Basic Switches
Definitions of Terms
Actuator
– Mechanism of the switch or
switch enclosure which operates the con-
tacts.
Auxiliary Actuator
– A mechanism, sold
separately, to provide basic switches with
easier means of operation and adjust-
ment and adapt switches to different op-
erating motions by supplying supple-
mental overtravel.
Basic Switch
– A self-contained switch-
ing unit. It can be used alone, gang-
mounted, built into assemblies or en-
closed in metal housings.
Bifurcated Contacts
– A movable con-
tact, generally gold plated, which is
forked to provide two contact mating sur-
faces in a parallel, for more reliable con-
tact.
Break
– To open an electrical circuit.
Break Distance
– The minimum open
gap distance between stationary and
movable objects.
Characteristics
– This term is used by
MICRO SWITCH in a restricted sense and
refers only to switch operating character-
istics such as pretravel, operating force,
etc.
Circuit
– The contact arrangement with
switch actuator and contacts in their nor-
mal position.
Dead break
– Exists in all mechanical
switches. Definition: When the switch
plunger is being depressed, dead break
is non-contact immediately before the
plunger reaches the operating point.
When the switch plunger is being re-
leased, dead break is non-contact imme-
diately before the plunger reaches the re-
lease point. Dead break is expressed in
distance of plunger travel during which
the non-contact occurs. Manufacturing
specifications for most BZ/BA basic
switches allow a maximum dead break of
0.00005 in. (0,001 mm) measured at the
switch plunger. Switches are evaluated
while moving the plunger with the switch
installed in a 10 VDC, 0.100 ampere cir-
cuit. This specifiction does not apply to
switches that have been in service or have
not received proper handling or storage.
For applications sensitive to dead break,
call Freeport for information on applica-
ble electrical and mechanical conditions.
Dead make
– When the switch plunger is
being depressed, dead make is non-con-
tact immediately after the plunger reac-
hes the release point. Dead make is ex-
pressed as the distance of plunger travel
during which the non-contact occurs.
Non contact
is a failure of open contacts
to close (that is, the switch resistance ex-
ceeds the specified value) within the
specified range of plunger positions. If a
plunger position is specified with respect
to time, a non-contact is a contact miss.
98
Honeywell Sensing and Control
Double Break Contacts
– (Twin break).
This breaks the circuit in two places. Re-
ferred to as form Z circuitry also.
Normally Open Contacts (N.O.)
– Pro-
vide a normally open circuit when actua-
tor is in free position.
Precision Snap-Acting Switch
– An
electromechanical switch having prede-
termined and accurately controlled char-
acteristics, and having a spring loaded
quick make and break contact action.
Projection Contacts
– A design in which
one or more truncated projections are ar-
ranged on the stationary contacts. When
closed on the smooth, spherical surface
of the opposing contact this configuration
tends to break thru oxides and other film
contaminants to avoid the particulate
contaminants. Used with silver contacts,
this design can be a useful substitute for
the more expensive gold or gold alloy
contact material.
Pulse Switch
– Provides a single pulse of
current for each cycle of operation.
Quick Connect Terminal
– A plug-in type
terminal designed for quick switch wiring.
Repeatability
– Ability of a switch to re-
peat its characteristics precisely from one
operation to the next operation.
Single-Pole Double-Throw (SPDT)
–
Switch which may either make or break a
circuit, depending on how it is wired. Also
referred to as form C circuitry.
Form Z
Double-Pole Double-Throw (DPDT)
–
Switches which make and break two sep-
arate circuits. This circuit provides a nor-
mally open and normally closed contact
for each pole.
Enclosed Switch
– A basic switch unit
(contact block) enclosed in a durable
metal housing. The enclosure protects
the switching unit, provides mounting
means, and fitting for conduit connection.
Environment-Proof Switch
– A switch
which is completely sealed to ensure con-
stant operating characteristics. Sealing
normally includes an ‘‘O’’ ring on actuator
shaft and fused glass-to-metal terminal
seals or complete potting and an elas-
tomer plunger-case seal.
Explosion-Proof Switch
– A UL listed
switch capable of withstanding an inter-
nal explosion of a specified gas without
igniting surrounding gases.
Hermetically Sealed Switch
– A switch
completely sealed to provide constant
operating characteristics. All junctures
made with metal-to-metal or glass-to-
metal fusion.
Magnetic Blow-Out Switch
– Contains a
small permanent magnet which provides
a means of switching high d-c loads. The
magnet deflects arc to quench it.
Maintained Contact Switch
– Designed
for applications requiring sustained con-
tact after plunger has been released, but
with provision for resetting.
Make
– To close or establish an electrical
circuit.
Momentary Switch
– A switch with con-
tacts that return from operated condition
to normal condition when actuating force
is removed. Unless otherwise stated, all
switches in this catalog are momentary.
Mounting Dimensions
– All dimensions
on the mounting dimension drawings in
this catalog are subject to change without
notice. Request current drawings from
the nearest MICRO SWITCH Sales Office
or write to Freeport.
Normally Closed Contacts (N.C.)
– Pro-
vide a normally closed circuit when actua-
tor is in free position.
Form C
Single-Pole Single-Throw (SPST)
–
Switch with only one moving and one sta-
tionary contact. Available either normally
open (N.O.) also referred to as form A cir-
cuitry; or normally closed (N.C.) also re-
ferred to as form B circuitry.
Form A
Form B
Terminal Enclosure
– A housing that fits
over switch terminals to protect against
electrical shock and accidental shorting,
and facilitate wiring.
Two Circuit Switch
– In one position,
moving contacts complete one circuit, in
the other position, contacts complete an-
other separate circuit.
For application help: call 1-800-537-6945.
HONEYWELL [ HONEYWELL SOLID STATE ELECTRONICS CENTER ]
