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Патент USA US3100831

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1 Aug~ 13, 1963
I '
T. K. KJELLMAN
3,100,826
SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE TO CURRENT FLOW _
Filed April 11, 1960
4 Sheets-Sheet 1
I
_ ‘FIG. 1..
W
10/,
INVENTOR
THOMAS K . KJELLMAN
ATTORNEY
Aug. 13, 1963
T. K. KJELLMAN I
v 3,100,826
SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE TO CURRENT FLOW
Filed April 11, 1960
4 Sheets-Sheet 2
FIG. 2,.
P16. 25.
3a
,
22 15 24 24' 29
1o’
INVENTOR
THOMAS K. KJELLMAN-.
BY
ATTORNEY
_ Aug- .13, 1963.
_
'r. K. KJELLMAN
I
3,100,826
.SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE Tb CURRENT FLOW
Filed April 11, 1960
Q
'4 Sheets-Sheet s
FIG. 8.
I
10
l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/
'
INVENTOR
THOMAS K. KJELLMAN
BY
/
o4.’
'
ATTéRNEY
Aug. '13, 1963
'
-
T. K. KJELLMAN
_
3,100,826
SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE T0 CURRENT FLOW
Filed April 11, 1960
4 Sheets-Sheet 4
13'.
FIG . 9.
INVENTOR
THOMAS K. KJELLMAN
MW
ATTORNEY
United States Patent 0 " ice
3,100,826
Patented Aug. 13, I963
2
1
' the travel of the power element with respect to the switch
3,100,826
blade throw line. At this point the switch blade is almost
to its dead-center position, requiring a minimum of force
,
SNAI’ SWITCH HAVING PRESETTING MEANS
RESPONSIVE T0 CUNT FLOW
Thomas K. Kjellman, Timoninm, Md, assignor to The
Bendix Corporation, a corporation of Delaware
Filed Apr. 11, I960, §er. No. 21,334
9 Claims. (ill. Mil-113)
' to throw it past dead center against the opposite contact.
This invention relatesto electrical switches of that type
for both heavy and light duty installations; it (the switch)
The spacing between the switch blade contacts and the
power arm contacts, however, remains ?xed according to
design requirements. The construction and arrangement
. of the various parts of the switch are readily adaptable
which utilize a temperature or current-responsive device 10 can take a high initial ?ow of current without danger of
destruction simply by substituting the proper type. of
such ‘as :a bimetal strip to assist or control the switching
thermal power arm or element. As the respective parts
operation; it is particularly adapted for, but not limited
of the switch go through the switching cycle, the con
to, sensitive instruments such as humidistats, thermostats
tacts rub againstone another with a resultant wiping or
and the like wherein the sensing element controls a quick
acting toggle or “snap” switch to avoid sparking at the 15 cleaning action which breaks, in shear, welds due to an
initial inrush of current and deters contact erosion.
contacts, with resultant contact erosion.
The foregoing and other objects and advantages will
An object of the invention is to provide a switch ‘of the
become apparent in view of the following description
type speci?ed wherein almost one hundred percent of
taken in conjunction with the drawings, wherein:
the work required to throw the switch is performed by
FIG. 1 is a view in perspective of a combined tempera
the line current, leaving practically zero work for the 20
ture and relative humidity controller embodying the fea
sensing element to effect the ?nal switching operation,
while .at'the same time all the advantages of a snap or
tures of the invention;
toggle action are retained with practically unlimited con
FIG. 2 is ‘a top plan view thereof;
FIG. 3 is a view in section and side elevation with the
tact forces available to meet design speci?cations.
Another object is to provide a highly sensitive snap 25 facing side wall removed;
switch capable of handling heavy-duty switching, and a
FIG. 4 is a view in end elevation partly broken away;
FIG. 5 is a view taken substantially on the line 5--5,
this with a minimumIZR drop across the switch.
