Question

What are the types of photoelectric sensor? What type of sensor might be used to detect the level or height of a stack of part blanks (we are looking for a distance measurement)? Why make this selection and how would that work?

Answer 1

1)Three Types of Photoelectric Sensors:

There are three major types of photoelectric sensors: thru-beam, retroreflective, and diffused. Each sensor has its own strengths and can be used in a variety of ways.

Thru-beam:

In thru-beam sensing, also known as opposed mode, two separate devices are used to make or break a beam. One sensor houses the light emitter while the other houses the receiver. A thru-beam sensor detects objects when an object interrupts the light beam between the two sensors.

Thru-beam sensors can be used to:

• Detect very small objects.
• Detect the fill levels inside containers.
• Detect spliced or overlapped materials.
• Detect the precise location of a specific object.
• Detect the contents of a container.
• Detect opaque objects.

The advantages of using a thru-beam sensor are that it’s the most accurate type of sensor and has the longest sensing range of the three. Thru-beam sensors are also the best choice when using them in a dirty environment. It’s important to keep in mind that there will be at least two separate parts which need to be installed in order to make this device work correctly.

Retro-reflective:

In retroreflective sensing, both the light source and the receiving device are found in the same housing. The sensor works in tandem with a reflector. The light emitted from the sensor is aimed at the reflector, which is then sent back to the light receiving element. The sensor detects the presence of an object when the light path is interrupted.

In addition to retroreflective sensing, there is polarized retroreflective sensing. Polarized retroreflective sensing features a polarized optical block which reduces the response to “hot spot” glare from a shiny surface of the detected object.

Retroreflective sensors can be used to:

• Detect large objects.
• Detect objects moving at high speeds.
• Detect reflective tape at high speeds.
• Sense a transparent (clear) glass or plastic product.

Retroreflective is a more affordable and only slightly less accurate option than thru-beam sensors. When working with clear or transparent products, retroreflective sensors are the best option. Another advantage is that retroreflective sensors only need to be wired on one side while thru-beam sensors require wiring on both sides of the device.

Diffused:

In optical proximity sensing, also known as diffuse, the light source and the receiver are housed in the same device. Diffused sensors detect objects when the light beam, emitted towards the target, is reflected back to the sensor by the target. What makes diffused sensors a great automation option is that they are more compact than typical units, as all components are in a single housing.

Diffused sensors can be used to:

• Detect multiple objects on a common conveyor system.
• Detect translucent objects.
• Detect the fill level inside containers.
• Detect the presence of parts, boxes, and web materials.
• Detect specific identifying features to determine an object’s orientation.
• Detect unwanted conditions for product inspection tasks.

Diffused sensors are the easiest to install because everything is included in a single device and is a cost-effective sensing solution. The drawbacks to diffused sensors are they are less accurate when used in position detecting than thru-beam and retroreflective sensors and they are not as effective on translucent objects. In addition, these sensors can be the most affected by color, texture, the angle of incidents, target characteristics, and dirty environments.

2)

Migatron ultrasonic sensors can precisely measure the distance to a target object. Among the advantages of ultrasonic sensors over traditional sensors is the ability to detect and measure moving objects. Ultrasonic sensors are not affected by the color of the object and they can detect small objects over long distances.

Ultrasonic sensors can measure the distance to a wide range of objects regardless of shape, color or surface texture. They are also able to measure an approaching or receding object. By using “non-contact” ultrasonic sensors, distances can be measured without damage to the object. They’re easy to use and, in many cases, can be used in place of other traditional sensors when the environmental conditions make traditional sensors unusable.

Migatron ultrasonic sensors can detect the distances to a variety of objects ranging from small spheres to large rolls of steel, and from bulk material on a conveyor belt to the liquid level in a storage tank and countless other distance measurements applications that need an ultrasonic sensor to get the job done. Ultrasonic distance measurement sensors are used in a wide array of industries like petroleum, chemical and manufacturing. Some examples of industry uses are roll diameter (either wind or unwind), bulk material conveyors and hopper/feeder level control.