How Capacitive, Inductive and Photoelectric Sensors Work

Hi, I’m Adam Ring with Innovative-IDM. You know, I was just teaching a class last week and a topic came up about different types of sensors that are used for industrial automation. So I thought, well, I’ll take a few minutes and go over some of the basics of how these types of sensors work.
The first thing I would like to talk about is the inductive proximity sensor, these are very widely used in automation, they’re used to sense various metal objects. So, basically any kind of metal objects that we need to know that’s present or absence or is there a part in place, is that part missing? Is an actuator retracted or extended? Anyway in which we need to sense something that is a ferrous metal we can use this.
Basically what it does, it has this tractor beam that emits from the tip of the sensor, and it’s really what we call an eddy current killed oscillator. What that means is that, there’s this electrical field generated outside the tip of this sensor, and when a ferrous object comes near-by, it actually absorbs that field and the sensor is then able to detect that there is something there and it gives us a signal.
Another type of sensor that is similar to the inductive proximity sensor is the capacitive proximity sensor. This uses a different sensing technology, in that, instead of looking for a ferrous metal object, it actually looks for a difference in the capacitance of an object. So, in other words, how much does it absorb electricity and so, a real common application for this is that we can mount this on a plastic tank that contains water. And we’re able to detect the level of water that’s inside the tank. So it can actually look through the outer surface, and see the material that’s in, as long as the capacitance properties of that material are different enough from the outer material, to where we can just tune out what that outer material is and figure out “Hey, is there something inside or not?”
Then we have another really common type of sensor that is used in automation; that’s called the photoelectric sensor. As its name implies, it basically uses light in order to detect objects. Something like this has an emitter and receiver, so it emits a light beam and it bounces off of an object and comes back to the receiver and if it sees the light, then it knows that there’s an object there. If it doesn’t get an object back, then it knows that there’s nothing there. So it’s able to easily detect when there’s an object present or absent. Real common use for these is on conveyors, if you want to detect if there’s a box moving on a conveyor, and as soon as it passes by, the photo eye reflects the light and says that object’s there. Very common use in the industry.
If you’d like to learn more about these types of sensors and others, please take a look at the Innovative-IDM knowledge base, our website is, and we’d love to share some information with you. Remember, we’re Home of the Legendary Customer Experience.

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