US3582853A - Time delay relay - Google Patents

Time delay relay Download PDF

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Publication number
US3582853A
US3582853A US859854A US3582853DA US3582853A US 3582853 A US3582853 A US 3582853A US 859854 A US859854 A US 859854A US 3582853D A US3582853D A US 3582853DA US 3582853 A US3582853 A US 3582853A
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discs
disc
relay
set forth
heater
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US859854A
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Rexford M Morris
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Therm O Disc Inc
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Therm O Disc Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H61/00—Electrothermal relays
    • H01H61/02—Electrothermal relays wherein the thermally-sensitive member is heated indirectly, e.g. resistively, inductively

Definitions

  • a time delay relay having a pair of bimetallic snap discs mounted so that they tend to produce movement in the opposite direction when their temperatures are changed in a similar manner.
  • the discs are connected so that they simultaneously move between their snap positions.
  • a heater is located between the discs immediately adjacent to one disc. Insulating means surrounding the other disc restricts the rate of flow to such other disc from the heater during heating operation and resist heat dissipation therefrom after the heater is turned off. The heater creates rapid rates of increase in differential temperature between the discs when operation of the heater is initiated and similar high rates of change in differential temperature occur when the heater is shut off.
  • the discs are selected so that a compressive force is applied to the connecting operator under all conditions normally encountered and snapping of the discs occurs when a predetermined differential temperature exists between the discs. Because the discs apply compressive forces to the operator under all normal operating conditions, a simple bumper-type connector may be used to connect the discs and the discs need not be trapped at their peripheries.
  • This invention relates generally to time delay relays and more particularly to a novel and improved time delay relay utilizing bimetallic snap discs in combination with a heater for the operation of the relay.
  • Time delay relays have utilized bimetallic snap disc operators in combination with electrical resistance-type heaters arranged to supply heat to the disc operators to cause actuation thereof.
  • two oppositely acting discs have been connected so that the relay is ambient temperature compensated. Examples of such devices are illustrated in the US. Pat. No. 2,203,558 to Wilson and Vaughan et al. US. Pat. No. 2,207,422.
  • a pair of snap discs are mounted in opposition and are interconnected so that they snap back and forth in unison.
  • the two discs are selected to have different operating temperatures so that when the two discs are at the same ambient temperatures, one disc provides greater force than the other and maintains the two discs in one position.
  • a heater is arranged to supply heat to the discs and produce adifferential temperature therebetween to cause the discs to simultaneously snap to an operated position.
  • each disc is fully trapped at its periphery in the mounting body and the discs are connected by an operator which extends through an aperture in the center of the disc and grips both sides of at least one of the discs adjacent to its aperture.
  • an operator provides a connection for transmitting forces in both directions between the disc and in many instancesf because of the gripping of the disc surface, adversely affects the calibration of the disc.
  • a time delay relay incorporating the present invention is provided with a pair of oppositely acting bimetallic snap discs connected by an operator for simultaneous snap action.
  • the discs are selected so that each disc loads the operator only in one direction.
  • a simple bumper is positioned between the discs and the combination is arranged so that the bumper is loaded only in compression. Consequently, apertured discs are not required and all lost motion is eliminated. With this arrangement, it is not necessary to provide full trapping of the periphery of each disc 'since they are always loaded in the same direction.
  • the illustrated embodiment of this invention is also arranged so that proper operation occurs even when the rate of heat input by the heater changes a substantial amount.
  • the operating heater is located between the'two discs so that heat flows from the heater along separate paths to the two discs.
  • the structure is arranged so that operation occurs along a relatively straight portion of the differential temperature curve. Therefore, the operating time of the relay is not severely affected by changes in the rate of heat output of the heaters. Further, the structure is arranged to control the ratios of rates of heat dissipation of the two discs so that the release time of the relay after the heater is deenergized can be accurately controlled.
  • both of the discs are selected so that they have a snap temperature above the temperatures normally encountered.
  • FIG. 1 is aplan view of a time delay relay incorporating this invention
  • FIG. 2 is a cross section taken generally along 2-2 of FIG. 1 illustrating the position of the various elements of the relay be fore the relay is actuated;
  • FIG. 3 is a cross section similar to FIG. 2 illustrating the position ofthe elements after the relay is actuated
  • FIG. 4 is a view taken generally along 4-4 of FIG. 2 with the mounting base removed;
  • FIG. 5a is a graph of the disc temperature vs. time ofa relay of the type illustrated in FIGS. 1 through 4;
  • FIG. 5b is a disc differential temperature vs. time graph corresponding to FIG. 50;
  • FIG. 5c is a differential temperature vs. time graph similar to FIG. 5b illustrating the effect on the relay when the heater is operated at a voltage greater than nominal voltage, and;
  • FIG. 5d is a differential temperature vs. time graph similar to FIGS. 5b and 5c illustrating the effect on the relay when the heater is operated at a lower voltage than nominal voltage.
