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Magnetic
reed switch technology has been a proven technology
for more than 50 years to dependably and safely sense
a wide range of liquids and positioning. The internal
switches are hermetically sealed and capable of switching
1/8" accuracy and 1/32" repeatability for standard vertical
switches. Magnetic reed switches, when used to electrical
specification, can switch reliably for millions of cycles
unaffected by everyday shock and vibration for years
of dependable operation.
Magnetic reed switch operation is
simple but reliable. The float moves a sealed permanent
magnet along the stem as the fluid rises and falls.
As the magnets pass over the switch, the reeds are pulled
together to create a highly reliable contact. The sealed
stem encapsulates the hermetically sealed reed switch
and its wires from the liquid environment. |
Cross Section View |
Most
SMD Float Switches can be configured for either Normally Open
(NO) or Normally Closed (NC) switching by changing the float
orientation. NO and NC refer to the switches position at rest
in a "DRY" tank! Single Pole Double Through
(SPDT) contacts are also available. Each SMD Float switch
is tested 100% before shipment for guaranteed performance!
Reed Switch Protection
One
of the greatest failures of reed switches is caused by over
current conditions. Most electrically listed products are
rated for the "Steady State" operating power. This is the
time when normal operation occurs and does not take into account
the "turn-on" or "shut-down" loads associated with capacitive
or inductive devices. The power created by these devices at
"turn-on" or "shut-down" can be 5 to 10 times the "Steady
State" current given as part of the power rating. The power
spikes created at these moments can cause arching which can
weld or completely burn open the reed contacts. SMD reed switches
list the UL resistive power ratings for the reed switches,
and maximum currents and voltages to be switched. In most
high power applications an inexpensive relay can be used to
isolate you switch from heavier loads. Improper wiring
is often the cause of switch failure. When wiring you
switch and relay combination (as shown in figure 6) remember
to tie the load and the switch as close as possible to the
ground source to reduce any load spikes from traveling through
the switch.
Listed
below are a few protection methods to insure many years of
dependable service.
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| Figure
1
DC Load Protection |
Figure
4
AC Load Protection |
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| Figure
3
Lamp Load |
Figure
6
Relay Switch Protection |
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