Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
  • H05B41/14—Circuit arrangements
  • H05B41/36—Controlling
  • H05B41/38—Controlling the intensity of light
  • H05B41/39—Controlling the intensity of light continuously
  • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
  • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations
  • H05B41/3924—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations by phase control, e.g. using a triac
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current 
  • G05F1/12—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC
  • G05F1/40—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC using discharge tubes or semiconductor devices as final control devices
  • G05F1/42—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC using discharge tubes or semiconductor devices as final control devices discharge tubes only
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S315/00—Electric lamp and discharge devices: systems
  • Y10S315/04—Dimming circuit for fluorescent lamps

Definitions

• the present invention relates to an electronic device for regulating the brightness of an electrical gas discharge lamp without a hot cathode, which is fed from an alternating current network, with a circuit arrangement for controlling the electrical energy supplied to the lamp by changing the ignition angle within each alternating voltage half-wave as a function of an adjustable direct control voltage.
• Numerous types of electronic devices for regulating the brightness of filament lamps are known and customary. They work on the principle of the so-called leading edge control, in which the ignition angle, measured from the zero crossing of the current, is controlled within each AC half-wave.
• leading edge control in which the ignition angle, measured from the zero crossing of the current, is controlled within each AC half-wave.
• phase control there are those in which the ignition angle can be changed as a function of an adjustable direct control voltage.
• a circuit arrangement for phase angle control of the type described is used for regulating the brightness of a gas discharge lamp without a hot cathode, for example a mercury vapor lamp or high-pressure sodium vapor lamp, it becomes apparent that when the brightness is regulated down, there is a risk of the lamp being completely extinguished, especially if the lamp is regulated down Voltage fluctuations or brief voltage interruptions occur in the AC network. Is once the gas discharge lamp goes out, it can only be switched on again after it has cooled to the ambient temperature and can thus be switched on.
• the object of the present invention is now to provide a relatively simple electronic device for regulating the brightness of an electric discharge lamp, with which device it is reliably prevented that the lamp goes out completely when the brightness is regulated down.
• a device of the type mentioned at the outset which has an additional circuit arrangement for generating a control voltage which is dependent on the current intensity of the current flowing through the gas discharge lamp, for automatically ensuring a given minimum current intensity of the current flowing through the lamp, regardless of the level of the control direct voltage .
• the DC control voltage is preferably fed to a voltage divider which is composed of a fixed resistor and a variable resistor which is electronically controlled by the control voltage, a connection point between the fixed resistor and the variable resistor being connected to an ignition angle control input of the first-mentioned circuit arrangement.
• the device is a two-pole system and can therefore be arranged in a simple manner similar to an ordinary on / off switch in the course of the one feed current conductor to the gas discharge lamp, which is why no additional installations are required.
• the device with the above-mentioned features according to the invention is particularly suitable for regulating the brightness of a mercury vapor lamp, the brightness of the lamp being able to be regulated down to about 3% of the brightness at full rated power without the risk of the lamp being inadvertently extinguished completely.
• control voltage for the minimum current fuse is made dependent solely on the current strength of the current flowing through the lamp and is dimensioned in such a way that the lamp does not go out if the DC control voltage is set to the value for minimum brightness at normal operating temperature, i.e. at full lamp power then there is only a relatively small reduction in the brightness of the high-pressure sodium lamp. As the cooling progresses, the lamp could reduce the minimum amperage and thus further reduce the brightness of the lamp without the risk of the lamp being completely extinguished. Therefore, a further development of the present invention provides for the electronic device to be designed in such a way that the additional circuit arrangement. also has devices for generating a component of the regulating voltage which is dependent on the voltage lying above the triac, for automatically regulating the minimum current intensity of the current flowing through the lamp in adaptation to the characteristics of the lamp.