  • a time delay relay in accordance with this present invention may be used when a delay is desired between the time an actuating signal is initiated and the actuation of the relay is desired, and where a delay is also desired between the termination of the actuating signal and the deactuation of the relay.
  • the illustrated relay is particularly suited where sequencing is desired since it provides a power switch which may be connected to an associated load and a control switch which may be connected to the heater ofa subsequent relay.
  • Such relays may be used in electric furnaces having a plurality of separate heating units. In such furnaces,.it is often desired to sequentially turn the heaters on and off so that the total load of the furnace can be connected and removed from the power line in sequential steps. Such an arrangements is often used to eliminate surges in the power line.
  • the illustrated embodiment of this invention includes a body assembly 10 including a metallic base assembly 11, a disc support member 12, an upper switch support member 13, and a closure member 14.
  • the members I2, 13, and 14 are molded from a plastic material such as a phenolic resin which is capable of withstanding relatively high temperatures and which has relatively low thermal conductivity when compared to the metal forming the base 11.
  • the disc support member 12 is provided with an apertured wall 16 and a pair of opposed disc receiving recesses 17 and 18 on opposite sides thereof.
  • An actuating disc 19 formed of bimetal is located in the disc recess 18 and is laterally positioned by the sidewall 21 thereof.
  • the compensating disc 22 also formed of bimetal is positioned in the recess 17 and is laterally positioned by its sidewall 23.
  • Four disc retaining fasteners 24 are mounted on the body member 11 and are provided with heads which extend inwardly beyond the sidewall 21 to engage the underside of the disc 19 and retain the disc in the recess 18.
  • the compensating disc 22 is retained in the recess 17 by a plate 26 secured to the upperside of the body member 12 and formed with a central aperture 27 proportioned so that the plate 26 extends inwardly over the recess 17 a sufficient amount to engage the edge of the upperside of the compensating disc 22.
  • a bumper or operator 28 is positioned within the aperture 29 in the wall 16 and is guided thereby for lengthwise movement.
  • the upper end of the bumper 28 engages the central part of the compensating disc 22 and the lower end of the bumper 28 engages the central part of the actuating disc 19.
  • the length of the bumper is preferably selected to equal the spacing between the adjacent surfaces of the discs at their periphery.
  • the discs 19 and 22 are selected so that in operation they are both arched in an upward direction when the relay is not actuated and are both arched in a downward direction when the relay is actuated. The selection of the discs to obtain this operation is discussed in detail below.
  • the bumper 28 is loaded in compression at all times during normal operation and the bumper holds the discs apart so that the periphery of the disc 19 is maintained against the heads of the fasteners 24 and the periphery of the disc 22 is held against the plate 26.
  • a power switch is mounted on the upper switch support member 13.
  • the power switch includes a cantilever spring arm 31 mounted on the member 13 by a rivet 32 and con nected thereby to a terminal member 33.
  • the stationary part of the switch is provided by a terminal member 34 secured to the member 13 by a rivet 36 and providing a stationary contact portion 37 underlying a mobile contact 38 carried by the cantilever spring arm 31.
  • a bumper 39 is positioned in a central aperture 41 through a wall 40 provided by the member 13 and is guided for lengthwise movement. The lower end of the bumper 39 engages the center part of the upper surface of the compensating disc 22 and its upper end engages the mobile switch arm 31.
  • the various elements are proportioned so that the mobile contact 38 is spaced from the stationary contact portion 37 when the two discs are arched in an upward direction as illustrated in FIG. 2.
  • the spring arm 31 causes the power switch to close.
  • a control switch assembly is mounted on the lower side of the disc support member 12. It includes a mobile contact arm 42, a cantilever mounted at one end by a rivet 43, and a stationary contact 44 on a stationary contact support arm 46.
  • the stationary contact 44 is a screw threaded through the arm 46 to permit adjustment of the stationary contact position.
  • a mobile contact 45 is secured to the free end of the mobile contact arm 42 and is located for movement into and out of engagement with the stationary contact 44.
  • a central bumper 47 formed of electrically insulating material is mounted on the mobile contact arm 42 for engagement with the lower side of the actuating disc 19 at its center.
  • the various elements of the control switch assembly are proportioned so that the switch is open when the discs are arched in an upward direction as illustrated in FIG.
  • the control switch is connected to the terminals 48 and 49 by straps 51 and 52, respectively, as best illustrated in FIG. 4.
  • An adjustment screw 53 is positioned to engage the underside of the mobile contact arm 42 to permit adjustment of the spring force of the arm.
  • a pair of heaters 54 and 56 are mounted adjacent to the wall 16 immediately above the actuating disc 19. These heaters extend across the recess 18 and are preferably formed of resistance wire wound flat around a support. One end of the heater 54 is connected to a terminal 57 and the other end to a connector 58 which in turn connects the adjacent ends of the heaters 54 and 56. The other end of the heater 56 is connected to a terminal 59 so that the two heaters 54 and 56 are connected in series between the two terminals 57 and 59.
  • An apertured piece of sheet mica 61 is positioned between the actuating disc 19 and the heaters 54 and 56 to electrically insulate the disc from the heater.
