US2586321A

US2586321A - Thermal starting switch

Info

Publication number: US2586321A
Application number: US25688A
Authority: US
Inventors: Ted E Foulke
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1948-05-07
Filing date: 1948-05-07
Publication date: 1952-02-19
Anticipated expiration: 1969-02-19

Description

Feb. 19, 1952 V FOULKE 2,586,321

' THERMAL STARTING SWITCH Filed May 7, 1948 Fggv.

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Patented Feb. 19, 1952 THERMAL STARTING SWITCH Ted E. Foulke, Chagrin Falls, Ohio, assignor to General Electric Company, a. corporation of New York Application May 7, 1948, Serial No'. 25,688

6 Claims.

This invention relates to starting switches for electric discharge devices, and more particularly to a thermal type starting switch particularly suitable for low voltage fluorescent lamps.

The glow discharge starting switches now in wide use with fluorescent lamps provide for heating the filamentary electrodes and for impressing a high voltage for a short duration across the electrodes at starting. However, in certain situations, such as in railroad'service where 60 volt D. C. is in use, starters of the glow discharge type are not available to operate at these voltages, and some other type of starter is required, for example, the so-called thermal starter. With thermal starters of the type commercially available, considerable difficulty is. often encountered due to slow and uncertain restart. This comes about by reason of the series heater which keeps the starting contacts open. Upon final cooling, after the circuit has been opened and then reclosed, the contacts slowly come" together and then begin to separate at the leastcontact. This action results in two serious disadvantages, one of which is insufficient preheating of the electrodes if a start. does occur, and the other of which is the many attempted starts if the lamp is not an easy starting one. In any event, the improper preheating of the electrodes on quick restart causes early failure of the lamp.

An object of my invention is to provide a new and improved thermal switch for operating electric discharge devices.

Another object of my invention is to provide a new and improved thermal switch which will provide for the necessary time delay in the application of the starting voltage to insure an adequate initial heating of the electrodes of the electric discharge device.

A further object of my invention is to provide a new and improved snap-acting thermal switch for electric discharge devices which will provide adequate preheating time for the initial and also for each and every repeated attempt of the discharge device to start or restart.

A feature of my invention is the provision of a new and improved snap-acting thermal switch which employs magnetic means opposing separation of the contacts, when closed, to delay ultimate separation thereof and also opposing closing ofsaid contacts, when open, to delay ultimate closing thereof.

In addition to the improved snap-acting thermal switch mentioned above, the present application discloses a new and improved circuit combination of an electric discharge device with a thermal switch which has decided advantages over the circuits previously employed in the art. This combination is characterized by positive starting of the lamps even on low direct current voltages, and by constant preheating time, notwithstanding diificult and unusual starting conditions as might result, for instance, from a momentary interruption of the power supply. This circuit combination may be used with other types of starting switches besides that specifically claimed in this parent application. Accordingly, it is being claimed in my divisional application Serial No. 147,050, filed March 1, 1950, and assigned to the same assignee as the present invention.

Further features and advantages of my invention will appear from the following detailed description of species thereof.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. Fig. 1 is a diagrammatic view of an electric discharge device and a starting and operating circuit therefor incorporating my invention; Fig. 2 is an elevation, partly in section, illustrating in more detail the snap-acting thermal switch shown in the starting and operating circuit of Fig. 1; Figs. 3 and 4 are perspective views of the snap-acting thermal switch of Fig. 2; Figs. 5 and6 are perspective views of a modification of the snap-acting thermal switch illustrated in Figs. 2, 3 and 4; and Figs. 7 and 8 are elevations of portions of further modifications of switches comprising my invention.

Referring to Fig. l, I have there illustrated one embodiment of my invention as applied to an.

electric discharge device I. The electric discharge device I, such as a fluorescent lamp, therein illustrated comprises anelongated tubular or cylindrical envelope 2 having sealed into the ends thereof filamentary electrodes 3 and 4, each herein illustrated as comprising a coil, preferably in the form of a coiled coil of tungsten wire activated with oxides of alkaline earth metals such as a mixture of barium and strontium oxides. The envelope 2 contains a gaseous atmosphere such as a rare gas like neon, argon or mixtures thereof at a pressure of a few millimeters and a small quantity of mercury which, during the operation of the lamp, has a low pressure of the order of 10 microns. The device I may be a low pressure positive column lamp of a fluorescent type provided with a suitable phosphor or fluorescent coating. This fluorescent coating, upon excitation by the radiation produced by an electric discharge between the electrodes, transforms a shorter wave radiation due to the discharge into longer wave radiation such as radiation within the visible range. For ease of startin a stripe or strip 5 of conductivematerial which, for example, may be a metallic paint or graphite mixed with potassium silicate, may be applied to the surface of device I. The starting strip 5 may be connected to one or both of the electrodes.

