WO2011077306A1

WO2011077306A1 - Apparatuses and methods for measuring uv absorption rate

Info

Publication number: WO2011077306A1
Application number: PCT/IB2010/055658
Authority: WO
Inventors: Levinus Pieter Bakker; Jun She; Peixin Hu; Haihui Wu
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-12-25
Filing date: 2010-12-08
Publication date: 2011-06-30

Abstract

The present invention proposes an apparatus and method for measuring the UV absorption rate of a liquid (130) in a container (120) comprising a UV lamp (110), using two sensors (141, 142) to measure intensities of two associated beams of light originating from the UV lamp (110) and passing through the liquid (130), and determining the UV absorption rate based on these two light intensities and at least one transmission distance of the two beams of light. One of the two associated beams of light is a beam of UV light, the other is a beam of UV light or visible light or near IR light.

Description

APPARATUSES AND METHODS FOR MEASURING UV ABSORPTION

RATE

Technical field

The present invention relates to apparatuses and methods for measuring the UV absorption rate of a liquid in a container comprising a UV lamp.

Background of the invention

In many countries, the quality of tap water is insufficient to allow safe consumption. This creates a market for residential water purifiers that remove harmful contaminants from tap water. Customers would like the water from the purifier to have a guaranteed quality. This can be achieved by choosing the proper treatment technology. Currently, the main treatment technology for residential purifiers is filtering. However, filters have to be replaced before they reach their end of life in order to guarantee proper functioning. Other treatment technologies such as UV (ultra-violet) disinfection also have to be monitored in order to guarantee proper functioning.

Now there are two technical solutions for monitoring the quality of water to be subjected to UV disinfection. The first one makes use of one UV sensor to measure the intensity of UV light at the reactor wall of the purifier, and compare the measured UV intensity with a predefined threshold to determine whether the UV light generated by the UV lamp is strong enough for disinfection. The second one is off-line measurement. First, by measuring a "reference water" a first measured UV intensity is obtained, and then the "target water" is measured and a second measured UV intensity is obtained. By comparing the first and the second UV intensities, the quality of the "target water" can be obtained. However, the above two solutions cannot avoid the effect caused by non-uniformity and fluctuation of the spatial pattern of UV emission nor the effect caused by fouling on the wall of the reactor.

Summary of the invention The present invention proposes a technical solution for measuring the UV absorption rate of a liquid in a container comprising a UV lamp, using two sensors to measure intensities of two associated beams of light originating from the UV lamp and passing through the liquid, and determining the UV absorption rate based on these two light intensities and at least one transmission distance of the two beams of light. One of the two associated beams of light is a beam of UV light, the other is a beam of UV light or a beam of visible light or a beam of near IR light.

According to one embodiment of the present invention, there is provided an apparatus for measuring the UV absorption rate of a liquid in a container comprising a UV lamp, the apparatus comprising: a first sensor configured to receive a first beam of UV light, emitted by the UV lamp, and passing through the liquid and to detect the intensity of the first beam of UV light; a second sensor configured to receive a second beam of light, associated with the first beam of UV light, passing through the liquid and to detect the intensity of the second beam of light; and a processor configured to determine the UV absorption rate on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light.

According to another embodiment of the present invention, there is provided a method of measuring the UV absorption rate of a liquid in a container comprising a UV lamp, said method comprising: receiving a first beam of UV light, emitted by the UV lamp, and passing through the liquid, and detecting the intensity of the first beam of UV light; receiving a second beam of light, associated with the first beam of UV light, passing through the liquid, and detecting the intensity of the second beam of light; and determining the UV absorption rate on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light.

With the apparatuses and methods provided in the present invention, the effect caused by non-uniformity and fluctuation of the spatial pattern of UV emission or the effect caused by fouling on the wall of the container can be well avoid, and the UV absorption rate of liquid can be measured more conveniently than before.

Brief description of the drawings The above and other objects, characteristics and merits of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which:

FIG. 1 illustrates a schematic view of a UV reactor 100 comprising an apparatus 140 for measuring the UV absorption rate of a liquid according to one embodiment of the present invention;

FIG. 2 illustrates a schematic view of a UV reactor 100 comprising an apparatus 240 for measuring the UV absorption rate of a liquid according to one embodiment of the present invention;

FIG. 3 illustrates a schematic view of a UV reactor 100 comprising an apparatus 340 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 4(a) illustrates a schematic view of a UV reactor 100 comprising an apparatus 440 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 4(b) illustrates a schematic view of a UV reactor 100 comprising an apparatus 440 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 5(a) illustrates a schematic view of a UV reactor 100 comprising an apparatus 540 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 5(b) illustrates a schematic view of a UV reactor 100 comprising an apparatus 540 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 6 illustrates a schematic view of a UV reactor 100 comprising an apparatus 640 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 7 illustrates a schematic view of a detection angle of a quartz stick according to one embodiment of the present invention; FIG. 8(a) illustrates a schematic view of a detection angle of a quartz stick having a cylindrical geometry and a length shorter than the diameter according to one embodiment of the present invention;

