The invention relates to a method for supervising the function of the incandescent filament in connection with one or several incandescent lamps, which method comprises electronic controlled automatic replacing of a burnt-out filament for a new one. The invention also relates to a circuit for the automatic replace¬ ment of filaments, and an incandescent lamp with several fila¬ ments for the implementation of said invention.

In connection with incandescent filaments or the like there is the problem, that the service life of the individual incan¬ descent filament is relatively limited. When a filament, due to the transfer of metal, has burned out the whole lamp must be replaced. This causes economical loss, because, in theory, only ^' a substitution of the filament would be necessary, while other parts of the lamp, like the glass bulb and the gas filling could be utilized during a longer time. Provided with a new incan¬ descent filament the same lamp could serve until the transfer of metal from the incandescent filaments to the glass bulb gradual¬ ly would cause a considerable loss of luminance. With the use of halogen gas this transfer of metal to the glass can also be effectively prevented, but the transfer of metal from the fila¬ ment irretrievable results in some filament spots being thinner than the rest of the filament, at which spots the filament will burn through.

The replacement itself of a burnt-out lamp is no problem when the lamp is in an easily accessible place. A lamp is, however, often situated in a rather difficult place, and then the cost of the labour needed for the replacement is greater than the value of the lamp itself. Further a lamp often may be in such a use, that its light going out may cause inconvenience or even danger.

In order to avoid said inconveniencies a method according to the

invention is developed for replacing an incandescent filament, and an automatic replacement circuit and a lamp with several incandescent filaments for utilizing said method, the charac¬ teristics being evident from the enclosed claims.

Thus it is characterizing for the method, that pulse generating means independent of the function of said incandescent filament are made, for each case respectively, to continually feed pulses to reference means having a certain storage capacity, which pulse storage is continually emptied by signals from detecting means dependent upon the function of said incandescent filament. Any lack of such signals, e. g. due to a burn-out of said incandescent filament, will make said reference means full, which in turn will cause said reference means to give a control signal to means arranged for replacing said incandescent fila¬ ment.

According to a preferred embodiment of the invention a 0-voltage circuit is used as pulse generating means, which at each 0-point of an alternating current gives a pulse to counting means working as reference means, and which continuously is emptied by a resetting pulse circuit detecting the current passing through said incandescent filament. When current ceases to pass through said incandescent filament said counter will fill up, and will give a signal to a trigger/selector circuit working as said means for changing said filament, and which in turns switches on connecting means arranged for each of said several filaments. According to one embodiment of the invention triac-semiconductor means are preferably used as connecting means for each filament.

For the automatic replacement circuit according to the the in¬ vention it is characteristic, that the circuit comprises a continuously working pulse generator, which is independent of the function of the incandescent filaments, and a continuously working resetting pulse circuit, which is dependent of said function of said filaments, and further means for comparing the pulses from said pulse generators, having means for replacing

filaments connected thereto.

The lamp according to the invention comprises a common socket and at least one transparent closed shell connected thereto, having within said shell a gas for the protection of each res¬ pective means ignited on any occasion. According to the in¬ vention the incandescent means of the lamp comprise several incandescent filaments, which preferably are used one at a time respectively, and which suitably are connected at one end to a common terminal. The other end of each shunt arranged filament is connected to said automatic .replacement means arranged e. g. in the socket of said lamp, said replacement means connecting, in the manner described above, a new incandescent filament into operation when the previously working filament has burned out or ceased to work for any other reason.

Now the invention will be discussed in more detail with refe- ^" rence to the enclosed drawings, where:

Fig. 1 shows a schematic view of said circuit according to the invention,

Fig. 2 discloses in detail the circuit diagram for an embodiment of the invention, said embodiment having 8 incandescent filaments,

Fig. 3 shows a physical design of the circuit according to fig. 2,

Fig. 4 shows a lamp with several incandescent filaments ac¬ cording to one embodiment of the invention, and

Fig. 5 shows an alternative embodiment of a multi-filament lamp seen from above.

In the block diagram according to fig. 2 the working principle of the invention is generally shown. The figure discloses incandescent filaments la... !«. of a practically arbitrary number. The number of said filaments is principally restricted only by the number which technically can be fitted into one lamp. The central part of said automatic replacement device is

the reference means 4, which in the embodiments according to figures 2 and 3 is shown as a CMOS logic circuit IC2, e. g. of the type MC14520B, working as a counter. Said counter receives regular 0-pulses from a pulse generator 2 and simultaneously, when one of said incandescent filaments 1».. . 1__ is working, resetting pulses 6 from a detecting means 5.

Said pulse generator 2, which in the embodiment according to figures 2 and 3 is shown as a zero voltage switch IC1, e. g. of the type UAA 10168, works essentially independently of said incandescent filaments when the power is on, and feeds pulses 3 to said reference means 4 at the rate of the alternating cur¬ rent. In the embodiment according to figures 2 and 3 said zero voltage switch IC1 gives voltage/trigger pulses at every zero

1 point in the alternating current.

When a filament is working a current 10 will pass, simultaneous¬ ly with said pulses 3, through said resetting circuit 5 working as a detecting means. When a filament i working said resetting circuit, which in the embodiments according to figures 2 and 3 is shown as a resetting pulse circuit 51, also continuously feeds resetting pulses 6 to said reference means 4. Thus said reference means 4, or a counter 41 working as one, will be continuously emptied in spite of said continuous pulses 3 from said pulse generator 2, and will hence not give any control signal showing essential unbalance between signals 3 and 6, i. e. any signal 7 urging for a change of filament being sent to fila¬ ment replacement means 8.