Another object is to provide a relatively simple snap '
FIG. 3;
switch which effects a self-cleaning or wiping action be
‘FIG. 6 is a view of the base assembly taken substan
30 tially on the line 6—-—6, FIG. 3;
tween contacts ‘during each switching cycle.
Another object is to provide a switch assembly par
FIG. 7 is a view of the said base ‘assembly as in FIG.
6 but with the switch blade and coacting parts removed
ticularly adapted‘ for instruments such as humidistats,
thermostats and the like utilizing sensing elements where
to expose the temperature-responsive power member;
in a relatively small amount of work is available to obtain
sensitivity.
,
FIG. 8 is a view similar to FIG. 7 but showing the
35 power member removed to expose the excess current
A further object is to provide an improved humidity
shunt bar;
and/ or temperature sensing and control instrument.
51G. 9 is a plan view of the leaf spring switch member;
an
In attaining the foregoing objects, a conductive thermal
FIGS. 10‘ to 10d are diagrammatic representations of
arm or bar (in practice a strip of bimetal) ‘is interposed 40
in‘ the control circuit and has located on the movable end
or other movable portion thereof a pair of contact mem
theswitch as it undergoes the switching cycle.
bers spaced to meet switch-throwing requirements. These
contacts remain in fixed spaced relation but move bodily
and relative temperature controldevice which can either
_ The improved switch is shown installed in a humidity
function as a thermostat, a humidistat, or‘ a combined
with said arm when it responds to current flow and when 45 thermostat and humidistat, i.e., it can regulate tempera
ture as a function of relative humidity. The working
it cools following current cut-off. This arm may be aptly
parts are encased as best shown in FIGS. '1 and 3; the
termed a “switdh-presetting power element” since it pre~
switch assembly proper being located in a bottom case,
sets the ‘actual switching member for the ?nal switch
here shown as being made up of a molded plastic top
throwing tact and it does practically all the switching
work. The switching member is in the form of a snap 50 section 10 and a base 10' ?tted into the open bottom of
the section 10. Removably ?tted over the section 10' is
vaction switch blade having coacting contacts movable be
a metallic case or shell 11, secured in place by small
tween the said power element contacts. This switch blade
screw bolts 12.
,
may be of the conventional toggle or snap type which as
The switch ‘proper comprises a leaf spring switch blade
it approaches its ‘dead-center position requires a progres
sively-increasing actuating force but needs only a rela 55 of the toggle or snap type, note FIG. 9, made of conduc
tive material such vas sheet copper; and since the instru~
tively small force to throw it past such position; it is
ment is here shown adapted to sense both temperature
preferably located in the control circuit posterior of and
and relative humidity, two of these blades 13 and 13' are
.in series with the motor or other device to be controlled,
utilized, :each blade being identical in construction and
so that when “on” contact is made, the current ?ows
hence like parts in each blade bear like reference nu
through the switch blade and the power arm or bar back
merals. The rear (leftlland end as viewed in FIG. 9)
-to the return side of the line. This flow of current does
ends [of the blades terminate in a common integral anchor
.not affect the contour of the switch blade‘ since its prefer
ing section. 'llhe manner in which these blades perform is
ably of nonithermal-responsive material, but it does de
well known although the speci?c structure t?or carrying
form the power 1arm in a direction to move the switch
blade toward its dead-center position in the “off” direc 65 vout the desired function may take various forms. In the
present instance, each blade terminates at its contact ex
tion. As soon as “o?” contact is made, the power arm or
element begins to cool, whereupon it un'deforrns in the
“on” contact direction. Thus the switch blade is ‘grad
tremity in a free snap-action section 14, having 1a bowed
and stressed toggle spring tongue 1-4’ cutlonigtudinally
out of its central portion. At its free end beyond the sec
either “on” or “off” contact is made, and this movement 70 tion 14, the blade has mounted on opposite sides thereof
a pair ‘of contacts 15 and 16‘. In practice, these contacts
continues until the thermal power ‘arm or element is
ually moved in a switch-throwing direction as soon as
broughtup against adjustable stop means which limits
are preferably adjustably mounted. While these contacts
3,100,826
3
4
are shown as being made of special contact material and
welded or otherwise secured to the switch blade, it will
be obvious that they could be made integral with the
blade, or the blade surface could function as a “contact”
then make up a return circuit in parallel with the remain
ing part of the arm 23 to the left'of contact 21, and the
resistance or" this shunt circuit is such as to provide the
within the scope of this term as used'in the claims. At
As heretofore noted, the instrument in which the switch
is used in the present instance is'a combined thermostat
and hu‘midistat. Accordingly, a humidity-sensing element
desired safety factor.