FIG. 8(b) illustrates a schematic view of a detection angle of a quartz stick having a cylindrical geometry and a length much longer than the diameter according to one embodiment of the present invention;

FIG. 9(a) illustrates a schematic view of a UV reactor 100 comprising an apparatus 940 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 9(b) illustrates a schematic view of a UV reactor 100 comprising an apparatus 940 for measuring the UV absorption rate of a liquid according to another embodiment of the present invention;

FIG. 10 illustrates a flow chart of a method of measuring the UV absorption rate of a liquid in a container comprising a UV lamp according to another embodiment of the present invention; wherein same or analogous reference numerals are used to represent same or analogous step features/devices (modules) throughout the Figures.

Detailed description of the embodiments

Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings.

FIG. 1 illustrates a schematic view of a UV reactor 100, comprising a UV lamp 110, a container 120 with a liquid 130 such as water, and an apparatus 140 for measuring the UV absorption rate of the liquid 130 in the container 120. The apparatus 140 comprises a first sensor 141, a second sensor 142 and a processor 143.

The first sensor 141 receives a first beam of UV light, emitted by the UV lamp 110 and passing through the liquid 130, and then detects the intensity of the first beam of UV light. The second sensor 142 receives a second beam of light, associated with the first beam of UV light, passing through the liquid 130, and then detects the intensity of the second beam of light. The processor 143 determines the UV absorption rate of the liquid 130 on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light.

It is to be understood by those skilled in the art that FIG. 1 is only a schematic view. The container 120 can be of various shapes and the UV lamp 110 can be located at any place in the container 120 besides the centre of the container 120 as illustrated in FIG. 1. According to the difference of the relationship of the two associated beams of light, the physical deployment of the two sensors 141 and 142 is, which will be described in detail in the following text. The first beam of light can be a beam of UV light. The second beam of light can be a beam of UV light or near IR light (0.75-2.5μπι) or visible light associated with the first beam of light.

FIG. 2 shows a schematic view of a UV reactor 100 comprising an apparatus 240 for measuring the UV absorption rate of a liquid 130 according to one embodiment of the present invention. The apparatus 240, compared with the apparatus 140 in FIG. 1, further comprises a beam splitter 144. The beam splitter 144 can be a semi-transparent mirror or a prism.

The beam splitter 144 is mounted in front of the first sensor 141 and transmits a first part of a third beam of UV light to the first UV sensor 141 and reflects a second part of the third beam of UV light to the second sensor 142. The first beam of light is formed by the first part of the third beam of UV light. The second beam of light is formed by the second part of the first beam of UV light. The processor 143 is further configured to determine the UV absorption rate of the liquid 130 on the basis of the two detected light intensities and the transmission distance of the second beam of light.

Without loss of generality, the definition of the UV absorption rate of a liquid 130 adopts the following formula:

I = I₀ exp(-a - d) ^

wherein a denotes the UV absorption rate of a liquid 130, d denotes the transmission distance of UV light, I and I₀ respectively denote the UV light intensity before and after a transmission distance of d .

Referring to FIG. 2, the UV absorption rate a can be obtained according to the following formula:

a = -ln(I₁₂ * f₁₂ */(_ySl₁₁ * f₁₁))/D₁₂ (2) wherein β is the split ratio of the intensity of the reflection part to the intensity of the transmission part, In denotes the intensity of the first beam of UV light detected by the first sensor 141, 1₁₂ denotes the intensity of the second beam of UV light detected by the second sensor 142, Di₂ denotes the transmission distance of the second beam of light, i.e. the distance from the beam splitter 144 to the second sensor 142. 1/fn and l/fi₂ respectively denote the intensity absorption coefficients of the fouling on the wall of the container 120 at locations where the first beam of UV light and the second beam of UV light pass through the wall. In FIG. 2, the beam splitter 144 is closely adjacent to the first sensor 141 and the transmission distance of the first beam of UV light, i.e. the distance from the beam splitter 144 to the first sensor 141, approximates zero, and hence is not taken into account. It is to be understood that the intensity absorption coefficients of the fouling, such as 1/fn and l/f₁₂, and other intensity absorption coefficients of the fouling mentioned in the following text, are not fixed values and will change dependent on the usage of the container 120.

The advantage of the apparatus 240 in FIG. 2 is that both the UV signal detected by the first sensor 141 and the UV signal detected by the second sensor 142 are emitted from the same position on the surface of the UV lamp 110, so any non-uniformity and fluctuation of the spatial pattern of the UV emission is cancelled out.

