Back to the Basics – Which light is the right light?

The emitters in photoelectric sensors give off a light that is received by a separate receiver, reflected back to a receiver by a reflector, or reflected back by the object itself. Back in the good ‘ol days, the light source was incandescent, however they ran hot and tended to have a short life. Now solid state devices, LED’s, are used because they use less energy, they can be pulsed very rapidly and you can use different colors for special applications.

Typically we refer to light sources in photoelectrics as red light, infrared, and laser. All have their advantages and disadvantages, and picking the wrong light source, can either make your application successful, or let’s say less desirable than you had hoped.

Red light photos are probably the most favored because they are easy to set-up, and confirmation that the sensor is working properly is easy since you have a bright light that you can focus on your target. However, it is important that you aim the sensor correctly if you have the sensor installed near an operator as the light can be rather annoying if it is in their eyes.

Recently laser photoelectric sensors have become more popular. Unfortunately, many think that since they are laser they are the most powerful light sources available. Lasers obviously are visible which aids in setup and alignment. They provide a consistent wavelength or color and best of all a small light beam diameter that is perfect for small part detection and precise measuring. One of the disadvantages of lasers is that they are more costly than standard red light sensors. If you are using a laser for measuring make sure your light beam is larger than any pits or crevasses in your part to insure your measurement is as accurate as possible. If you decide to use a laser insure that they are installed so that the laser is not aimed into an operator or passerby’s eyes.

A lot folks think that lasers provide the most power for a photoelectric sensor however, they do not. Although the light beam is small and concentrated, they can be easily interrupted by airborne particles. So, if there is dust or mist in your environment the light will be scattered making your application less successful than desired. Infrared LED’s provide the most power with the least amount of heat and is the most efficient light source and provides some of the longest ranges. 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.

So, which light source do I use? The answer is…it depends on your application, environment, target and so forth. Once you have decided on your light source be sure to test it for the most successful results.

Back to the Basics – What Makes Background Suppression Sensors Capable of Solving Difficult Applications?

Diffuse photoelectric sensors have been and are used to successfully solve numerous applications in automation.  However, there are some applications that are too difficult or impossible to solve with standard diffuse sensors.  In some cases, these difficult applications can be solved with a background suppression sensor that is also based on the diffuse operation principal.  So the question is then raised, what makes the background suppression sensor capable of solving these difficult applications?

 This may be a good time to review…  Diffuse sensors operate on the principal that when a light source is shined on a surface, the light is scattered or diffused in many directions. A small portion of the light is reflected back to the sensor receiver. The receiver used in this style of sensor is designed to be sensitive to a smaller or larger amount of light, depending on the sensor configuration, that is reflected back from the target surface.  There are a number of factors that affect how well diffuse sensors operate including, but not limited to, surface finish, color, texture or surface irregularities, target size, dirty or dusty environment and the background of the application.

Background sensors, sometimes referred to as BGS, actually have two receivers built into the sensor.  These two receivers detect the angle of the light reflected back from the target, referred to as triangulation.  If the target is between the focal point and the receiver the light is reflected to one receiver and if the target is beyond the focal point the light is reflected to the second receiver.  The sensor compares the amount of light on each receiver and sets the output accordingly.

Applying Sensors in Real Applications

Whenever you are providing sensor training or even talking with someone about sensor inevitably, you will be asked about the applications where they are used. Try as you may, it’s sometimes difficult to explain the various ways sensors are used to solve the multitude of applications that exist.

Recently, one of my colleagues brought an interesting article to my attention that I am passing on in this blog post. Check out this article on Sensoring for In-Die Tapping. The author explains the application and provides possible solutions varying from mechanical sensors, photoelectrics, and inductive proximity sensors. In my opinion, it is worth reading to give you another perspective on how to solve one of the many ways to use sensors. Let me know what you think! Did this give you another perspective?

A Sound Solution for Object Detection and Measurement

Ultrasonic sensors can detect objects that many traditional sensing technologies cannot because of their ability to see targets regardless of color, transparency and surface texture. Even in dusty, humid, or hazy environments, they may be the only sensor that is able to provide the desired results. Ultrasonic sensors are often used in liquid level measurement applications and detecting clear films.

