GB2529690A

GB2529690A - Method and system for powering a flash tube

Info

Publication number: GB2529690A
Application number: GB1415318.3A
Authority: GB
Inventors: Leo William Pollard
Original assignee: Cooper Technologies Co
Current assignee: Cooper Technologies Co
Priority date: 2014-08-29
Filing date: 2014-08-29
Publication date: 2016-03-02
Also published as: GB201415318D0

Abstract

A flashing beacon 100 can emit a pulse of light each time a capacitor 145 discharges electricity into a flash tube 140, such as a xenon tube. A circuit can charge the capacitor in preparation for each discharge. The circuit can vary the rate of capacitor charging during the charging cycle. The circuit can gradually ramp up the charging rate. For example, at the beginning of the charging cycle, the capacitor can receive electricity more slowly than during a later portion of the charging cycle. The circuit can feed the capacitor a series of pulses of electricity, with at least some of the pulses having progressively increasing energy content, for example by varying the pulse duration. The circuit can reduce current spikes and avoid simmering of the flash tube.

Description

METHOD AND SYSTEM FOR POWERING A FLASH TIJBE

TECHNICAL FIELD

[000 I] The present technology relates generally to beacon circuitry and more specifically to powering a xenon flash tube by gradually building up charge on a discharge capacitor.

BACKGROUND

[0002] Beacons are useful as warning lights and may flash to draw attention, for example to indicate status of a gas or oil leak, evacuation alert, or situation. A xenon beacon is a type of beacon that utilizes a xenon tube to produce a bright flashing light.

[0003] Flashing xenon beacons are powered by electrical circuits that iteratively build up an electrical charge in an electrical capacitor and discharge the capacitor into the xenon tube to produce a series of flashes. Conventional flashing xenon beacon circuits can exhibit a problem known as "simmering," Simmering occurs when the xenon tube has not fully extinguished before the capacitor charging circuit is triggered for the next charging cycle. Simmering is characterised by a continuous low output glow from the xenon tube, [0004] Simmering can occur at any operating temperature but is most likely at low temperatures when the charging characteristics of electrolytic capacitors can be compromised. At temperatures around -40°C and below, simmering can be particularly problematic. One approach for avoiding simmering involves forcing a delay after each tube discharge, so that the circuit pauses before commencing the next charging cycle.

However, in many instances the delay needed to avoid simmering would be too long for the application. Additionally, this approach has the disadvantage that the available time for the charging cycle is compressed, leading to circuitry complications and application issues, [0005] Another problem faced by conventional charging circuits relates to current spikes associated with conventional capacitor charging approaches. High inrush currents can produce spikes that create disruptive transients for control panels and electrical devices operating nearby, and can cause problematic electromagnetic interference (EMT).

[0006] Accordingly, there are needs in the art for improved circuitry for flash tubes, including for flashing xenon beacons. Need exists for an electrical circuit that can avoid simmering. Further need exists for an electrical circuit that can avoid current spikes. A technology addressing such a need, or some related deficiency in the art, would result in benefits that may include improved beacons and beacon performance.

SUMMARY

[0007] A circuit can cause a flash tube, such as a xenon tube, to emit a pulse of light by charging a capacitor and then discharging the capacitor through the tube. The circuit can vary the rate of capacitor charging during a charging cycle. During an initial phase of the charging cycle, the capacitor can receive electricity more slowly than during a later phase of the charging cycle. Thus, the capacitor can be charged relatively slowly at the beginning of the charge cycle.

[0008] For example, the circuit can charge the capacitor by feeding the capacitor a series of pulses of electricity, with at least some of the pulses having progressively increasing energy content The pulses can be current pulses of increasing duration, for

example.

