self-contained sensor Archives - AUTOMATION INSIGHTS

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.

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.