Basic Switches
Definitions of Terms
Actuator – Mechanism of the switch or Double Break Contacts – (Twin break). Normally Open Contacts (N.O.) – Pro-
switch enclosure which operates the con- This breaks the circuit in two places. Re- vide a normally open circuit when actua-
tacts.
ferred to as form Z circuitry also.
tor is in free position.
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.
Precis ion 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.
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.
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
Bas ic Switch – A self-contained switch-
ing unit. It can be used alone, gang-
mounted, built into assemblies or en-
closed in metal housings.
Enclos ed Switch – A basic switch unit tends to break thru oxides and other film
(contact block) enclosed in a durable contaminants to avoid the particulate
metal housing. The enclosure protects contaminants. Used with silver contacts,
the switching unit, provides mounting this design can be a useful substitute for
means, and fitting for conduit connection. the more expensive gold or gold alloy
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.
contact material.
Environment-Proof Switch – A switch
Break – To open an electrical circuit.
which is completely sealed to ensure con- Puls e Switch – Provides a single pulse of
stant operating characteristics. Sealing current for each cycle of operation.
Break Dis tance – The minimum open
gap distance between stationary and
movable objects.
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.
Quick Connect Terminal – A plug-in type
terminal designed for quick switch wiring.
Characteris tics – 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.
Repeatability – Ability of a switch to re-
peat its characteristics precisely from one
operation to the next operation.
Explos ion-Proof Switch – A UL listed
switch capable of withstanding an inter-
nal explosion of a specified gas without
igniting surrounding gases.
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.
Circuit – The contact arrangement with
switch actuator and contacts in their nor-
mal position.
Hermetically Sealed Switch – A switch
completely sealed to provide constant
operating characteristics. All junctures
made with metal-to-metal or glass-to-
metal fusion.
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
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.
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.
Maintained Contact Switch – Designed
for applications requiring sustained con-
tact after plunger has been released, but
with provision for resetting.
switches allow a maximum dead break of Make – To close or establish an electrical
0.00005 in. (0,001 mm) measured at the circuit.
switch plunger. Switches are evaluated
while moving the plunger with the switch
Momentary Switch – A switch with con-
tacts that return from operated condition
Form A
Form B
installed in a 10 VDC, 0.100 ampere cir-
to normal condition when actuating force
cuit. This specifiction does not apply to
is removed. Unless otherwise stated, all
switches that have been in service or have
switches in this catalog are momentary.
not received proper handling or storage.
Terminal Enclos ure – A housing that fits
over switch terminals to protect against
electrical shock and accidental shorting,
and facilitate wiring.
Mounting Dimens ions – 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.
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.
Two Circuit Switch – In one position,
moving contacts complete one circuit, in
the other position, contacts complete an-
other separate circuit.
Normally Clos ed Contacts (N.C.) – Pro-
vide a normally closed circuit when actua-
tor is in free position.
98 Honeywell Sensing and Control
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HONEYWELL [ Honeywell ]