  • the actuating disc 19 is a disc which snaps, from one position of stability to its other position of stability, when it is free, on rising temperature within a range of temperatures between 350 F. and 356 F. On decreasing temperature, it snaps back to its initial position of stability within a range of temperatures between 325 F. and 331 F. Therefore, the disc provides a 25 F. nominal differential temperature in operation.
  • the compensating disc 22 is selected to snap on increasing temperatures within the range between 300 F. to 306 F. and to snap back on decreasing temperatures within the range between 275 F. and 281 F.
  • the compensating disc has a nominal differential temperature in operation of 25 F.
  • Discs having these high temperatures of operation with relatively low differential temperatures in operation are preferably of a type disclosed in the copending application of Anton Gerich, Ser. No. 859,853, filed Sept. 22, I969 which application is assigned to the assignee of the present invention.
  • the disc 19 is mounted in the body assembly with its high expansion side on the top or upward side, and the disc 22 is mounted in the body assembly so that its high expansion side is on the lower side. Therefore, when the two discs are at temperatures below their operating temperatures, the disc 19 tends to curve upwardly and the upper disc 22 would curve downwardly if it were not for the bumper 28.
  • the upward force created by the disc 19 on the bumper 28 is greater than the downward force created by the compensating disc 22 so the two discs are maintained in their upward position as illustrated in FIG. 2. This is because the force produced by a disc tends to be a function of the difference in temperature of the disc from its operating temperature. Therefore, since the disc 19 is at a greater temperature differential from its operating temperature than the disc 22, when the two discs are at the same temperature, upward force of the disc 19 is greater than the downward force of the disc 22.
  • the tempera tures of the discs continue to increase until an equilibrium condition is reached. At such time the rate of heat flow to the actuating disc 19 from the heaters equals the rate of heat dissipation from the disc, principally into the lower part of the relay and out through the base 11. Similarly, when the temperature of the compensating disc 22 reaches equilibrium the rate of heat flow from the heaters 54 and 56 through the wall 16 to the disc 22 equals the rate of heat dissipation therefrom.
  • the rate of heat flow to the disc 22 is much less than the rate of flow of heat directly to the disc 19 and relatively rapid rates of increase in differential temperature are obtained when the heaters are turned on. Similarly, relatively rapid rates of decrease in differential temperature are obtained when the heaters are shut off, because the disc 22 is surrounded by materials which are relatively nonconductive and because such materials provide a thermal mass resisting cooling of such disc. Also, the fact that the disc 19 is initially at a higher temperature when the heater is turned off, causes a greater cooling rate in the disc 19 than in the disc 22.
  • the discs When discs having operating temperatures substantially as described above are used in the relay, the discs remain in the position of FIG. 3 and the relay remains actuated until the difference in temperature between the discs is sufficiently low to return to a force condition in which the upward force of the disc 19 is greater than the downward force of the disc 22 and the discs then snap back to the position of FIG. 2. This tends to occur when the difference of temperature between the discs is about 25 F.
  • FIG. 5a is a time-temperature diagram of the operation of a relay having discs as mentioned above and having a heater rated for operation at 24 volts.
  • the heater is turned on and supplied with 24-volt power at the point 71.
  • the temperatures of the two discs are the same.
  • the temperature of the disc 19 increases along a temperature-time curve 72.
  • the temperaturetime curve of heating of disc 22 is along a curve 73 and the rate of heating of the disc 22 is much slower.
  • the disc temperature of the disc 19 was about 265 F. and the temperature of the disc 22 was about 185 F. Both of these temperatures were well below the operating temperatures of the respective discs so the disc 19 continued to produce an upward force on the bumper 28 and the disc 22 continued to produce a downward force thereon.
  • the downward force of the disc 22 was greater than the upward force of the disc 19, so the discs remained in the downward position of FIG. 3.
  • the heaters were shut off at a time point indicated at 77 and 78. Because the heaters had a small thermal mass, the temperature of the disc I9 began to drop almost immediately. Also because the disc 19 was in free air where heat dissipation was substantially unrestricted, its cooling occurred at a fast rate. However, because the disc 22 was surrounded by materials having a relatively high resistance to heat flow, and because such materials had a relatively high thermal mass, the rate of cooling of the disc 22 was much slower. Further, the rate of cooling of the disc 19 was faster because its absolute temperature was higher. Consequently, the temperature of the disc 19 rapidly approached the temperature of the disc 22. When the temperature of the disc 19 was approximately equal to F. higher than the temperature of the disc 22, the upward force of the disc 19 was greater than the downward force of the disc 22 and the two discs snap back to the position of FIG. 2 deactuating the relay.
  • the differential in temperature to curve of the discs represented by the curve from the point 81 to 82 is relatively flat and the discs snapped at about the point 82. Because the disc 19 moved away from the heaters when it snaps through to the operated position of FIG. 3, the rate of increase in differential temperature decreased after it snapped and equilibrium was reached at a differential temperature in the order of 80 F. If the disc 19 had not snapped away from the heaters, the differential temperature curve would have followed the dotted curve and equilibrium would have been reached at a differential temperature of about 95 F.
