Proximity sensors are a subgroup of position sensors. Unlike many position sensors, proximity sensors do not need to touch their target to function.
For example, in a bottling plant, beverage bottles used to trip a mechanical limit switch during counting. Now a proximity switch can provide the same information without using a mechanical device that will eventually wear out.
A proximity sensor is used to detect the physical presence or absence of a target object within their nominal range.
Because they don't require touch, and usually have no moving parts, proximity sensors should have long lifespans without intrinsic reliability issues. This makes them very popular for all kinds of automation. You might find a proximity sensor
As we examine these broad categories of sensors, we'll also look at some vulnerabilities of each sensor type. In many cases, sensor manufacturers have come up with clever methods to reduce these vulnerabilities, often by using additional components and specific setups tailored to the exact sensing job at hand. So when learning about generalized flaws in each sensor type, remember that these issues can sometimes be mitigated.
Inductive proximity sensors require ferrous metal in their targets. (Ferrous metals contain iron.) Not sure which metals are ferrous? Here are some common ores and alloys.
An inductive proximity sensor generates an electromagnetic field in front of the active face.
If a ferrous item enters the sensor's nominal range, the field shrinks. This triggers a response from the sensor that the target has been detected. The black wire carries the sensor signal — voltage if the sensor is Normally Open (NO), or no voltage if the sensor is Normally Closed (NC).
(Don't worry about the details in the transparent state, unless, of course, you want to!)
The schematic symbol for a proximity sensor uses the standard sensor square envelope, packed with very specific information. Let's look at what each of the 4 symbols inside are telling us.
This symbol indicates a proximity sensor.
This symbol tells us whether the sensor is PNP or NPN.
The elemental symbol for iron indicates that this is an inductive sensor.
This symbol tells us whether the sensor is Normally Open or Normally Closed.
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