GB2280262A

GB2280262A - Halogen lamp circuit with safety switch

Info

Publication number: GB2280262A
Application number: GB9413894A
Authority: GB
Inventors: Wilfried Poellet
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-07-09
Filing date: 1994-07-11
Publication date: 1995-01-25
Also published as: DE9316994U1; GB9413894D0

Abstract

An article 19, e.g. a door edge, which comes too close to a halogen lamp 13 and risks burning is sensed by photodetectors 21 responsive to reflected light 22 which is guided 20 thereto and actuates one or more of a plurality of switch-off devices 14 to interrupt or reduce the lamp supply. Periodic checking can be effected in respect of the operational readiness of the switch-off control arrangement by way of test signals which from time to time after the light is switched on simulate sensor actuation of the switch-off devices or even excite the sensors by way of a separate radiation source as a substitute reflection radiation, but without thereby influencing the feed for the lamp. Alternatively the current function of the switch-off devices which operate in parallel is monitored by comparison logic means to ascertain whether they always have the same steady-state operating behaviour. In the event of irregularities in function a fuse element 31, for example in the control circuit for the working contact relay 17 upstream of the halogen lamp, can then be burnt out in order definitively to put that light out of operation; or the whole lamp supply is prevented by a transformer 42 being switched off on the load side. <IMAGE>

Description

SENSOR CONTROLLED SAFETY SWITCH The invention concerns a safety device as set forth in the classifying portion of the main claim.

Such a device is described in greater detail in the present applicant's German utility model No 92 00 222. It has proved to be excellent in a practical context. For, if on the one hand for example a door of an item of kitchen furniture has remained unnoticed in a critical position closely below one of the downwardly radiating fitted lights in a forwardly projecting canopy, then the risk, which is considerable in itself, at least of the surface of the door panel melting, if not actually catching fire, is averted by the lamp automatically switching off by virtue of the sensed strong reflection directly fram the endangered door panel, while in other respects the lighting remains unaffected.

The present invention is based on the development of such a device, for the purpose of a further increase in operational safety and range of use.

According to the invention that problem is essentially solved by the features of the main claim, in which respect, in regard to disclosure of the invention, as a precaution attention is also expressly directed to the following discussion and the appendant claims, to the drawing and the description thereof, and to the acccmpanying abstract.

In accordance with the fundamental solution therefore a switchoff device which for example is arranged entirely or partially separately but which is preferably entirely integrated into the housing of the light is provided a plurality of times and/or is separately monitored in regard to its functional readiness. In the event of a risk of charring occurring, there is then a sufficient degree of certainty that at least one of the switch-off devices provided will then respond or if necessary finally switch off the specific light which at the present time involves that danger, initially at least periodically and finally entirely, more specifically if the automatic switch-off unit thereof should perhaps no longer operate reliably.

As a result the light which hitherto only temporarily switches off to prevent overheating has been made into a true 'safety light'. It can now be supplied, installed and operated without any limitations in terms of fitment, in regard to a radiation distance to be maintained.

For, in the event of a fault in the functioning of one of the switchoff devices which operate in parallel relationship in the light, one of the other devices responds. In addition, there may be provided an automatic arrangement which finally takes the light entirely out of operation automatically if, in the event of any additional monitoring of the operational readiness of the switch-off devices, serious irregularities should be found to exist. If the arrangement has a single switch-off device, accidental malfunctioning cannot be sufficiently reliably excluded, especially if it is not separately monitored in regard to operational readiness. With the present multiple function on the other hand, especially with the possibly additional functional monitoring system, there is practically no avoidable safety risk involved.It is therefore now permissible for a (safety) light which is equipped in that way to be fitted for example directly over the plane of pivotal movement of the upper edge of a movable door leaf member where the safety spacing which is otherwise required (for the manentary position of the door leaf member under a radiating device) cannot be in any way observed.

The 'safety' criteria as laid down by the relevant provisions are specifically now fulfilled as, besides the known one switch-off function, there is now also at least one substitute function or, in accordance with further developments of the invention, even a functional gradation of additional safety measures (for example an operational comparison between the multiple structure of the switch-off devices). Additional monitoring also of the consequential effect, that is to say the switch-off operation itself, is not required in accordance with the safety standard which is applicable here because it can be assumed that a plurality of functions of a safety operational chain do not fail at the sane time.

Before it is definitively switched off, the light in question can be desirably at least temporarily switched over to a particular operating state, for example that in which it is fed with a reduced level of effective power, in order to reduce the currently critical radiation output, before it is finally taken out of operation entirely.