its opposite end |(left-hand end as viewed in FIG. 3) the
switch blades are anchored to the base section 10’ by bolts
17.
,
‘
‘
c
a
a
in the form of a hair rope 31 is looped over a stationary
hook 32 at one end of the case or cap 11 and has its free ‘
ends secured in terminals which are hooked to the one end
of an adjustable bracket 33. The bracket 33 is knife .
Each one of the switch blades is formed with a slot '
'18, to accommodate connecting or banger brackets for
the humidity and temperature elements in a manner to be
described. A plate '19 overlies both switch blades and at
edged at one extremity for engagement’ in a notch 34,
formed in the adjacent top wall of the case 11 and about
which the bracket pivots when adjusted. A short control
its front end is formed with downturned abutment mem
bers 19', one r?or each blade, while its opposite end is
vsecured to the said base by the screws. 17. Each down
turned abutment 19’ is notched as at 20, and the free end 15 shaft 35, adapted to receive a control knob, not shown,
is threaded through a bushing 36 to the ?xed adjacent
edge of each bowed spring tongue 14' engages in these
notches. The notch 20 is so located with respect to the
wall of the casing 11 and carries a member v37 at its
axial line of thrust of the tongue 14' and the point of
lower or inner end which projects through a key slot
connection of the blade to its actuator (here the humidity
formed in the bracket 33 and engages beneath the latter.
responsive element 31 or temperature-responsive element 20 A spring 38 biases the bracket 33 to its “down” position.
46, to be described) that whenthe latter point passes
By adjusting the shaft 35 in or out, the tensioning effect
through the blade’s over-center thrust line in either a con
of the hair element 31 may be regulated. A “feel” cam
39, rotates with the shaft 35 and is engaged by a resilient
friction and stop member 40, to provide the proper ‘feel
.“break” position. The contacts 16 and 21 or 15 and 22, 25 when rotating the said shaft and also limit rotation to one
however, remain in engagement until the said point of
full or partial turn, depending upon how the control is
connection ?exes past dead center in either direction. The
term “snap switc ,” as used herein, refers to switches in
At an intermediate point the hair element projects
tact “make” or “break” direction, the contact-carryingsec
.tion. or extremity 14 will snap to contact “make” or
calibrated.
,
‘
~
corporating a switch blade or resilient switch [assembly
which function in a generally similar manner, i.e., main
tain contact until flexed or otherwise actuated past a dead
icenter position. At its rear end, the plate 19 has a tongue
. through an eye 41 ?xed in the upper end of a hanger
projecting therefrom, which is bent downwardly and passes ,
through a slot and terminates in an exteriorly accessible
then through the slot 18 in the leaf spring blade 13, and
terminal ‘19".
bracket 42, note FIG. 5, and the latter extends through
registering slots 43 and 44 formed, respectively, in the
top wall of the case 10 and the abutment \plate 19 and '
at its lower or inner end is extended laterally beneath the
35 said blade.
