GB2164215A - Photodetectors used for monitoring discharge tube starting - Google Patents

Abstract

When power is switched on switch 14 (eg thyristor) is arranged to pass current for a preset time to heat the filaments 11 & 12. Then the switch 14 is opened so that the supply voltage is applied directly across the tube. If the tube lights photodetector 16 provides a signal to microprocessor 15 to maintain switch 14 open. If the tube fails to light the operation is repeated until it does. A plurality of tubes may be operated from the microprocessor (Fig. 2). <IMAGE>

Description

SPECIFICATION Control device This invention relates to control devices for starting up and operating gas discharge tubes, particularly fluorescent tubes as widely used for lighting and, in the form of UVA tubes, in solariums, sunlamps and sunbeds.

The most commonly employed control equipment for fluorescent tubes comprises a choke for operative connection to an AC power supply in series with the tube, and a switching device, commonly referred to as a "starter", having contacts which are initially closed to pass current through the tube electrodes for initial heating and excitation of the tube, these contacts being incorporated in a glow lamp or other heater device in parallel with the switch contacts and which cause the latter to open thermostatically after an interval dependent on the heating effect within the starter.

When the switch contacts are opened, the interruption of current flow produces a voltage surge in the choke which has been commonly believed to be essential or desirable to initiate the gas discharge within the tube.

With this arrangement it is necessary to provide an individual choke, which is a costly, bulky and heavy wire-wound component, together with a "starter" for each tube. Not only does this add considerably to the cost of the electrical equipment itself, it also adds to the cost of supporting structure and housing, e.g. for ceiling mounted or suspended lighting units, and makes portable equipment such as multi-tube sunbeds heavier and/or cumbersome.

The glow lamp or other heating devices used in the "starter" have a limited service life and may need replacement from time to time and the choke is a particularly costly item to replace if it should fail.

The object of the invention is to provide a gas discharge tube control device which is of particularly simple construction, compact and light in weight, cheap to produce, and which can be readily adapted to start up and operate a plurality of tubes. It is another object of the invention to provide a control device which dispenses with the need for a choke and which can be readily adapted for operation from AC power supplies of a range of voltages, for example 110 or 240 volts; or even DC power supplies, e.g. on a car or boat.

According to the invention there is provided a control device for a gas dicharge tube including a switching device, preferably an electricaily triggered solid state device; sensing means responsive to radiation emitted by the tube, and logic means for automatically continuing to actuate the switching device until the tube is operating normally.

The sensing device may be a photo-cell, phototransistor or other light responsive sensor, or a sensor responsive to radiation of other wavelengths, e.g. ultra violet emitted by the tube in operation, operatively mounted adjacent to the tube to respond to radiation emitted when the tube is operating.

Conveniently a single logic means is connected to operate a plurality of tubes and is programmed to initiate their start up in a predetermined sequence so that the full supply voltage can be applied to each in turn.

Commercially available tubes commonly operate on 110 volts AC, the choke hitherto used serving to drop this voltage from the 240 v AC mains supply (hence the choke is constantly loaded and emitting unwanted heat). With the use of the invention a 240 v AC supply is dropped to the operating voltage by incorporating an appropriate resistor in series with the lamp which can be a cheap, compact and lightweight component.

It is contemplated that the control device will use miniaturised components, for example the logic means can be in the form of a micro-chip device incorporated with the thyristor or other switching means and possibly the sensing means as an integrated unit, e.g. utilising a hybrid integrated circuit package, which can be very compact, of minimal weight, and cheap to produce by volume manufacturing techniques.

The absence of the conventional components, in particular the need for a heavy wire wound choke for each tube, means that the only supporting structure necessary is, in effect, that needed for mounting and location of the tube or tubes, so providing a much more flexible application of the tubes particularly for portable equipment incorporating an array of tubes such as sunlamps, sunbeds and the like.

The invention will be particularly convenient for small lighting units, e.g. those used in display cases, aquaria and the like where the housing of the choke and the heat it generates has hitherto been a problem and the cost and bulk of the starting gear has been disproportionate to the size of tube required.