In that case the unusually reduced radiation output is a clear indication that, although the lamp is still working, the light could suffer fran a safety deficiency and therefore is accordingly to be replaced as a precaution by a new light with a switch-off arrangement which is actually intact.

The above-mentioned optional additional monitoring of operational readiness when the arrangement has a plurality of switchoff devices which respond in parallel relationship can be effected by reciprocal status comparison. As soon as operational differences occur between the switch-off devices, operation of the associated lamp is temporarily or definitively influenced, and in the event of doubt the lamp is finally entirely switched off. For, the detected operational difference indicates that at least one of the switch-off devices has at least at that time a malfunction. Preferably however a self-test procedure is also permitted, prior to the light being definitely switched off, for example by the lamp being fully switched on again automatically or manually, by external test excitation of the switchoff devices, or by an input signal simulation.If in that situation there is still uncertainty in regard to the proper performance of all the switch-off devices, then the lamp is finally definitively switched off. Thereafter therefore as a precaution the entire light, irrespective of the actual operational readiness of its halogen lamp itself, must be replaced by a new light which is fully operational (in regard to its switch-off devices).

Function-monitoring procedures of that kind are advantageously effected for each light by means of at least one additional switch-off device of the same or a different structure or mode of operation but of substantially the same response characteristic. Those switch-off devices are preferably arranged in close proximity with each other so that they are exposed to the same environmental influences because in fact they serve reciprocally as references for comparison logic means.

In order not to be able to forget fitting same and bringing them into operation when installing the light, the switch-off devices are preferably all arranged radially within the internal peripheral surface of the light housing or in the rear region of the light housing which is disposed around the halogen radiation reflector.

Alternatively they are fitted facing rearwardly, that is to say as view on the installation side behind the conventional halogen radiating device housing in order to avoid involving a bore of enlarged diameter for installation of the radiating device. The switch-off devices are all operated directly by way of the supply line, which is provided in any case, to the halogen lamp, that is to say only if and as long as the lamp is to be switched on by the light switch which is installed elsewhere. For, when the lamp is switched off, there also cannot be any overheating of an article disposed in front of the radiating device.

The sensors can in principle be installed in the housing directly beside the radiating device opening which is on the irradiation side, that is to sav in the edae reaion, while however , . , ,, ,,f;pm d;ect,radiationo ,. .

being snieiaea / rran me lamp, preferably Demg sllgntly mclmea towards the beam centre relative to the irradiation direction. In principle a single sensor is sufficient for actuating all switch-off devices. If necessary, for example by transmissive and/or reflective light-guide measures, it is possible to ensure that the sensor is sufficiently excited at any angle of incidence of critical reflected radiation. For the sake of safety however the arrangement should have a plurality of sensors, preferably a specific sensor for each functional channel, that is to say for each switch-off device, in order to ensure truly autarchical functions.The sensors are then preferably all excited as far as possible with the sane degree of intensity by way of optical fibres, irrespective of the current direction of incident radiation1 so that even in the event of one of the sensors not responding, at least. one other sensor will initiate its switch-off device.

For such enhanced freedom in terms of functional configuration, preferably at least one optical fibre extends fran the irradiation opening along the side wall of the housing rearwardly into the region of the circuitry where the sensors are also arranged behind the lamp reflector on the circuit carrier for the components of the switch-off devices thereof. In that way, either directly by way of directionchanging optical fibre means or indirectly by way of reflectors, all reflection positions which are possible in a practical context, in front of the radiating device, are optically coupled to all sensors in the rearward region of the radiating device housing.Instead of an individual distribution system comprising a plurality of individual optical fibre strands or bundles, a single, approximately dane-shaped light guide member which is easier to fit is preferred so that the sensors in the centre of a circuit board, behind the radiating device housing, can be uniformly actuated in a neutral fashion in regard to direction.

A working current relay is desirable for the supply for the lamp because when the lamp is switched off it is released into the safe, current-less condition. In principle all switch-off devices can act on the same relay by way of OR-gates. In order however reliably to interrupt the feed to the lamp even if sticking contacts prevent release of the relay, in spite of the absence of the field supply, the arrangement may involve a series circuit of a plurality of relays, going as far as involving at least one respective relay behind each switch-off device.

