US2332492A - Starting switch - Google Patents

Description

9ct., 19, 1943. 1. B. BEN-:51N

STARTNG SWITCH Filed Dec. 3o', 1941 BINET/ UIUC Inventor: Igor- BBensin,

a'. /9 is Attcrneg.

Patented Oct. 19, 1943 STARTING SWITCH Y Y Igor B. Bensin, Schenectady, N. Y., assigner to Y .17

General Electric Company, a corporation of NewJ York A Application December so, 1941, serial No. y424,912 s claims. (Omoo-122) My invention relates to switches for starting electric 'discharge devices.

-A common form of electric discharge device, such as a fluorescent lamp, is provided at opposite ends with thermionic electrodes of filamentary form which after the lamp has been connected with the source of current supply and prior to the starting of the discharge in the lamp have' their temperature raised Yto the point of electron emission by current passed through them in series. When the temperature of the electrodes Ahas reached that point the circuit is interrupted between them automatically by a. switch whereby a surge of sufficient voltage is produced across the lamp to start the discharge therein.

A common form of starting switch employed in such apparatus is a thermal switch. A well known disadvantage of that. type of switch as usually vemployed to start the discharge is that because of the slow separation of the contacts it does not produce the desired sudden interruption of the circuit which it controls in order to be most effective for starting the discharge.

One object of my invention is the provision of an improved switch which will produce a sudden interruption of the circuit controlled by it notwithstanding the fact that its contacts may, in response to an increase in heat, have a slow relative movement.

Another object of my invention is the provision of a starting switch for the purpose described which initiallyprovides a low resistance path for the electrode heating current and which is constructed to open that path in substantially the same time as that required for the electrodes to become heated to the. desired temperature regardless of the temperature of the ambient.

A further object of my invention is the provision of a. starting switch which, if the device is not started at the rst attempt will make successive further attempts to start it and in the event that the device cannot be started after a reasonable number of attempts have been made l will cease making further attempts.

A still further object is the provision of a ,starting switch which, if the device to be started will not start after making a reasonable number of attempts and the switch then ceases making any further attempts to start it, will thereafter maintain the circuit controlled by the switch in open circuitposition.

An additional object of my invention is the provision of an improved thermal switch which compensates for variations in the ambient -temperature.

My invention will be better understood from the following description vtaken in connection with the accompanying drawing, and its 4scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram of 4an embodiment of my invention; Fig. 2 is a perspective view of" the complete switch involving my invention in its normal unenergized position; Figs. 3, 4, `5 and 6 are similar views limited to the essential parts of the switch showing them in their various different `positions; and Fig. 7 is a detail view of one thermal member of the switch. As represented by Fig. 1, the'switch I comprising my invention is arranged to be connected between the electrodes 2 of the discharge device 3 which may be a fluorescent lamp so that before it starts the discharge in the device it vcontrols the heating of the electrodes in Aa Well :known manner. The device is shown connected with a source of supply 4 of alternating current which, for example, may be a 60 cycleyllvolt lighting circuit, the connections including the control switch 5 and the ballast reactor' 6. The device may be of the usual tubular form of fluorescent lamps comprising the glass envelope lcontaining mercury vapor at a low pressure and having the inner surface of its side `walls coatedwith a suitable phosphor which 'under the infiu'ence of an electric discharge through the mercury vapor produces fluorescence. YThe electrodes 2 lare shown of lamentary form and may comprise a suitable refractory metal `such Aas tungsten wire extend ,the two switch-securing 'terminals l0.

Secured to the' base is the cup-like casing Il which is shown having an insulation lining I2.

`Secured to the terminals I0 -are the angles I3 and I4 to which are attached the pla'te I5 of insulating material which snugly fits within the casing I I. Secured to the front face of the plate I5 is the third angle I6 and to the rear face thereof is the capacitor Il.

The switch which I have devised employs two thermal members each of Awhich lmay .be 'a blmetallic member which moves cooperating con-l tacts in directions at right angles to eachother. The one thermal member 20 has overlapping portions wh-lch in configuration somewhat resemble an inverted J, the lower end of the long arm being rigidly secured to the angle I4, the lower end of the short arm being provided with the laterally extending contact 2| and the loop between the two arms receiving the high resistance heater 22. This thermal member I term the controlling thermal member. The heater 22 is supported by the conductor 23 forming a part of the circuit thereof which is suitably secured as by soldering or welding to the short arm of the thermal member. 'l'he other connection to the heater is the conductor 24 which is fastened to the angle I3. The other thermal member shown at 26 which I term the timing thermal member is more sensitive than the thermal member 20. At its lower end it is fixed to the angle I6 and at its upper end has projecting therefrom the two spaced contacts 21 and 28. Thermal member 26 is heated by the low resistance heater 29 which is shown secured at one end to the upper end of the member and connects at its lower end with the angle 3. In the normal unenergized positions of the two thermal members as shown by Fig. 2, a low resistance electrode heating circuit is completed through the heater 29, thermal member 26, contacts 21 and 2|, and thermal member 20, it being understood that thecontacts 21 and 2| engage each other at that time with light pressure.

