US2523020A

US2523020A - Magnetic starting system for electric discharge devices

Info

Publication number: US2523020A
Application number: US765352A
Authority: US
Inventors: Hehenkamp Theodorus; Jong Klaas De
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1947-01-14
Filing date: 1947-08-01
Publication date: 1950-09-19
Anticipated expiration: 1967-09-19

Description

Sept. 19, 1950 T. HEHENKAMP' ETAL 2,523,020

MAGNETIC STARTING SYSTEM FOR ELECTRIC DISCHARGE DEVICES Filed Aug. 1, 1947 mll 5 Fig. 5

Tnyerfiror s: Theodovus Hehenkomp, KIQQS cle xlOl'l g, by W 0 Their- Afii'irorneg.

Patented Sept. 19, 1950 MAGNETIC STARTING SYSTEM FOR ELECTRIC DISCHARGE DEVICES Theodorus Hehenkamp and Klaas de J ong, Eindhoven, Netherlands, assignors to General Electric Company, a corporation of New York Application August 1, 1947, Serial No. 765,352 In the Netherlands January 14, 1947 14 Claims. 1

Our invention relates to magnetic starting systems for electric discharge devices such as fluo-' rescent discharge lamps.

Gas discharge devices or tubes are quite often connected to a current source the voltage of which is sufficient to cause the tube to conduct, but insufficient to ignite the tube. The words gas discharge tubes mean not only those tubes which are filled with one or more gases, but also tubes which contain a vapor or a gas vapor mixture. In order to light such a tube, an ignition switch generally is applied which short circuits the tube through at least one glow or filamentary electrode. The short circuit current preheats the electrode and when the switch opens an additional voltage is generated in one of the supply lines to the tube by means of an inductive ballast. The preheating, as well as the additional voltage, facilitates the ignition of the tube. When, however, the tube does not ignite upon the first opening of the switch the operation is repeated until the ignition conditions are obtained.

One type of discharge device to which this type of starting has been applied is the fluorescent lamp. Usually a thermal bimetal switch is used as an ignition switch in which a glow discharge or a resistor is used for the heating element. The glow discharge switch is the more common. The switch with the resistor is used preferably in direct current installations and with tubes which are very difficult to ignite (tubes which are very long or which are used at very low ambient temperatures). Arrangements with thermal switches have the disadvantage that it takes a few seconds before the tube is ignited, In alternating current installations the magnitude of the additional voltage is not constant; for example, when the switch opens as the current goes through zero, the generated additional voltage is zero; the switch then must repeat its operation so that a further ignition delay occurs. It has been attempted previously to eliminate these disadvantages with a switching mechanism which has far less delay and can operate synchronously with the frequency of the supply voltage, for example, an electromagnetic switch.

It is an object of our invention to provide new and improved magnetic starting systems for electric discharge devices.

It is another object of our invention to provide new and improved magnetic switches of the vibratory type for starting fluorescent lamps.

The present invention relates to an arrangement for a gas discharge tube which is connected in series with an inductive ballast and the tube is bridged by a magnetic repetitive switch and is provided with at least one glow or filamentary electrode, which is inserted in the bridging branch and in which the energizing or actuating winding of the switch is connected in parallel with the contacts of the switch. When not energized this switch is open; that is to say, the contacts are not touching each other. When power is applied to the arrangement, current flows through the actuating winding, causing the switch to close and a larger current flows through the bridging current branch and the ballast which is connected in series with the discharge tube. The actuating winding becomes short circuited by the closing of the switch, causing the switch to open again. As a result of this, a surge is generated in the circuit including the inductive ballast, which tends to cause ignition of the tube. If the ignition does not occur immediately the closing and opening of the switch is repeated. It has been assured that the switch does not keep on repeating this operation after the ignition of the discharge tube. This can be accomplished by constructing the switch so that the burning or operating voltage of the discharge tube is not high enough to cause the switch to close.