In order to be able to verify a probable operational fault, that is to say in order not to have to take steps unnecessarily to replace the complete radiating device with its integrated safety arrangement, it can possibly be provided that the automatic safety switch-off effect is temporarily manually reversed, for example by a procedure whereby the relay which has already been released is briefly supplied with current once again as a test over a period of time of maximum predetermined duration, for example by way of a switch or key which can be actuated from outside the radiating device. This test procedure does not give rise to an unreasonable level of risk, because of the short duration of the test, especially as someone is also directly handling the radiating device in question and is therefore keeping the situation under observation.If the situation does not involve a just temporary fault or disturbance, for example due to a different response characteristic on the part of the switch-off devices which are being operationally compared to each other in response to a radiation situation which is entirely unusual from a geometry point of view, then the switch-off action will take effect again immediately.

After a small number of such brief manual resetting operations by way of testing, the number thereof being predetermined by the circuitry involved, the arrangement is then definitively switched off and therefore replacement of the light is accordingly definitively required.

Instead of a multiple or at any event duplicated (two-channel) design configuration in respect of the switch-off device, or in addition thereto, in accordance with a further development of this invention operational readiness of the prepared safety measures can be tested fran time to time and for that purpose a test signal can be automatically supplied for example by a test device optically by way of the sensors or electrically directly to the input circuit stages of the switch-off devices, in order in that way to ascertain whether they would then actually also respond in an emergency situation.If an extraneous light shielding means for the sensors is temporarily opened, for example by way of an electromagnetically actuable lever construction, that provides for an operational test over the entire operative chain, although that is structurally more expensive than feeding in extraneous light as a test procedure from a small separate radiation source such as a light emitting diode. Such a response for test purpose can also be provoked by the switching thresholds at the inputs of the switch-off devices being temporarily reduced so that the switching stages would already have to respond to ambient brightness (instead of responding to direct reflection of the halogen radiation at a very close article). In that connection it is in principle desirable to provide at the light a manually actuable change-over switch for response sensitivity.Depending on the ambient conditions which are to be encountered upon installation of the light, the change-over switch is set in such a way that, under normal lighting conditions, the switch-off devices do not already respond to reflections from for example a shiny work surface which is further away, but in actual fact only respond to reflected radiation from an article which has moved critically closely into the conical space defined by the radiation.

In any case the switching-off or switching-over effect in respect of the lamp which is in operation, such effect being triggered off in itself by switch-off devices which correctly respond in the testing procedure, should be intercepted or absorbed by the circuitry in order not to give rise to irritation on the part of the user who is in fact not involved in the test cycle which is being carried out at that time.

To increase the safety level, instead of the switch-off devices which operate in parallel relationship or in addition thereto, it is possible to provide for checking by way of a further brightness sensor whether the lamp radiation is actually also switched off or switched over, when a switch-off sensor responds. If it should not be possible to detect that, then a consequential fault has possibly occurred. For safety reasons, drastic intervention in operation of the assembly is now effected, for example short circuiting of the feed line for switching off the transformer. If the transformer is in the form of a so-called electronic transformer with short-circuiting current limitation, that will not cause it any damage.

The solution according to the invention and further developments of the invention are shown in greater detail by way of example in the drawing in which: Figure 1 shows a block circuit diagram in highly abstract form in terms of structure and circuitry for a halogen light with two switch-off devices behind a carrnon reflective optical system for reflection radiation fran a dangerously intensively irradiated article, and Figure 2 shows a modified construction of the light with direct optical fibre excitation of the switch-off sensors.

As discussed in above-mentioned DE 92 00 222 U1 in regard to the specific embodiment thereof, a radiation light 1l is provided in front of its reflector 12 with at least one low-voltage halogen lamp 13.

Because of its strong directed heat irradiation, such a light 11 in operation must in itself maintain a safety distance, which is defined in specific terms in regard to the kind of structure involved, from heat-sensitive or even combustible articles 19 (see Figure 1). As however, due to the conditions of installation, it is often not possible to ensure that to be the case, in particular not for every configuration which may occur even only temporarily in a practical context, for example upon installation in the top part of a display cabinet or case or in a forwardly projecting canopy 43 (see Figure 2) above the path of pivotal movement of the movable door leaf member of a kitchen cupboard or wardrobe, the light 11 in such conditions of installation is equipped with a sensor-controlled switch-off device 14.The device 14 can be mounted at a remote location and connected by cable to the light 11. However it is desirably disposed directly behind or beside the reflector 12 in or behind the housing 41 of the light 11 in order to ensure that the installation thereof is not possibly forgotten when the light 11 is fitted in position. The sensors 21 for actuating the switch-off device 14 are in any case mounted directly to the light 11 in order to ensure the switch-off function upon the critical approach of an article 19, such as in particular the top edge of a door panel.The possibility of forgetting to make feed connections to the switch-off device 14 is practically excluded if the switch-off device 14 is connected in the interior of the light 1l to the feed for the lamp 13 and is thus operated by way of the same supply line 15 as the halogen lamp 13 which produces dangerously bright radiation. Thus the switch-off device 14 is also only brought into operation with the halogen lamp 13 by way of a light switch 16 which is usually installed at a remote location on the input side of a transformer 42, in order to avoid rest current consumption and heating, while the switch-off function is not required at all because the light 11 is in any case switched off.

