GB1405388A - Irradiation device provided with a gas and or vapour discharge tube - Google Patents

Abstract

1405388 Timing circuits for discharge lamps PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 3 Jan 1974 [25 Jan 1973] 00302/74 Heading H2H An irradiation system includes a discharge lamp 4 connected in series with a stabilizing resistor 3 across supply terminals 1, 2, a circuit including a diode 6 and a resistor 7 being connected in parallel with the resistor 3, and a timing circuit for automatically terminating the radiation from the lamp. The lamp is an ultraviolet emitting sun lamp and the timing circuit includes a potentiometer 18-21 having a tap 24 which is set according to the skin sensitivity of a person to be irradiated as well as a potentiometer 10-17 having a tap 23, the position of which is changed daily to gradually increase the duration of irradiation. On manually closing a switch 5 to the position shown a relay 30 is energized and holds the switch in its closed position thereby supplying power to the lamp. The voltage across the lamp is initially low so that the diode 6 is conductive and the low voltage at the point 8 results in a slow charge of a capacitor 22 in the timing circuit. As the temperature and voltage of the lamp increase, the diode 6 becomes reverse biased and the voltage at the point 8 is determined by the potentiometer 18-21 and the resistor 7. This voltage is therefore increased and the capacitor 22 charges until a threshold voltage of a transistor amplifier 28 is reached whereupon the relay 30 is short-circuited. The switch 5 is changed over to terminate the radiation and discharge the capacitor 22. The system enables the supply of an approximately constant quantity of radiation despite mains voltage variations and variations in lamp characteristics such as variations in the warming up time of the lamp.