A reed switch is an assembly containing ferromagnetic contact blades, hermetically sealed in a glass envelope and filled with an inert gas. The blades (flexible reeds) are overlapped but separated by a small gap. The contact area of each blade is plated with a noble metal, such as Rhodium or Ruthenium, to provide the switch with stable characteristics and long life. It can be operated by an externally-generated magnetic field, e.g. that from an actuating coil. The inert gas atmosphere protects the contact resistance of the reed switch, which is one of its most important electrical performance characteristics. The inert atmosphere is maintained by the integrity of the critical glass-to-metal seal of the switch. This seal is defined as a "residual stress seal", which means that the seal is sensitive to handling. When properly made, this seal with maintain the inert gas atmosphere of the reed switch for a minimum of thirty (30) years. However, improper handling of the switch and the application of excessive mechanical force during modification of the switch leads may result in a loss of the seal hermeticity. If damage is caused, it might be immediately visible as a glass crack in the seal area with or without the evidence of chipped glass particles. Or a latent defect may be created that will deteriorate the seal hermeticity over time due to the residual stress of the seal being altered through the improper application of a mechanical force. Once the seal integrity is compromised, atmospheric oxygen and other contaminants will degrade the contact resistance and the life expectancy of the switch will be severely impacted.

The glass seal of the reed switch has a very high resistance to pressure, but a low resistance to pull forces. The ability of the seal to properly withstand a switch lead modification is dependent on several factors: the relation of the wire-to-glass dimensions, the length of the seal, the pull force or type of modification to be performed, and the distance and direction of the mechanical force in relation to the seal itself. Therefore, the proper support and clamping of the leads is necessary to avoid damage to the seal. Even then, the plastic deformation strain of the NiFe lead wires can be transmitted through the clamping area and into the seal. Depending on the combination of the force and the distance of the clamping area to the seal, damage may still result.

Reed switches are designed for, and used in, the most demanding applications; these include computer keyboards, telephone equipment, automatic test equipment and automobiles. Therefore their quality must be exceptionally high with regard to conformity and reliability. This quality is built into our battery-free LED flashlights during every stage of their design and manufacture. The typical characteristic parameters of the reed switches are inclusive of operate and release values, operate and release times, bounce time, contact resistance, breakdown voltage, insulation resistance, and life expectancy, etc.

Operate and Release Values are dependent on the measuring coil, the rate of energization (0.1AT/ms), the detection of the operate (closing) and the release (opening) moment, the position of the measuring coil relative to the earth's magnetic field and on the environmental conditions.

Operate and Release Times are dependent mostly on the energization and de-energization rate. They are proportional to the R/L time of he coil. Operate time is inversely proportional to the ratio of energization to operate value. Release time is proportional to the ratio of energization to release value.

Bounce Time is almost independent of the energization, however, a high energization gives a somewhat shorter bounce time. The bounce time is dependent on the current to be switched; above approximately 100mA the bounce time is almost zero.

Contact Resistance is dependent on the wire composition, wire diameter, energization and contact layer. The commercially published contact resistance is normally measured with an open contact voltage of 20mV and a current through the closed contacts of 10mA, using Kelvin method. Distance between measuring points for all switch types is normally 41mm.

Breakdown Voltage depends on the gap between the contact blades, kind of gas filling, gas pressure, material of the contact layer and the availability of free electrons in the gas.

Insulation resistance is dependent on the condition of the inside of the glass envelope and on the environment, e.g. relative humidity, conducting layers on the outside of the glass envelope.

Life Expectancy of a reed switch is influenced by the contact layer, the wire diameter, the load, the load circuit parameters and the applied magnetic field. The contact layer and the wire diameter are determined by the manufacturer. Lead, load circuit parameters and magnetic field are determined by the user. The load should be within the maximum published values. The load circuit parameters (wiring capacitance and inductance), should be kept as low as possible and the applied magnetic field must be stronger than necessary for obtaining the maximum operate value.

FEATURES:

1. Compact and Light: it can be mounted in a very limited space and ideal for use in miniaturized equipment.

2. Hermetically Sealed: its switching elements are hermetically sealed in an inert gas atmosphere, so that they are never exposed to the external environment.

3. Long Life: it employs no sliding parts, so there is no fatigue related to degradation in the equality of the materials used, ensuring a virtually unlimited mechanical life.

4. High Speed Operation: every movable element has a very low mass resulting in a high speed of operation. This enables the reed switch to be used as an interface to a transient or integrated circuit.