Ultrasonic sensors emit a burst of short, high frequency sound waves that propagates in a cone shape towards the target. When the sound waves strike the target, they are bounced back to the sensor. The sensor then calculates the distance based on the time span from when the sound was emitted until the sound was received.

Flush or Non-Flush – What’s the Difference?

In a previous blog Flush or Non-Flush, Looks Can Be Deceiving, Jeff mentions the two common housing designs of inductive sensors, flush and non-flush. So what does this mean to you when you are applying an inductive or even a capacitive sensor?

Flush-style sensors actually have a shield that restricts the magnetic field so that it only radiates out of the face of the sensor. Flush-style, or shielded sensors, can be mounted flush in a metal bracket or even in your machine without the metal causing the sensor to false trigger. When mounting two shielded inductive proximity sensors next to each other, you should typically leave one diameter of the sensor between adjacent sensors. The shielded-style of sensor will typically have approximately one-half of the sensing distance that a non-shielded version will have. For example, a 12mm shielded inductive sensor will have a sensing distance 2mm whereas a non-shielded version will have a sensing distance of 4mm. Although shielded style sensors have a shorter sensing range they can be buried in a machine or a bracket that will offer protection against damage.

Inductive Proximity Sensor Principle of Operation

Written by: Jeff Himes

An inductive proximity sensor is a non-contact device that is used to detect a metal target.  When power is applied to an inductive proximity sensor the sensor’s coil will generate an oscillating electromagnetic field out of the face of the sensor.  This field will vary in shape and size depending on the diameter of the sensor and whether the sensor is a shielded or non-shielded model.  For example, a M12 size sensor will generate a smaller electromagnetic field than an M30 size sensor.   When the metal target gets close enough to the sensor’s face it begins to penetrate the electromagnetic field.  When this happens, eddy currents are generated on the surface of the metal target.  As the metal target gets closer to the sensor face – the eddy currents increase – which in turn decrease the amplitude of the electromagnetic field.  Once the electromagnetic field’s amplitude is reduced to a certain level – the sensor will activate indicating it has detected the metal target.  

 This explanation is a little wordy and, as in most cases, a visual demonstration can be of great help.  Watch this short video explaining the basic functionality of an inductive proximity sensor.

For more information on inductive proximity sensors, click here.

Mechanical Probe Eliminates Impact for Inductive Proximity Sensor

Written by: Jeff Himes

An inductive proximity sensor is meant to be a non-contact device.  If contact is made with the face of the sensor by its metal target – it will typically fail.  What if you want the reliability of an inductive proximity sensor – yet you want physical contact with the device too?  Is this really possible?  Yes – by using a mechanical device I call a Banking Screw.

Are Limit Switches Obsolete?

Being the “product guy” for mechanical or limit switches I am often told that I have the obsolete products. Well I am here to say that mechanicals are still around and definitely have their place in automation.

Mechanical switches, at least the ones I deal with, are precision limit switches. How can a mechanical switch be a precise device? These switches use a cam or trip dog and once the switch and cam are secured in the application, the repeatability, with a chisel plunger, can be .002mm – that’s two microns. Applications for these switches include actuators for automatic controls, positioning and end of travel for machine tools, transfer lines, transport equipment, and gantries.

Looking for some excellent online resources? Read this!

I was trying to locate some information on capacitive sensors so naturally, I turned to the World Wide Web to see what I could find. As I was looking through the search engine results, I found a link to Sensors Magazine, and a two-part article on capacitive sensors that I highly recommend you read. Capacitive Sensor Operation Part 1: The Basics and Capacitive Sensor Operation Part 2: System Optimization do an excellent job in describing the basics through what you need to consider in applying capacitive sensors.

Save Space with Miniature Rectangular Proximity Sensors

Historically the most popular selling housing style for an inductive proximity sensor has been the tubular style.  The more popular sizes tend to be M8, M12, M18 and M30.  Smaller tubular sizes of 3 mm, 4 mm, M5, and 6.5 mm are also available and have seen increased sales in the most recent years.  One issue that may affect a tubular sensor’s application is its length.  Most standard models are 50 mm to 65 mm long while some shorter body types may be in the 30mm range.  What if your application requires 1.5 to 3 mm of sensing range, but you only have 10mm of depth to allow for the sensor?  Try looking at a block or rectangular style inductive proximity sensor.