GB2557974A

GB2557974A - Lamp with improved UV output sensing

Info

Publication number: GB2557974A
Application number: GB1621794.5A
Authority: GB
Inventors: Cherry Richard; slater Mark
Original assignee: Alpha Cure Ltd
Current assignee: Alpha Cure Ltd
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2018-07-04
Anticipated expiration: 2036-12-21
Also published as: GB2557974B; GB201621794D0

Abstract

A lamp includes a main body 10 and a light guide 12 attached to the lamp body and a sensor 13 mounted at an output end or exit of the light guide. Alternatively, the light guide may be attached to the main body of the lamp via extension 11 which may be coaxial with the lamp body. The lamp body, extension and the light guide element may be formed of quartz or fused silica or other material with total internal reflection properties which allows for light transmission to the light guide exit where a sensor is positioned. The sensor may be calibrated to give an accurate reading of the lamp UV intensity. The sensor may be used to monitor the UV light (e.g. to determine degradation of the lamp output) or to control the lamp (e.g. to calibrate for loss of light intensity). Use of many sensors may provide measurements of different lamp characteristics. The lamp may be used for water sterilisation.

Description

(71) Applicant(s):

Alpha-Cure Limited

Great Central Way, WOODFORD HALSE, Northamptonshire, NN11 3PZ, United Kingdom (72) Inventor(s):

Richard Cherry Mark Slater (56) Documents Cited:

JP 2000258247 A US 7429742 B1 (58) Field of Search:

INT CL A61L, C02F, G01J, G02B, H01J Other: EPODOC, WPI, TXTE (74) Agent and/or Address for Service:

Urquhart-Dykes & Lord LLP Altius House, 1 North Fourth Street,

MILTON KEYNES, Buckinghamshire, MK9 1NE, United Kingdom (54) Title ofthe Invention: Lamp with improved UV output sensing

Abstract Title: Lamp with light guide attached directly to the lamp or to a lamp extension (57) A lamp includes a main body 10 and a light guide 12 attached to the lamp body and a sensor 13 mounted at an output end or exit of the light guide. Alternatively, the light guide may be attached to the main body of the lamp via extension 11 which may be coaxial with the lamp body. The lamp body, extension and the light guide element may be formed of quartz or fused silica or other material with total internal reflection properties which allows for light transmission to the light guide exit where a sensor is positioned. The sensor may be calibrated to give an accurate reading ofthe lamp UV intensity. The sensor may be used to monitor the UV light (e.g. to determine degradation of the lamp output) or to control the lamp (e.g. to calibrate for loss of light intensity). Use of many sensors may provide measurements of different lamp characteristics. The lamp may be used for water sterilisation.

1/1

Lamp with Improved UV Output Sensing

The present invention relates to a lamp, particularly a lamp that emits Ultraviolet (UV) radiation having features to improve monitoring of its own UV output, i.e. by way of an integral light guide.

Background to the Invention

UV lamps are used in many applications where the UV radiation generated is used to effect a specific chemical reaction. Typical applications include: the curing of specially formulated UV sensitive coatings (e.g. inks, varnishes and adhesives), sterilisation (e.g. water, air or surface). Measuring the UV output of the lamp in many of these applications is desirable to ensure that the process receives the required dose of radiation. It is also known that the radiation emitted from a lamp deteriorates over time, therefore, a UV monitor can also be used to indicate the condition of the lamp and the end of its useful life.

In order for UV output to be measured it is common for a UV sensor to be positioned at some distance from the lamp, otherwise the lamp operating temperature can be detrimental to the sensor. Furthermore, contact of any other material with the lamp envelope is known to cause a breakdown in that material. The downside of this common sensing method is that it is drastically effected by any form of external contamination, which will show a drop off in UV output as delivered to the process, but it is not necessarily indicative of the actual aging or performance of the lamp. This leads to misinformation regarding the system and therefore the remedial action is not immediately obvious to an untrained eye.

In UV lamps the characteristic spectrum comes predominantly from the excitation of mercury in an electric arc. It is also common practice to modify the output spectrum with the addition of other chemicals, e.g. in the form of metals or metal halides. In this way the output of the lamp can be more closely tuned to the specific absorption characteristics that the process requires and, therefore, be more effective.

Most UV lamps are manufactured from pure fused silica or quartz, as this is highly transmissive to the shorter wavelengths of UV radiation and is also capable of withstanding the operating temperature found in higher powered lamps (e.g. Medium Pressure or MP). Quartz is a naturally occurring crystal which is opaque to light and not greatly transmissive to UV radiation, however, in order to be formed into tubing for a lamp the ground crystal is melted and drawn into the required section where it takes on its fused form, in a process known as vitrification. This vitrified material is transparent to both visible and UV radiation. Quartz operates in MP lamps at quite elevated temperatures (e.g. 800-900°C) but at these temperatures any surface contamination can bring about a reaction whereby the vitreous form turns back to the natural crystalline state, in a process known as devitrification.