One example of the invention is now more particularly described with reference to the accompanying drawings in which: Figure lisa diagram of a form of the.invention for operating a single tube, Figure 2 is a diagram of an arrangement for operating a plurality of tubes, Figures 3 and 4 are detailed circuit diagrams of the above arrangements.

Afluorescent lighting or UVAtube 10 has electrode filaments 11, 12 at its opposite ends and is connected, in use, across a 240 V AC supply through a voltage dropping resistor 13 so that the voltage applied to the tube is of the order of 110 V.

A solid state switching device 14 is connected between the filaments 11, 12 in parallel with the tube so that, when.device 14 is passing current, the two filaments are connected in series across the 110 V supply.

Logic means in the form of an opto-isolated micro-processor unit 15 is connected to control switching device 14.

Adjacent a central region of tube 10 is a sensing means in the form of a photo-transistor 16 connected to unit 15.

Assuming that tube loins unlit and is to be brought into operation the power supply will be switched on and, with the tube in this condition, switching device 14 is arranged to pass current for a predetermined period to heat the tube filaments 11,12. At the end of this period switching device 14 is disabled so that the 110 V supply is applied directly across the tube to start the gas discharge so that the tube lights up.

If the tube lights photo-transistor 16 responds to the emitted light and provides a signal fed to unit 15 which is programmed to hold switching device 14 inoperative while this condition continues. On the other hand, if the tube fails to light, the switching operation will continue to be repeated until lighting up occurs.

Figure 2 shows an arrangement for starting up a plurality of tubes 10, 10A, 10B etc (tube 10 only shown).

The other tubes are connected in the same way as tube 10 to the main supply through respective voltage dropping resistors and have respective switching devices connected in parallel with them as in the case of tube 10. There is also a photo transistor associated with each tube. The switching devices and photo-transistors are connected to a common micro-processor unit 15a and the latter is programmed to start up the plurality of tubes in a predetermined sequence so that the full supply voltage is available to start each tube in turn. Any number of tubes can be controlled and started in sequence in this way, for example a sunbed or solarium may incorporate as many as 20 or 24 6ft UVA tubes. For operation in this way a second switching device 20, controlled from unit 15, is provided between each resistor 13 and the associated tube.These second devices are also controlled from unit 1 5a to switch the supply voltage to each tube in turn during start-up.

The second switching device 20 of each tube may incorporate atnac device, and the other switching device(s) 14 may incorporate thyristor devices.

Figures 3 and 4 are respective circuit diagrams for single and multi-tube operation incorporating said components.

It is also contemplated that the logic unit and/or the control circuit of the invention can incorporate other forms of control of lamp operation, for example to provide operation from a DC power source and/or to regulate or smooth the frequency changes at the tube or tubes (possibly operating a plurality of tubes out of phase relative to each other) to reduce or remove the stroboscopic effect which is undesirable and possibly dangerous for some applications such as the lighting of environments containing moving machinery.

Claims (10)

1. A control device for a gas discharge tube including a switching device, sensing means responsive to rdiation emitted by the tube, and logic means controlled by the sensing means for automatically continuing to actuate the switching device until the tube is operating normally.

2. A device as in claim 1 wherein the switching device is an electrically triggered solid state device.

3. A device as in claim 1 or 2 wherein the sensing device is a light responsive sensor operatively mounted adjacent to the tube.

4. A device as in claim 1 or 2 wherein the sensing device is a sensor responsive to ultra-violet or other non-usable radiation emitted by the tube in operation.

5. A device as in any preceding claim for controlling a plurality of gas discharge tubes, the logic means being programmed to initiate start up of the respective tubes in a predetermined sequence applying the full supply current to each in turn.

6. A device as in any preceding claim including means for supplying current to the or each lamp including resistor means in series with the lamp or lamps to reduce the input voltage to a lower operating level.

7. A device as in any preceding claim made up of miniaturised components in an integrated circuit package.

8. A lighting unit including a control device as in any preceding claim and one or more gas discharge tubes.

9. A unit as in claim 8 in the form of a sunlamp or sun bed.

10. A control device substantially as hereinbefore described with reference to and as shown in Figures 1,2,3 or 4 of the accompanying drawings.