Thus far the arrangements which have been provided with electromagnetic switches have shown serious disadvantages. Quite often the discharge tubes do not ignite, or are very slow in igniting, and when they do ignite quickly this has proven to go hand in hand with a shortening of the life of the discharge tubes.

In accordance with the present invention, the switch has been so constructed, and the switch and the associated circuit constants, particularly the inductance thereof, are so adapted to each other, that the switching cycle is shorter than 0.3 second (this is the time between two successive closings of the switch). Preferably, this cycle should be shorter than 0.1 second. The time that the switch is actually closed (that is, the holding time) should be such a large part of the switching period that the efiective heating current of the electrode is larger than 0.8 of the operating current, and by preference equal to the operating current of the tube.

An important feature of the invention is to adapt the holding or sticking time of the switch, when it repeats relatively rapidly, in order to produce a strong preheating current through the filamentary electrode(s). The relatively short switching cycle causes the switch to attempt to ignite the tube at short intervals. The relatively long holding time produces a strong current which flows through the electrode during a large part of the switching cycle and thus heats the electrode rapidly. One must of course try to make the efiective current as large as possible in order to bring the electrode up to the operating temperature as rapidly as possible. In this manner we use the stored magnetic energy and switch operation to increase preheating current and to produce suitable starting voltages.

With elaborate investigations it has been proved that with the known arrangements the switch opened so rapidly that the preheating of the electrodes was insufiicient so'that the tube, if it ignited at all, started with practically cold electrodes, which explains the reduction of the life of the tube.

The present invention can be used in direct current installations, in which case, besides the inductive ballast, a resistor also may be connected in series with the discharge tube. case the switching cycle does not need to be made so short that the preheating current does not have the opportunity of increasing during the holding time of the switch. It has been shown that in practice good results can be obtained with the holding time between 3 and milliseconds and with such a long switching period that the holding time amounts to at least per cent or even more than per cent or 60 per cent of the switching period.

The invention can also be used in circuit arrangements which are supplied with alternating current. The circuit and the switch are preferably given such constants or dimensions that the switch will be closed 2 f/n times per second, in

which i represents the frequency of the supply alternating current (for example, cycles) and n is equal to a whole number larger than zero. The switch will operate 2 f/l, 2 f/2, 2 ,f/3, etc. times per second. It has been proved during tests that a switching cycle of 0.5 to 1.5 cycles of the alternating current (12 equals 1 to 3) gives very good results, in which case the holding time of the switch can be made to be equal to 0.2 to 1 cycle of the supply alternating current. By preference, the switching period is made equal to 1 cycle of the supply alternating current (12 equals 2), in which case the holding time of the switch can be made equal to 0.3 to 0.5 cycle of the supply alternating current.

When the holding times and switching cycles are thus chosen an advantageous use can be made in alternating current applications of the large switching current surges or transient currents which occur after the closing of the switch in the heating circuit which is provided with the inductive ballast. A heating current larger than the static short circuit current can be obtained through the repeated switching current surges incident to the time of closure of the switch with respect to the alternating supply voltage. (Static short circuit current is the current which will flow if the switch were to remain constantly closed.) Through the proper saturation of the magnetic circuit of the inductive ballast these current surges can be increased to a more advantageous value. If necessary this inductance may consist of the leakage reactance of a leakage transformer or an alternating current generator.

The series impedance may consist also of a capacitor in series with an inductive ballast instead oi an inductance alone. In this case the capacitance is larger than the inductance. Such combinations of series impedances have been pro- In this posed for discharge tubes which have been provided with thermal ignition switches. For that purpose one has inserted in the current branch which bridges the discharge tube an extra inductance in order to reduce the total alternating current resistance of the tube when being ignited, thus making the current which preheats the electrode larger. It has now been proved that this extra self-inductance, known by the name of compensator, is superfluous when the described combined series impedance is being used in an arrangement in accordance with the invention. The connections between the contacts of the switch and the electrodes of the tube do not need to contain the extra inductance.