FIG. 3 shows a schematic view of a UV reactor 100 comprising an apparatus 340 for measuring the UV absorption rate of a liquid 130 according to another embodiment of the present invention. The apparatus 340 comprises a first sensor 141, a second sensor 142 and a processor 143. The apparatus 340 makes use of the fact that the emission of the UV lamp contains not only UV light but also visible and near IR radiation. Some of the non-UV radiation produced by the UV lamp 110, such as the visible and near IR radiation, is correlated with the UV output of the UV lamp 110. The fluorescence of quartz, which usually constitutes the surface of the UV lamp, can be used for instance. Part of the radiation produced by the quartz is in the visible/near IR range. It is also possible to have an additional phosphor layer on the inside of the UV lamp 110 to generate a reference signal that can be used to monitor the UV output of the UV lamp. This phosphor should convert the UV radiation into an easily measurable radiation such as visible or near IR light. By measuring both the UV and the non-UV radiation, the UV absorption rate of the liquid 130 in the container 120 can be determined. In FIG. 3, the second beam of light can be a beam of visible light or a beam of near IR light. The first beam of UV light and the second beam of light are emitted from substantially the same position on the surface of the UV lamp in substantially the same direction, i.e. the first beam of UV light and the second beam of visible or near IR light pass through the wall of the container 120 at substantially the same position. The position of emission of the first beam of UV light and the position of emission of the second beam of visible or near IR light can be the same position or two adjacent positions on the surface of the UV lamp 110. The aim is to make "the second beam of light" represent "a beam of visible or near IR light from the position of emission of the first beam of UV light", or to make the difference of the intensity between "the second beam of light" and "the visible or near IR light emitted from the position of emission of the first beam of UV light" negligibly small, so as to avoid effects caused by non-uniformity and fluctuation of the spatial pattern of the UV emission and the visible or near IR emission.

In FIG. 3, the first sensor 141 and the second sensor 142 abut against each other.

Alternatively, the apparatus 340 comprises two collimators (not shown in FIG. 3) to guide the first beam of UV light and the second beam of light respectively to the first UV sensor 141 and the second sensor 142. The two collimators abut against each other, and the first sensor 141 and the second sensor 142 need not abut against each other. The two collimators can be made of a flexible optical fiber.

In FIG. 3, the processor 143 is further configured to calculate the intensity of the first beam of UV light at the surface of the UV lamp 110 on the basis of the detected intensity of the second beam of light at the second sensor 142, and to determine the UV absorption rate of the liquid 130 on the basis of the detected intensity of the first beam of UV light at the first sensor 141 and the calculated intensity of the first beam of UV light at the surface of the UV lamp 110 and the transmission distance of the first beam of UV light.

Without loss of generality, the ratio of intensity of UV emission to intensity of near IR or visible emission of the UV lamp 110 is taken to be γ by way of example. If the absorption rate of near IR or visible light of a liquid 130 can be regarded as nearly zero, the UV absorption rate a can be obtained according to formula (3):

a = -ln(I₂₁ * f₂₁ * /( - I₂₂ * f₂₂)) / D₂₁ (3) wherein I₂₁ denotes the intensity of the first beam of UV light detected by the first sensor 141, 1₂₂ denotes the intensity of the second beam of visible or near IR light detected by the second sensor

142, l/f₂i and l/f₂₂ respectively denote the intensity absorption coefficients of the fouling on the wall of the container 120 where the first beam of UV light and the second beam of visible or near IR light pass through. The transmission distance of the first and the second beam of light can be regarded as being the same, which is denoted as D₂i_. χ · 1₂₂ · f₂₂ is the calculated intensity of the first beam of UV light at the surface of the UV lamp 110.

Since the first beam of UV light and the second beam of visible or near IR light pass through the wall of the container 120 at substantially the same position, f21 and f22 can be regarded as being the same, and formula (3) is simplified to:

a = -ln(I₂₁ /0- I₂₂)) / D_{21 (4)}

If the absorption rate of near IR or visible light of a liquid 130 is R0, which is usually fixed and will not change with organic compounds in the liquid 130, then the UV absorption rate ^a can be obtained according to formula (5):

« = -ln(I₂₁ /(_r- I₂₂ -e^(¾A))) /D_{21 (5)}

wherein γ · \₂₂ · e^(E>21'Ko is the calculated intensity of the first beam of UV light at the surface of the UV lamp 110. The advantage of the apparatus 340 is that measurements of the first beam of UV light and the second beam of visible or near IR light are taken at substantially the same position on the surface of the UV lamp 110 and substantially the same position on the wall of the container 120, so that the apparatus 340 is insensitive to fouling of the container 120 and to fluctuations and non-uniformity of the spatial pattern of the emission of the UV lamp 110.