• This design of the device according to the invention allows, in a surprisingly simple and practical manner, to make the control voltage used to ensure the minimum current strength of the high-pressure sodium vapor lamp not only dependent on the current intensity of the current flowing through the lamp but also indirectly on the respective temperature of the lamp, because the AC voltage lying above the triac always changes inversely to the voltage lying above the lamp and the latter is dependent on the respective lamp temperature.
• An additional conductor for detecting the voltage above the lamp is not necessary; the device is still a two-pole system.
• the brightness of a high-pressure sodium vapor lamp can be regulated in a large range from full brightness at nominal power down to less than 1% thereof, without the risk of undesired extinguishing of the lamp.
• FIG. 1 shows as a first example the electrical circuit diagram of a device for regulating the brightness of a mercury vapor lamp
• FIG. 2 shows, as a second example, the electrical circuit diagram of a device for regulating the brightness of a high-pressure sodium lamp.
• Fig. 1 20 denotes a mercury vapor lamp, the brightness of which is to be regulated.
• a choke 21 is in the usual way for limiting the current flowing through the lamp below a maximum value.
• An electronic device 22 and a potentiometer R1 with two end connections ⁇ 23, 24 and an adjustable tap 25 serve to regulate the brightness of the mercury vapor lamp 20.
• the tap 25 By adjusting the tap 25, the brightness of the lamp 20 can be between a maximum value and a minimum value which is only about 3 % of the maximum value is arbitrary.
• the electronic device 22 has two mains connection terminals 26, 27 for connecting to an AC network with a voltage of, for example, 220 V, furthermore two lamp connection terminals 28, 29 for connecting the mercury vapor lamp 20 and the inductor 21, and three control line connection terminals 31, 32, 33 for connecting of control conductors that lead to the connections 23, 24, 25 of the potentiometer R1.
• the one mains connection terminal 26 and the one lamp connection terminal 28 are connected directly to one another.
• a triac TR1 Between the other mains connection terminal 27 and the second lamp connection terminal 29, a triac TR1, a high-frequency blocking inductor L1 and the primary winding L2 of a current transformer 30 are connected in series.
• capacitors C1, C2 and the series connection of a capacitor C3 and a resistor R2 are provided.
• the triac TR1 has a control electrode 34, which must be supplied with an ignition pulse in each half-wave of the mains AC voltage in order to bring about the current flow.
• the following circuit arrangement which is known per se, is provided for generating the ignition pulses:
• a commercially available integrated circuit IC1 for example of the type TCA 280 A from Philips, is connected to the mains connection terminal 26 on the one hand with its connection 13 via a resistor R3 and a rectifier diode D1, and on the other hand with its connection 16 connected directly to the mains connection terminal 27 in order to be supplied with electrical energy from the AC mains.
• the ground conductor 35 of the circuit arrangement is also connected to the connection 16.
• the integrated circuit IC1 provides a constant DC voltage at a connection 11, which is, for example, + 14 V with respect to the ground conductor 35.
• a capacitor C4 located between the connection 11 and the ground conductor 35 smoothes the DC voltage.
• Between the connection 11 and the directly connected connections 2 and 6 of the integrated circuit IC1 is the series connection of a resistor R4 and an adjusting resistor R5, while a capacitor C5 is connected between the ground conductor 35 and the connections 2 and 6. This creates a sawtooth voltage at terminals 2 and 6, the rise steepness of which changes within certain limits by means of the adjusting resistor R5 is cash.
• the sawtooth voltage is synchronized with the half-waves of the AC mains voltage in that a current path containing a resistor R6 is connected between the mains connection terminal 26 and a trigger input 1 of the integrated circuit IC1.
• a reverse voltage connection 3 of the integrated circuit IC1 is connected via a resistor R7 to the electrode 36 of the triac TR1 facing away from the ground conductor 35, which means that the beginning of the increase in the sawtooth voltage does not lie before the zero crossing of the current in the supply circuit of the mercury vapor lamp.