The holding time of the switch is accomplished by electromagnetic, mechanical and residual magnetic causes. The actuating winding with the closed contacts produces a circuit in which the self-inductance can be designated by L and the resistance by R. After the closing of the contacts the stored up energy in the self-inductance produces a current through this circuit which, when sufliciently large, can hold the switch closed. The time during which the switch remains closed by this cause can be called the electromagnetic holding time. This electromagnetic holding time in seconds is equal to L/R Zn p, in which p represents the proportion of the current causing the switch to close to the current at which the switch opens again, while Zn 79 represents the natural logarithm of p. One can control the electromagnetic holding time with the proper choice of L, R, and p. The mechanical holding is caused by the inertia of the mass of the switch. Changing the inertia is also a means of obtaining the desired holding time.

We have found that it is advantageous to obtain the holding time through electromagnetic causes and to make the electromagnetic holding time at least 50 per cent, and preferably more than 60 per cent, of the total holding time. When the electromagnetic holding time is made larger the inertia of the switch can be reduced. The adjustment of the holding time by means of mechanical dimensions is usually critical. Furthermore, one can obtain a large number of switching operations per second only with a moving system of high natural frequency; that is to say, with a small mass and a stiff spring, which is difiicult to combine with a long mechanical holding time. For the mentioned purpose, it is advantageous to have a constant air gap in the magnetic circuit of the switch in which the armature of the switch moves. For this purpose the part of the yoke which contains the constant air gap may have an opening through which the armature can move in the direction of the core.

It has also been proved that it is advantageous to limit the holding caused by the residual magnetism. For that purpose a non-magnetic solid material can be added between the parts of the armature and the core, which consists of magnetic material. The thickness of the non-magnetic material influences the current at which the armature is released and can be smaller than microns, for example.

A spark may occur between the contacts when opening. The sparking appears to prolong the holding time because a spark current remains arcing over the opened contacts, which adds .to the heating current. The sparking, however, is disadvantageous to the contact material and this reduces the life of the switch. To counteract this effect it has been found advantageous to I 1000 to 100,000, for example, 30,000 lfarads.

The magnitude of the preheating current depends on the short circuit current of th series switching apparatus of the discharge tube. The construction of this series switching apparatus also can have an influence upon the preheating current.

Certain important aspects of our invention relate to improved constructions of magnetic switches of the vibratory type wherein the switching cycle may be accurately controlled or adjusted and wherein the electrical characteristics of the switch are employed in order to control the current during starting operations of an associated discharge device and for controlling the starting voltage impressed across the electrodes of such a device.

One form of a repetitive switch of the vibratory type constructed in accordance with our invention has the characteristic that the switching period, measured with direct current, is shorter than 0.3 second and preferably shorter than 0.1 second, and that the holding time is more than 35 per cent and preferably more than 60 per cent of the switching cycle. further characteristic of the invention, the electromagnetic holding time of the switch can be at least 50 per cent and preferably 60 per cent of the total holding time. A constant air gap can be made in the magnetic circuit of the switch W in which the armature of the switch moves. The part of the yoke containing the constant air gap may be provided with an opening through which the armature can move in the direction of the core. By preference, a non-magnetic material, preferably less than 100 microns thick, is inserted between the parts of the armature and the core, which consist of magnetic material. In accordance with a preferred form of the switch construction, the contacts of the switch are bridged by an in-series connected capacitor and resistor. The switch may be constructed so that the armature, or at least the supporting part of the armature, rests against an adjustable stop in the deenergizcd condition, preferably against a resilient formed wire.

For a better understanding of our invention reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the our invention may be applied to direct current and alternating current systems respectively.

The magnetic circuit of a switch constructed in accordance with our invention is shown in Figs.

In accordance with a 1 and 2 and comprises a core I, the yoke consistjects through the same in the direction ofthe core. The spring 5 is provided with a contact 6 at the free end which can be made to touch a counter contact I. This counter contact is fastened to an extension of part 2 of the yoke with a spacer 8 of insulating material in between. A rectangular bent wire 9 has been fastened to part 3 of the yoke. The spring 5 rests against the horizontal part of this wire. The core I is surrounded by a magnet spool I0 which is connected in parallel to the contacts 6 and 1. These contacts do not touch each other when therelay is deenergized. The connection terminals of the relay are shown as H and I2.