FIG. 4(a) shows a schematic view of a UV reactor 100 comprising an apparatus 440 for measuring the UV absorption rate of a liquid 130 according to another embodiment of the present invention. The apparatus 440 comprises a first sensor 141, a second sensor 142 and a processor

143. In FIG. 4(a), the apparatus 440 makes use of the fact that the emission of the surface of the UV lamp 110 is approximately a Lambertian radiator. This means that for a certain position on the lamp surface, the radiation intensity in different directions is correlated. According to Lambertian's cosine law, the radiant intensity observed from a "Lambertian" surface is directly proportional to the cosine of the angle Θ between the observer's line of sight and the surface normal.

In FIG. 4(a), the first and second beams of light are UV light emitted from the same position on the surface of the UV lamp 110 in two directions. The processor 143 can determine the UV absorption rate on the basis of the two light intensities detected by the two sensors 141 and 142 and the two transmission distances of the first and second beam of UV light.

Without loss of generality, by way of example, the first beam of UV light extends perpendicularly to the surface of the UV lamp 110 and the angle between the first and second beam is ^ . According to Lambertian's cosine law, formula (6) is obtained:

^{132 " f32} = ^{(l31 - f3l )} - cosfl (6)

exp(-a · D₃₂ ) exp(-a · D₃₁ )

wherein I31 denotes the intensity of the first beam of UV light detected by the first sensor 141, ½ denotes the intensity of the second beam of UV light detected by the second sensor 142, D31 denotes the transmission distance of the first beam of UV light, D32 denotes the transmission distance of the second beam of UV light, and a denotes the absorption rate of the UV light, l/f3i and l/f32 respectively denote the intensity absorption coefficients of the fouling on the wall of the container 120 where the first beam of UV light and the second beam of UV light pass through.

The UV absorption rate a can be obtained according to formula (6), as shown in formula

(V): a = -(ln( ) - ln cos0) /(D₃₂ - D₃₁) (7)

The first sensor 141 and the second sensor 142 can be arranged towards a same position on the surface of the UV lamp 110. Alternatively, the first sensor 141 and the second sensor 142 can also be aligned by using two collimators 145 and 146 arranged towards a same position on the surface of the UV lamp 110, as shown in FIG. 4(b).

In FIG. 4(a) and FIG. 4(b), since the measured two beams of UV light are emitted from the same position on the surface of the UV lamp 110, the apparatus 440 is insensitive to fluctuations and non-uniformity of the spatial pattern of the emission of the UV lamp 110.

FIG. 5(a) shows a schematic view of a UV reactor 100 comprising an apparatus 540 for measuring the UV absorption rate of a liquid 130 according to another embodiment of the present invention. The apparatus 540 comprises a first sensor 141 , a second sensor 142 and a processor 143. In FIG. 5(a), both the first and the second beam of light are UV light. The two beams of UV light are emitted from different positions on the surface of the UV lamp 110. The two beams of light pass through substantially the same position on the wall of the container 130. The first sensor 141 and the second sensor 142 of apparatus 540 can be arranged towards a same position on the wall of the container 120 to respectively receive the first and second beams of UV light. Alternatively, the first sensor 141 and the second sensor 142 can also be aligned by using two collimators 145 and 146 arranged towards a same position on the wall of the container 120, as shown in FIG. 5(b).

Let l/f41 and l/f42 denote the intensity absorption coefficients of the fouling on the wall of the container 120 at locations where the first and second beam of UV light pass through said wall; since the measurements of the first and second beams of UV light are taken at substantially the same position on the wall of the container 120, f41 can be regarded to be the same as f42, i.e., f41=f42.

Without loss of generality, by way of example, the first beam of UV light extends perpendicularly to the surface of the UV lamp 110 and the angle between the first and second beam is ^ . Suppose that the spatial non-uniformity intensity factor from the first beam of UV light to the second beam of UV light is ^ , according to Lambertian's cosine Law, formula (8) is obtained.

~λ= ^{(l41 ' f4l)} cos<9 (8)

exp(-a · D₄₂) exp(-a · D₄₁)

wherein I41 denotes the intensity of the first beam of UV light detected by the first sensor 141, I₄₂ denotes the intensity of the second beam of UV light detected by the second sensor 142, D₄i denotes the transmission distance of the first beam of UV light, D₄₂ denotes the transmission distance of the second beam of UV light and a denotes the UV absorption rate.

The UV absorption rate a can be obtained according to formula (9).

a _ ln(I₄₁ · f₄₁ - cosff) - !^ !^ · f₄₂ · λ) _ ln(I₄₁ - cosff) - ln( I₄₂ · λ)

From formula (9), it can be seen that the advantage of apparatus 540 is that it is insensitive to fouling on the wall of the container 120. FIG. 6 shows a schematic view of a UV reactor 100 comprising an apparatus 640 for measuring the UV absorption rate of a liquid 130 in the container 120 according to another embodiment of the present invention.