In the embodiment according to figures 2 and 3 said resetting pulse circuit 51 is shown as a circuit comprising a transistor Ql (e. g. of the type MMST 3906) and resistors R13, R14 and R15 (e. g. metal film resistors of the type MCR18J-2R2, -2R2 and -680R). Said circuit generates pulses in every second (negative) half cycle, and will thus see to a frequent enough resetting of said counter"41 (IC2), which cannot then be filled as long as a current 10 through any of said filaments 1»... In flows through

said circuit.

When a filament la... ln-i in use ceases to work the current 10 through said detecting means 5 will be interrupted, said reset¬ ting signal 6, which until then was essentially continuously given, will cease, and said reference means 4, in the embodiment shown as said counter 41, will gradually be filled with signals 3 from said continuously working pulse generator 2. Then said reference means 4, i. e. said counter 41 in the case shown, will give a signal 7. Any suitable counter component fulfilling the requirements of the function can be utilized as said counter 41. Said counter 41 is always either empty and filling up, or full, i. e. not full or full. Said counter must be able to give a sig¬ nal 7 indicating, that the counter is full. Said counter 41 will be filled up with signals 3 from said pulse generator 2 only in the case, that said detecting means 5, due to a burnt-out or the like of the filament, does not continuously give resetting pul¬ ses 6. A signal "COUNTER FULL" from said counter can hence always be interpreted as an instruction 7 to replace a filament.

When the replacement means 8 for replacing a filament receives an instruction 7 from said reference means 4, i. e. from counter 41, to replace a filament said replacement means 8 switches the power supply from said filament ... l _n -ι which burned out or not working for another reason, to a next incandescent filament la _* ι... x . In the embodiment according to figures 2 and 3 said filament replacement means 8 comprise a CMOS logic circuit IC3 with the reference 81, e.g. of type MC14051B. Said CMOS logic circuit acts as a trigger/selector and decides when which incandescent filament la... In will glow. Preferably this is accomplished through switching means 9a...9n specific for each filament. In the embodiment according to figures 2 and 3 said filament specific switching means 9a...9n comprise triac-semi- conductor means Tl... T8 (e.g. of type 2N60773A).

In the embodiment shown in figures 2 and 3 said resetting pulse circuit 51 will be controlled by the very same current 10

passing through the filament when the lamp is lit. If no current 10 passes, i. e. if the light goes out when the lamp is connected to a fed voltage, indicating that a filament is burnt-out, no resetting pulse will come and said counter 41 (IC2) will be filled. This leads then, to start with, to a change of triac and this way to a change of filament. When a current 10 again passes through an incandescent filament, resetting pulses will con¬ tinuously be originated (in every second half-cycle, i. e. 25 pulses/sec), and so said counter 41 (IC2) cannot be filled up or change incandescent filament, but will keep the current in one and the same filament.

The number of switching means 9a...9«. used depends upon the number of filaments and upon the characteristics of said re¬ placement means 8 respectively. In figures 2 and 3 there is shown an embodiment having 8 incandescent filaments, at which the number of said switching triaσ-semiconductors 9a...9«. also' will be 8. If the number of filaments is greater than the capa¬ city of said replacement means 8 another replacement means with attached switching means can simply be connected after the first one. Instead of the triac-semiconductor circuit shown also other switching means can be utilized as said switching means 9a...9n. According to an advantageous embodiment of the invention a special indicating means is connected to said changing means 8 in addition to said switching means 9a...9», which indicating means give an alarm outside the lamp when a certain predeter¬ mined number of filaments have burned out.

The other components shown in figures 2 and 3 serve for the adaptation of said main components. The values for the adap¬ tation components will be chosen according to the actual mains voltage, the effect of the incandescent filaments used and other such variables, respectively.

The method and arrangement according to the invention for re¬ placing incandescent filaments can be utilized, as such, for connecting, in turn, several normal incandescent lamps with one

incandescent filament. Simply, in such a case a shunted lamp will be connected instead of the lamp which has burned out.

However, a lamp arrangement with several individual lamps will need several shunted lamps, each with it own mounting socket, respectively, and hence all of the invention' s advantages cannot be achieved with such an arrangement. For this reason the in¬ vention also relates to a special lamp, having several incan¬ descent filaments la... I connected to the same socket 11. Thus the filaments, as shown in figures 4 and 5, can be placed in one common gas space 12, i. e. all filaments can exist in a space defined by a common shell 13. Then the filaments can be arranged e. g. one above the other, as shown in figure 4, or in a star¬ like arrangement according to figure 5, and arrangements com- ' bining said structures can also be considered.

Said incandescent filaments la... I can also be arranged so, ' that for every filament Id. there is a gas space closed around said filament, respectively, defined by a shell 13 being either separate or formed by a transparent isolating wall common with another filament. An advantage of a separate gas space for each filament is, that the vaporization of metal occurring in con¬ nection with any working incandescent filaments does not have any influence upon the function of other filaments. The separate gas spaces can, within the concept of the invention, be arranged in lines, in an arch, as a cluster or in any other shape, e. g. for indicating the lamp' s lifetime.

In the embodiment shown all the individual filaments la... In are connected to a common terminal 15, but the filaments can also be interconnected in other ways so, that each individual filament Id. can be individually connected to work in such a manner, that the current 10 through said lamp can be detected with said detecting means 5.