In one switch or relay constructed in accordance with our invention the core or yoke dimensions were 8 x 8 x 21 mm., and the armature diameter was 2.5 mm. and the height thereof was 4 mm. Part 3 of the yoke was made to have a thickness of 1 mm., and a width of mm., with a 3 mm. diameter opening for the armature. The little spring 5 was 0.2 mm. thick and 3 mm. Wide. The armature was mounted at a distance of 16 mm. and the contact 6 at 25 mm. distance on the horizontal part away from the vertical part of the spring. The magnet winding had 17,000 turns of enamelled copper wire of a diameter of microns. The opening between the contacts 6 and I when de-energized was 1 mm. The length of the fixed air gap between part 3 of the yoke andthe core I was 1.15 mm.; the one between the armature 4 and the core was 0.9 mm. A brass foil It with a thickness of 50 microns was located on the free end of the core I. Under these conditions the relay had a self-inductance of 22 henries and a resistance of 12,000 ohms. The energizing current at the moment the contacts closed was 8 milliamps. measured with direct current. The closed switch opened when the current through the winding was lowered to 1 milliamp. The stored magnetic energy of the self-inductance or inductance of the switch circuit causes a current to flow through the closed contacts which attempts to keep the armature in the closed condition for a time, which can be designated as the electromagnetic holding time and which amounts to L/R Zn p:22/l2,000 Zn 8/1 seconds:4 milliseconds. In this, p is the proportion of the mentioned energizing current and the release current.

armature on the mechanical holding time.

milliseconds in this case; that is, less than 0.1

second and the total holding time 49 per cent of this switching cycle.

Fig. 3 is the connection diagram of the de scribed switch used in connection with a gas discharge tube to be fed with alternating current. In this figure, element I4 represents the self-inductance of the magnet spool and such other self inductances as may occur in the chain consisting of the magnet spool and contacts 6 and I connected in parallel thereto. Element represents the resistance and such other resistances as may occur in the chain. The spring, which biases the contacts open, is designated as I6 and represents schematically the operation of the leaf spring 5 in Figures 1 and 2. The switch is connected to the glow or filamentary electrodes I1 and I8 of an electric discharge tube :0, which tube may be connected through a reactor 20 of 1.2 henries and a switch 2! to an alternating cur- The total holding time amount-- ed to 6 milliseconds so that one can assign 2: milliseconds to the effect of the inertia of the- The switch operated on 220 volts D. C. 82 times per second. The switching cycle amounted to 12.2:

7 rent source 22 of 220 volts and 50 cycles. The reactor 20 may be saturable. The tube IS in one form may be 120 cm. long with an internal diameter of 35 mm. and may be filled with argon under a pressure of 2 mm. The burning or operating voltage of one such tube was 105 volts and the operating current 420 milliamps. with an energy consumption of 40 watts. Although we have described a tube using argon, it will be understood that we may apply our invention to other types such as fluorescent lamps wherein mercury vapor and a starting gas are employed.

The above described tube ignited after 0.1 second during which time a heating current of 790 milliamps. passed through the electrodes I! and I8. The resistance of the heating chain amounted to about 90 ohms. The switch operated at a frequency of 50 times per second. The switching cycle was thus 20 milliseconds and the holding time 0.3 cycle of the supplied alternating current. This means that while the contacts are closed an effective current of 1.45 amps. passed through the heating chain or circuit including elements 20-lll-6l8. This important fact is due to the advantageous application of the holding time of the switch to the switching characteristics which appear in the heating chain. It should be noted that the static heating current with constantly closed contacts 6 and 1 (that is, without interruptions) amounted to only 0.66 amp. When the switch was replaced by the usual glow-light-bimetal relay the tube ignited after about 5 seconds while the voltage of the current source 22 had to be raised to 275 volts.