When the halogen lamp 13 is supplied with power, more specifically by way of the working contact 17' of a self-releasing relay 17 which is activated for example from a supply line 15 by a control circuit 27, then the halogen light radiation 18 is reflected at an article 19 which has not only moved with a pivotal movement through the conical space defined by the radiation but which has also come really close in a stationary situation, such as in particular the adjacent edge of the above-mentioned door panel which has just been left in a critical position. Reflection radiation 22 of sufficient intensity is passed by way of optical fibres or light guides 20 to the at least one sensor 21.When the radiating device is installed, the sensitivity switch 44 (see Figure 1) of the sensor 21, for example an input voltage divider which is variable in steps, said switch 44 being manually accessible fran outside the light casing 45 (Figure 2), was manually set in such a way that, under the specified ambient conditions, it is only the reflection radiation 22 of critical intensity fran an article 19 which has moved into the vicinity of the light, that gives rise to the necessary potential displacement for response on the part of a switching stage 23 at the input of the switch-off device 14.It may be of an analog configuration or a hybrid analog and digital configuration; to provide for the above-mentioned functional comparison between switch-off devices 14 which are designed to be the same, the aim that is sought to be achieved is a circuitry configuration which is a digital configuration as far as possible.

The switching stage 23, when activated by the sensor 21, starts a timing member 24 in the switch-off device 14. With the digital circuitry which is shown by way of example, the timing member 24 comprises a clock generator 24' and an initially reset counter 24". If the reflection radiation 22 received disappears again in good time because an article 19, for example a movable door leaf member, has only quickly moved with a pivotal movement through the radiation 18, the timing member 24 is reset to its initial operational condition with resetting of the switching stage 23, without the halogen lamp 13 first being caused to be switched off.

Otherwise, when the timing member 24 reaches its counting capacity which is predetermined in terms of the circuitry involved, the timing member 24 sets a previously reset output memory 25, that is to say, if by the expiry of that time delay the article 19 is still at risk and therefore the reflection radiation 22 is still acting on the sensor 21. Then, by way of an inverter 26, the output memory 25 switches off the control circuit 27 for operation of the relay coil 17", whereby the relay 17 is released, the working contact 17' therefore opens again and accordingly the lamp 13 goes out. The radiation 18 which was dangerous to the article 19 which had moved into the vicinity of the lamp at the radiation side therefore disappears.In spite of the light switch 16 continuing to be switched on therefore the circuit from the supply line 15 to the halogen lamp 13 is now interrupted and the halogen lamp is switched off in order to avoid critical overheating of the article 19 which was subjected to the radiation effect directly at a particularly short range.

When the light is switched off, excitation of the sensor 21 is also terminated, and as a result of the nowrd potential change the switching stage 23 goes back into its rest condition. That causes resetting of the output memory 15 and in that way the blocking action in respect of the control circuit 27 is removed again so that the relay 17 is again actuated and the lamp 13 is again supplied with power, in order to be switched off again after the above-mentioned period of time if the article 19 is still reflecting at a level of radiation intensity which is critical in a steady-state condition.Now however so that the arrangement does not involve an excessively fast and therefore still critical sequence of such switch-on operations, the return of the switching stage 23 into its rest condition is designed to occur with a greatly time-delaying hysteresis effect; or re-enablement of the relay control circuit 27 still remains temporarily prevented by a delay stage 28. If finally after the expiry of such a buffer time of the order of magnitude of typically 10 seconds, the halogen lamp 13 switches on again, then, as described, it is switched off again straightaway by way of the timing member 24 in order to protect the article 19 in the event that it should still be exposed to critical radiation.

Instead of the lamp 13 being periodically completely switched off, the output signal of the switch-off device 14 can also provide that the feed is at least temporarily switched over for example by way of a series resistor, or the effective power supply for the lamp 13 is reduced in some other fashion, for example by a chopper procedure, to such an extent that the radiation 18 is in any case no longer of a dangerous intensity. That has the advantage of avoiding complete darkness in the switched-off phase and also more clearly indicating to a technically lay person that the lamp 13 is still ready for operation, but for example the door leaf member which is just disposed therebeneath should be pivoted somewhat further towards the open or closed position in order to move it out of the danger zone.