When the control switch is closed a relatively heavy current flows through the ballast 6, the electrodes 2, and the switch by way of the path just mentioned above to produce a rapid heating of the electrodes. By the time they have reached an electron emitting temperature or soon thereafter the thermal member 26 will have been bent as a result of heat received from its heater 29 to such an extent that the contact 21 will have slid along the contact 2| until it will have passed the end thereof at which time the contacts quickly separate to produce a sudden interruption of the circuit controlled thereby. This quick separation of the contacts is due to the resilience of either one or both of the thermal members carrying the contacts for it will be seen that as soon as the member is released it springs from the position shown in Fig. 2 to a position s uch as that shown by Fig. 3. Likewise when the member 26 is released from the restraint of the friction between the contacts 2| and 21 it springs lforward to a position such asfshown by Fig. 3. Because of heat inertia, the movement of the member 26 will continue somewhat after the contacts have separated. Thus the circuit of the electrodes is quickly interrupted in spite of the fact that the movement of the contact 21 along the contact 2| was relatively slow. This interruption' of the electrode heating circuit occurring between the electrodes presumably starts the discharge in the device. Assuming that it does start, the thermal member 26 and its heater 29 soon cool down so that the member will tend to return toward its original position. The thermal member 20, however, immediately begins to receive heat from its heater 22 since the'breaking of the circuit between contacts 21 and 2| removes the low resistance path which formerly existed around the heater 22. The voltage now 'applied to the heater 22 is the arc drop voltage across the device 3 and the resulting heat supplied to the thermal member 20 is uillcient to move the contact 2| thereof to a position between the contacts 21 and 28 before the thermal member 26 has returned to a position near its normal or starting position.

trated by Fig. 5.

This heating of the thermal member 2U prevents yinterference of the contacts carried by the two thermal members after the device is started, the relative positions of the switch parts during the normal operation of the device being as represented by Fig. 4.

In the event that the device fails to start at the first attempt, as above described, the voltage applied to the heater 22 will be considerably greater than it would have been had the lamp started, since then it is approximately double the arc drop voltage of the device. As a result thereof the greater heat applied to the thermal member 20 will continue to move the contact 2| after the thermal member 26 has approximately reached its originalv position so that the contact 2| will engage the contact 28, as illus- These contacts thereby reestablish the low resistance electrode heating current path through the heater 29 to again raise the temperature of the electrodes to the point of electron emission- The thermal member 26 accordingly is again bent whereby the contact 28 thereon slides along the contact 2| until it slips off the end thereof causing a second quick interruption of the electrode heating circuit in a second attempt to start the device. Ifit starts, the voltage applied to the heater 22 immediately reduces 4to the arc drop voltage of the lamp whereby the thermal member 20 cools somewhat to bring its contact 2| into a position between the contacts 21 and 28 before they return, upon cooling, to their original position. The switch parts will then again assume approximately the position shown by Fig. 4.

Should the device fail a second time to start, the thermal member 20 would not return its contact 2| between contacts 21 and 28, but rather will tend to move it farther outward. As the member 26 cools oi, its contact 28 will again engage-the contact 2| but this time on the end thereof whereupon the heater 29 will again become energized and cause the contacts to interrupt the electrode heating circuit in a third attempt to start the device. If this attempt is not successful the apparatus may make several more attempts, each time the contact 28 engaging the end of the contact 2|. However, the thermal member 20 gradually accumulates heat partly from its heater 22 and partly from the heater 29 as a result of the series of unsuccessful starting attempts so that the contact 2| finally is out of the path of movement of the contact 28 and as a, result thereof the switch will make no further attempts to start the device. In this position of the thermal member 20 the switch is locked in an open circuit position it being maintained by heat constantly supplied by the heater 22,

If the failure of the device to start is due to a defect in the device and it is replaced by a device in good condition or if the controlling switch 5 should be moved to open position and after the switch parts have had an opportunity to cool down is reclosed, then the thermal member 2|) in cooling would move its contact 2| into engagement with the outer or opposite side of the contact`28 from that normally engaged. Although the contact 2| now is in engagement with the contact 28 at its outer side, the switch nevertheless will function in a, manner similar to the first starting attempt already described above.

An imporant feature of my invention is that the operation of the switch is independent of the effect of changes in the temperature of the ambient- -By reason of the shape of the thermal member 20 and the proportions of the two arms thereof, the short arm being approximately onehalf to one-third the length of the long arm, the

contact 2l is moved in a path substantially parallel to the member in response to changes in the ambient temperature. This property of the thermal member is illustrated by Fig. 7 where the thermal member 20 at normal room temperature the dotted line positions, the contact 2| carried thereby moves up or down, as shown by Fig. '1, in substantially a straight line. Since the contacts 21 and 28 which cooperate with the contact 2| stand substantially vertical the effect of changes in the ambient temperature have substantially no eiect on the contact pressure and very little effect on the time of interruption of the electrode heating circuit.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

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

1. A quick opening switch comprising cooperating switch contacts, means for sliding one of said contacts over the other and beyond the end thereof, and means for resiliently pressing said contacts together during the sliding movement thereof and for producing relative movement of the contacts in a. direction transversely of said sliding movement after the one contact passes beyond the end of the other.

2. A quick opening thermal switchcomprising cooperating switch contacts, means for sliding said contacts over each other to a point at which one passes` beyond the end of the other, and means for yieldingly holding said contacts in engagement with each other and for causing them to separate suddenly with a movement transversely of the direction of said sliding,

3. A quick opening switch comprisingY cooperating current carrying contacts, means for causing said contacts to slide over each other in frictional engagement to a point at which one contact slips olf the end of the other, said means including a resilient member arranged to be tensioned by the friction of saidengagement.

4. A thermal switch having terminals and having cooperating contacts connected therebetween and normally engaging each other, a thermal member arranged to move one of said contacts out of engagement with the other contact, a heater for said thermal member connected in series with said contacts, a second thermal member arranged to move said other contact out of the path of movement of said one contact when the thermal moving member therefor cools, and a heater for said second thermal member connected between said terminals.

5. A thermal switch. having terminals and having cooperating contacts connected therebetween and normally engaging each other, a thermal member arranged to move one of said contacts in va direction to disengage said other contact, a heater for said thermal member connected in series with said contacts, a second thermal member arranged to move said other contact in a direction substantially at right angles to the direction of movement of said one contact to prevent re-engagement of said contacts when the thermal moving member for said one contact cools and a heater for said second thermal member connected between said terminals.

6. In combination, an electric discharge lamp-y having spaced electrodes adapted to be preheated by current flow therethrough, a. ballast for said lamp, means including said ballast for 'connecting one end of each of said electrodes with a source of current supply and a starting switch for said lamp connected between the other ends of said electrodes, said switch comprising a pair of spaced contacts and a single contact normally engaging one of the contacts of Asaid pair of con-'- tacts, means responsive to said current flow for causing said one contact to disengage said single v contact thereby making an attempt to start the lamp, means responsive,v to the resulting voltage between said other ends of the lamp electrodes if the lamp fails to start for causing said single contact to engage the other contactof said pair, said other contact being then operative in response to said current ow to disengage saidone contact to make' a second attempt to start the lamp.

'7. In combination, an electric discharge lamp having spaced electrodes adapted to be preheated by,` current iiow therethrough, a ballast for said lamp, means including said ballast for connecting one end of each of said electrodes with a source of current supply and a starting switch for said lamp connected between the other ends of said electrodes, said switch comprising cooperating contacts, a heat accumulating heater connected between said other ends of the lamp electrodes, means responsive to said heater for causing one of said contacts to engage the other, means responsive to the resulting current ow for causing said other contact to disengage said one contact, said heater being responsive to the heat accumulated therein after a number of unsuccessful attempts to start the lamp for thereafter maintaining said contacts disengaged.

8. A thermal switch comprising a plurality of thermal strips constructed and arranged to warp in directions substantially at right angles to each other when heated, cooperating contact members each carried by one of said strips, one of said contact members sliding over and off the end of the other contact member when the strip which carriessaid one contact member is heated, theA strip which carries the other contact member having two substantially parallel over-lapping arms joined together at corresponding ends, one arm being approximately twice the length of the other, the free end of the longer arm being xed and said other contact member being secured to. the free end of the shortery arm, and means for heating said last mentioned strip to cause said contact members to separate.

IGOR B. BENSIN.

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