In accordance with my invention, device I is connected across a suitable power supply circuit 6, 6 which, for example, may be a 118 volt, 60 cycle source, for supplying current to device I through the usual ballast I which serves as a starting inductance. A manual make-and-break control switch 8 may be used to connect device I to the power supply. A starting or heating circuit 9, 9' embodies a snap-acting thermal switch ID in series with filamentary electrodes 3 and 4, and with ballast l in series therewith, across the current supply 6, 6. A capacitance II of 0.006 microfarads rating is preferably connected directly across the thermal switch III.

The snap-acting thermal switch I comprises a bimetallic strip I2 actuated by a heater element I3 which is in series with ballast 1 across the supply circuit 6, 6'. The bimetallic strip I2 carries an armature I4 which is in magnetic coupling with a permanent magnet I5, so that when strip I2 deflects and opens a pair of normally closed contacts comprising a stationary contact I6 and a movable contact II, the armature simultaneously coacts with the permanent magnet.

Referring to Fig. 2, the switch I8 is mounted on an insulating disc I8 and enclosed in a suitable can or incasement I9. An insulating support member 20 mounted on disc I8 supports a pair of ternmerature-compensating elements 2| and 22 which are formed from bimetallic strips and are designed in such a manner so as to conform to the shape of the bimetallic strip I2. Thus, when elements 2| and 22 and bimetallic strip I2 are mounted on support member 20 in a definite space relationship, these elements will retain this space relationship regardless of the ambient temperature. Heater element I3 is mounted on a pair of lead-in

wires

23 and 24 supported by disc I8 in heat-transfer relationship to bimetallic strip I2. Permanent magnet I5, which, for example, may be an insulating cylindrical-shaped magnet supported on a rod 25, which is embedded in magnet I along its longitudinal axis, is supported by

extensions

26 and 21 secured to the free ends of elements 2| and 22, respectively. This insulating magnet may comprise a sintered mixture of magnetizable metallic oxides, for example, a mixture of 30 parts of F8203, 44 parts of F6304, and 26 parts of C0203.

Armature I4, comprising a cylindrical magnetic sleeve, substantially surrounds permanent magnet I5 and is supported by the free end of the bimetallic strip I2. Stationary contact I6 is secured to element 2| by means of an extension arm 28. Movable contact I! is securedito armature I4 and is mounted thereon to engage stationary contact I6 when the bimetallic strip is in its inactive, or cold, position. It is sometimes found desirable to mount an additional arm 28' to element 2| adjacent arm 28. Arm 28 usually comprises a long, thin deformable metallic strip with stationary contact I6 mounted on the free end thereof. The size and weight of contact I6 may, when switch I6 is subjected to a shock, cause arm 28 to obtain a permanent set. Thus, arm 28' serves as a bufier to restrain arm 28 from deforming to a point beyond its elastic limit when exposed to shock. A pair of

terminal contacts

29 and 30 are connected through lead-in wires 3| and 32 to contacts I6 and I1 whereby to connect said contacts I6, IT to the filamentary electrodes of an electric discharge device. The heater I3 is connected through

leads

23 and 24 to another pair of terminal contacts 38' (only one of which is shown in Fig. 2).

Fig. 3 indicates the relative positions of the armature I4 and magnet I5 when contacts I6 and I! are in their normally closed position,

while Fig. 4 indicates the relative positions of armature I4 and magnet I5 when the contacts I8 and H are in their open position.

