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.

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. 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.

Fork sensor, effective beam_emitted beamTraditional 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.

Fork Sensors, the Best Choice for Range, Reliability, Ease of Installation

Photoelectric sensors are a staple within many industries when it comes to automation thanks to their non-contact detection over longer ranges than many other sensing types. Also available in a variety of housing types and protection classes to meet the specific demands of an application, they offer manufacturers many different variants and models. The range of styles can make selecting the perfect photoelectric sensor for your specific application challenging. This post highlights the benefits of through-beam sensors and why fork sensors specifically, are often the ideal sensor for the job.

Through-beam sensors can detect anything, regardless of color, texture or reflectivity. This makes them highly efficient in any application where material or parts need to be detected during the process. They require an emitter and receiver. The emitter sends a light beam toward the receiver. When this light beam is blocked, the sensor will trigger. A common example of this is the sensor system on a garage door that detects obstructions and keeps the door from closing. (The software can also inverse this, so the sensor triggers when the light beam is not obstructed. Read more about these light-on/dark-on modes).

Traditional Through-Beams vs. Fork Sensors

Through-beam photoelectric sensors are simple technology that are non-contact, reliable and can operate over distances up to 100 meters, making them a go-to for many applications. But they aren’t without fault. Because the emitter and receiver are typically in separate housings, the two parts must line up perfectly to work. This alignment takes extra time during assembly and is prone to problems in the future if the emitter or receiver move,  even slightly. Machine vibrations can cause a misalignment.

Fork sensors, also called C slot or U slot sensors, incorporate both the emitter and the receiver into a single body, providing the benefits of a through-beam sensor without the installation issues.

This allows for reduced installation and maintenance time of the sensor in several ways:

    • Mounting a single sensor instead of two
    • Half as many cables needed for networking
    • No touchy alignment needed when installing the sensor
    • No maintenance needed re-aligning the sensors in the future

Photoelectric fork sensors come with sensing windows widths up to 220 mm and a range of light sources to accommodate many application needs. Check them out the next time you are considering a photoelectric sensor and see if they’re the best choice for your application.

Which Photoelectric Sensor Should I Be Using?

There are many variations within the category of photoelectric sensors, so how do you select the best sensor for your application? Below, I will discuss the benefits of different types of photoelectric sensors and sensing modes.

Through Beam

Through beam sensors consist of an emitter and a receiver. The emitter produces a beam of light, while the receiver identifies whether that light is present or not. So, when an object breaks the beam, an output is triggered by the receiver. Some of the advantages of using the simple through beam technology is that, unlike some of the other photoelectric sensors, it doesn’t matter the color, texture or transparency of your target.

Retroreflective

What if you would like to have a through beam sensor, but don’t have enough room for two sensor heads in your application? Retroreflective sensors have an emitter and receiver within one housing and use a high-quality reflector to reflect the light beam back to the sensor head. This allows for easy connection of just one sensor head, but it doesn’t have the range of your typical through beam sensor. When using these types of sensors, you must factor in how small or reflective your target material is. If you are trying to sense a highly reflective material, then the light reflected back to the receiver could cause the sensor to think an object is present. If you are having these problems, but still want to use a retroreflective sensor, then you should consider versions with a polarizing lens. These lenses make the sensors insensitive to interference with shiny, reflective material.

Fork

Fork sensors include the transmitter and receiver in one housing, and they are already aligned. This saves time and energy during set up. Fork sensors are fantastic for small component and detail detection.

Diffuse

If you don’t have room for a sensor head on each side of your application or even a reflector, or you have had trouble with the alignment of a retroreflective sensor, a diffuse sensor may be a good choice. Diffuse sensors use technology to be able reflect light off the material and back to the sensor. This eliminates the need for a second device or reflector. This significantly reduces set up. You can simply place your target material in front of the sensor and teach it to that point. Once your object reaches that point, the light will be reflected back to the sensor, producing the output. While they are simpler to install, they also have a shorter range compared to through beam sensors and may be affected by your material’s color or the reflectivity or your background… Unless, you have a diffuse sensor with background suppression.

Background Suppression

Diffuse sensors have an emitter and receiver in one housing. In diffuse sensors with background suppression, the emitter and receiver are at a fixed angle so that they intersect at the position of your target material. This will help narrow the operating area (area in which your target material will be entering) and not let reflective material in the background have an influence in your detection.

Conclusion

Photoelectric sensors are simple to use when you need non-contact detection of a material’s presence, color, distance, size or shape, and with their various types, housing and sizes, you can find one that is ideal for your application.

Fork Sensors – The Ideal Through-Beam

Through-beam sensors are a true time proven solution to many photoelectric applications.  These sensors can detect anything regardless of color, texture or reflectivity, all that needs to happen is the light beam needs to be blocked.  Add an optional aperture and you can detect even the smallest of parts.  With the various light sources available and you can detect small parts (with a laser light) or blast through the harshest of environments with an infrared light source.  These sensors come in several housings or styles for instance tubular (as small as 8mm), block, fiber optic and the fork style sensor.

Through-beam sensors are used in applications that require sensing ranges from 2 millimeters to 100 meters and in some cases longer.  Since these sensors require a light emitter and a receiver that are in separate housings, you have to mount and wire each component separately.  Once mounted you have the task of aligning the receiver to the emitter, which could be a tedious task.  Just imagine trying to line up the devices that use an infrared light source with a working range of 50 meters or even 150 millimeters.

forksensorFork sensors, also referred to, as c slot or u slot, are the ideal through-beam sensor.  First, they are self-contained in one housing so there is no need to align the emitter and receiver.  This is important because in the harsh environments if the sensor is bumped or jarred the receiver and emitter stays aligned.  Secondly, the housings are typically metal offering an extremely robust sensor.  Third, since the sensor is integrated into one housing installation is much easier, one part to mount and only one wiring connection.  These sensors are available from 5mm to 220 mm wide openings.

Continue reading “Fork Sensors – The Ideal Through-Beam”

Timing is everything – Which light is the right light?

Shortly after posting my last blog, Which light is the right light, I had a customer call with a problem in a machining cell.  They are using a self-contained through-beam sensor, in the form of a fork sensor, with a red light source. They required a small light spot to detect a tool.  As in most machining centers, there is a lot of coolant flying around in the cell and a fine mist in the air.  When water based coolants dry, they separate and leave a white film on surfaces, including photoelectric lenses.  This customer had to shut down their cell and clean off the lens at least once per shift, which was costing them production, time, and money because of false signals.

As we spoke on the phone, I suggested that they use the infrared version because we can burn through the contamination in the environment, in this case the film left behind from the coolant.  The customer wanted some sort of idea of how much residue we could burn through so I did some simple testing and sent him the following pictures.  Picture 1 is a heavy dusting, of all things, coffee creamer.  Picture 2 is a nice dollop of grease from a grease gun and picture 3 is a film of hand cream.

Continue reading “Timing is everything – Which light is the right light?”