• the control line connection 31 is connected by means of a conductor 37 to the connection 11 of the integrated circuit IC1 carrying the constant direct voltage, while the control line connection 32 is connected to the ground conductor 36, so that the constant direct voltage of, for example, 14 V lies above the potentiometer R1.
• the control line connection 33 connected to the potentiometer tap 25 is connected via a resistor R8 and a conductor 38 to an ignition angle control input 5 of the integrated circuit IC1.
• the level of the DC voltage at input 5 determines the ignition angle or ignition timing within each V / e voltage half-wave.
• the ignition pulses appear at an output 10 of the integrated circuit IC1. This output 10 is connected via a resistor R9 to the control electrode 34 of the triac TR1.
• Each ignition pulse begins when the instantaneous value of the sawtooth voltage at connection 6 matches the DC voltage at the ignition angle control input 5.
• the duration of each ignition pulse is determined by a resistor-capacitor combination R10, R11, C6, which is connected to further connections 7, 8 and to the Earth conductor 35 is connected.
• R10, R11, C6 which is connected to further connections 7, 8 and to the Earth conductor 35 is connected.
• the previously described circuit arrangement for controlling the triac TR1 is known, which is why it is not necessary to explain its mode of operation in detail here. To facilitate understanding, it suffices to mention that, depending on the position of the tap 25 on the potentiometer R1, there is a more or less high DC control voltage U S between the connections 32 and 33.
• this control voltage U S is equal to zero, ie if the tap 25 is located directly at the end connection 24 of the potentiometer R1 connected to the ground conductor 35, the firing angle is zero.
• the ignition pulses at the output 10 of the integrated circuit IC1 then begin immediately after each zero crossing of the AC line voltage, which is why the mercury vapor lamp 20 is fed at full power and reaches its maximum brightness.
• the control DC voltage U S between the connections 32 and 33 increases, which increases the ignition angle accordingly and increases the ignition pulses after the zero crossings experience the mains voltage. Consequently, current flows through the triac TR1 and through the mercury lamp 20 only during part of each half cycle of the AC voltage, so that its brightness is reduced.
• the potentiometer tap 25 is located directly at the end connection 23 of the potentiometer R1, the ignition angle is greatest and the brightness of the mercury vapor lamp 20 is lowest.
• an additional circuit arrangement is provided in the device 22, which automatically ensures that the intensity of the current flowing through the mercury vapor lamp never falls below a certain minimum value. The additional circuit arrangement for minimum current protection is described below.
• the current transformer 30 has a secondary winding L3, which is loaded with a parallel resistor R 13 and is connected to the input terminals 40, 41 of a rectifier arrangement 42.
• the rectifier arrangement 42 has a positive output terminal 43 connected to the ground conductor 35 and a negative output terminal 44. Between the output terminals 43, 44 are a Zener diode D2 for deriving overvoltages in the case of a; Short circuit in the supply circuit of the mercury lamp 20, a load resistor R14 and a capacitor C7 switched on in parallel to smooth the rectified voltage.
• the negative output terminal 44 of the rectifier arrangement 42 is connected via a voltage divider comprising a resistor R15, a potentiometer R16 and a further resistor R17 to the conductor 37, on which the constant DC voltage of, for example, + 14 V is applied.
• the potentiometer R16 has an adjustable tap 45, on which a control voltage U R which is dependent on the current strength in the supply circuit of the mercury vapor lamp is tapped. This control voltage U R is fed to the base of a pnp transistor T1, the emitter of which is connected to the ground conductor 35 and the collector of which is connected via a resistor R12 to the conductor 38 leading to the ignition angle control input 5 of the integrated circuit IC1.
• the collector-emitter path of the transistor T1 serves as a variable resistor whose resistance value can be controlled electronically by the control voltage U R at the base.
• the resistance value of the resistor R12 is much smaller than that of the resistor R8 and is practically negligible.
• the voltage supplied to the ignition angle control input 5 of the integrated circuit IC1 by means of the conductor 38 is tapped off.