[0009] The foregoing discussion of flash tubes and flash circuitry is for illustrative purposes only. Various aspects of the present technology may be more clearly understood and appreciated from a review of the following text and by reference to the associated drawings and the claims that follow. Other aspects, systems, methods, features, advantages, and objects of the present technology will become apparent to one with skill in the art upon examination of the following drawings and text. It is intended that all such aspects, systems, methods, features, advantages, and objects are to be included within this description and covered by this application and by the appended claims of the application.

BRIEF DESCRTPTTON OF THE DRAWINGS

[00101 Figures 1A and lB (collectively Figure 1) respectively illustrate a functional block diagram and a high-level schematic for a xenon beacon circuit in accordance with an example embodiment of the present technology.

[00111 Figure 2 illustrates two pulse series for charging a capacitor in a xenon beacon circuit in accordance with an example embodiment of the present technology.

[0012] Figure 3 illustrates oscilloscope traces of voltage for two, overlaid waveforms for charging a capacitor in a xenon beacon circuit in accordance with an example embodiment of the present technology.

[0013] Figure 4 illustrates an oscilloscope trace of current for charging and discharging a capacitor in a xenon beacon circuit that results in current spikes.

[0014] Figure 5 illustrates an oscilloscope trace of current for charging and discharging a capacitor in a xenon beacon circuit in accordance with an example embodiment of the present technology.

[0015] Figure 6 illustrates a flowchart of a process for controlling a xenon beacon in accordance with an example embodiment of the present technology.

[0016] Many aspects of the technology can be better understood with reference to the above drawings. The elements and features shown in the drawings are not necessarily to scale, emphasis being placed upon clearly illustrating the principles of exemplary embodiments of the present technology. Moreover, certain dimensions may be exaggerated to help visually convey such principles.

DESCRIPTION OF EXAMPLE EMBODIMENTS

[00171 A circuit for a flashing beacon, such as for a xenon beacon, can prevent simmering events that otherwise may occur at low operating temperatures, such as temperatures around -40°C and below, and further can avoid disruptive current spikes from occurring at the start of every charging cycle. As discussed in further detail below, in some example embodiments, the circuit can charge a capacitor using a variable charge rate or a soft-start charge.

[0018] Some example embodiments of the present technology will be discussed in further detail below with reference to the figures. Figure 1 describes a representative circuit. Figure 2 describes representative charging waveforms. Figures 3, 4, and 5 describe representative electrical characteristics associated with charging and discharging. Figure 6 describes a representative process.

[0019] The present technology can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the technology to those having ordinary skill in the art.

Furthermore, all "examples," "embodiments," "example embodiments," or "exemplary embodiments" given herein are intended to be non-limiting and among others supported by representations of the present technology.

[0020] Some of the embodiments may comprise or involve processes that will be discussed below. Certain steps in such processes may naturally need to precede others to achieve intended functionality or results. However, the technology is not limited to the order of the steps described to the extent that reordering or re-sequencing does not render the processes useless or nonsensical. Thus, it is recognized that some steps may be performed before or after other steps or in parallel with other steps without departing

from the scope and spirit of this disclosure.

[0021] Turning now to Figures 1A and lB. these figures, respectively, are illustrations of a functional block diagram and a high-level schematic for an example xenon beacon circuit 100 according to some embodiments of the present technology.

[0022j Tn the illustrated example embodiment, the xenon beacon circuit I 00 comprises a direct current (DC) power supply 106, for example a battery or a circuit that converts alternating current (AC) electricity into DC electricity.

[00231 A soft start circuit 105 comprises a soft start transistor 155. The soft start circuit 105 reduces inrush of current during startup and operation of the beacon circuit 106.

[0024] The illustrated beacon circuit 106 further comprises a control circuit 115 that comprises a microcontroller 130 and associated memory 135, The microcontroller can comprise a microprocessor or other appropriate processor, for example. An embodiment of the memory 135 can comprise volatile and nonvolatile memory, such as random access memory (RAM) and flash memory, for example. The control circuit I I 5 has two output lines, one for producing electrical pulses by controlling a charging switch 110, and another for firing a xenon tube 140.