If the switch-off device 14, downstream of the sensor 21 and upstream of the control circuit 27 for the relay 17, suffers fram an operational defect which prevents the occurrence of the change-over switching procedure for release of the relay 17 so that the full intensity of the radiation 18 continues to act on the dangerously close article 19 (for which a minimum spacing specific to the kind of construction involved was not maintained when the article 19 was in that critical position directly closely beneath the lamp 13, by virtue of having trust in the system for switching off the arrangement in the event of overheating), then in principle the article 19 can still suffer fran overheating to the extent of a charring fire or the outbreak of open fire.In order also to eliminate that residual risk, the function of the switch-off device 14 can be provided a plurality of times, at least twice as shown in the example of the illustrated circuit. The radiation light 11 is therefore provided with (at least) one complete further switch-off device 14, preferably of the same circuit configuration, which is also actuated by the reflection radiation 22, preferably by way of its own additional sensor 21. That therefore ensures that the response on the part of at least one of the parallel-operating switch-off devices 14 already results in release of the relay 17.

Coupling of the reflection radiation 22 to the sensors 21 of a light 11 can be by way of individual strand-like light guides or optical fibres 20 or by way of an integral light guide or optical fibre 20 which is substantially cylindrical at the radiation entry end. If the housing of the light 11 is of sufficient depth, the light guide 20 extends at the periphery of the housing of the radiating device out of the plane of the irradiation opening thereof laterally past the reflector 12 and thereafter, tapering for example in a frustoconical-like configuration, extends further rearwardly to the sensors 21 which are disposed therebehind.A reflector ring 38 (see Figure 1) for deflecting the radiation on to the sensors 21 may be disposed in the rear region of the installation housing 45 (see Figure 2), the sensors 21 being arranged at the centre of a circuit carrier 40 for the switch-off devices 14. The circuit carrier 40 is mounted for example by a thermal shielding means 39 behind the housing 41 which accommodates the lamp reflector 12. That permits a radially compact structure in the interests of having small installation bores for the safety light 11, while affording a functionally optimised circuit connection for the sensors 21.

Because of the low number of components to be fitted together, even more desirable than reflective diversion (Figure 1) is an arrangement which involves the radiation being guided by transmission, that is to say by light conduction, for exciting the sensors 21 with the reflection radiation 22. For that purpose the light guide or optical fibre which is initially once again hollow-cylindrical in the front region at the receiving end at first decreases in cross-section in a dome-like configuration, behind the circuit carrier 40, but then towards the centre again adopts a configuration which bends over in a forward direction - in the manner of a hanging keystone in a late Gothic arch - instead of the vertex configuration of a dome, as can be seen in geometrical terms fran Figure 2. That represents a form which is very stable and which therefore can be handled without problems in the fitting procedure and which also leads to optimum illumination of the sensors 21 which are disposed under the inwardly extended centre, very substantially irrespective of the region in terms of the reception periphery at which the reflection radiation 22 passes into the cylindrical region of the light guide 20. An installation housing 45 serves for holding the light housing 41 in the light guide 20 and for protecting same. With its installation ring which extends around it in a flange configuration, the housing 45 conceals the installation bore in the support board for the light at the visible side, that is to say at the side at which the radiation is produced.

When critical reflection radiation 22 occurs, all provided switch-off devices 14-14 respond at any event practically simultaneously independently of each other and give rise to a reduction or interruption in the supply of power to the lamp, for which purpose all switch-off devices 14 can act on a common relay 17 by way of an OR-member 29.

That therefore already provides for the full function of a safety lamp 11, with which there is no longer any need to observe minimum spacings in front of the lamp 13 of the halogen radiating device.

However in order to increase the level of reliability a plurality of working current relays 17 can also be connected in series upstream of the lamp 13 (as indicated as an alternative in Figure 1), being individually associated with the individual ones or a plurality of the switch-off devices. Therefore by virtue of such further redundancy the lamp circuit is reliably switched off or switched over even in the event of a response on the part of only one of the relays 17.

In addition to such a relay series circuit or in place thereof, reciprocal operational monitoring can also be provided, as is also taken into consideration by way of example in terms of circuitry in the illustrated embodiment, for example in such a way that each switch-off device 14 monitors at least one of the others (when there are only two switch-off devices therefore each one monitors the other). That is effected for example by a procedure whereby, upon the occurrence of an operational deviation in the steady-state mode of operation of the switch-off devices 14-14 which are being compared to each other, that is to say after the disappearance in time of initial transient change-over switching phencmena at the :;ginning of sensor excitation, the halogen lamp 13 is switched off as a precaution.That ensures that the protective function cannot ultimately be reduced to a single switch-off device 14 which still remains ready for operation.