Figs. 5 and 6 illustrate a modification of the thermal switch shown in Figs. 2, 3 and 4 and embody, in general, the same constituent parts thereof except that insulating permanent magnet I5 is replaced with a conductive permanent magnet 33. The cylindrical magnetic sleeve I4 is replaced with a U-shaped armature 34, and rod 25 is replaced with a non-magnetic metallic support member 35 in the form of two strips of brass or copper between which the magnet is supported. The metallic support member 35 in turn is secured to the free ends of elements 2| and 22. In order that contacts I6 and II, when open, be not short-circuited by support member 35 directly contacting armature 34 on the side supporting movable contact an insulating sheet of mica 36 is secured to the inner surface of armature 34. This insulating feature is necessary in the type of switch employing a conductive permanent magnet. The stationary contact I6 may be secured to an extension arm 31 of the metallic support member 35, which in turn is secured to element 2|. Fig. 6 illustrates the position of the metallic permanent magnet 33 when the contacts I6 and I1 illustrated in Fig. 5 are in the open position.

When the entire installation is energized as indicated in Fig. 1 by closing switch 8, current flows through the ballast I, heater coil I3, filamentary electrode 3, bimetallic strip I2, contacts I1 and I6, element 2|, and filamentary electrode 4. Permanent magnet I5 retains contacts I6 and I1 in their normally closed position for a predetermined period 01' time until the stress and strain within the bimetallic strip I2, due to the heat transferred by heater element I3, overcomes the magnetic attraction of permanent magnet I5 for armature I4. At this point thermal switch I0, and more particularly the bimetallic strip I2, disengages the normally closed contacts with a snap action and the-permanent magnet I5 engages another portion of armature I4 to retain contacts I6 and H in an open position.

During the period of time contacts I6 and I1 are closed, the filamentary electrodes 3 and 4 are sufficiently heated to support an electrical discharge therebetween, and the induced voltage supplied by the inductance 1 initiates .an are discharge between the electrodes 3 and 4. After an arc discharge has occurred between filamentary electrodes 3 and 4, contacts I6 and I1 remain disengaged due to the discharge current flowing through the series heater coil I3 which continually heats the bimetallic strip I2 and does not permit it to cool to that predetermined temperature at which point the strain within the bimetallic strip overcomes the magnetic attraction of magnet I5 for armature I4. If, however, device I should not start after the initial arc discharge has occurred or if it should be restarted immediately after having been turned off, the magnetic attraction of the magnet and armature of my thermal switch will retain the contacts l6 and I! in their open position until the bimetallic strip has cooled to a predetermined temperature. At this temperature, contacts l6 and I! will snap closed and will remain closed until the bimetallic strip has been reheated and the filamentary electrodes 3 and 4 have again reached a temperature sufficient to support an arc discharge.

In Fig. '7 I have illustrated a modification wherein the mounting of the armature and magnet is the reverse of that shown in the modifications previously described. To this end, a magnet 38 is mounted on the bimetallic element I2 and an armature 39 is fixedly mounted in proper relation thereto. The armature 39 may be mounted on a support member corresponding to the

members

25 and 35 in Figs. 2 and 5, respectively.

Whereas, in the modifications previously described, I have, in effect, provided a single magnet and armatures located on opposite sides of, and in the path of movement of, said magnet, in Fig. 8 I provide a modification employing a single armature 40 mounted on the bimetallic element 12, and in effect, two magnets mounted on opposite sides of said armature. In this case, the magnetic means is shown as a horseshoe-shaped ma net 41 with the armature 40 located between poles of the magnet.

The operation of the modifications shown in Figs. 7 and 8 is essentially the same as that of the modifications shown in Figs. 2 and 5.

The above described new and improved snapacting switch performs the functions of a thermal switch, namely, to retain open a pair of normally closed contacts during the operation of a lamp, without the need for storing in the switch a quantity of heat sufficient in itself to perform the holding open function mentioned above. The provision of a permanent magnet replaces the need for the storage of a larger quantity of heat which in turn must be dissipated before closure of the switch contacts occur. The snap-acting switch comprises a permanent magnet which provides a predetermined preheat period for filamentary electrodes associated with the switch by retaining the switch contacts closed, and, then opening the contacts of the switch with a snap action to provide the greatest possible voltage impulse With the given starting circuit elements. Upon opening of the switch contacts, the magnet retains the contacts open without the need of a large amount of thermal energy; all that is required is a temperature gradient large enough to retain the bimetallic support for the movable contact in engagement with the magnetic means holding open the contacts. The result is a switch which will close a pair of contacts held open by a discharge circuit as rapidly, if not more rapidly than a thermal switch employing only storage of thermal energy to perform the same function.