  • the differential temperature between the discs dropped at a rapid rate and the discs snapped back to their initial position at about the point 86 while the rate of change of differential tern perature is still occurring at a relatively high rate.
  • FIG. 5c is a time-differential temperature diagram of the same relay excepting that the voltage applied to the heaters 54 and 56 was raised to 265 volts instead of 24 volts.
  • the consequence of this change is that the rate of increase in differential temperature was slightly more rapid and the relay was actuated at the point 87. Also, the differential temperature reached at equilibrium was in the order of 95 F. However, since the temperature of the actuated disc 19 at equilibrium compared to the temperature of the compensating disc was higher, the rate of change after the heater was turned off at 88 was greater and the time lag before relay deactuation at 89 was not significantly greater than the time lag under the 24-volt condition of FIG. 5b
  • the curve of FIG. 5d was obtained by applying a control voltage of 2] .5 volts to the heaters.
  • the slope of the curve to the operating point at 9! is steeper than the slope of the corresponding part of the curve of FIG. 5b, so the delay was slightly longer.
  • the differential temperature dropped after the discs snapped and stabilized at a differential temperature of about 63 F. This drop in differential temperature occurred because the disc 19 snapped away from the heaters and consequently the rate of heat flow to the disc 19 was less.
  • the differential temperature stabilized at a differential temperature well above 25 F., so the relay remained actuated. Operational reliability is insured however, since the differential temperature curve would have followed the dotted line to equilibrium at if the discs had not snapped,
  • the relay It is desirable to arrange the relay so that the relay is actuated at a differential temperature which is substantially below the ultimate differential temperature which would be reached under nominal conditions, if disc snapping did not occur.
  • the differential temperature when operation occurs under nominal conditions should be about 63 percent of such ultimate differential temperature.
  • the adjustment screw 53 provides some adjustment of the relay off-time by permitting adjustment of the force applied to the disc 19 when the relay is actuated. Such adjustment does not affect on-time, however, since the bumper 47 is spaced from the disc 19 when the relay is not actuated.
  • the rate of change in differential temperature occurring when the heater is actuated can be increased by providing a greater thermal mass in the wall 16 as by increasing its thickness. This also tends to decrease the rate of heat flow to the compensating disc since it increases the thermal insulation. Further, the structural arrangement wherein the compensating disc is substantially completely confined by material which has relatively low heat transfer rate, when compared to metal, tends to retain the heat in the compensating disc and increases the rate of differential temperature change after the heater is turned off. Consequently, if a shorter off-time is desired, the thickness of the wall 40 can be increased to reduce the rate of heat flow from the compensating disc and to provide a larger thermal mass to slow the cooling of the disc 22. Also the screw 53 can be adjusted inward to increase the force of the spring arm 42 on the disc 19.
  • both of the discs have operating temperatures higher than the temperatures normally encountered in operation of the relay, a similar result can be obtained by selecting discs having operating temperatures which are below the temperatures normally encountered.
  • a relay comprising a body assembly, first and second bimetallic snap discs in said body assembly each having two positions of stability, said discs being positioned in said body so that they tend to move in opposite directions in response to similar temperature changes, operator means connecting said discs maintaining them in the same position with respect to each other and causing them to simultaneously snap between their two positions of stability, one of said discs producing a greater force on said operator means than the other of said discs when said discs are at substantially equal temperatures, heater means positioned between said discs substantially adjacent to said first disc, said body assembly providing thermal insulation means resisting flow of heat from said heater means to said second disc while allowing substantially unrestricted flow of heat from said heater means to said first disc, and switch means connected for operation when said discs move between their two positions of stability, said body including thermal insulating means restricting the flow of heat from said second disc to a rate substantially less than the rate of heat flow from said first disc when said heater means is shut off.
  • said body assembly includes opposed surfaces with one engaging each of said discs adjacent to its periphery to resist movement of the adjacent periphery in a direction away from the periphery of the other disc, said body assembly being free of means tending to prevent movement of the peripheries of said discs toward each other.
  • a relay comprising a body assembly, first and second bimetallic snap discs of said body assembly each having two positions of stability, said discs being positioned in said body so that they tend to move in opposite directions in response to similar temperature changes, operator means connecting said discs and maintaining them in the same position with respect to each other and causing them to simultaneously snap between their two positions of stability, one of said discs producing a greater force on said operator means than the other of said discs when said discs are at substantially equal temperatures, heater means operable to heat said first discs to a temperature higher than said second disc, at least one of said discs having an operating temperature when free of restraint which is not reached during normal operation, said one disc applying a force to said operator means which is in the same direction under all temperatures normally encountered.