Based on the apparatus 540, the apparatus 640 further comprises a third sensor 147 and a fourth sensor 148. The third sensor 147 receives a third beam of UV light, emitted by the UV lamp 110, and passing through the liquid 130 and then detects the intensity of the third beam of light. The fourth sensor 148 receives a fourth beam of UV light, emitted by the UV lamp 110, and passing through the liquid 130 and detects the intensity of the fourth beam of light.

As shown in FIG. 6, the first beam of UV light and the third beam of UV light are emitted from the same position on the surface of the UV lamp 110. The second beam of UV light and the fourth beam of UV light are emitted from the same position on the surface of the UV lamp 110. The first beam of UV light and the second beam of UV light pass through substantially the same position on the wall of the container 120. The third beam of UV light and the fourth beam of UV light pass through substantially the same position on the wall of the container 120.

It can be seen from FIG. 6 that the first sensor 141 and the third sensor 147 work as shown in FIG. 4(a) or FIG. 4(b) and the same is true for the second sensor 142 and the fourth sensor 148. The first sensor 141 and the second sensor 142 work as shown in FIG. 5(a) and FIG. 5(b) and the same is true for the third sensor 147 and the fourth sensor 148.

The processor 143 determines the UV absorption rate on the basis of the four light intensities detected respectively by the four sensors, and the transmission distances of the four beams of UV light. There are many ways to get the UV absorption rate of a liquid 130, which will be well elaborated in the following examples.

Without loss of generality, by way of example, the first and third beams of UV light extend perpendicularly to the surface of the UV lamp 110 and the angle between the first and the second beam of UV light is the same as the angle between the third and the fourth beam of UV light , which is denoted as Θ . Four UV absorption rates a_u , a₃₂ , a_n and a₃₄ can be obtained according to different ways of working of four sensors in FIG. 6, wherein a_l4 denotes the absorption rate obtained according to formula (7) based on the light intensities detected by the first sensor 141 and the fourth sensor 148, a₃₂ denotes the absorption rate obtained according to formula (7) based on the light intensities detected by the third sensor 147 and the second sensor 142, a_l2 denotes the absorption rate obtained according to formula (9) based on the light intensities detected by the first sensor 141 and the second sensor 142, and a₃₄ denotes the absorption rate obtained according to formula (9) based on the light intensities detected by the third sensor 147 and the fourth sensor 148. a₁₄ = -(ln( ^{54 '} ^⁵⁴ ) - In cos£)/(D₅₄ - D_S1) (10) )-lncosfl)/(D₅₂-D₅₃) (11)

_ln(I₅₃-cos6>)-ln(I₅₄-l)

a₄- wherein I51, 152, 153 and I54 respectively denote light intensities detected by the first, second, third and fourth sensors; D41, D₄₂, D43 and D₄₄ respectively denote the transmission distances of first, second, third and fourth beams of UV light; l/f₅₁, l/f₅₂, l/f₅₃ and Ι/Ϊ54 respectively denote the intensity absorption coefficients of the fouling on the wall of the container 120 at locations where the first, second, third and fourth beams of UV light pass through the wall. Since the

measurements of the first and second beams of UV light are taken at substantially the same position on the wall of the container 120, f₅₁ can be regarded as being the same as f5₂, i.e., f5i=f₅₂, and f53=f₅₄ for the same reason. Obviously, D₅₄ = D₅₂ , D₅₃ = D₅₁ according to symmetric properties of UV light transmission.

The UV absorption rate ^a of liquid 130 can be obtained based on a_l4 and a₃₂ : ln ^I^^I^-21ncos^ In ^{I¾1 ' I¾3} ^⁰⁸' °

a = (a₁₄ + a₃₂)/2 = llL = li (i₄₎

2-(D₅₄-D₅₁) 2-(D₅₄-D₅₁)

Alternatively, the UV absorption rate can be obtained based on _l2 and a₃₄ : L, · I„ - cos² Θ

In

a = (a₁₂ + a₃₄)/2 (15)

2 (D₅₄ - D₅₃)

It can be seen that the UV absorption rates of formula (14) and (15) are the same, and the effect caused by non-uniformity and fluctuation of the spatial pattern of UV emission and the effect caused by fouling on the wall of the reactor can be well avoided.

It is to be noted that, optionally, each sensor in FIG. 1 to FIG. 6 can also have a collimator to guide light to itself. As mentioned above, such a collimator can be made of a flexible optical fiber or of a quartz stick. Optionally, the quartz stick has a cylindrical geometry and the diameter of the quartz stick does not exceed the length of the quartz stick. This means that the quartz stick can be used as a collimator to minimize the detection angle of the sensor.

Referring to FIG. 7, a quartz stick 700 is shown with a cylindrical geometry according to one embodiment of the present invention, in which D and L denote respectively the diameter and the length of the quartz stick. The detection angle of the sensor δ can be approximately regarded as δ = 2arctan(— ) .