Should. the moisture content or relative hu
The contacts 21 and 22 are carried on the free end of
midity of the air increase, the hair element will relax and ‘
a contact preset and power bimetal arm 23, which at its
permit the switch blade to ?ex downwardly, and if the
one end is also ?xed to the base member 10’ by the screw
moisture content or the ‘relative humidity decreased, the "
opposite effect will occur.
'
.
bolts 17. In the present instance, the upper contact 22 is ‘
?xed on the ‘free end of the power arm 23 by means of an 40
A temperature-responsive element is indicated at 46,”
offset piece 24, secured to the arm 23 as at 24'. ln prac
and this element, as is the case with the humidity element,
, tice, the piece 24 is bendable ‘for the purpose of adjusting
is anchored at one end to a hook 47 and at its opposite
the spaced relation of the contacts. Obviously, other
means may be adopted for adjustably and shiftably
_mounting these contacts; they could be mounted on a
shiftable support independently of the arm 23 and moved
or F‘driven” by the arm to’ their respective preset positions.
Adjacent the center throw line of the switch blade 13
end to a bracket 47", the latter being provided with a pivé
otal knife edge engaging in a notch 34' and is adjustably,
supported by means of a control or setting assembly sim
ilar in all respects to that used for the humidity element,’
the two outer screws 17 and at its opposite‘ end is bent
opposite effect will occur.
and hence like parts have been given like reference nu- .
merals with the exception that a prime (’) has been
'(or 13') the power bimetal arm or bar 23 is brought up ‘ ' added. The center bracket indicated at 48 is provided
against stop means, which may be provided in any suit
to hold the knife edge pivots of the brackets 33 and 33'
able manner. As best shown in FIGS. 4 and 7, the stop
e in place; it has oppositely projecting spring legs which
means is provided by laterally-projecting contact portions
engage in slots formed in said brackets.
25 and 25’ dormed on the bar 23, which come against
A hanger'bracket 49 has its upper end connected to
. abutment screws 26, 26' and 27, V27', adjustable to deter- '
the bimetal temperature element‘ 46 by' means of‘a pin
mine withexactitude the point where the movement of the 55 and slot connection, as indicated at 50, and at its lower
arm 23 terminates in the switching operation.
end projects through registering slots 5-1 and 52 formed,
, Preferably, but not necessarily, the switch is provided
respectively, in the top wall of the case 10' and the abut
with means (tor shunting excess current‘ from ?owing
ment member 19 and also through the slot 18’ formed in
‘through the power arm or bar 23 in the case of a short
the leaf spring blade 13' and at its lower end is projected
circuit or other malfunctionwhich might cause an excess
laterally for engagement beneath the said blade. Should
flow of current through said bar. Such means as here
the temperature of the surrounding ambient air increase, I
shown consists of a shunt bar 28, note FIGS. 3 and 8,
the bimetal temperature element 46 will relax in a down
which at its rear end is ?xed to the base member 10' by
ward direction, and should the temperature decrease, the
upwardly and inwardly to accommodate a shuntcontact 65
_
The hanger brackets 42 and 49 may be made up of a
29. At its rear end the shunt bar has a tongue out from
single piece of plastic or other insulating ‘material and
its center and bent rearwardly and downwardly to provide
‘ assembled by inserting each through the registeringislots '
a wiring terminal 28'. The power arm 23 is extended
provided‘ therefor from beneath the‘ switch blade 13 and I
13'.
along the longitudinal center line of'the shunt bar and at
Operation >
'its far end has ?xed thereto a coacting shunt contact 30, 70
compare FIGS. 3 and 7. When current ?ows through the
The switch, as exempli?ed herein, is of the simple “on- .
