OI/LMS100-EN Rev. A |
LMS100 Magnetic Level Gauge Switch 9
5.3 Typical Applications
Some ABB switch products (LMS100, MS50, MS10) are based
on magnetically operated reed switches. Since reed switches
have the inherent characteristic of very closely spaced switch
contacts, it is extremely important to protect these contacts
from high voltage transients caused by inductive loads. When
an inductive load is de-energized., the collapsing magnetic field
induces a high voltage of opposite polarity into itself and thus the
switch . Two basic methods exist to clamp this voltage and thus
protect the switch contacts.
5.4 Typical D.C. Applications
For D.C. applications, a diode is placed in parallel with the induc-
tive load (note the polarity of the diode and power supply). A
1N4001 general purpose diode is normally sufficient to clamp the
induced voltage of the inductive load to as safe level. NOTE: Not
evaluated for use in hazardous locations
5.5 Typical A.C. Applications
For A.C. applications, a Metal Oxide Varistor (MOV transient
surge suppressor) is placed either in parallel with the switch or
the inductive load. The MOV changes from a high impedance to
a very low impedance when the voltage across the MOV exceeds
its rated voltage (the MOV rating must correspond with the power
supply voltage). For 120 VAC control systems a typical MO
would be the GE (General electric Co.) part number V130LA10A.
In either case shown, the result is the limiting of the switch volt-
age to approximately 130 volts. NOTE: Not evaluated for use in
hazardous locations
D.C. Contact Protection
A.C. Contact Protection
DC POWER SUPPLY
INDUCTIVE
LOAD
DIODE
WHITE
(COMMON)
BLACK OR RED
(NO)
(NC)
+
-
AC POWER SUPPLY
INDUCTIVE
LOAD
MOV
WHITE
(COMMON)
BLACK OR RED
(NO)
(NC)
+
-
DC POWER SUPPLY
INDUCTIVE
LOAD
DIODE
WHITE
(COMMON)
BLACK OR RED
(NO)
(NC)
+
-
AC POWER SUPPLY
INDUCTIVE
LOAD
MOV
WHITE
(COMMON)
BLACK OR RED
(NO)
(NC)
+
-
