Tech Tip: Overview of Simple Object Detection and Sensing
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Learn about the different kinds of industrial sensors and when to use each type.
Simple object detection in automation is typically done using mechanical switches, proximity sensors and photo electric sensors. Switches will be the least expensive option, but since they have moving parts, they should only be used in applications where they won't get a lot of continuous repetitive use. Proximity and photoelectric sensors don't have moving parts, so while they tend to be more expensive, they last a LOT longer. When figuring cost, realize that while switches can get by with just an ordinary pair of inexpensive copper wires, you'll need more expensive connectorized cables for these two. And if you are using a through beam photoelectric sensor where you have both a transmitter and receiver to wire, then the cabling cost for labor and materials doubles because now you have to wire both ends. Of course since proximity and photoelectric sensors tend to last a lot longer than switches, the cable cost pays for itself over time, just be ware there will be a larger up front installation cost with the proximity and photoelectric sensors. In general, switches require physical contact with the object so the object has to be within a few inches of the switch. Most Proximity sensors are also limited to just a couple inches. Photoelectric sensors, on the other hand, can detect objects out to hundreds of feet. The bottom line is if cost is an issue and you have a low cycle rate application, inexpensive mechanical switches will be more than adequate. But, if you have a high cycle rate and need the long term reliability, you definitely want to look at using Proximity sensors. You won't save any money if you have to keep shutting down the line to replace worn out switches, right? Finally, if you need to detect objects more than a few inches away, then photoelectric sensors are definitely the way to go. Could you use an ultrasonic or laser distance sensor to do object detection? Sure. Those are covered in more detail the video on distance sensing, so we aren't going to cover them here. But we should point out that the Ultrasonic proximity sensors can detect clear bottles and clear liquids, where typical photoelectric sensors will pass right through them, so Ultrasonics can still be a viable option for simple object detection, though they do tend to be more expensive. Check out the other tech tip videos in this series to learn more specifics about mechanical switches, proximity sensors and Photoelectric sensors.
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