power arm or bar 23 and it is deformed upwardly to
off” type. In FIG. 10, the switch assembly is shown dia
preset the section 14 of the switch blade 13, contact 30
grammatically; it could be either the humidity or tem
engages contact 29. That part of the power arm 23- lying
perature control switch of FIGS. 1 to 9, inclusive, which
between the contacts 21 and 30 plus the shunt bar 28 will 75 constitute actual assembly drawings.‘ Here ‘the switch
3,100,826
6
blade :13, 14 and 14' of the assembly drawings is made
switch blade responsive to movement of said actuator and
up of a blade proper 13A, which corresponds to the
having a snap action across a dead-center throw line to
tongue 14' of the leaf spring type of blade of the actual
switch, ‘and a spring 14A, which corresponds to the re-v
silient extremity 14 of the blade. The contact presetting
and power arm or bar is indicated at 23A and the abut
ment member at v19A. The switch contacts and stops for
the power arm have been given numbers corresponding
to like parts in the assembly drawings. in FIG. 10, the
bottom of the casing functions as'the stop 26. The switch 10
alternate switching positions, said blade having a pair of
contacts coacting with and disposed between said arm
contacts, stop means located on opposite sides of said
throw line for limiting the travel of said presetting arm,
said contacts and arm being wired in circuit in a manner
such that when one of the switching contacts engages its
coacting arm contact in a ?rst switching position current
?ows through the arm and deforms the latter causing its
free extremity to advance said blade towards the opposite
switching position a distance determined by said stop
In the position of the parts in FIGS. 10 and 10a, the
means to thereby preset said member adjacent one side
contact 16 is against the “on” contact 21, and at this
of said throw line'ready for throw past dead center} in
time the motor will be energized,v current ?owing from
the line to the motor and then throughthe abutment 15 response to movement of said actuator, and when the
other of the switching contacts engages its coacting arm
member 19A, switch blade 13A, and to the return side
is shown controlling a motor ‘532
i
of the line by way of power arm 23A. FIG. =10a shows
contact current ?ow is cut off from said arm and its free
extremity moves back towards its ?rst switching position
and repositions said switching member adjacent the op
motor circuit, and FIG. 10b shortly after the motor has
ben energized and current ?ows through the power arm 20 posite side of said throw line ready for throw past dead
the relative positions of the parts upon closing of the
23A. Note that at this time the power arm has been de
formed due to current flow, so that its free contact-carry
ing extremity has moved upwardly against its stop 27
(stops 26 and 27 not shown'in FIGS. l0a-l0d) to the
point where the contact end of the switch blade lies
center by said actuator.
2. A switch as claimed in claim '1 ‘wherein said switch
' blade is anchored at one extremity and at its opposite con
tact extremity is formed with an integral prestressed
bowed spring tongue having a free end edge thrusting
against an abutment member approximately on the dead
slightly short of its throw line when moving in the “off”
center throw line of the blade and the switching force of
direction, and which line passes through the pivot point
said actuator is applied to the blade back of this point of
20A of the blade and the point of connection 54 of its
thrust in a plane substantially parallel to blade ?exure.
spring to the hanger bracket 42 or 49. These points cor
3. A switch as claimed in claim 1 wherein the switch
respond, respectively, to the notch 20 of FIG. 3 and thev 30
blade and contact-presetting arm are mounted in a manner
point where the hanger bracket 42 engages beneath the
blade 13. As the free extremity 'of the power arm 23
moves upwardly or counterclockwise, the contact 21 re
such that when the switching and arm contacts are en
quired to preset the switch blade 13A togthis position is
furnished entirely by the power arm 23A.‘
FIG. 10c shows the relative positions of the switch
blade 13A and its associated parts immediately following 40
an actuator responsive to a switching force, a switch-pre
setting arm anchored at one extremity and having a free
gaged and the armmoves to preset the switch blade, the
engaged contacts rub against one another and reduce the
mains in engagement with the contact 116 while at the
same time the spacing between the contacts 2!]. and 22 as tendency toward contact erosion.
