IMPROVEMENTS IN OR RELATING TO SEARCH LAMPS AND TORCHES

Abstract: A torch (118) having a lamp (12), a pair of thermistors (134, 136) secured to the outer centre of the lamp (12) and connected to an electric circuit (10), the electric circuit (10) being arranged to switch off the power supply to lamp (12) of the torch (118) when the temperature at the thermistors (134, 136) reaches a pre-determined value.

Description: Improvements in or relating to Search Lamps and Torches This invention relates to search lamps and torches, hereinafter referred to as torches. In particular the invention relates to an improvement or modification in the torch described and claimed in our UK patent GB 2 222 449B the contents of which are hereby incorporated by way of reference. The torch in GB 2 222 449B is intended for use in situations where there are likely to be explosions due to for example leakages of gas or chemicals. If such a torch has its light output obscured, this obscuration can cause an undesirable temperature rise in the torch. Such a temperature rise may in certain circumstances cause hazard, fire, explosion or melting of torch components. In order to obtain BASEEFA approval for use in hazardous conditions or areas one requirement for approval is that if a torch has been covered so that its beam is obscured then the surface temperature of the torch must not rise above a pre¬ determined level, the level being determined by the specific application of the torch for which approval is sought. An obvious application is for use in mines or sewers where explosive gases or explosive mixtures of air and dust are present. The present invention seeks to overcome this problem by detecting when the light output from the torch is restricted, thus causing a rise in temperature. Accordingly the present invention provides a torch having means for detecting any obscuring of the light output from the torch which could cause a temperature rise in the torch and having means for switching off the power supply to the lamp of the torch. The detecting means can take a number of forms eg an appropriate sensor detecting the rise of temperature caused by the heating effect of the obscured beam and when the temperature reaches a pre-deter ined value, switching off the bulb power supply until the torch is cooled sufficiently so that it can be used safely again. The heat detector or sensor can be mounted in a suitable position in a torch and can cause the lamp to be switched off at a pre-set temperature eg by using a thermistor, a thermocouple, a thermopile, passive infra-red sensors, a heat expansion switch eg. aluminium bar and micro switch, a switching thermometer or any other temperature monitor can be used to switch off the torch at a pre-set temperature so that it will only be allowed to come on again at a pre-set lower temperature. The presence of any obscuring material that would be sufficient to cause an undue temperature rise can be detected by measuring the presence of any obscuring substance that may be enough to cause the light to be obscured sufficiently so as to cause temperature rise above the pre-determined value. Once the pre-determined temperature value has been reached the lamp can be switched off. Again as before the torch can include a temperature sensor which can be arranged to switch off the power supply before the pre-determined temperature value is reached. The presence of any obscuring substance can also be determined by detecting the change in electrical capacity at the lens of the torch caused by the presence of obscuring substance eg capacitive detection. Alternatively the change in reflective value of the lens can be detected by opto-electrical means or by measurement of the electro-static change caused by the obscuring substance, or by monitoring the actual light output and detecting any reduction caused by the obscuring material. Also opto-electrical means can be used to sense that the outer surface is clear of any obscuring material. The present invention may also use a time control so as not to allow the torch to be on sufficiently long for it to over heat in any suitable time interval. The present invention will now be more particularly described by reference to the accompanying drawing in which; Figure 1 shows diagram atically the lens end of one form of torch according to the present invention; Figure 2 shows diagrammatically front end of a further torch according to the present invention; Figure 3 shows diagrammatically the front end of a further form of torch according to the present invention; Figure 4 shows a fourth form of torch according to the present invention; Figure 5 shows a part sectioned side elevation of one form of torch according to the present invention; Figure 6 shows a view on arrow A in figure 5; and Figure 7 shows a circuit for the torch shown in figures 5 and 6. Referring to figure 1 there is shown part of a torch body (10) in which is located a sealed beam lamp unit (12) the end of the torch body being closed off by protective glass (14) . The torch includes a temperature sensor (16) which can be located in either one of three positions (a) , (b) or (c) . In position (a) the sensor is located on the front face of sealed beam lamp (12) in position (b) the sensor is located on the inside of the protective glass (14) and in position (c) the sensor is located on the exterior of the protective glass (14) . The output of the sensor (16) is connected to a detect circuit. If the torch overheats so that the temperature at positions (a) , (b) or (c) reaches an unacceptable pre-determined value due for example to the obscuring of the light being emitted from the torch then the temperature sensors will cause the power supply to the sealed beam lamp unit to be switched off via an output from the detect circuit. Referring to figure 2 in which corresponding components have been given the same reference numerals. A detector (18) which can measure capacity or electro-static change can be located either at position (a) on the inside of the protective glass (14) or at position (b) on the exterior of the protective glass at (14) . The detector (18) is connected to a detect circuit. Any change in capacity or electro-static voltage is detected due to anything which obscurs the light emitted from the torch then if the changing capacity or electro-static voltage is sufficient to indicate the potential overheating of the torch then the signals from the detectors will switch off the power supply to the sealed beam lamp unit (12) via the detect circuit. Referring to figure 3 again in which corresponding components have been given the same references a photo electric reflective change detector (20) is located on the inside of the protective glass (14) and the detector (20) is connected to a detect circuit. Any changes in the reflectivity of the protective glass due to obscuring of light emitted from the torch is detected and if the change is sufficient for the temperature of the torch to rise above the pre-determined level then the power supply to the torch is arranged to be switched off via an output from the detect circuit. Referring to figure 4 in which corresponding components having the same references an opto-electric sensor (22) is located on the exterior of the protected glass (14) in either one of positions (a) or (b) and is connected to a detect circuit. The photo-electric detector (22) will detect the presence of any obscuring substance to the light emitted from the torch and if that signal is sufficiently high for the temperature of the torch to rise above the pre-determined value then the power supply to the sealed beam bulb unit is arranged to be switched off via an output from a detect circuit. In order to prevent any voltages on the torch exterior being present that may generate a spark, the torch circuit is modified so that an external voltage needs to be applied to the torch charging socket before any of the internal torch voltages are present at this socket. Thus the torch is only allowed to be charged in a safe area away from any hazardous gasses and then if the safe area only, will have a voltage applied to the charging socket from an external charger. This will then cause the internal battery of the torch to be made available at the socket for charging. When the charging voltage is removed from the torch the charging socket is again isolated from any internal voltages. A means of achieving this is to have a relay coil connected internally across the charging socket which when energised by an external voltage switches the torch battery across the charging socket rendering the torch internal battery available for charging. The arrangement of the switching circuit and the values of the components in the switching circuit render the torch switching circuit intrinsically safe to BS 5501 standards. The material of which the torch body is made has been arranged so that it is non-electrostatic ie it will not hold a charge sufficient to generate a spark. A torch having sensing and detecting means according to the present invention is arranged to prevent a dangerous temperature rise occuring in the torch when it is switched on in conditions where the beam output can be obscured eg by coal dust, or when the torch is placed with its lens against a floor or wall or switched on whilst in a packing case. The present invention arranges that the torch is switched off when the temperature reaches a pre-determined value and if required the torch circuit can be arranged to give an alarm signal before the pre-determined temperature value is reached. Referring to figures 5, 6 and 7 components common to the figures in GB 2 222 449B have been given the same reference. There is shown a circuit for a torch in which the circuit (10) , bulb (12) , circuit (14) , line (16), line (18) , line (20) , switch (22) , contacts (24) and (26) and power source (34) are the same or similar to the corresponding components in GB 2 222 449B. Thus the torch (118) comprises an integrally moulded body including a battery housing (120) and a lamp housing (124) . The battery housing (120) is rectangular in form as is also the lamp housing (124) there having radius corners. The base of the battery housing (120) is continuous with the base of the lamp housing (124) and since both the battery housing (120) and lamp housing (124) are rectangular in section there is not tendency for the torch to roll. Also the torch can be stood upright, on both ends or also on the handle (122) without tipping. The lamp housing (124) includes a cover (126) together with a circular translucent protective closure (128) which locates in a recess (130) in the lamp housing (124). The contacts (24) and (26) (figure 7) are located in the recess (130) as shown - lo ¬ in figure 6. The frangible conductive element (132) is arranged so that its ends contact the terminals (24) and (26) . Referring particularly to figure 7 the circuit (10) includes two thermistors (134) and (136) which are both secured to outer centre of the lamp (12) , resistor (138) , transistor (140), relays (142, 144), resistor (145), transistor (146), relay (148) contact (150), diodes (152, 154), resistor (156), transistor (158), thyristor (160) and resistor (162, 164). When thyristor (160) is switched on it diverts the base drive which is supplied through the resistor (138) from the transistor (140) so allowing relays (142) and (144) to de- energise. At the same time when thyristor (160) is switched on it diverts the base drive which is supplied through resistor (145) from transistor (146) , so allowing relay (148) to de- energise thus removing the power supply to the lamp (12) , the lamp being supplied through contact (150) . The thyristor (160) is switched on when sufficient gate current flows through diodes (152) and (154) which are supplied through resistor (156) . During normal working this gate current is diverted through thermistors (134) and (136) and transistor (158) . The thyristor (160) gate current can be allowed to flow into the gate of thyristor (160) if transistor (158) is switched off. This occurs when the battery voltage is low causing the voltage at resistors (162) and (164) junction to be low so there is insufficient base drive to transistor (158) causing it to switch off. The thyristor (160) gate current is also allowed to flow into the gate when the thermistors (134) , (136) which are both in one unit across the front of the lamp reach a high pre-set temperature. When their combined resistance changes from 200 ohms to 2,000 ohms. This change in resistance causes a high impedance path through transistor (158) so allowing the current to be diverted through the lower impedance path to the thyrister (134) gate, thus turning the thyristor (160) on. Again when ever thyristor (160) is switched on the lamp supply is switched off. Because component (160) is a thyristor it will remain switched on until the supply is removed by operating the torch on/off switch (22) so that even after the lamp cools down the reduction of the thermistors (134) , (136) resistance will not cause the lamp to switch on again until the switch (22) has been operated. This gives the user a chance to remove any obstruction that may have caused overheating eg. by the covering the lens cap.