The factors L, R, and p which determine the electromagnetic holding time of the switch can be changed easily. By omitting the layer l3 on the core and by changing the air gap between the yoke and the core to 1.05 mm., the selfinductance of the chain of the holding circuit (6'||4I5) changes to 25 henries, the energizing or actuating current to 10 milliamps, and the release current to 0.1 milliamp. The electromagnetic holding time amounted to 10 milliseconds, the total holding time to 12 milliseconds, and. the heating current to 0.72 amp, while the relay switched at a rate of 33 times per second, which means a switching cycle of 30 milliseconds and a holding time of 40 per cent of this switching cycle. The tube ignited in this case after 0.4 to 0.8 second, which averages 0.6 second. It should be mentioned that this switch On direct current had a, switching cycle of 13.5 milliseconds.

When the resistance 15 was changed to 28,500 ohms, the air gap between the yoke and the core was changed to 2.5 mm., and the layer 13 with a thickness of 50 microns was located on the core, the self-inductance l4 became 17 henries, the energizing current became 6.25 milliamps, and the release current became 5.75 milliamps, so that an electromagnetic holding time of practically zero and a total holding time of 2 milliseconds resulted. The switch operated 100 times per second, the heating current was only 300 milliamps, while the tube had not yet ignited after 180 seconds. The switching cycle of this switch on direct current was 11.1 milliseconds.

From these and other measurements it has been shown that with the described examples of the invention the maximum heating current at a frequency of 50 cycles of the alternating current supply occurs with a holding time of about 8 milliseconds. The heating current decreases slowiy with longer holding times; how- 8 ever, with shorter holding times it decreases relatively rapidly.

In order to prevent sparking in the usual manner a capacitor was connected directly in parallel with the contacts 6 and 1. It was noticed that the contacts often welded together. This was remedied by connecting a resistor between the capacitor and the contacts. It was found that the resistatnce of one or two filamentary electrodes sufiiced, so that the capacitor 23 as in Fig. 3 could be located in the place shown. The capacitance amounted to 1000 to 100,000, by preference 30,000 uufaIadS. The generated over voltage when the contacts opened amounted to 1000 to 1500 volts.

It is obvious that the switch is not allowed to close again when the tube is ignited. This means that the closing voltage of the switch must be greater than the burning voltage of the tube, at least greater than the voltage which occurs across the switch when the tube is conducting. The burning voltage increases slightly during the life of the tube, while the supply voltage can come down. The energizing voltage is chosen in preference between 60 and 90 per cent, preferably about per cent of the supply voltage when the burning voltage of the tube amounts to about 50 per cent of the supply voltage. One should understand that supply voltage, in a circuit in accordance with Fig. 3, is the effective voltage of the current source 22, or when fed by means of a leakage transformer, it is the open circuit voltage of the secondary winding.

During development of the switch the contact distance (that is, the distance between the armature and the core), and the mechanical tension of the spring were varied with separate means. This is probably much too complicated in practice. For large production the adjustment by means of a wire 9 that can be bent is suihcient. The adjustment is made by moving the free end of the wire carefully up and down. After the desired adjustment is obtained the wire can then be cut shorter.

Fig. 4 shows the circuit for a direct current installation in accordance with the invention. Certain of the elements in this figure correspond to elements shown in Fig. 3 and have been assigned like reference numerals. The reactor 20 has been replaced by a resistor 24 with a smaller reactor 25 in series and the A. C. source 22 replaced by a D. C. source 26 of 220 volts. Next the ends of the glow electrodes H, which now act as anode, are connected together. The resistance of the heating chain 2l--25I-6|8 was 300 ohms, the self-inductance 70 millihenries. The holding time should be at least 3 milliseconds and at least 35 per cent or preferably 45 per cent or even 60 per cent of the switching cycle. For practical reasons a holding time longer than 25 milliseconds does not need to be considered. The heating current proved to be proportional to the square root of the proportion: holding time to switching cycle, which proportion is obviously always smaller than one. Inasmuch as the switch always opens on direct current at the maximum current value, it is desirable to locate the capacitor in parallel with the contacts of the switch, preferably in the location designated as 23. The switches which on alternating current in accordance with Fig. 3 gave good results may also be applied successfully to direct current installations.