4‘. In a thermal switch for an electrical control circuit,
remains constant. It will be observed that the force re- ‘
‘extremity deformable in clockwise and counterclockwise
responseof the hair element to a decrease in the relative
directions as a :function of current ?ow, a pair of contacts
?xed in predetermined spaced relation on the free extrem~
humidity of the ambient air beyond a predetermined or
ity of said arm, one of said contacts being electrically in
sulated from the arm and the other contact being in con
ductive relation to the arm, a resilient switch blade an~
moved counterclockwise to almost its dead-center posi 45 chored at one extremity and having a pair of contacts on
selected value, causing a slight upward pull on the hanger
bracket 42. Since the switch blade had already been
its opposite extremity interposed between and coacting
tion, the force and distance required to trip the blade is
very small. Hence the switch can be made highly sensi
‘with said arm contacts, said blade being designed to have
tive and its plus or minus tolerances reduced to meet ex
a snap action past a dead-center throw line in response to
movement of said actuator, stop means located on op
acting speci?cations. This also provides for utilization of
a wider range of humidity element types than would 50 posite sides of and adjacent to said throw line for limiting
the travel of said arm and the contacts carried thereby,
said contacts and arm being Wired in circuit in a manner
FIG. 10d shows the relative positions of the switch
such that when one of the switch blade contacts engages
blade and its associated parts shortly after “off” contact
its coacting arm contact in a ?rst switching position cur
is made. Since current is no longer ?owing through the power arm or bar 23A, the latter has cooled and its free 55 rent flows through the arm and deforms the latter where
upon its free extremity advances said blade toward the op
extremity has undeformed downwardly against its stop
otherwise be possible.
26, presetting the blade 13A slightly short of its throw or
posite switching position, while contact is maintained, a
‘distance determined by the location of said stop means
ready for throw past dead center in response to movement
crease above its selected value, the humidity element will 60 of said actuator, and when the other of the switching con
tacts engages its coacting arm contact current ?ow is cut
relax and the suspension point :54 will be pulled downh
oif from said arm and the free extremity of the latter
wardly below the over-center line by spring 14A, return
‘moves back towards its undeformed position and resets
ingrthe parts to the “on” position shown in FIG. 10a,
over-center line when the blade is moving toward its
“on” position.
Now should the relative humidity in
, said blade adjacent the opposite side of said center line for
.
In the event it is desired to use the switch to energize 65 return throw past dead center by said actuator.
5. An instrument for switching an electrical circuit as a
a control circuit in both switch blade positions, then the
function of ambient air conditions, comprising: a ?exible
upper contact 22 need only be wired into the ‘other con
switch blade provided with a pair of contacts and having
trol circuit and the latter provided with a return which
a snap action past a dead-center throw line to alternate
by-passes the bimetal power arm or bar 23A.
What I claim is:
switching positions in response to a switching force, a
blade-presetting arm at least in part deformable as a func
1. in a thermal switch for an electrical control circuit,
an actuator responsive to a switching force, a switch-pre
tion of current ?ow, said arm being anchored at on extrem
setting arm having a free extremity deformable as a
ity ‘and carrying on its opposite free extremity a pair of
function of current ?ow, a pair of spaced contacts
spaced contact-s, one of which is electrically insulated
mounted on the free extremity of said arm, a resilient
from the arm and the other of which. is in electrical con
completing the cycle.
3,100,826
7
a
.
ducting relation .to the arm, said contacts and arm being
wired in circuit in a manner such that when one of the
blade contacts engages the conducting arm contact current
?ows through said
and deforms the latter in a direc
"tion to move the switch blade back towards the insulated
tongue in a manner such that the free end of the latter
thrusts against said abutment member at a point approxi- "
mately on the dead-center throw line of the blade, and
biases the contact extremity of the blade toward one or
the other of its alternate contact positions, an actuator con
contact position and when the other blade contact engages
nected directly at its one extremity to an intermediate
the insulated arm cont-act current flow is cut off from said
arm and it undeform-s and moves the said blade back to
portion of said blade between said thrust point and the an
wards the insulated or conductivefcontact position, stop
chored extremity of the' blade, means responsive to changes .
in a condition of the ambient ‘air directly connected to the
means effective to limit the travel of said arm in either 10 opposite extremity of said actuator, the switching force of '
said actuator being applied to the blade in a plane substan
sponsive to changes in ambient air conditions for snapping
tially parallel to the direction of blade ?exure.
