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Difference between Reed Switch Pull-in and Drop-out

This page describes Reed Switch terms pull-in and drop-out and mentions difference between Reed Switch Pull-in and Drop-out.

What is Reed Switch?:
• It is magnetically activated mechanical switch.
• It consists of two metallic contacts enclosed in a small enclosure usually glass capsule.
• The contacts are magnetic and move in response to a magnetic field. Permanent magnet is needed to activate the switch.
• There are two types of reed switches viz. SPST and SPDT. Most common one is SPST which is either normally open or normally closed type. The bistable version is also available.

Reed Switch construction and symbol

The figure-1 depicts reed switch construction and its circuit symbol.

Reed Switch Pull-in

➤The minimum magnetic field strength required to activate the switch.
➤It is measured in ampere-turns (AT).
➤In other words, it is the magnetic field strength at which the reed switch is activated.

Reed Switch Drop-out

➤The maximum magnetic field strength which allows contacts of the switch to relax.
➤It is measured in ampere-turns (AT).
➤In other words, it is the magnetic field strength at which the reed switch is de-activated.
➤Pull-in will be higher in value than drop-out.


Reed Switch Related Links

How Reed Switch works
Reed Switch advantages and disadvantages
Reed Switch manufacturers
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