In Fig. 5 an alternating current installation is shown in accordance with the invention in which the reactor as in Fig. 3 has been replaced by a capacitor 21 with an inductive reactor 28 in series. When the capacitive reactance of the capacitor is larger than the reactanceof the reactor the current through the tube will be leading. This gives the advantage of a more efficient and a considerably more steady light when used in combination with the arrangement of Fig. 3. The installation of a tube with a leading discharge current required an additional reactor in combination with the previously used bimetal relays in order to obtain a sufficiently large heat ing current. It has been shown that when using the electromagnetic ignition switch in accordance with our invention the additional reactor is not necessary any more, and on the contrary the tube even ignites easier than in the circuit in accordance with Fig. 3. The capacitance of the capacitor 21 may be 3.5 farads, the self-inductance of the reactor 1.2 henries, the resistance of this reactor and the electrodes together totaling about 90 ohms;

Although our invention has been described above in connection with a particular type of electric discharge device, it will be appreciated that the systems disclosed and the magnetic switch may be applied to electric discharge devices generally wherein it is desired to obtain a predetermined current through filamentary electrodes during starting in order to cause the electrodes to rapidly assume safe operating temperatures at which electrode deterioration is neg1igible during starting and where it is desired to correlate the starting current through the electrodes, or the pre-heating current, with respect to the starting voltage requirements.

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

1. In combination, a supply circuit, an electric discharge device of the type employing an ionizable medium capable of supporting an arc discharge and comprising at least one electrode of the filamentary type, an inductive ballast connected between said supply circuit and said discharge device, and a repetitive magnetic starting switch connected acros electrodes of said device and comprising an inductive actuating winding and a pair of contacts, said winding and said contacts being connected in parallel relation, an armature for actuatingone of said contacts, said switch having a switching cycle less than 0.3 second and a holding time which is a substantial part of the switching cycle to increase the effective heating current transmitted through said filamentary electrode to avalue greater than eight-tenths of the normal operating current of the discharge device.

2. In combination, a supply circuit, an electric discharge device of the type employing an ionizable medium and comprising at least one electrode of the filamentary type, an inductive ballast connected in series relation between said circuit and said electrode, and a repetitive magnetic switch of the vibratory type connected across the electrodes of said device and comprising an inductive actuating winding, an armature, and a pair of contacts one of which is actuated by said armature, said contacts and said winding being connected in parallel relation, said switch having a switching cycle shorter than 0.1 second, and a holding time constituting a principal partof the switching cycle by virtue of the self-inductance ofsaid winding, to increase the heating current for the filamentary electrode to a value 10 greater than eight-tenths of the normal operating current of the discharge device.

3. In combination, a direct current supply circuit, an electric discharge device of the type employing an ionizable medium and having at least one electrode of the filamentary type, an inductive ballast connected in series relation between said supply circuit and said device, a repetitive magnetic starting switch of the vibratory type including an actuating winding, an armature, and a pair of contacts at least one of which is actuated by said armature, said winding and said contacts being connected in parallel relation across electrodes of said device, said switch having a holding time greater than 60 per cent of the switching cycle and whereby the self-inductance of said winding serves to increase the voltage surge produced upon the opening of said contacts.

4. In combnation, an alternating current supply circuit, an electric discharge device of the type employing an ionizab le medium capable of supporting an arc discharge and comprising at least one electrode of the filamentary type, an inductive ballast connected between said supply circuit and said discharge device, and a repetitive magnetic starting switch connected across the electrodes of. said device and comprising an actuating winding, an armature and a pair of contacts one of which is actuated by said armature, said winding and said contacts being connected in parallel relation, and said switch having a switching cycle ranging from 0.5 to 1.5 cycles of the alternating current supplied and a holding time ranging from 0.2 to 1 cycle of said alternating current.