For, the output switching states which are being compared together must in fact always be the same as in principle it is to be assumed that all switch-off devices 14 are equally addressed by way of the light guide 20 and the sensors 21 thereof, but they do not all fail simultaneously in the malfunction situation.

Therefore, in such an operational comparison procedure, a comparison logic means 30 which is diagrammatically shown in symbolically simplified form as an EXCLUSIVE-OR-stage does not switch through only when the output switching conditions of the switch-off devices 14 do not differ fran each other but operate in rtutual conformity. If however, after the elapse of a short response period, the steady-state output condition of only one of the switch-off devices 14 differs fran that of another, then obviously at least one of the switch-off devices 14 is operating defectively.

If, when the lamp power supply is switched on, one of the comparison logic means 30 responds, the lamp 13 is again switched off as a precaution, even if no reflection radiation 22 whatsoever is being sensed. If for that purpose the step of switching off the relay 17 is triggered by way of a change-over switch 46 which can be manually reset again (for example by means of a small key or pushbutton switch which is fitted in the light 11 or which can be actuated frcm the exterior only by means of a pointed article), then the ccmplete illumination can be restored. That is an aspect of interest if for example one of the comparison logic means 30 had responded only because of a temporary synchronisation fault.

However the electromechanical change-over switch 46 more desirably co-operates with a for example electronic counting unit 47 which definitively switches off the change-over switch 46 after a small number, which is predetermined by the circuitry, of manual resetting procedures, because obviously that situation does not involve just a temporary fault, but in fact a malfunction in one of the switch-off devices 14 which operates in parallel. The switch-off action is now irreversible in order to cause the user as a precaution to replace that light ll which can no longer be switched on by a new light which has been tested as being ready for operation, complete with its switch-off control devices.

Equipped at any event with an ultimately irreversible switch-off action, the halogen light 11 represents in a wide range of respects a true safety radiating device in the sense discussed in the opening part of this specification.

For that irreversible switch-off procedure the counting unit 47 can act on a short circuit switch 32 when reaching its counting capacity (of for example four manually successive attempts at switching the arrangement back on again). The switch 32 can switch off the transformer 42 as a result of overload on the output side, in which case an inadmissibly high switch-off (short circuit) current does not flow because of an incorporated current limitation in the transformer 42. It will be noted that in that case all other lamps 13 which are supplied by the transformer 42 also go out, although no malfunctions in respect of the switch-off devices 14 had occurred therein. Because now all lights 11 of a set are dark, it is no longer readily possible to ascertain which of the lights 11 on the output side of that transformer 42 has to be replaced because of a functional defect.Instead the user could be obliged unnecessarily to replace the apparently defective transformer 42.

It is therefore more desirable for the safety switch-off procedure which is irreversible at the latest after a repeated fault situation has occurred (as a result of manual attempts at switching on the arrangement) to be restricted to the light 11 in question. For that purpose, a series fuse upstream of the lamp 13 can be overloaded by means of a short circuit switch 32 which operates in parallel with the lamp 13. Due to the relatively high nominal current in the normal mode of operation however the size of such an overload fuse, to be appropriate to the response involved, is critical.

In accordance with a further development of the invention, that difficulty is circunvented if, instead of intervening in the power supply for the lamp 13, the switch-on function of the relay 17, by way of its control circuit 27, is irreversibly interrupted by a low-load fuse element 31 burning out. The fuse element 31 which is essential for operation of the arrangement is therefore now not disposed in the high-current path to the halogen lamp 13 but in the low-current control, which is easier to govern, for the relay 17.

The fuse element 31 may be a definedly weakened region of a conductor track or a microfuse. In the interests of affording a clear function however the fuse element is most desirably a resistor which is specifically designed in the customary way for burning out in a defined manner and which can be part of a network for setting the working point in the control relay 27. If the working point has moved due to failure of that resistor, then the relay 17 remains released and it can no longer be switched on.

The fuse element 31 is therefore briefly overloaded for example by means of an electronic short circuit switch 32, more specifically upon the first response of a comparison logic means 30 by way of an OR-gate 29 or only when the counting unit 47 has detected the admissible number of futile attempts at switching on the arrangement again.

