Comus Reed Switches : Line Card

Introduction 

    Reed switches consist of two or three ferromagnetic blades (or reeds) hermetically sealed inside a glass envelope.   
   The construction ensures protection from the external environment.
   Two types are generally available : Form A  (normally open) and Form C (changeover).
   Sensitivity of a reed switch is measured in ampere turns and it should be noted that lower switch ratings are more
   sensitive as they require less magnetic field strength to operate them.
   Various voltage and current switching levels are available and contact plating materials can be varied to accommodate 
   specific types of load.

Operation  
       Reed switches are operated by a magnetic field, this may be a magnet or a current carrying coil. When the field is removed
      the switch reverts to its previous state.
      Operating by magnet can be achieved in a large variety of ways either moving the magnet toward an away form the reed 
      either perpendicularly of parallel to the glass.  
      Reed switches are used in a variety of Assmetech products including proximity switches, float switches and Reed relays. 
      They are also available in moulded packages affording protection from damage and surface mount styles.
    

 Contact Protection
     Inductive loads
       A reverse voltage is generated by store energy in an inductive load when reed contact open. This voltage can reach very
      high levels and is capable of damaging the contacts. An RC network may be used as shown below to give protection.
      Capacitive loads
      Unlike inductive loads , capacitive and lamp loads are prone to high inrush currents, which can lead to faulty operation and 
      even contact welding.
      When switching charged capacitors sudden unloading can occur, the intensity of which is determined by the capacity and 
      length of the connecting leads to the switch. The inrush peak can be reduced by a series of resistors. The value is dependent on 
      the particular application but should be as high as possible to ensue  the inrush current in within the allowable limits.
      Lamp Loads
      With lamp load applications it is important to note that cold lamp filaments have a resistance 10 times smaller than already glowing
      filaments. This means that when being turned-on, the lamp filament experiences a current flow 10 times greater than when already
      glowing. This high inrush current can be reduced to an acceptable level through the use of a series of current limiting resistors.
      Another possibility is the parallel switching of a resistor across the switch. This allow just enough current to flow to the filament to 
      keep it warm, yet not enough to make it glow. 

Cutting and Bending
     As the reed Switch blades are part of the magnetic circuit of a Rees Switch shortening the leads results in increased pull-in and    
     drop-out values
     When cutting or bending Reed Switches , it is important that the glass body should not be damaged. Therefore, the cutting or
     bending point should be closer then 3 mm to the glass body.