5. In combnation, an alternating current supply circuit, an electric discharge device of the type employing an ionizable medium capable of supporting an arc discharge and comprising at least one electrode of the filamentary type, an inductive ballast connected between said supply circuit and said discharge device, and a repetitive magnetic starting switch connected across the electrodes of said device and comprising an actuating winding, an armature and a pair of contacts one of which is actuated by said armae ture, said winding and said contacts being connected in parallel relation, said switch having a switching cycle corresponding to 1 cycle of the alternating current supplied and a holding time ranging from 0.3 to 0.5 cycle of said alternating current.

6. In combination, a supply circuit, an electric discharge device of the type employing an ionizable medium capable of supporting an are discharge and comprising at least one electrode of the filamentary type, an inductive ballast connected between said supply circuit and said discharge device, a capacitor connected across the electrodes of said device, and a repetitive magnetic starting switch connected across electrodes of said device and comprising an inductive actuating winding, an armature and a pair of contacts one of which is actuated by said armature, said winding and said contacts being connected in parallel relation, and said switch having a switching cycle less than 0.3 second and a holdin time which is a substantial part of the switching cycle to increase the effective value of the heating current transmitted through said filamentary electrode during the starting operation of said device.

11' able medium capable of supporting an are discharge and comprising at least one electrode of the filamentary type, an inductive ballast connected between said supply circuit and said discharge device, a magnetic starting switch of the vibratory type connected across electrodes of said device and comprising an inductive winding, an armature, and a pair of contacts one of which is actuated by said armature, said winding and said contacts being connected in parallel relation, and said switch having an electromagnetic holding time greater than 60 per cent of the total holding time and wherein the electromagnetic holding time t is defined in the following manner:

t=L/ R Zn p where L is the self-inductance of the actuating winding circuit, R is the resistance of the actuating winding circuit, is the proportion of the current at which the switch closes to the current at which the switch opens, and Zn 10 represents the natural logarithm of p.

8. A magnetic vibratin switch comprising a core and a bridging yoke having one end abutting against said core on one side thereof and the other end forming an overlapping portion on the other side of said core, said core and said yoke constituting a magnetic circuit wherein there is included, between said core and said portion, a gap of fixed length in which the magnetic flux is axial to the core and normal to the :portion, an opening through said portion in alignment with said core, contact means, spring support means for said contact means and an armature carried by said support means, extending through said opening, and movable in the direction of said core for establishing therewith an air gap shorter than said fixed gap, and thereby actuating said support means, said armature being of substantially smaller size than said overlapping portion whereby the magnetic character of said circuit is less influenced by the position of said armature, and a winding on said core for providing an electromagnetic holding time greater than the total holding time of said switch.

9. A magnetic vibrating switch in which the electromagnetic holding time is in excess of 50 per cent of the total holding time due to electromagnetic, mechanical and residual magnetic causes, comprising a, core and a bridging yoke having one end abutting against said core on one side thereof and the other end forming an overlapping portion on the other side of said core, said core and said yoke constituting a magnetic circuit wherein there is included, between said core and said portion, a gap of fixed length in which the magnetic flux is axial to the core and normal to the portion, an opening through said portion in alignment with said core, contact means, spring support means for said contact means, and an armature carried by said support means extending through said opening and movable in the direction of said core for establishing therewith an air gap shorter than said fixed gap, and thereby actuating said support means, said armature being of substantially smaller size than said overlapping portion whereby the magnetic character of said circuit is less influenced by the position of said armature and the mechanical holding time of said switch is minimized, a layer of non-magnetic material interposed between said core and said portion at said gap for reducing the holding time due to residual magnetic causes, and a winding on said core for providing said electromagnetic holding time.