With any type of UV lamp the output tends to reduce over the lamp running time. Taking medium pressure lamps as an example, a typical life expectancy is something around 1000 to 5000 hours, depending on the operating environment. In an ideal environment, where the cooling is optimum and there is little risk of external contamination, the mode of failure is typically a build-up of deposits on the inner wall of the lamp envelope. This is predominantly tungsten sputtered off from the electrodes during operation which in itself blocks the UV radiation generated and also tends to combine with some of the mercury or metal halides that produce the UV, thus further reducing the output of the lamp.

If a method can be found to monitor the lamp output without the interference of external contaminants then the lamp aging can be measured directly without any consideration needed to be given to lamp environment. In addition to this, applying an external sensor would further increase the information available for the system 'wellbeing'. In this way all the variables would be known in respect to the factors that affect the radiation received by the process. As most system employ some form of programmable control, decisions can be made regarding the state of the system based on simple mathematical algorithms.

Summary of the Invention

The present invention seeks to provide a lamp construction that enables improved monitoring of UV output. Since it is known that quartz exhibits Total Internal Reflection, the invention proposes forming an integral 'light pipe' or 'light guide' with the quartz lamp that is able to transmit light from an entrance to an exit, where a sensor can be positioned. The phenomenon of Total Internal Reflection is the foundation of fibre optic technologies. As quartz has a good transmittance to UV wavelengths this can also be used to transmit shorter wavelengths outside the visible spectrum.

In a broad aspect of the invention there is provided a lamp according to claim 1 and corresponding method of constructing such a lamp. In a preferred form the lamp is comprised of a quartz tube housing mercury vapour and electrodes at each end that, when energised, form an arc through the vapour thereby emitting UV light, with the provision for a light guide fused directly to the lamp. A sensor is mounted at an output end of the light guide so that a reading of the UV intensity can be taken.

In broad terms the lamp includes a main body, a mounting leg or extension and a light transmitting guide element fused directly to the main body or mounting extension. A sensor is mounted at an output end of the light transmitting guide element for the purposes of measuring a characteristic, such as UV output intensity. Preferably the body, extension and light guide element are formed from quartz which has total internal reflectance characteristics, thereby enabling light to be directed to the sensor without it being impeded by external contamination/fouling influences.

Brief Description of the Drawings

Figure 1 illustrates a first embodiment of the invention wherein a light guide extends perpendicularly from a lamp body;

Figure 2 illustrates a second embodiment wherein a light guide extends perpendicularly from a mounting leg of a lamp body;

Figure 3 illustrates a third embodiment wherein a light guide extends axially from a mounting leg of a lamp body; and

Figure 4 illustrates an application of the invention for water sterilisation, incorporating a lamp body according to the second embodiment of Figure 2.

Detailed Description of Preferred Embodiments of the Invention

Figure 1 illustrates a first embodiment of a lamp according to the invention, comprised of a lamp body 10 and coaxial mounting extensions 11 preferably formed in one piece from fused quartz. In the known way, electrodes (not shown) would be embedded in the extensions 11 that, when energised, form an arc across the void of the lamp body (that is filled with mercury vapour). Light is emitted from the lamp body 10 as indicated by arrows E and, as a natural consequence of the quartz or equivalent material, transmitted by internal reflection along its length as indicated by arrows R. In the preferred form of the invention it is UV light that emitted/transmitted but in principle the invention could be configured for any light wavelength.

As exemplified by Figure 1, a length of solid quartz is fused directly to the lamp body 10 to act as a light guide 12, i.e. light R transmitted by internal reflection is directed through guide 12. A sensor 13 is mounted at a distal end of guide 12, i.e. opposite the end fused with body 10. The arrangement enables direct measurements from the emitting area of the lamp. A strong signal is delivered to the sensor 13 that is unimpeded by external influence. The sensor 13 can be calibrated to give an accurate reading based on the light guide 12 mounting position which may be subject to signal loss during transmission, but such being constant and predictable. The illustrated form shows a perpendicular configuration for light guide 12 relative to body 10, however, alternative angles and configurations would be possible.

Figure 2 illustrates a variant where a length of solid rod is fused to the lamp leg/mount 11 to form a light guide 14. In this embodiment the quartz body 10 transmits, by internal reflection, a proportion of the lamp output light R to the leg and onwards into the light guide 14. The principle is the same as Figure 1 but represents a more convenient position for mounting the sensor 13. In practice this configuration potentially results in a weaker signal but still in proportion with the total output. In other words, while weaker, any signal loss can be accounted for in calibration to provide an accurate reading during normal use.