[0025] To create a pulse, the control circuit 115 closes the charging switch 110, which comprises a charging switch transistor 160 (and thus is solid state as illustrated).

When the charging switch I 1 0 closes, current flows through a charge transformer I 50 that is part of a charging circuit I 20. The charge transformer 1 50 steps up voltage of the pulse. Energy from the stepped up pulse is stored as charge in a charge capacitor 145, which is also an element of the charging circuit 120. With each pulse, charge on the charge capacitor 145 builds. Accordingly, the charging circuit 120 stores elecftical energy for delivery to the xenon tube 140.

[0026] The xenon tube 140 is part of a xenon circuit 125 that further comprises a trigger coil 165. When sufficient charge has built up on the charge capacitor 145, the microcontroller 130 emits a signal that flows through the trigger coil 165. The trigger coil 165 steps up that signal, so that the signal has sufficient voltage to control the xenon tube 140. More specifically, the stepped up trigger signal causes the xenon tube 140 to accept current from the charge capacitor 145, and the charge capacitor 145 discharges through the xenon tube 140. In response to the discharge, the xenon tube 140 emits a pUlse of light.

[0027j Turning now to Figure 2, this figure is an illustration of two example pulse series 200, 250 for charging the capacitor 145 in an example xenon beacon circuit 100 according to some embodiments of the present technology. The horizontal axis represents time. The pulses in the sequence 200 are of equal duration and thus have equal energy content. In contrast, the pulses of the series 250 have progressively increased duration and thus progressively increased energy content.

[0028] In an example embodiment, the microcontroller 130 of the xenon beacon circuit 100 opens and closes the charging switch 110 to vary pulse duration for progressively increased duration, consistent with the illustrated pulse series 250. During a charge cycle, the microcontroller 130 can further transition from valying the pulse duration, to holding pulse duration constant as illustrated in the pulse series 200. For example, the pulse series 250 can be representative of charging during an initial phase of a charging cycle, while the pulse series 200 can be representative of charging during a subsequent phase of the charging cycle. Accordingly, Figure 2 illustrates an example of controlling pulse duration in order to vary the rate of building up charge on the charge capacitor 145, [0029] However, in some example embodiments, the microcontroller 130 varies the time between pulses, so that the period of the pulse series chmges. For example, the pulse duration may remain fixed, but the time between pulses varies in order to adjust charge rate, [0030] In some example embodiments, the time between pulses and the pulse duration are both varied in order to achieve a gradually increasing rate of building charge on the charge capacitor 145.

[003 I] Tn one example embodiment, pulse height or pulse shape may be varied in order to manipulate charge rate on the charge capacitor 145, [0032] Turning now to Figure 3, this figure is an illustration of example oscilloscope traces 300, 350 for two, overlaid waveforms for charging a capacitor 145 in an example xenon beacon circuit 100 according to some embodiments of the present technology. The traces 300, 350 are from laboratory circuit testing, as discussed below, More specifically, an oscilloscope captured each of the traces 300, 350 by measuring and C) plotting voltage verses time across the charge capacitor 145 while the xenon beacon circuit 100 charged and discharged the charge capacitor 145. By tracking voltage across the charge capacitor 145, the traces 300, 350 likewise represent charge level of the charge capacitor 145.

[00331 The horizontal axis is time, with 250 ms per division. The vertical axis is voltage, with 50 volts per division. The trigger voltage is 74 volts.

[0034] Each of the traces 300, 350 includes two full charge/discharge cycles, along with a trailing portion of a third cycle arid a leading portion of a fourth cycle. The vertical lines of the traces 300, 350 represent discharge events. The time between discharges is one second (four divisions at 250 ms per division). The voltage applied to the xenon tube 140 at discharge is approximately 275 volts (5.5 divisions at 50 volts per division). Thus, the oscilloscope waveforms have amplitudes of approximately 275 volts and periodicity of one second. At the peak amplitude of 275 volts, the charge capacitor is fully charged.