• a diode D3 is connected between the base and the emitter of the transistor T1 and is poled in such a way that it prevents the occurrence of negative polarity voltages at the base of the transistor.
• a resistor R19 is connected between the reference voltage conductor 37 and the control voltage conductor 38.
• Another resistor R20 and a charging capacitor C8 connected in parallel lie between the ground conductor 35 and the control voltage conductor 38.
• an AC voltage is induced which corresponds to the strength of the Feed circuit of the mercury lamp 20 flowing current is proportional.
• the induced AC voltage is rectified in the rectifier arrangement 42 and smoothed by the capacitor C7.
• a direct voltage which is substantially proportional to the lamp current and is therefore negative across the capacitor C7 is negative with respect to the ground conductor 35.
• This DC voltage is related to the constant positive DC voltage on the conductor 37 by means of the series connection of the resistor R15, the potentiometer R16 and the resistor R17.
• the tap 45 of the potentiometer R16 can be adjusted so that for a given, relatively low strength of the in the supply circuit of the mercury vapor lamp 20 current flowing, the influences of the negative voltage at the output terminal 44 of the rectifier arrangement 42 on the one hand and the positive reference voltage on the conductor 37 on the other hand just cancel out the potential at the tap 45.
• the rectified voltage at the output terminal 44 of the rectifier arrangement 42 is more negative compared to the ground conductor 35 disturbed in such a way that the potential at the tap 45 would become negative with respect to the ground conductor 35 if this were not prevented by the diode D3. Consequently, there is no positive control voltage U R at the base of the transistor T1, and the brightness regulation of the lamp 20 is determined solely by the DC control voltage U S.
• the negative potential increases at the output terminal 44 of the rectifier arrangement 42 with respect to the ground conductor so far that a positive potential with respect to the ground conductor 35 arises at the tap 45 of the potentiometer R16 and at the base of the transistor T1.
• the collector-emitter path of the transistor T1 is controlled in a conductive state.
• the voltage divider R8, R12, T1 takes effect and the DC voltage at point 39 becomes lower than the control DC voltage U S set at the potentiometer R1 at point 39.
• the ignition angle also decreases accordingly, as a result of which the energy supply to the lamp 20 is increased and thereby a further decrease in the current intensity in the supply circuit of the lamp is counteracted.
• the tap 45 of the potentiometer R16 is adjusted to match the individual properties of the lamp 20 to be controlled so that when the DC control voltage U S is increased to its maximum value, the current-dependent control voltage voltage U R assumes a value which is sufficient in order to prevent the extinction of the lamp 20 with certainty.
• the minimum current intensity in the supply circuit of the lamp must be chosen as low as possible.
• the control range of the automatic current-dependent ignition angle control must therefore be set certain limits. This is achieved through resistors R12, R19 and R20.
• the automatic control described to ensure a given minimum current in the supply circuit of the mercury lamp 20 also comes into effect when the current would drop below the permissible minimum value for reasons other than by adjusting the potentiometer R1, e.g. in the event of fluctuations in the AC mains voltage or in the event of brief voltage drops.
• the capacitor C8 ensures that a cold start of the mercury vapor lamp 20 is also readily possible if the tap 25 of the potentiometer R1 is set to minimum lamp brightness, ie is located directly at the end connection 23 of the potentiometer. After connecting the mains connection terminals 26, 27 to the AC network, the capacitor C8 is charged only gradually, for example within 20 seconds, via the resistor R19. Since the voltage across capacitor C8 is initially zero and then rises slowly, the firing angle is initially zero, regardless of the setting of the tap 25 of the potentiometer R1. The mercury vapor lamp 20 is thus supplied with the full current for a few seconds after it is switched on, so that the lamp quickly reaches its operating temperature, after which the current gradually levels itself out to the value determined by the DC control voltage U S or the control voltage U R.
• each of these lamps is assigned its own device 22, while the DC control voltage U S can be generated for all these devices 22 by means of a single potentiometer R1, the end connection 24 and tap 25 of which are connected to the control line connection terminals 32 and 33 of all devices 22 are connected.
