Reed Switch Contact Protection
When a reed switch is to be connected to an inductive load or a load where surge current or in-rush current flows (such as a capacitive load or a lamp load), contact protection circuits are required. This board displays some of the commonly used circuits.
7 Pins
·11y
When a reed switch is used with an electromagnetic relay or solenoid, the energy stored will cause an inverse voltage when the reed contacts break. The voltage, although dependent on the inductance value, sometimes reaches as high as several hundred volts and becomes a major factor to deteriorate the contacts. This circuit provide inductive load protection for the reed switch.
When a standard reed switch is used to switch a tungsten filament lamp, the resistance of the cold filament is very small before it is switched on and increases after switching on, followed by lighting with a steady-state current. This circuit is recommended. R = Parallel Resistance By connecting R, the filament is heated and its resistance made higher R < Filament resistance / 3
When a capacitor is connected in series or in parallel with a reed switch in a closed circuit, the in-rush current which flows during charge and discharge of the capacitor, will cause deterioration of the reed contacts. This Circuit is without contact protection. The energy stored in capacitor C will cause the rush current (Is) when the contact closes.
Protection Circuits for Reed Switches
When a reed switch is connected to a load by cable, over a long distance, static capacitance caused by the cable will affect the contact characteristic of the reed switch. Although it depends on the type of cable used, it is recommended that if the cable length exceeds 50 meters, protection as per this circuit is required for longer operating life of the reed switch.