In order still further to increase the safety level, by means of a current sensor between the relay 17 and the lamp 13 or by means of a voltage sensor across the relay contact 17' or by means of a further opto-electronic sensor which is now disposed in the lamp radiation 18, it would also be possible to check whether, in the event of a response on the part of the switch 32, the supply line to the lamp 13 is actually without voltage on the output side of the relay 17, or the radiation 18 fram the lamp 13 has been terminated. Should that not be the case, the relays 17 can in fact not drop back into the open rest condition because of stuck working contacts 17'. At any event in that exceptional situation switching-off of the transformer 42 by shortcircuiting on the load side is then finally justified, for reasons of safety.

Although this is no longer in any way necessary frcm the safety procedure point of view, it is possible in addition to take account of the fact that under sane circumstances none of the for example only two switch-off devices 14 responds to the occurrence of the reflection radiation 22. Admittedly both the devices may have still correctly uniformly operated, in past operation of the light, but now both have became defective at the sane time when the light 11 is switched on again, so that for that reason the comparison logic means 30 cannot detect that the switch-off devices 14 are functioning differently fran each other.In order however also to detect that extremely improbable possible situation, a further timing member 33 responds straightaway after the relay 17 is switched on and thereafter periodically at longer intervals of time in order on each occasion to output at least one test signal to the switch-off devices 14. With the test signal for example the response threshold of the switching stages 23, which is predetermined for the normal mode of operation, can be temporarily lowered or sufficient actuation of the sensors 21 can be simultated, to cause a response on the part of the switch-off devices 14.In order however to include in the test not only the function thereof but also the function of the sensors 21 themselves, instead or in addition it is possible to provide a small test radiation source 34, for example a light-emitting semiconductor diode (LED) which upon actuation excites the sensors 21 directly or by way for example of a secondary path 35 on the light guide 20, in other words, as though reflection radiation 22 were passing into same.

That operational test which is successful in the event of the switch-off devices 14 responding to simulated reflection radiation, during operation of the halogen lamp 13, should of course not result in the relay 17 being switched off or switched over, because in actual fact no malfunction is occurring. Therefore, when that test is carried out, excitation of the control circuit 27 is temporarily disabled by the timing member 33, as is indicated in the example of the circuit illustrated by means of an inverting logic input at the inverter 26.

If all switch-off devices 14 react in the same way as a reaction to one of those test measures, the emergency switch-off system by way of the comparison logic means 30 does not respond and the timing member 33 is reset for the beginning of a new test interval.

In contrast, possibly after a plurality of manual attempts to cancel again the switch-off procedure when it has already been initiated, the short-circuit switch 32 responds to put the light 11 irreversibly entirely out of operation if the test either results in no response whatsoever or a different response on the part of the switch-off devices 14, and if therefore evidently at least one of the switch-off devices 14 is not working correctly.

Although therefore the halogen lamp itself is still in working order, it can now no longer be switched on, for example after the fuse element 31 has burnt out, and can therefore no longer endanger any article 19 which moves into the vicinity thereof; in other words, the light 1l overall must be replaced by a light with switch-off devices 14 which are still intact, in order to restore the original safety standard.

Claims

1. A sensor-controlled safety device for switching off a radiation light (11) with halogen lamp (13) by a switch-off device (14) which responds to reflection radiation (22) of its awn radiation (18) at a closely adjacent article (19) characterised in that the radiation light (11) is in the form of a safety light in that it is provided with at least one second switch-off device (14) and/or it is provided with an automatically operating test device for testing for correct operation or operational readiness of its switch-off device or devices (14).

2. A safety device according to claim 1 characterised in that there are provided comparison logic means (30) for switching off or switching over the normal mode of operation of the lamp (13) in the event of different operating behaviours on the part of the switch-off devices (14) thereof.

3. A safety device according to claim 1 or claim 2 characterised in that the lamp (13) is temporarily switched off at least anca prior to the lamp being definitively switched off.

4. A safety device according to claim 1 or claim 2 characterised in that, before the lamp (13) is definitively switched off, it is temporarily switched over at least once into a particular operating condition, such as in particular with a clearly reduced level of effective radiation (18).

5. A safety device according to one of the preceding claims characterised in that, in the event of response on the part of a comparison logic means (30) between switch-off devices (14), prior to the light (11) being temporarily switched over or definitively switched off, test excitation of switch-off devices (14) which operate in parallel mode and which in themselves have a similar response is triggered by way of their input switching stages (23) or sensors (21).

6. A safety device according to at least one of the preceding claims characterised in that the switch-off devices (14) are mounted in close mutual proximity and are preferably installed in or behind the light (11).

7. A safety device according to at least one of the preceding claims characterised in that the switch-off devices (14) with the lamp (13) respectively associated therewith can be set in operation by way of a common supply line (15).

