor and is referred to as the emitter. Some light sources can be seen and may be of different colors or wavelengths for instance red, blue, green, white light or laser or one you cannot see, infrared. Many years ago photoelectric sensors used incandescent lights which were easily damaged by vibration and shock. The sensors that used incandescence were susceptible to ambient light which limited the sensing range and how they were installed.

Today light sources use light emitting diodes (LED’s). LED’s cannot generate the light that the incandescent bulbs could. However since the LED is solid state, it will last for years, is not easily damaged, is sealed, smaller than the incandescent light and can survive a wide temperature range. LED’s are available in three basic versions visible, laser and infrared with each having their advantages.

Visible LED’s which are typically red, aid in the alignment and set up of the sensor since it will provide a visible beam or spot on the target. Visible red LED’s can be bright and should be aimed so that the light will not shine in an operator’s eyes. The other color visible LED’s are used for specific applications such as contrast, luminescence, and color sensors as well as sensor function indication.

Laser LED’s will provide a consistent light color or wavelength, small beam diameter and longer range however these are generally more costly. Lasers are often used for small part detection and precision measuring. Although the light beam is small and concentrated, it can be easily interrupted by airborne particles. If there is dust or mist in the environment the light will be scattered making the application less successful than desired. When a laser is being used for measuring make sure the light beam is larger than any holes or crevasses in the part to ensure the measurement is as accurate as possible. Also it is important to ensure that the laser is installed so that it is not aimed into an operator or passerby’s eyes.

Lastly, the infrared LED will produce an invisible, to the human eye, light while being more efficient and generating the most light with the least amount of heat. Infrared light sources are perfect for harsh and contaminated environments where there is oil or dust. However, with the good comes the bad. Since the light source is infrared and not visible setup and alignment can be challenging.

LED’s have proved to be robust and reliable in photoelectric sensors. In the next installment we will review LED modulation.

You can learn more about photoelectric sensors on our website at www.balluff.us

Tag: infrared

Food for Thought: Should a Fork Sensor be Your First Choice?

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Photoelectric Methods of Operation

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Imagine the Perfect Photoelectric Sensor

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