• a potentiometer R1 common to all devices 22, it is of course also possible to provide another source for the generation and delivery of the DC control voltage U S.
• the second exemplary embodiment of the subject matter of the invention serves to regulate the brightness of a high-pressure sodium lamp, which in turn is designated by 20 in FIG. 2 and has assigned a current limiting choke 21.
• 2 again shows an electronic device 22 and a potentiometer R1 with an adjustable tap 25 for arbitrarily changing the brightness of the lamp 20.
• the difference from the exemplary embodiment described with reference to FIG. 1 lies only in the electronic device 22. Although this contains exactly the same and identically labeled circuit arrangements as in the case of the example according to FIG. 1, it also contains the further circuit means and explained below electronic components.
• Another voltage divider which is formed from two resistors R21 and R22, is located parallel to the voltage divider R15, R16, R17.
• connection point 47 between the resistors R21 and R22 is connected to the base of a second transistor T2, the collector-emitter path of which is connected in parallel to that of the transistor T1.
• a diode D4 which is poled in such a way that it prevents the occurrence of voltages of negative polarity at the base of the transistor T2.
• the input 50, 51 of a second rectifier arrangement 52 is connected in parallel with the triac TR1 located in the supply circuit of the high-pressure sodium vapor lamp 20.
• the positive output terminal 53 of the rectifier arrangement 52 is connected to the ground conductor 35 and the negative output terminal 54 to the one end of a voltage divider composed of two resistors R25 and R26.
• the other end of the voltage divider R25, R26 is connected to the conductor 37, on which the constant DC voltage, for example + 14 V, is located.
• the connection point 55 between the two resistors R25 and R26 is connected to the base of the transistor T1 via a resistor R27 and a diode D5.
• a smoothing capacitor C9 and a Zener diode D6 for deriving overvoltages are each connected between the connection point 55 and the ground conductor 35.
• the rectifier arrangement 52 simply consists of a diode for one-way rectification, the input terminal 50 and the positive output terminal 53 as well as their connections to the ground conductor 35 are omitted in the diagram shown, since the ground conductor 35 itself then forms the relevant connection.
• the mode of operation of the device according to FIG. 2 is fundamentally the same as that described with reference to FIG. 1, insofar as the parts of the circuit arrangement are the same. Therefore, for the sake of simplicity, only the mode of operation of the additional circuit arrangements and electrical components compared to FIG. 1 is explained below.
• the control voltage U R1 at the base of the transistor T1 is composed of two components, namely a first component, which is obtained by means of the current converter 30, the rectifier arrangement 42 and the voltage divider R15, R16, R17 in the manner already described and from which Strength of the current flowing through the high-pressure sodium vapor lamp is dependent, and a second component, which is obtained by means of the second rectifier arrangement 52 and the voltage divider R25, R26 and is dependent on the voltage lying above the triac TR1.
• the control voltage U R2 at the base of the second transistor T2 is obtained exclusively by means of the current converter 30, the rectifier arrangement 42 and the voltage divider R21, R22 and is therefore solely dependent on the strength of the current flowing through the lamp 20.
• the tap 45 of the potentiometer R16 is to be set such that when the DC control voltage U S is rapidly increased to its maximum value, the current-dependent component of the control voltage U R1 assumes a value which is sufficient to extinguish the sodium vapor Prevent high-pressure lamp 20 with certainty even if the lamp 20 has its normal operating temperature in accordance with the full power.
• the following can be said about the production and the effect of the second component of the control voltage U R1 :
• the alternating voltage lying above the triac TR1 is practically zero when the lamp 20 is fed at full power, ie when the ignition angle is zero. If the firing angle is increased by increasing the control direct voltage U S that can be set by means of the potentiometer R1 in order to reduce the brightness of the lamp 20, the alternating voltage across the triac TR1 increases, the output terminal 54 of the rectifier arrangement 52 simultaneously becoming negative with respect to the ground conductor 35. The negative potential of the output terminal 54 is then at one end of the voltage divider R25, R26 and the positive potential of the reference voltage conductor 37 at the other end.