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US859854A 1969-09-22 1969-09-22 Time delay relay Expired - Lifetime US3582853A (en)

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3735319A (en) * 1971-02-22 1973-05-22 Therm O Disc Inc Adjustable thermostat
US3848213A (en) * 1973-10-15 1974-11-12 Therm O Disc Inc Time delay relay
US3885222A (en) * 1972-06-06 1975-05-20 Robertshaw Controls Co Thermostat construction
US3943478A (en) * 1974-12-18 1976-03-09 Therm-O-Disc Incorporated Adjustable thermostat
US4006451A (en) * 1974-10-03 1977-02-01 Humberto Nobile Modular alarm circuit
US4177443A (en) * 1978-03-31 1979-12-04 Essex Group, Inc. Thermal relay and electric range control utilizing the same
US4198616A (en) * 1978-02-21 1980-04-15 Texas Instruments Incorporated Bimetallic thermostats with several response temperatures
US4481494A (en) * 1983-01-31 1984-11-06 Therm-O-Disc, Incorporated Bi-metal snap disc operated relay
US5121094A (en) * 1991-02-26 1992-06-09 Texas Instruments Incorporated Dual condition responsive switch apparatus
US20090115566A1 (en) * 2005-11-07 2009-05-07 Chia-Yi Hsu Manually Resettable Thermostat
US11476066B2 (en) 2019-09-20 2022-10-18 Marcel P. HOFSAESS Temperature-dependent switch