It will be obvious to those skilled in the art that various modifications may be made in the switches comprising my invention without departing from the spirit of the invention, including variations in the construction and mounting of the magnet IE or 33 and armature I4 or 34, and the appended claims are intended to cover any such modifications coming within the scope thereof.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A thermalswitch comprising a fixed contact and a movable contact carried by a thermally-deformable actuating member, a substantially cylindrical armature carried by said actuating member, and a permanent magnet mounted within said armature to alternatively attract opposite sides of said armature when said actuating member is in either its closed-contact position or its open-contact position whereby to oppose both opening and closing of said contacts, a conductive support member carrying both said fixed contact and said magnet, said actuating member and said support member providing circuit terminals for said contacts, said magnet being composed of insulating material in order to prevent short-circuiting said terminals when said contacts are open.

2. A thermal switch comprising a pair of thermally-deformable members mounted in ambient temperature compensating relationship for maintaining a normally constant spatial interval therebetween, a heater element mounted in heat transfer relationship with one of said members for actuation thereof, a pair of cooperating contacts carried by said members, and means for delaying both the opening and the closing of said contacts, comprising a permanent magnet and a cooperating armature carried by respective ones of said members, said magnet and armature having cooperating portions disposed to attract and hold each other in either position of said one member corresponding to the open and closed contact positions of said members.

3. A thermal switch comprising a pair of bimetallic strips of similar configuration and characteristics, and mounted in substantial parallelism for maintaining a normally constant spatial relationship therebetween despite variations in ambient temperature, a heater element mounted in heat transfer relationship with one of said strips for actuation thereof, a pair of cooperating contacts carried by said strips, and means for delaying both the opening and closing of said contacts comprising a permanent magnet and a cooperating armature carried by respective ones of said strips, said magnet and armature having cooperating portions disposed to attract and hold each other in either position of said one strip corresponding to the open and closed contact positions of said strips.

4. A thermal switch comprising a pair of thermally-deformable members mounted in an ambient temperature compensating relationship for maintaining a normally constant spatial interval therebetween, a heater element mounted in heat transfer relationship with one of said members for actuation thereof, a pair of cooperating contacts carried by said members, a substantially cylindrical armature carried by one of said members and a permanent magnet carried by the other of said members and located to lie within said armature in order to alternately attract opposite sides of said armature when said one member is actuated to either its closed or open contact position, whereby to oppose both the opening and the closing of said contacts.

5. A thermal switch comprising a pair of bimetallic strips of similar configuration and characteristics, and mounted in substantial parallelism for maintaining a normally constant spatial relationship therebetween despite variations in ambient temperature, a heater element mounted in heat transfer relationship with one of said strips for actuation thereof, a pair of cooperating contacts carried by said strips, a substantially cylindrical armature carried by said one strip,

and a permanent magnet carried by the other oi. said strips and mounted within said armature to alternately attract opposite sides thereo! when said one actuating strip is in either its closed or its open contact position, whereby to oppose both the opening and the closing 0! said contacts.

6. A thermal switch comprising a pair of bimetallic strips 01 similar configuration, dimensions and characteristics and mounted in substantial parallelism for maintaining a normally comtant spatial relationship therebetween despite variations in ambient temperature, a heater element mounted in heat transfer relationship with one of said strips for actuation thereof, a

I pair of cooperating contacts carried by said strips,

a substantially cylindrical armature carried by said one strip, and a permanent magnet composed of substantially nonconductive material carried by the other of said strips and mounted within said armature to alternately attract opposite sides thereof when said one actuating stri isin either its closed or its open contact position, whereby to oppose both the opening and the closing 0! said contacts.

TED E. FOUIKE'.

REFERENCES crran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,746,827 Fry et al Feb. 11, 1930 1,793,904 Carter et al Dec. 2. 1930 2,181,294 Blggs Nov. 28, 1939 2,238,282 I Ayers Mar. 25, 1941 2,302,250 Penn Nov. 17, 1942 2,305,583 Hodgkins Dec. 15, 1942 2,388,951 Bower NOV. 13, 1945 2.412.883

Gasser Dec. 17. 1948