Things to Consider When Choosing a Magnetic Sensor
Magnetic sensors compared to traditional mechanical switches have the following advantages:
• Low cost
• Contacts are protected against dust, oxidization, and corrosion because they are sealed in hermetic glass bulbs and inert gas; contacts are activated by means of a magnetic field rather than mechanical parts
• Special surface treatment of contacts assures normal electrical conditions in many working cycles.
• The reed magnetic switches offer many electrical and mechanical characteristics together with various output functions.
• When in normally open (N.O.) mode, the open reed contact closes as the magnet approaches; they are supplied with two wires.
• When in the selectable changeover (S) mode, both N.O. and N.C. functions are made available by means of a single glass bulb. Placing the magnet near or far from the reed switch activates the two different positions; they are supplied with three wires: one common, one N.O., and one N.C.
• In the bistable function, an internal magnet pre-polarizes the reed contact but does not close them. When placing a magnet with the same polarity close to it, the magnetic field is intensified, causing the contact to close and remain that way even when the operating magnet moves away from the sensing area. The contact opens again when a magnet with opposite polarity, compared to the magnetic field, is placed close to it.
The lifespan of a magnetic proximity sensor, at low values of tension and current, depends on the mechanical characteristics of the contact. At high tension and current values, the characteristics of the load influence the lifespan. In these cases, it is suggested to apply a form of external protection at the sensor’s output.