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5043690A (en) * 1990-07-12 1991-08-27 Sundstrand Data Control, Inc. Balanced snap action thermal actuator

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2203558A (en) * 1937-06-25 1940-06-04 Metals & Controls Corp Thermostat
US2207422A (en) * 1938-11-14 1940-07-09 Metals & Controls Corp Protective motor starting switch
US2543040A (en) * 1946-09-24 1951-02-27 Charles S Mertler Snap-action thermostatic switch
US3489976A (en) * 1966-01-03 1970-01-13 Texas Instruments Inc Self-protected time delay relay

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2203558A (en) * 1937-06-25 1940-06-04 Metals & Controls Corp Thermostat
US2207422A (en) * 1938-11-14 1940-07-09 Metals & Controls Corp Protective motor starting switch
US2543040A (en) * 1946-09-24 1951-02-27 Charles S Mertler Snap-action thermostatic switch
US3489976A (en) * 1966-01-03 1970-01-13 Texas Instruments Inc Self-protected time delay relay

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3735319A (en) * 1971-02-22 1973-05-22 Therm O Disc Inc Adjustable thermostat
US3885222A (en) * 1972-06-06 1975-05-20 Robertshaw Controls Co Thermostat construction
US3848213A (en) * 1973-10-15 1974-11-12 Therm O Disc Inc Time delay relay
US4006451A (en) * 1974-10-03 1977-02-01 Humberto Nobile Modular alarm circuit
US3943478A (en) * 1974-12-18 1976-03-09 Therm-O-Disc Incorporated Adjustable thermostat
US4198616A (en) * 1978-02-21 1980-04-15 Texas Instruments Incorporated Bimetallic thermostats with several response temperatures
US4177443A (en) * 1978-03-31 1979-12-04 Essex Group, Inc. Thermal relay and electric range control utilizing the same
US4481494A (en) * 1983-01-31 1984-11-06 Therm-O-Disc, Incorporated Bi-metal snap disc operated relay
US5121094A (en) * 1991-02-26 1992-06-09 Texas Instruments Incorporated Dual condition responsive switch apparatus
US20090115566A1 (en) * 2005-11-07 2009-05-07 Chia-Yi Hsu Manually Resettable Thermostat
US7663467B2 (en) * 2005-11-07 2010-02-16 Chia-Yi Hsu Manually resettable thermostat
US11476066B2 (en) 2019-09-20 2022-10-18 Marcel P. HOFSAESS Temperature-dependent switch

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DE2046277A1 (de) 1971-04-01
FR2061436A5 (de) 1971-06-18

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