2L

The detection angle will be within 90 degrees when the diameter of the collimator does not exceed the length of the collimator. For instance, for quartz with a diameter of 6 mm and a length of 35 mm, the detection angle will be smaller than 10 degrees. For quartz with a diameter of 6 mm and a length of 6 mm, the detection angle will be slightly larger than 50 degrees. An illustration of these two instances can be found in FIG. 8(a) and FIG. 8(b). This means that the quartz stick can decrease the detection angle by an increase of the ratio of its length to its diameter. Hence, the uniformity of the light detected by the sensor can be well improved.

In one embodiment, each collimator 145 or 146 can be plugged into a standard fitting (not shown in the FIGs.) mounted through a wall of the container 120. The standard fitting, such as a DMfit push-in tube fitting, is widely used in water purification systems and can be used to quickly connect pipes and plugs. It shows excellent performance at a reasonable price. Each collimator 145 or 146 acts as a plug and can be easily installed into the standard fitting through the wall of container 120. Besides the several technical solutions described above, the UV absorption rate can also be obtained by means of the apparatus 940 shown in FIG. 9(a) and FIG. 9(b). In FIG. 9(a) and FIG.

9(b), the apparatus 940 have a first sensor 141, a second sensor 142, a first collimator 145 , a second collimator 146 and a processor 143. The first collimator 145 guides the first beam of UV light to the first sensor 141. The second collimator 146 guides the second beam of UV light to the second sensor 142.

The first and the second collimators 145,146, which are made of the same material and are immersed in the liquid 130 over different lengths, point to substantially the same position on the surface of the UV lamp 110. The aim is to make the intensity of the first beam of UV light at the surface of the UV lamp 110 equal to the intensity of the second beam of UV light at the surface of the UV lamp 110 or to make the difference negligibly small. This can be achieved in two ways: one is shown in FIG. 9(a), wherein the two collimators 145, 146 abut against each other and point to substantially the same position on the surface of the UV lamp 110; the other is shown in FIG. 9(b), wherein the two collimators 145, 146 pointing to a same position on the surface of the UV lamp 110 are symmetrically distributed at two sides of the normal plane of the surface of the UV lamp 110.

Then the processor 143 determines the UV absorption rate ^a , based on the two detected intensities of the two beams of UV light and the length difference of the two collimators 145, 146, as shown in formula (16):

AD

wherein I₆₁ denotes the intensity of the first beam of UV light detected by the first sensor 141, 1₆₂ denotes the intensity of the second beam of UV light detected by the second sensor 142, and AD denotes the transmission distance difference of the second and the first beam of UV light, AD = L_L — , wherein Li and L₂ respectively denote the length over which the first collimator

145 is immersed in the liquid 130 and the length over which the second collimator 146 is immersed in the liquid 130, and Li>L₂. It is to be noted that Li can also be shorter than L₂.

The advantage of apparatus 940 is that it is immune to non-uniformity and fluctuation of the spatial pattern of UV emission or the fouling on the wall of the container 120. It is to be noted that each of the first sensor 141, the third sensor 147 and the fourth sensor 148 can be a UV sensor, or can be a visible sensor with a phosphor layer. The phosphor layer absorbs UV light and converts the UV light into visible light. The same applies to the second sensor 142 when it is used to detect the intensity of UV light.

It is to be understood that, besides the above-mentioned formulas, use can be made of calibration by processor 143 to determine the UV absorption rate of the liquid 130. The calibration process is performed as follows: before the UV reactor 100 is used, a group of standard UV absorption rates is measured using organic compounds of different densities in the liquid 130 by a UV spectrophotometer, meanwhile, recording takes place of the detected values of the two or four sensors corresponding to each standard UV absorption rate, and subsequently the process of making and storing a table based on the values detected by these sensors and the UV spectrophotometer is carried out.

When the UV reactor 100 is used, the processor 143 can determine the UV absorption rate of liquid 130, based on the table and the detected values of these sensors.

FIG. 10 shows a schematic flow chart of a method of measuring the UV absorption rate of a liquid in a container comprising a UV lamp, which will be described in detail with reference to FIG. 1.

Firstly, in step 1001, a first beam of UV light, emitted by the UV lamp 110, and passing through the liquid 130 is received, and the intensity of the first beam of light is detected. In one embodiment, step 1001 can be performed by the first sensor 141 as shown in FIG. 1.

Secondly, in step 1002, a second beam of light, associated with the first beam of UV light, passing through the liquid 130 is received, and the intensity of the second beam of light is detected. In one embodiment, step 1002 can be performed by the first sensor 142, as shown in FIG. 1.

It is to be understood that step 1001 can also be performed before or together with step

1002.