The embodiments described herein could feature alternatively shaped/angled light guides 12/14 to make the position of the sensor 13 more convenient. The quartz rod is effectively equivalent to a fibre optic cable so bending it would have little effect on the signal transmitted.

A third embodiment, illustrated by Figure 3, utilises the existing 'leg' 11 that is formed during manufacture of the lamp as part of (or all of) the length of light guide 15, directing a light signal to sensor 13. Compared to Figures 1 and 2, this embodiment could potentially yield an intermediate output and would require the senor 13 to be mounted directly on the end of the lamp. This embodiment may be preferable from the perspective of system design but could present issues due to the electrical connections which are normally made in this position, i.e. to electrodes.

All construction methods outlined herein would require the use of a simple calibration to give reasonably accurate measurements of the total output. This could be as simple as setting the reading to 100% when the lamp is new which would then give a proportionally falling output percentage over the lamp life.

With reference to a particular application of the invention, Figure 4 illustrates a water sterilisation example. Although the method could be implemented for all UV irradiation processes it lends itself particularly well to water sterilisation systems where UV sensors are commonly used. In this situation the radiation dose is critical to achieve the level of disinfection required. These systems commonly use external UV sensors S that are mounted on the outside of a water jacket J behind a quartz window W. In the known way the lamp 10 operates in a sealed tube or sleeve T inside the water jacket to keep the water being treated in the annular gap.

The major problems experienced with a conventional system are the variable quality (clarity) of the water affecting the UV radiation transmission and fouling of the inner tube T and sensor window W from waterborne contaminants. Although fouling can be somewhat alleviated by the use of a mechanical wiper system, both of the identified problems result in a reduction in UV exposure at the sensor which is regularly interpreted as a lamp degradation issue. Using the method of the invention, e.g. where both a direct lamp reading and a system reading are compared, will allow a much more accurate diagnosis of the problem in order to avoid a lamp being changed that was still serviceable.

Operating temperature is also critical to lamp operation and good control of the cooling system is essential for optimising lamp life. This parameter could also be monitored in a similar way as described above using a suitable sensor. For example, since the measuring area 13 is a distance away from the lamp envelope 10, a contact probe (e.g. thermocouple) could be applied to the sensor array on the end of the light guide 12/14/15 which, if applied directly to the higher operating temperature areas of a lamp, would cause the quartz to devitrify. The optical sensor 13 used for the UV measurement could also be employed to this end by being adapted to also look at some of the longer wave infrared radiation being emitted from the lamp which would also indicate temperature with some suitable calibration.

It will be apparent that variations on the above described embodiments will be possible that still fall within the scope of the invention defined by the appended claims. For example, the primary example of the invention is described with reference to quartz lamps and ultraviolet (UV) light applications, but alternative materials may exist, or come to exist, that present similar properties. As such the scope of the invention should not be ultimately limited by specific materials or applications.

Claims

Claims:

1. A lamp including a main body and a mounting extension, wherein a light transmitting guide element is attached directly to the main body or mounting extension, further including a sensor mounted at an output end of the light transmitting guide element.

2. The lamp of claim 1 wherein the main body and mounting extension is formed from fused quartz or equivalent material with internal reflectance characteristics.

3. The lamp of claim 1 or 2 wherein the light transmitting guide element is formed from a body of fused quartz or equivalent material with internal reflectance characteristics, fused or otherwise attached to the main body or mounting extension.

4. The lamp of any preceding claim wherein the light transmitting guide element is attached at an angle from the main body or mounting extension.

5. The lamp of claims 1 or 2 wherein the light transmitting guide element is integral with and/or parallel/coaxial with the mounting extension.

6. A method of constructing a lamp including mounting a sensor at the distal end of a light transmitting guide element that is attached at its proximate end to a light transmitting portion of the lamp.

7. The method of claim 6 wherein the light transmitting portion of the lamp is a main body or mounting extension.

8. The method of claim 7 wherein the light transmitting guide is integral with the mounting extension.

9. The method of any one of claims 6 to 8 wherein the sensor is associated with a control means to provide an output measurement of the lamp to be monitored, thereby being capable of determining degradation of the lamp output over time.

10. The method of claim 9 wherein the control means is calibrated to account for signal loss of light through the lamp and/or light transmitting guide.

11. The method of any one of claims 6 to 10 wherein the lamp and light transmitting guide

5 element are formed from fused quartz or equivalent material with internal reflectance characteristics.

12. The method of any one of claims 6 to 11 wherein a plurality of sensors are mounted adjacent the distal end of the light transmitting guide element, each measuring a different

10 characteristic of the lamp or its light output.

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Application No: GB1621794.5