How can I protect the FS 90 or FS 202 reed switch?
Reed switch contact ratings, as listed in the FS 90 or FS 202 data chart, are based on use with a resistive type load. For applications requiring the control of an inductive or capacitive load, additional interface circuitry may be required. When the current is interrupted, the inductance of the load generates a voltage which appears across the switch contact. If the voltage is large enough, it can cause arcing. Arcing can cause the contacts to weld to each other resulting in unreliable switching performance. It is essential to protect the circuit by suppressing the voltage to prevent arcing. This can be accomplished through the use of a diode for DC circuits (figure 1) and a resistor-capacitor network or Quencharc for AC circuits (figure 2).