Finally, in step 1003, the UV absorption rate of the liquid 130 is determined on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light. In one embodiment, step 1003 can be performed by the processor 143, as shown in FIG. 1. The way of determining the UV absorption rate depends on the relationship of two associated beams of light, which will be well elaborated by examples in the following part of the text.

In one embodiment, the first beam of UV light is the transmission part of a third beam of UV light, emitted by the UV lamp 110, and passing a beam splitter 144, and the second beam of UV light is the reflection part of the third beam of UV light passing the beam splitter 144, as shown in FIG. 2. In step 1003, the UV absorption rate can be determined on the basis of the two detected light intensities and the transmission distance of the second beam of light, as shown in formula (2).

In another embodiment, the second beam of light is a beam of visible or near IR light, the first beam of UV light and the second beam of light being emitted from substantially the same position on the surface of the UV lamp 110 in substantially the same direction, as shown in FIG. 3. In step 1003, first the intensity of the first beam of the UV light at the surface of the UV lamp is determined on the basis of the detected intensity of the second beam of light, then the UV absorption rate is calculated on the basis of the detected intensity of the first beam of UV light, the calculated intensity of the first beam of UV light at the surface of the UV lamp 110 and the transmission distance of the first beam of UV light, as shown in formula (3) to formula (5).

In another embodiment, the second beam of light is a beam of UV light, the first beam of UV light and the second beam of UV light being emitted from the same position on the surface of the UV lamp 110 in two directions, as shown in FIG. 4(a) or FIG. 4(b). In step 1003, the UV absorption rate can be determined on the basis of the two detected light intensities and the two transmission distances, as shown in formula (7).

In one embodiment, the first beam of UV light and the second beam of light, which is a beam of UV light, are emitted by the UV lamp 110 from different positions on the surface of the UV lamp, the two beams of light passing through substantially the same position on the wall of the container 120, as shown in FIG. 5(a) or FIG. 5(b). The UV absorption rate can be determined on the basis of the two detected light intensities and the two transmission distances, as shown in formula (9).

In one embodiment, the flow chart in FIG. 10 further comprises the following two steps: one step including receiving a third beam of UV light, emitted by the UV lamp 110, and passing through the liquid 130, and detecting the intensity of the third beam of light, and the other step including receiving a fourth beam of light (UV light), emitted by the UV lamp 110, and passing through the liquid 130, and detecting the intensity of the fourth beam of light. The first beam of UV light and the third beam of UV light are emitted from the same position on the surface of the UV lamp 110. The second beam of UV light and the fourth beam of UV light are emitted from the same position on the surface of the UV lamp 110. The first beam of UV light and the second beam of UV light pass through substantially the same position on the wall of the container 120. The third beam of UV light and the fourth beam of UV light pass through substantially the same position on the wall of the container 120; as shown in FIG. 6.

In step 1003, the UV absorption rate of liquid 130 can be determined on the basis of the four detected light intensities and the transmission distances of the four beams of UV light, as shown in formula (14) and (15).

It is to be understood that there is no sequence requirement for receiving the four beams of UV light.

It should be noted that the above-described embodiments are for the purpose of illustration only and are not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or in the description. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the apparatus claims enumerating several units, several of these units can be embodied by one and the same item of hardware or software. The usage of the words first, second and third, et cetera, does not indicate any ordering. These words are to be interpreted as names.

Claims

What is claimed is:

1. An apparatus for measuring the UV absorption rate of a liquid (130) in a container (120) comprising a UV lamp (110), the apparatus comprising:

a first sensor (141) configured to receive a first beam of UV light, emitted by the UV lamp (110) and passing through the liquid (130), and to detect the intensity of the first beam of UV light;

a second sensor (142) configured to receive a second beam of light, associated with the first beam of UV light, passing through the liquid (130) and to detect the intensity of the second beam of light; and

a processor (143) configured to determine the UV absorption rate on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light.

2. An apparatus according to claim 1, further comprising:

a beam splitter (144) mounted in front of the first sensor (141) and configured to transmit a first part of a third beam of UV light to the first sensor (141) and to reflect a second part of the third beam of UV light to the second sensor (142), the first beam of light being formed by the first part of the third beam of UV light, the second beam of light being formed by the second part of the third beam of UV light;

wherein the processor (143) is further configured to determine the UV absorption rate on the basis of the two detected light intensities and the transmission distance of the second beam of light.

3. An apparatus according to claim 1, wherein the second beam of light is one of a beam of visible light and a beam of near IR light, the first beam of UV light and the second beam of light being emitted from substantially the same position on the surface of the UV lamp (110) in substantially the same direction; and

wherein the processor (143) is further configured to calculate the intensity of the first beam of the UV light at the surface of the UV lamp (110) on the basis of the detected intensity of the second beam of light, and to determine the UV absorption rate on the basis of the detected intensity of the first beam of UV light at the first sensor (141) and the calculated intensity of the first beam of UV light at the surface of the UV lamp (110) and the transmission distance of the first beam of UV light.

