Magnetic sensors

Reed switches are magnetically-actuated proximity sensors. They consist of two contact blades in a small glass tube filled with protective gas. The action of a magnet causes the contact between the two blades to close so that an electrical current can flow (cf. Figure 4.1). In the case of reed switches that work as N/C contacts, the contact blades are preloaded using small magnets. This preload is overcome by the then much stronger switching magnet.

Reed switches have a long service life and a short switching time (approx. 0.2 ms). They are maintenance free, but must not be used in areas with strong magnetic fields (e.g. in the vicinity of resistance welders or CAT scanners).