Claims: Claims 1. A torch having means for detecting any obscuring of the light output from the torch to which could cause a temperature rise in the torch and means for switching off the supply to a bulb of the torch. 2. A torch as claimed in claim 1 having temperature sensing means and means to switch off the power supply to the bulb when the temperature reaches a pre-determined value. 3. A torch as claimed as claimed in claim 2 in which the heat detector or sensor is mounted in a appropriate position in the torch and causes the lamp to be switched off at a pre-set temperature for example by using a thermistor, a thermocouple, a thermopile, a passive infrared sensor, a heat expansion switch or a switching thermometer. 4. A torch as claimed in claim 1 in which the presence of any light obscuring matter is determined by detecting the change in electrical capacity at the lens of the torch caused by the presence of the obscuring material. A torch as claimed in claim 1 in which the presence of any obscuring material is detected by a change in the reflective value of the lens of the torch, for example by opto-electrical means or by measurement of the electro¬ static change caused by the obscuring material or by monitoring the actual light output of the torch and detecting any reduction caused by the obscuring material.

Inventors: MCGRAIL PETER, MCGRAIL, PETER
Applicants: MCGRAIL PETER, TOPLITE TECHNOLOGY LIMITED
Application year: 1993
Main classification: F21V25
IPC codes: F21V25