4. An apparatus according to claim 1 , wherein the second beam of light is a beam of UV light, the first beam of UV light and the second beam of UV light being emitted from the same position on the surface of the UV lamp (110) in two directions, and

wherein the processor (143) is further configured to determine the UV absorption rate on the basis of the two detected light intensities and the transmission distances of the first and second beams of UV light.

5. An apparatus according to claim 1, wherein the first beam of UV light and the second beam of light, which is a beam of UV light, are emitted by the UV lamp (110) from different positions on the surface of the UV lamp (110), the two beams of UV light passing through substantially the same position on the wall of the container (120) ;

6. An apparatus according to claim 5, further comprising:

a third sensor (147) configured to receive a third beam of UV light, emitted by the UV lamp (110), and passing through the liquid (130) and to detect the intensity of the third beam of light; and

a fourth sensor (148) configured to receive a fourth beam of UV light, emitted by the UV lamp (110), and passing through the liquid (130) and to detect the intensity of the fourth beam of light;

wherein the first beam of UV light and the fourth beam of UV light are emitted from the same position on the surface of the UV lamp (110), the second beam of UV light and the third beam of UV light are emitted from the same position on the surface of the UV lamp (110), the third beam of UV light and the fourth beam of UV light passing through substantially the same position on the wall of the container (120);

wherein the processor (143) is configured to determine the UV absorption rate on the basis of the four detected light intensities and the transmission distances of the four beams of UV light.

7. An apparatus according to claim 1, wherein the container (120) further comprises two standard fittings mounted through a wall of the container (120), the apparatus further comprising:

a first collimator (145) configured to guide the first beam of UV light to the first sensor (141), the first collimator (145) being sized to be plugged into one of two standard fitting; and a second collimator (146) configured to guide the second beam of light to the second sensor (142), the second collimator (146) being sized to be plugged into the other of the two standard fittings.

8. An apparatus according to claim 1, wherein the second beam of light is a beam of UV light, and the apparatus further comprises two collimators (145,146) to guide the two first beams and the second beam of UV light respectively to the first and the second sensor (141, 142), the two collimators (145,146) pointing to substantially the same position on the surface of the UV lamp (110), and being made of the same material and being immersed in the liquid (130) over different lengths;

wherein the processor (143) determines the UV absorption based on the two detected intensities of the two beams of UV light and the difference in length over which the two collimators (145,146) are immersed in the liquid (130).

A UV reactor (100), comprising the apparatus as claimed in any one of claims 1 to

10. A method of measuring the UV absorption rate of a liquid in a container comprising a UV lamp, comprising:

- receiving (1001) a first beam of UV light, emitted by the UV lamp (110), and passing through the liquid (130), and detecting the intensity of the first beam of UV light;

- receiving (1002) a second beam of light, associated with the first beam of UV light, passing through the liquid (130), and detecting the intensity of the second beam of light; and

- determining (1003) the UV absorption rate on the basis of the two detected light intensities and at least one of the transmission distance of the first beam of UV light and the transmission distance of the second beam of light.

11. A method according to claim 10, wherein the first beam of UV light is the transmission part of a third beam of UV light, emitted by the UV lamp (110), and passing a beam splitter (144), and the second beam of UV light is the reflection part of the third beam of UV light passing the beam splitter (144); and

wherein the step of determining (1003) comprises:

- determining the UV absorption rate on the basis of the two detected light intensities and the transmission distance of the second beam of light.

12. A method according to claim 10, wherein the second beam of light is one of a beam of visible light and a beam of near IR light, the first beam of UV light and the second beam of light being emitted from substantially the same position on the surface of the UV lamp (110) in substantially the same direction; and

wherein the step of determining (1003) comprises:

- determining the intensity of the first beam of the UV light at the surface of the UV lamp (110) on the basis of the detected intensity of the second beam of light, and calculating the UV absorption rate on the basis of the detected intensity of the first beam of UV light, the calculated intensity of the first beam of UV light at the surface of the UV lamp (110) and the transmission distance of the first beam of UV light.

13. A method according to claim 10, wherein the second beam of light is a beam of UV light, the first beam of UV light and the second beam of UV light being emitted from the same position on the surface of the UV lamp (110) in two directions; and

wherein the step of determining (1003) comprises:

- determining the UV absorption rate on the basis of the two detected light intensities and the transmission distances of the first and second beams of UV light.

14. A method according to claim 10, wherein the first beam of UV light and the second beam of light, which is a beam of UV light, are emitted by the UV lamp (110) from different position on the surface of the UV lamp (110), the two beams of light passing through the substantially same position on the wall of the container (120) ;

wherein the step of determining (1003) comprises: