US3458757A - Automatic starter switch for preheating and ignition of fluorescent lamps having heated cathodes - Google Patents

Description

July 29, 1969 F. KNOBEL-DUBS 3,458,757

AUTOMATIC STARTER SWITCH FUR PREHEA'IING AN!) IGNITION O1" FLUORESCENT LAMPS HAVING HEATED CATHODES Filed March 16, 1967 2 Sheets-Sheet 1 0 600 Q 51 T 52 3 400- C Sek.

INVENTOR. /Z/7z fivoaa flags y 1969 F. KNOBEL-DUBS AUTOMATIC STARTER SWITCH FOR PREHEATING AND IGNITION OP FLUORESCENT LAMPS HAVING HEATED CATHODES 2 Sheets-Sheet 2 Filed March 16. 196

INVENTOR. 202 {4x0542- fla s United States Patent M 3,458,757 AUTOMATIC STARTER SWITCH FOR PREHEAT- ING AND IGNITION OF FLUORESCENT LAMPS HAVING HEATED CATHODES Fritz Knobel-Dubs, Ennenda, Glarns, Switzerland, assignor to Elektro-Apparatebau F. Knobel & Co., Ennenda, Glarus, Switzerland Filed Mar. 16, 1967, Ser. No. 623,587 Claims priority, application Switzerland, Nov. 9, 1966, 16,125/ 66 Int. Cl. H0510 41/18; H01h 61/017 US. Cl. 315-99 Claims ABSTRACT OF THE DISCLOSURE The invention relates to starters or ignition switches of the type having a tapped choke coil or ballast and a normal off contact operated by the expansion and contraction of a hot wire for preheating and igniting fluorescent lamps having heated cathodes.

Background of invention In conventional starters of the above mentioned type, when ignition does not occur, the attempt of effecting ignition is automatically repeated upon retarded opening of the normal off contact, but the ratio of the opening period to the closing period of the contact is unfavorable to such a degree that the temperature of the cathodes decreases to a value which is insuflicient for obtaining a correct ignition, so that ignition is rendered diflicult and sometimes impossible. Flickering of the lamps will occur over long periods resulting in increased wear of the contacts and in shortening the lifetime of the lamp.

In my copending application, Ser. No. 516,570, a starter switch for fluorescent lamps is described, in which a flicker suppressor is provided using a temperature responsive member to hold the switch open and prevent continued repeated operation of the starter.

The object of the present invention is to operate the normal olf contacts in such manner that upon repeated switching the temperature of the cathodes does not decrease to a value below that required for ignition.

Summary of the invention The invention consists in an automatic starter device for preheating and igniting fluorescent lamps, said starter device controlling a preheating circuit including a normal off contact operated by a hot wire, wherein the said normal off contact is formed as a quick action snap contact controlling the opening and closing of the preheating circuit to prevent a temperature decrease of the cathodes of the luminescent tube at the moment of ignition during repeated switching action to below a value required for the emission of electrons.

Brief description of the drawing FIGURE 1 of the drawing is a diagram representing the temperature curve of the cathodes as a function of time in a conventional fluorescent tube.

FIGURE 2 illustrates one form of embodiment of an ignition switch and its associated circuit diagram according to the present invention.

FIGURE 3 represents a modification of the switch mechanism.

FIGURE 4 represents a diagram of the temperature curve for the tube according to the invention.

Referring to FIGURE 1, the cathodes of a conventional fluorescent tube are preheated to a temperature of about 800 to 1000 C., whereafter the normal off contact is opened at the point A. When the discharge lamp 3,458,757 Patented July 29, 1969 ice does not ignite, the temperature of the cathodes decreases to the point B, at which the normal off contact closes again, the cathode temperature then slightly increasing. The closure period, as represented, however, is substantially shorter than the opening period, so that the cathode temperature does not rise above a minimum value C of about 700 C. required for the emission of electrons, but continuously decreases.

FIGURE 2 diagrammatically represents an ignition switch according to the invention.

A switch housing 31 is provided with four terminals 5a, 6a, 9a and 10a. In the housing 31, a hot wire 11 has one end 2 fixed to the housing, while the other end 3 is secured to the hub portion 14 of a control lever 15 pivotally mounted in the housing on a pin 16. The end 2 of the hot wire is connected to terminal 9a and the end 3 to the terminal 10a. The terminal 9a is connected to the movable contact 9 of an inductance coil or choke 4 having its end 10 connected to the terminal 10a. Thus the hot wire 11 is connected in circuit with a selective number of windings of the coil 4. The normal off contact comprises a movable contact member 5 carried by a resilient contact arm 23 and a fixed contact 6. One end of the resilient contact arm is fixed to the housing 31 at point 24 and is connected to the terminal 5a of the housing. The contact arm 23 further carries a ferromagnetic armature 21 which is associated with a permanent magnet 20. A tension spring 22 fixed with one end to the housing 31 acts upon the pivoting control lever 15 for tensioning the hot wire 11 by urging the lever to turn in the direction of the arrow. The opening movement of the contact arm 23 is limited by a stop member 26 carried by the arm and coacting with a fixed abutment 30 on the housing 1. Due to the ferromagnetic armature being attracted by the permanent magnet 20, the resilient contact arm 23 is flexed and a sufliciently strong contact pressure is exerted on the normal off contact pair 5, 6.

The electric diagram represented outside the housing 31 is of conventional design. When the supply current is switched in between the conductors 7 and 8, a preheating current flows from the conductor 7 through the coil 4, the electrode 2 of the cathode tube 1, terminal 5a, normal off contacts 5, 6, terminal 6a, electrode 3 of the cathode tube to the conductor 8. At the same time, a control current flows from the coil 4 through contact 9, terminal 9a, hot wire 11, terminal 10a to the end 10 of the coil 4. Due to this current, the hot wire 11 is gradually heated and expands correspondingly. The control lever 15 now can pivot in counterclockwise direction owing to the action of the spring 22 and acts upon the contact arm 23 at a point 25 intermediate the permanent magnet 20 and the place of attachment 24 of the arm. At the moment when the pressure exerted by the end of the control lever due to the action of springs 22 exceeds the force of attraction of the permanent magnet 20, the contacts 5, 6 open suddenly in the manner of a snap switch and interrupt the preheating circuit of the cathode tube, while producing in the coil 4 an induced electromotive force which normally effects a flicker free ignition of the tube 1.

If, however, the contacts '5, 6 open at such an instant which is unfavorable with respect to the momentary value of the current, or when the voltage of the net mains 7, 8 is too low, or the ambient temperature very low, it may happen that the tube 1 does not ignite and the normal off contacts 5, 6 close again or, switching is repeated once or several times. Such a case is represented in the diagram according to FIG. 4. It is seen from this figure that the normal off contacts have substantially identical opening periods A1-B1, A2-B2, A3B3, A l-B4, and closing periods B1-A2, B2-A3, B3-A4, so that the cathodes, after each closure of the contacts, are heated with a suflicient margin of safety above the minimum value C, and safe ignition occurs after the first or second repetition of the switching operation, provided that the lamp is intact. The closing periods B1-A2, B2-A3, B3-A4 can be modified by varying the number of windings of the coil 4, so that they can be made substantially equal to the opening periods Al-Bl, A2-B2, A3-B3. The stop member 26 relieves the hot wire 11 from mechanical stress and limits the opening gap between the contacts 5, 6 to a minimum value as determined by experience.

In the modification according to FIG. 3 a ferromagnetic contact strip 29 is secured to the contact arm 23 and is provided with an offset armature finger 27 coacting with a permanent magnet 28. The control arm 15a acts upon the contact arm 23 at the place where the strip 29 is secured to the arm. The circuit diagram of this modified switch is the same as that shown in FIG. 2 and operation of the switch is identical with the operation as explained in relation with FIG. 2.

In both examples according to FIGS. 2 and 3, the normal ofl contacts 5, 6, due to the permanent magnet associated with the resilient contact arm 23, operates as a magnetic quick action or snap switch. Instead of a magnetically operated quick action switch, the same effect can be obtained by a mechanical quick action switch in which the movable contact is provided on a biased contact spring which, however, requires adjustment and causes switching noises.

I claim:

1. An automatic starter switch for control-ling a preheating and igniting circuit for luminescent tubes having a cathode which emits electrons at a temperature above a predetermined temperature, said switch comprising a hot wire, a pivotally mounted control lever operatively connected to one end of said hot wire tobe actuated upon dilatation of the hot wire, a normally off contact means including a movable contact for controlling the opening and closing of said circuit, a contact arm carrying said movable contact between open and closed positions, biasing means urging said contact arm and holding said movable contact in a closed position against the initial force exerted on said contact arm by said hot wire and thereby controlling the period of opening for said contacts when said force exerted by said hot wire overcomes said biasing force and causes the contacts to open, and means electrically connected to said hot wire for adjusting the force exerted thereby on said control lever, said last mentioned means and said hot wire controlling the closing period so that the temperature of said luminescent tube is maintained above said predetermined value required for the emission of electrons during opening and closing of said contacts.

2. The starter switch of claim 1 in which said means for biasing said movable contact includes a permanent magnet for attracting said movable contact and said contact arm to its closed position and in which said normally olf contact means acts as a quick action snap contact.

3. An ignition switch as claimed in claim .1, in which stop means are provided for limiting the opening movement of said movable contact and mechanically relieving stress from said hot wire upon opening of the normal off contact.

4. An ignition switch as claimed in claim 3, in which the movable contact arm of said normal oft contact means is provided with a ferromagnetic strip having an armature portion olfset with respect to the contact arm and coasting with said permanent magnet.

5. An automatic starter switch as claimed in claim 1 said means for adjusting including a choke coil having a movable tapping contact electrically connected to the other end of said hot wire, one end of the choke coil being electrically connected to said first named end of the hot wire, whereby said hot wire is selectively connected in circuit with a variable number of windings of the choke coil, so that by varying the number of windings of the choke coil in circuit with the hot wire, substantially identical opening and closing periods of the normal off contact means may be obtained upon repeated switching action.

References Cited UNITED STATES PATENTS 2,355,296 8/1944 Holmes 200137 X 2,479,372 8/1949 Knobel 315-104 X 3,086,141 4/1963 Rubinstein 315- JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.'R. 3 37-23

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