Aleph Reed Switch Application Notes
Lead Forming (cutting and bending)
- When cutting or bending external leads extreme caution should
be exercised not to exert any undue stress that can result in
damage or deterioration of the glass-to-metal seal. Proper clamping
is necessary (see Fig. 1)
- Recommended distance, from end of glass capsule, for lead
bending and cutting (dimension “1” on Fig. 1) are
3 mm minimum for miniature reed switches (glass length 9 to
20 mm) and 8 mm minimum for large reed switches (glass length
of 30 mm and more).
- As a result of cutting external leads, Pull-In and Drop-Out
AT (Ampere Turns) will increase. Take this into consideration
during design (see Fig. 2). Similarly, bending of external leads
will increase Ampere Turns.
Figure 1 |
Figure 2 |
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Mounting (soldering and welding)
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Figure 3 |
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Excessive
high temperature and exposure time may cause damage of the glass-to-metal
seal (crack, leakage, etc.). Quick and reliable soldering techniques
(procedures) need to be applied.
Recommended soldering conditions are : 280 to 300 deg. C for
hand soldering, and 250 to 300 deg. C for wave soldering.
- When welding reed switch leads, the electromagnetic field
generated by the welding current can operate the switch, that
in turn may cause contact damage.
Special precautions should be used during welding, regarding
welding voltage, current and timing.
Never weld both leads of reed switch at the same time.
- When mounting on a printed circuit board (pcb) attention should
be given to pcb warpage and thermal expansion characteristics.
Stress caused by these factors may also damage the glass-to-metal
seal.
When mounting a reed switch on a pcb, it is recommended to form
the leads and provide adequate spacing between the pcb and the
reed switch, or to drop the reed switch into an opening (cutout)
in the pcb (see Fig. 3).
Shock and Vibration
- When a reed switch is dropped onto a hard surface (floor)
from more than 30 cm height, electrical characteristics (Pull-In,
Drop-Out, etc.) shall be altered.
After a reed switch has been dropped and before use in the actual
application, make sure that its characteristics are still within
acceptable limits.
The same is applicable after applying pulling or twisting stress
forces to the reed switch.
- Do not use reed switches above their specified resonant frequencies.
Reed Switch Protection
- Inductive Loads:
When using reed switches for inductive loads such as motors,
relay coil, solenoids, etc., the contacts will be subjected
to high induced voltages during opening of the contacts (load
circuit).
Such high induced voltages (transients) may cause damage to
the reed switch or significantly reduce its life.
Therefore, protective circuits such as : RC (snubber), varistors
or clamping diodes, are recommended (see Fig. 4).
- Capacitive Loads:
When using reed switches for capacitive loads such as capacitors,
incandescent lamps or long cables (harnesses), the contacts
will be subjected to high surge (inrush) current. Therefore,
protective circuits such as : surge suppressors or current limiting
resistors, are recommended (see Fig. 5).
Figure 4 |
Figure 5 |
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External Magnetic Interference
- When reed switch and its actuating magnet or coil are located
near sources of strong magnetic interference such as steel plates,
transformers, etc., the reed switch operational characteristics
will be altered and false operation is likely.
Specific cases may be very different from one another, and therefore
sources of possible interference (interaction) should be investigated
in a given application.
- When using multiple reed switches in close proximity to one
another, similar magnetic interference may cause changes of
characteristics and false operation.
If such interference is observed, the reed switches should be
spaced more than 15 mm from one another.