8. A safety device according to at least one of the preceding claims characterised in that specific sensors (21) are provided at least for some respective ones of a plurality of switch-off devices (14).

9. A safety device according to at least one of the preceding claims characterised in that the sensors (21) are arranged in the rear part of the housing (41) of the radiation light (11) or also behind the housing (41) thereof on the circuit carrier (40) for their switch-off devices (14) and can there be excited by way of light guides (20) for receiving reflection radiation (22) at the irradiation side.

10. A safety device according to claim 9 characterised in that the reflection radiation (22) is passed to the sensors (21) by way of a hollow-cylindrical light guide (20) which is fitted into the light (all), and a reflector (38).

11. A safety device according to claim 9 characterised in that the reflection radiation (22) is guided on to the sensors (21) by way of a hollow-cylindrical light guide (20) which is fitted into the light (1l) and which in the rearward region narrows in a dome-like configuration in order finally at the centre to terminate closely above the centrally disposed sensors (21), facing forwardly again in the manner of a hanging keystone instead of a vertex region and facing towards the sensors.

12. A safety device according to at least one of the preceding claims characterised in that there is provided a timing member (33) which during operation of the light (11) excites the switch-off devices (14) thereof at long time intervals optically by way of the sensors (21) thereof and/or electrically directly by way of the input switching stages (23) thereof 1 but in that procedure intercepts by virtue of the circuitry involved any switching-off or switching-over of the lamp (13).

13. A safety device according to claim 12 characterised in that a test signal temporarily influences the response characteristic of switch-off devices (14).

14. A safety device according to claim 12 characterised in that there is provided an extraneous light feed to the sensors (21) thereof.

15. A safety device according to claim 14 characterised in that a test radiation source (34), in particular a light emitting diode, is coupled into the light guide (20) upstream of the sensors (21).

16. A safety device according to at least one of the preceding claims characterised in that there is provided a monitoring circuit which checks the switching-off or switching-over of the radiation (18) upon the response of a sensor (21) and otherwise prevents any further feed to the light (11).

17. A safety device according to at least one of the preceding claims characterised in that the feed for the lamp (13) is by way of a relay (17) which can be switched off by the switch-off devices (14).

18. A safety device according to claim 17 characterised in that provided in the supply line (15) to the halogen lamp (13) is the working contact (17') of a relay (17) which can be temporarily switched off by the switch-off devices (14) but definitively switched off by a comparison logic means (30) monitoring the switch-off devices.

19. A safety device according to claim 17 characterised in that a plurality of relays (17) are connected with their contacts (17') in series into the feed line to the lamp (13) and are connected downstream of different switch-off devices (14).

20. A safety device according to at least one of the preceding claims characterised in that there is provided a change-over switch (46) which can be actuated from outside the lamp (11) for switching on again, as a test, the lamp (13) which has already been switched off for the sake of safety.

21. A safety device according to at least one of the preceding claims characterised in that, after a predetermined number of futile attempts at manually externally switching on again the light (11) which has been switched off or switched over because of probable operational deEsienafs in one of the switch-off devices (14), a counting unit (47) definitively puts the light (11) out of operation.

22. A safety device according to at least one of the preceding claims characterised in that there is provided a short circuit switch (32) for definitively putting the light (ill) out of operation, which switch can be actuated by a synchronisation comparison logic means (30) for the switch-off devices (14) and/or by a counting unit (47) for limiting manual attempts at switching the light on again.

23. A safety device according to claim 22 characterised in that the short circuit switch (32) short circuits the feed line from the transformer (42) to the lamp (13) in order irreversibly to interrupt the supply by way of the transformer (42).

24. A safety device according to claim 22 characterised in that the short circuit switch (32) overloads a series fuse upstream of the lamp (13) in order irreversibly to interrupt the supply to the lamp (13) by way of the transformer (42).

25. A safety device according to claim 22 characterised in that the short circuit switch (32) burns out a fuse element (31) in the control circuit (27) for a relay (17) in the feed circuit of the lamp (13) in order irreversibly to interrupt the supply of the lamp (13) by way of the transformer (42).

26. A safety device according to at least one of the preceding claims characterised in that, in the event of response of a triggering means for irreversibly switching off the light (11), the current-less condition of the lamp supply and/or the absence of the lamp radiation (18) is additionally monitored and possibly results in the supply transformer (42) being switched off.

27. A safety device according to at least one of the preceding claims characterised in that provided at the light (ill) is an externally accessible sensitivity switch (44) for setting the response sensitivity of the switch-off devices (14).

28. A sensor controlled safety switch substantially as hereinbefore described with reference to the accompanying drawings.