What is a Photoelectric Sensor?

Photoelectric sensors are a collection of non-contact sensing devices that are one of our key offerings at TRI-TRONICS. Now more reliable than ever, thanks to technological advancements dating back to the 1970’s, photoelectric sensors have revolutionized machine automation in manufacturing and packaging facilities worldwide.

Industrial automation applications can be especially demanding, which is why we pride ourselves on providing the highest performance photoelectric sensors available in today’s market. In order to select the right sensor for your industrial application, it is important to understand how photoelectric sensors work and what makes different types of sensors unique. In today’s blog post we’ll be going over the three major types of sensors that we offer here at TRI-TRONICS, each developed to suit a different set of environmental constraints. Before we get into that, let’s start by going over how a photoelectric sensor operates.

How Photoelectric Sensors Use Object Position Feedback

There are three key process steps to how photoelectric sensors work:

1.     A light source from the sensor emits a beam of light.

2.     The light interacts with an object that passes through its path.

3.     The sensor detects variations in the light.

In a general sense, those are the fundamentals upon which all types of photoelectric sensors operate. Although those three distinct steps happen in every sensor, they are hardly discrete to the human eye. Our sensors perform these three operations over and over again at incredible speeds in just micro-seconds. This speed is unmatched by our competitors and is one of the many reasons to choose TRI-TRONICS for your photoelectric sensor needs.

There are two major categories of sensing modes based on how they get position feedback on objects: beam make mode and beam break mode. In beam make mode, the reflection of a photoelectric sensor’s light beam is at its brightest when an object is introduced to the light path. Conversely, beam break mode is when the reflection is at its darkest when an item is introduced to the light path. In both cases, the sensor receiver identifies the contrast between the state in which an item is present versus when it is not. That identification of contrast is key to performance in photoelectric sensors.

Whether you will use a sensor in beam make or beam break mode depends on the kind of object it will be sensing. Object size, material, opacity, and even color can all have an effect on the level of contrast between itself and its background, the difference of which is crucial to effective sensing.

Struggling with contrast in your sensing applications? TRI-TRONICS has the right experience to develop an effective solution for you. Contact us today to learn more.

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3 Major Types of Photoelectric Sensors

When it comes to photoelectric sensing, there are three major types of sensors to take into account. Each type comes with its own benefits and drawbacks in terms of initial setup cost and overall sensing reliability.

No matter which type you choose, each sensing method covered below can be achieved with a wide selection of lenses and fiberoptic light guides.

Diffuse-Reflective Sensors

A diffuse-reflective sensor best exemplifies the beam make mode of sensing. In a diffuse-reflective sensor, both the emitting light source and the contrast sensor are housed in the same casing and no external reflectors or sensors are required. This type of photoelectric sensor can operate in optical proximity mode or convergent mode.

Optical proximity mode is a mode in which light is further diffused as the distance from the source increases. In contrast, convergent mode- also sometimes called V-axis mode- is characterized by a beam that is most highly focused just a few inches away from the light source. If your sensor setup options are very limited, a diffuse-reflective sensor could be a good choice, considering both the light source and the sensor are housed together. This option is most effective in cases where there is already a high contrast between the object and its background.

Retro-Reflective Sensors

Like diffuse-reflective sensors, retro-reflective sensors contain a light source and a receiver in the same housing. However, this type of sensor does require an external reflector. What makes retro-reflective sensors different is that the light beam travels across a set axis to the reflector and is then directed along the same axis back to the receiver. This is possible thanks to a dual lens system, or a bifurcated fiber optic light guide.

Retro-reflective sensors employ the beam break mode of photoelectric sensing. When an object passes through the light beam, it blocks the path between the light and the reflector; therefore, light is not returned to the receiver, and that contrast triggers the sensor to switch its output.

Although this sensing method is very effective in most cases, high-shine objects can sometimes act as a reflector themselves and unintentionally fail to trigger the sensor as they pass through the light beam. This can be solved by polarizing the light beam; however, this reduces the effective operating distance of the sensor.

Thru-Beam Sensors

Lastly, we have thru-beam sensors. Unlike the two previous sensor types, thru-beam sensors do not house the light source and the receiver in the same unit. In this case, a light source and a sensor are installed on opposite sides of an object path (such as a conveyor belt) to sense when an object passes between the two of them. This method of sensing eliminates the issues associated with highly reflective objects, although it is substantially more expensive than both diffuse-reflective and retro-reflective sensors.

While the initial investment may be higher, thru-beam sensing is undoubtedly the most reliable sensing method for opaque objects of all kinds. As we say here at TRI-TRONICS: when opaque, go beam break.

Now you should have a clear idea of the major types of photoelectric sensors we offer here at TRI-TRONICS, and what sets each of those sensors apart from each other. Which type of sensor would be best for your operations? TRI-TRONICS is eager to hear from you.

Ready to learn more about your sensor of choice? Contact TRI-TRONICS today to connect with one of our photoelectric sensing experts!