• the voltage at the tap 55 of the voltage divider R25, R26 lies somewhere between the potentials mentioned and is smoothed by the capacitor C9 . As long as the voltage at the tap 55 is positive with respect to the ground conductor, this has no influence on the control voltage U R , because the diode D5 keeps positive voltages of the tap 55 away from the base of the transistor T1.
• the two resistors R25 and R26 are now dimensioned such that a voltage equilibrium prevails at the tap 55, that is to say the voltage is zero with respect to the ground conductor 35, when the current in the supply circuit of the high-pressure sodium lamp 20 is reduced to the above-described minimum current which is necessary to safely prevent the lamp 20 from completely extinguishing when the lamp is still at its normal operating temperature according to full power.
• the second transistor T2 and the control voltage U R2 obtained by means of the voltage divider R21, R 22 it is ensured that the strength of the current flowing through the lamp still has a certain minimum value when the lamp is at its minimum brightness in the manner described above has been controlled.
• the two resistors R21 and R22 are dimensioned such that a voltage equilibrium then prevails at the tap 47, that is, the potential with respect to the ground conductor 35 is zero if the current strength in the supply circuit of the lamp 20 is just sufficient to reliably prevent the lamp from going out completely after the brightness has been reduced to the minimum value.
• the mode of operation of the transistor T2 is otherwise analogous to the mode of operation of the transistor T1 as detailed above, depending on the strength of the current flowing through the lamp 20.
• the resistors R12, R19 and R20 additionally limit the ignition angle adjustment range.
• the automatic control described to ensure a given minimum current in the supply circuit of the high-pressure sodium vapor lamp 20 also comes into effect when the current would drop below the permissible minimum value for reasons other than by adjusting the potentiometer R1, e.g. in the event of fluctuations in the AC mains voltage or in the event of brief voltage drops.
• the capacitor C8 ensures that a cold start of the high-pressure sodium vapor lamp 20 is readily possible even if the tap 25 of the potentiometer R1 is set to minimum lamp brightness, i.e. is located directly at the end connection 23 of the potentiometer.
• each of these lamps is assigned its own device 22.
• the control direct voltage U S can be generated for all these devices 22 by means of a single potentiometer R1. whose end connection 24 and tap 25 are connected to the control line connection terminals 32 and 33 of all devices 22.
• a potentiometer R1 common to all devices 22, it is of course also possible to provide another source for the generation and delivery of the DC control voltage U S.
• the described embodiments of the device according to the invention are e.g. Suitable for the brightness regulation of mercury vapor lamps or high pressure sodium vapor lamps in interior, roadway and tunnel lighting systems.
• one or the other embodiment of the device described can also be used to regulate the brightness of other electric gas discharge lamps, depending on their burning characteristics.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Automation & Control Theory (AREA)
• Circuit Arrangements For Discharge Lamps (AREA)
• Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
• Television Receiver Circuits (AREA)

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• 1979
  • 1979-01-24 EP EP79100202A patent/EP0003528B1/de not_active Expired
  • 1979-01-24 DE DE7979100202T patent/DE2961104D1/de not_active Expired
  • 1979-01-29 US US06/189,923 patent/US4320326A/en not_active Expired - Lifetime
  • 1979-01-29 WO PCT/CH1979/000012 patent/WO1979000615A1/de unknown
  • 1979-01-29 JP JP50034879A patent/JPS55500308A/ja active Pending
  • 1979-02-06 FI FI790394A patent/FI790394A7/fi unknown
  • 1979-02-09 CA CA321,193A patent/CA1112293A/en not_active Expired
  • 1979-02-09 NO NO79790422A patent/NO790422L/no unknown
  • 1979-10-10 DK DK427379A patent/DK427379A/da not_active Application Discontinuation

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