[0035] To generate the trace 300, the microcontroller 130 was set to cause the xenon beacon circuit I 00 to produce a series of capacitor-charging pulses of equal duration, as in the series 200 illustrated in Figure 2. Thus, the energy in each pulse remained substantially constant across the charging cycle. The resulting trace 300 rises abruptly following discharge (see the trace region 302) and generally follows a logarithmic curve.

[0036] Tn contrast, the trace 350 was generated by selling the microcontroller 130 to cause the xenon beacon circuit I 00 to produce a series of capacitor-charging pulses of progressively longer duration, as in the series 250 illustrated in Figure 2. Accordingly, the energy in each pulse varied during the charging cycle and more specifically increased at the beginning of the charging cycle. Thus, the soft charge utilizes charging pulses of gradually increasing length during an initial phase of the charging cycle. The resulting trace 350 rises relatively gradually following discharge (see trace region 352). In the illustrated example embodiment, the trace 350 follows a sigmoid curve and may be characterized as "s-shaped." [0037] Gradually starting the charging of the charge capacitor 145, as illustrated in the trace 350, avoids simmering and current spiking without compromising the length of the charging duty cycle. To avoid simmering, the s-shape of the trace 350 provides the xenon tube 140 sufficient time to fully extinguish before the xenon beacon circuit 100 is in a position to re-trigger the tube 140, even at low temperatures. To avoid current spiking, the gradual start of the trace 350 prevents an initial high rate of change of charging voltage.

[0038] Turning now to Figures 4 and 5, Figure 4 is an illustration of an oscilloscope trace 400 of charging and discharging the charge capacitor 145 with a series of current pulses of equal duration, resulting in current spikes 401, 402. Figure 5, in contrast, is an illustration of an example oscilloscope trace 550 of charging and discharging the charge capacitor 145 with current pulses of varying duration, resulting in elimination of current spiking in the example xenon beacon circuit 100 according to some embodiments of the present technology. Both traces 400, 550 are from laboratory circuit testing, as discussed below.

[0039] The trace 400 of Figure 4 plots current flowing into and out of the charging capacitor 145 with the capacitor 145 being charged using pulses of equal duration, as depicted in the pulse series 200 of Figure 2 and the trace 300 of Figure 3, Thus, the trace 300 of Figure 3 and the trace 400 of Figure 4 correspond to one another, with the trace 300 illustrating voltage characteristics of charge-discharge cycles, and the trace 400 illustrating current characteristics of the cycles.

[0040] Meanwhile, the trace 550 of Figure 5 plots current flowing into and out of the charging capacitor 145 with the capacitor 145 being charged using pulses of increasing duration, as depicted in the pulse series 250 of Figure 2 and the trace 350 of Figure 3. Thus, the trace 350 of Figure 3 and the trace 550 of Figure 5 correspond to one another, with the trace 350 illustrating voltage characteristics of charge-discharge cycles, and the trace 550 illustrating current characteristics of the cycles.

[0041] Referring now to Figure 4, following a discharge at a time 406, the xenon beacon circuit 100 recharges the capacitor 145 by feeding the capacitor 145 the series of current pulses 200 of equal duration during the recharge phase 403 of the cycle. The trace 400 is substantially flat during that phase 403 since each pulse carries substantially the same amount of current. At discharge, the trace 400 has a downward spike 401 as the capacitor 145 discharges current opposite the charging direction. The trace 400 then has an upward spike 402 due to current rushing back into the discharged capacitor 145. Such spiking can be detrimental as discussed above.

[0042] Referring now to Figure 5, variable rate charging eliminates the spiking issue that appears in Figure 4. Following a discharge at a time 506, the xenon beacon circuit 100 recharges the capacitor 145 by ramping up the duration of the current pulses during an initial phase 554 of the charge cycle. Following the ramping phase 554, the xenon beacon circuit 100 recharges with equal duration pulses during the second phase 553 of the charging cycle. At discharge, the trace 550 has a downward step 551 as the capacitor 145 discharges current into the xenon tube 140. After discharge, the trace 550 has a ramping section 552 during which the current gradually ramps up as pulse duration increases as illustrated in the example series of current pulses 250 depicted in Figure 2.

[0043] Turning now to Figure 6, this figure is an illustration of a flowchart for an example process 600 for controlling a xenon beacon according to some embodiments of the present technology. Process 600 will be discussed below with example reference to the preceding figures, without limitation.

[0044] In some example embodiments, instructions for execution of the relevant parts of process 600 can be stored in the memory 135 and executed by the microcontroller 130, for example.

[0045] At block 605 of process 600, a person or an automated system, for example an emergency system or a warning system, turns the beacon on.

[0046j At block 610 of process 600, the soft start circuit 105 reduces inrush current to the xenon beacon circuit 100.

[0047j At block 615 of process 600, the microcontroller 130 initializes, Tnitialization may comprise readying the microcontroller 130 for process execution by loading or otherwise accessing instructions from a program stored in the memory 135, for

example,

[0048] At block 620 of process 600, the microcontroller 130 sets threshold values and timing counters, for example by reading the values from the memory 135, [00491 At decision block 625, the microcontroller 130 determines if the voltage on the charge capacitor 145 is of sufficient magnitude for flashing the xenon tube 140. If the voltage is deemed sufficient, then process 600 branches to decision block 670.

[0050] At decision block 670, the microcontroller 130 determines whether the timer (which was initialized at block 620) indicates that it is at an appropriate time for the xenon to flash, This timing function provides the required flash pattern for example 60 flashes per minute, 80 flashes per minute etc. If the microcontroller 130 determines that the timing constraints are not met, then process 600 loops back to block 625 and iterates until the timing constraints are satisfied, [0051] When at block 670 the microcontroller 130 determines that the timing constraints are met, then the xenon beacon circuit 100 flashes the xenon tube 140 at block 675. Following flashing of the xenon tube 140, process 600 loops back to block 620 and iterates, [0052] When the microcontroller 130 determines at decision block 625 that the voltage across the charge capacitor 145 has not yet reached a sufficient value for discharging, then process 600 branches to block 640 to charge the capacitor 145. More specifically, in the flowcharted embodiment, decision block 640 executes from a negative determination at decision block 625.

[0053] At block 640, the microcontroller 130 determines whether the line voltage is low, for example as determined by pre-configured hardware feeding an input of the microcontroller.

[0054] If the determination at decision block 640 is negative, then process 600 executes decision block 650 and determines whether the line voltage is high, for example as determined by pre-configured hardware feeding an input of the microcontroller, [0055] If the line voltage is deteniined to be low at block 640, block 635 executes. If the line voltage is determined to be high at block 650, block 645 executes. If the line voltage is determined to be neither low at block 640 nor high at block 650, then block 655 executes.

[00561 At block 635, the microcontroller 130 selects and executes a lower voltage routine. This routine differs from other routines in that the charging switch 110 on duration after the soft charge cycle has finished is longer than that of the normal voltage routine in order to supply the same energy to the xenon tube.

[0057] At block 645, the microcontroller 130 selects and executes an upper voltage routine. This routine differs from other routines in that the charging switch 110 on duration after the soft charge cycle has finished is shorter than that of the normal voltage routine in order to supply the same energy to the xenon tube.

[0058] At block 645, the microcontroller 130 selects and executes a normal voltage routine. This routine sets charging switch 110 on duration after the soft charge cycle has finished to a length appropriate for the nominal supply voltage.

[0059] Following execution of block 635, block 645, or block 655, as deteniiined by the logic of decision blocks 640 and 650, process 600 executes block 630.

[0060] At decision block 630, the microcontroller 130 checks to see if a flag has been set to enable the soft charge. The xenon beacon circuit 100 can charge either using only the series of pulses 200 of equal duration, or by initially utilizing the series of pulses 250 of increasing duration and then the pulses 200 of equal duration. By checking the flag at block 630, the microcontroller 130 determines the mode in which the xenon beacon circuit 100 has been set.

[0061] If the microcontroller 130 determines at block 630 that the xenon beacon circuit 1 00 is set for ramping current during the charge cycle, then block 660 executes.

At block 660, the microcontroller 1 30 switches the charging switch transistor 160 on and off to create the series of pulses 250 of increasing duration as illustrated in Figure 2.

[0062] Following execution of block 660 or a negative determination at decision block 630, block 665 executes. At block 665, the microcontroller 130 switches the charging switch transistor 160 on and off to create the series of pulses 200 of equal duration as illustrated in Figure 2.

[0063j From block 665, process 600 determines at decision block 670 whether the timing conditions are satisfied and either loops back to block 625 or flashes the xenon tube 140 at block 675 as discussed above.

[00641 Technology for powering a flash tube, for example a xenon tube, has been described. From the description, it will be appreciated that embodiments of the present technology overcome limitations of the prior art. Those skilled in the art will appreciate that the present technology is not limited to any specifically discussed application or implementation and that the embodiments described herein are illustrative and not restrictive. From the description of the exemplaiy embodiments, equivalents of the elements shown therein will suggest themselves to those skilled in the art, and ways of constructing other embodiments of the present technology will appear to practitioners of the art.

Claims

CLAIMSWhat is claimed is: 1. A method for producing flashes of light, comprising the steps of: building up a charge on a capacitor by feeding the capacitor a series of electrical pulses that comprises electrical pulses of progressively higher energy content; and producing a flash of light by discharging the charged capacitor through a flash tube.
2. The method of Claim 1, wherein the series of electrical pulses further comprises pulses of substantially equal energy content that temporally follow the electrical pulses of progressively higher energy content.
3. The method of Claim 1, wherein the electrical pulses of progressively higher energy content have progressively longer pulse durations.
4. The method of Claim 1, wherein the flash tube comprises a xenon flash tube.
5. The method of Claim 1, wherein feeding the capacitor the series of electrical pulses that comprises electrical pulses of progressively higher energy content comprises controlling pulse duration with a microcontroller.
6. The method of Claim 1, further comprising producing a sequence of light flashes by iterating the building and discharging steps.
7. The method of Claim 6, wherein following a capacitor discharge, charge is built up on the capacitor by initially feeding the capacitor the electrical pulses of progressively higher energy, and wherein the electrical pulses of progressively higher energy comprise electrical pUlses of progressive'y longer duration.
8. A system for producing flashes of light, comprising: a flash tube; a capacitor connected to the flash tube for discharging through the flash tube to produce a flash of light; and a controller that is connected to the capacitor and a power input and that is configured to build up a charge on the capacitor by feeding the capacitor electricity at a rate that gradually increases over time.
9. The system of Claim 8, wherein the controller is further configured to feed the capacitor a series of current pulses.
10. The system of Claim 9, wherein the series of current pulses comprises current pulses of progressively longer duration.
11. The system of Claim 9, wherein the series of current pulses comprise initial current pulses of progressively increasing duration and subsequent current pulses of substantially equal duration.
12. The system of Claim 8, wherein the flash tube comprises a xenon tube.
13. The system of Claim 8, wherein the controller comprises a memory storing instructions for feeding the capacitor electricity at the rate that gradually increases over time.
14. The system of Claim 8, wherein feeding the capacitor electricity at the rate that gradually increases over time comprises the controller manipulating a solid state switch to feed to the capacitor current pulses of varying duration.
15. The system of Claim 8, wherein the system comprises a flashing xenon beacot