Reed Switch Symbol
According to the old standard for reed switches (GB/T5094-1985), it is S or SQ; the new standard (GB/T5094.2-2003) uses B or (GB/T20939-2007) BG.
 
Function of a Reed Switch
As the name suggests, a switch is used to connect and disconnect circuits. A reed switch is similar to a relay; it has contacts and a coil. When the coil is energized, the contacts close, connecting the circuit; conversely, when the coil is de-energized, the contacts open, disconnecting the circuit.

The reed switch is a unique technology. Its fully sealed characteristic allows it to be used in almost any environment. Although the structure of a reed switch is simple, its manufacturing process involves multiple techniques. Over the years, the size of reed switches has evolved from approximately 50 mm (2 inches) to as small as 6 mm (0.24 inches). These smaller sizes allow it to be applied in more fields, especially meeting the needs of radio frequency and fast time domain applications.

The performance of the reed switch is as follows: It can switch up to 10,000 volts; it can switch up to 5 amps; it can switch or loads down to 10 nanovolts without signal loss; it can switch or loads down to 1 femto-Amps without signal loss; it can switch or loads up to 6 gigahertz with only minimal signal loss; the contact insulation is 10Ω; the contact resistance is typically 50 milliohms (mΩ); it requires no energy or power when normally open; it provides bistable operation; the operating time range is 100μs to 300μs; it can operate in extreme temperature ranges from -55°C to 200°C; it can operate in various environments, including air, water, vacuum, oil, fuel, and dusty environments; it can withstand impact forces up to 200Gs; it can withstand magnetic induction intensities up to 30Gs; it can withstand oscillations from 50Hz to 2000Hz; it has a long service life, capable of operating up to one billion times under 5V 10mA operating conditions.