10. A magnetic vibrating switch in which the electromagnetic holding time is in excess of 50 per cent of the total holding time due to electromagnetic, mechanical and residuaI magnetic causes, comprising a core and a bridging yoke having one end abutting against said core on one side thereof and the other end forming an overlapping portion on the other side of said core, said core and said yoke constituting a, magnetic circuit wherein there is included, between said core and said portion, a gap of fixed length in which the magnetic flux is axial to the core and normal to the portion, an opening through said portion in alignment with said core, a leaf spring carrying a contact and an armature, said armature extending through said opening and being movable in the direction of said core for establishing therewith an air gap shorter than said fixed gap and thereby actuating said spring, said armature being of substantially smaller size than said overlapping portion whereby the magnetic character of said circuit is less influenced by the position of said armature and the mechanical holding time of said switch is minimized, a layer of non-magnetic material interposed between said core and said portion at said gap for reducing the holding time due to residual magnetic causes, and a winding on said core for providing said electromagnetic holding time.

11. A high-speed magnetic vibrating switch in which the closed circuit time is a substantial proportion of an oscillatory cycle, such characteristic being attained by increasing the electromagnetic holding time at the expense of the mechanical and residual magnetic holding time, comprising a core and a bridging yoke having one end abutting against said core on one side thereof and the other end forming an overlapping portion on the other side of said core, said core and said yoke constituting a magnetic circuit wherein there is included, between said core and said portion, a gap of fixed length in which the magnetic flux is axial to the core and normal to the portion, an opening through said portion in alignment with said core, a leaf spring carrying a first contact and an armature, said armature extending through said opening and being movable in the direction of said core for establishing therewith an air gap shorter than said fixed gap and thereby actuating said spring and contact, said armature being of substantially smaller size than said overlapping portion whereby the magnetic character of said yoke is less influenced by the position of said armature and the mechanical holding time of said switch is minimized, a second fixed contact coacting with said first contact, a layer of non-magnetic material interposed between said core and said portion at said gap for reducing the holding time due to residual magnetic causes, and a winding on said core connected across said contacts for providing said electromagnetic holding time.

12. In a starting and operating device for an electric discharge device of th type employing an ionizable medium capable of supporting an arc discharge and comprising at least one electrode of the filamentar type wherein a current-limiting ballast is connected between a supply circuit and said discharge device, a repetitive magnetic starting switch connected across the electrodes of said discharge device and comprising an inductive actuating winding and a pair of contacts, said winding and said contacts being connected in parallel relation, an armature for actuating one of said contacts, said switch having a switching cycle less than 0.3 second and a holding time which is a substantial part of the switching cycle to increase the effective heating current transmitted through said filamentary electrode to a value greater than eight-tenths of the normal operating current of the discharge device.

13. In a starting and operating circuit for an electric discharge device of the type employing an ionizable medium capable of supporting an arc discharge and comprising at least one electrode of the filamentary type wherein a current-limiting ballast is connected between a supply circuit and said discharge device, a repetitive magnetic starting switch of the vibratory type including an actuating winding, an armature, and a pair of contacts at least one of which is actuated by said armature, said Winding and said contacts being connected in parallel relation across the electrodes of said discharge device, said switch having a holding time greater than 60 per cent of the switching cycle and whereby the self-inductance of said winding serves to increase the voltage surge produced upon the opening of said contacts.

14. In a starting and operating circuit for an electric discharge device of the type employing an ionizable medium capable of supporting an arc discharge and comprising at least one electrode of the filamentary type wherein a current-limiting ballast is connected between a supply circuit and said discharge device, a repetitive magnetic starting switch connected across the electrodes of said discharge device and comprising an inductive actuating winding, an armature and a pair of contacts one of which is actuated by said armature, said winding and said contacts being connected in parallel relation, and said switch having a switching cycle less than 0.3 second and a holding time which is a substantial part of the switching cycle to increase the effective value of the heating current transmitted through said filamentary electrode during the starting operation of said device.

THEODORUS HEHENKAMP.

KLAAS DE JONG.

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

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