'
the blade ‘from its preset position past said throw line.
8. In a switch for controlling ‘an electrical circuit as a
‘6. An instrument for switching an‘electrical circuit as a
function of changes in the condition of the ambient air, a
‘function of ‘ambient air conditions, comprising: a ?exible 15 housing, a pair of spaced contacts supported by said hous
switch blade anchored at one extremity and having op- > ing, a resilient switch blade anchored at its one extremity,
positely disposed contacts on its opposite tree extremity,
to said housing and having a pair of contacts on its op‘
said blade being characterized, by a snap action past a
po'site extremity interposed between and coacting with said
dead-center throw line when a switching force is exerted
spaced contacts, said blade being ‘formed with an integral »
, direction with respect to said center line, and means re
thereon, a blade-presetting arm at least in part’ deformable 20 prestressed bowed spring tongue having one end projecting
as a function of current ?ow, said arm being also anchored
tree, an abutment member coacting with said tongue and
at one extremity and having mounted on its opposite free
providing a ?xed thrust point for the free end of the latter 1
extremity a pair of contacts in ?xed spaced relation, one
approximately on the dead-center throw line of the blade
of which'is electrically insulated from'the arm and the
to bias the contact extremity of the blade‘toward one or
, other of which is in electrical conductive relation to the 25 the other of its alternate'contact positions, an actuator
having its one extremity connected directed to an interme
arm, said ‘blade contacts being located for alternate switch
diate portion of said blade between said thrust point and
ing engagement with said arm contacts, said contacts being
wired in circuit in a manner such that when one of the
the anchored extremity of the blade, an elongated ?exible
blade contacts engages the conductive arm‘ contact current
humidity-responsive element supported at its'opposite ex
?ows through said arm and deforms the latter in a direc 30 tremities from said ‘housing and at an intermediate point
tion to move the switch blade back towards the insulated
having a connection with the opposite extremity of said
contact position, and when the other blade contact en
actuator, and means accessible exteriorlyof said housing
for adjusting the tension of said humidity element.
gages the insulated arm contact, current ?ow is cut off
from said aim and it moves the said blade back towards
the insulated or conductive contact position, stop means
effective to limit the travel of said blade in either direction
with respect to said center line, an actuating member en
gaging said blade, means responsive to changes inarnbient
air conditions for applying a switching force to said actu~
a-ting member, and a shunt circuit for limiting the ?ow of 40
current through said blade-presetting arm to a safe value.
7. In a switch for controling an electrical circuit, a
pair of spaced contacts, a resilient switch blade anchored
at one extremity only and having a pair of contacts on its
opposite’extremity interposed between and coacting with 45
said spaced contacts, said blade being, formed with an in
tegral prestressed bowed spring tongue having one end '
projecting free, an abutment member coaeting with said
9. A switch as claimed in claim 8 wherein a temperature
responsive element is also connected directly to said actu
ator ‘and there are me ans accessible exteriorly of said hous
ing for adjusting the temperature response of said tem
perature element.
References (Zited‘ in the ?le of this patent ‘
UNITED STATES PATENTS
2,052,564
Grady ________________ .._ Sept. 1, 1936
_ 2,170,748
Eaton _______________ __ Aug. 22, 1939
2,189,996
‘Riche ________________ -_ Feb. 113, 1940
2,351,408
Marcy ________ _, ______ __ Oct. 12, 1943
‘2,454,320
2,813,173
Hornbostel ___________ __ Nov. 23, 1948
Risacher et a1 _________ __ Nov. 12, 1957
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