Every technology commonly in use today exists for a reason. Technologies have life cycles: they are invented out of necessity and are often widely used as the best available solution to a given technical problem. For example, at one time bronze was the best available metallurgy for making long-lasting tools and weapons, and it quickly replaced copper as the material of choice. But later on, bronze was itself replaced by iron, steel, and ultimately stainless steel.
When it comes to detecting the presence of an object, such as a moving component on a piece of machinery, the dominant technology used to be electro-mechanical limit switches. Mechanical & electrical wear and tear under heavy industrial use led to unsatisfactory long-term reliability. What was needed was a way to switch electrical control signal current without mechanical contact with the target – and without arcing & burning across electrical contacts.
Enter the invention of the all-electronic inductive proximity sensor. With no moving parts and solid-state transistorized switching capability, the inductive proximity sensor solved the two major drawbacks of industrial limit switches (mechanical & electrical wear) in a single, rugged device. The inductive proximity sensor – or “prox” for short – detects the presence of metallic targets by interpreting changes in the high-frequency electro-magnetic field emanating from its face or “active surface”. The metal of the target disrupts the field; the sensor responds by electronically switching its output ON (target present) or OFF (target not present). The level of switched current is typically in the 200mA DC range, which is enough to trigger a PLC input or operate a small relay.
In my next post, I will explain the do’s and don’ts for applying inductive prox sensors.