Method, device and apparatus for monitoring halogen levels in a body of water

Abstract

A method and an apparatus are presented for monitoring a concentration of a specific halogen in a body of water such as a spa or bathing unit for example. The apparatus comprises a housing in which is positioned an optical absorption analyzer for making first and second measurement of transmission of ultraviolet light from a light source emitting light at a specific wavelength. The second and first measurements are taken respectively before and after the ultraviolet light has travelled through a sample of water and are used to derive a concentration of the specific halogen. The derived concentration may then be communicated to a user using a display device and/or may be used to control operational components of a bathing unit for adjusting the concentration of halogen in the water. In some practical implementations, the apparatus may be embodied as a standalone device, which may be configured to float on the water of the bathing unit or, alternatively, may be configured for being installed in-line in a water circulation path of the bathing input by connecting the housing to circulation piping.

Claims

1. A device for monitoring a concentration of a specific halogen in a bathing unit, said device comprising: a. a housing configured for floating on top of a body of water held in a receptacle of the bathing unit, said housing having a lower portion configured for being at least partially submerged in water during use and an upper portion configured for extending at least partially above the water, said lower portion including walls extending into the water and defining spaced apart opposing windows made at least in part of a material permeable to ultraviolet light; b. an optical absorption analyzer positioned within said housing, said optical absorption analyzer being configured for making measurements of transmission of ultraviolet light from a light source through a sample of the water held in a receptacle, the sample being between the spaced apart opposing windows, said light source emitting light at a specific wavelength, wherein the specific wavelength of the light source corresponds to the specific halogen whose concentration is being monitored, said optical absorption analyzer comprising a processing unit configured for: i. deriving the concentration of the specific halogen at least in part by processing results of the measurements of transmission of ultraviolet light from a light source through the sample of water; and ii. releasing a signal conveying the derived concentration of the specific halogen.

2. A device as defined in claim 1, wherein the spaced apart opposing windows are made of at least one of quartz, optical glass, cellulose diacetate, polyethylene, acrylic and polyester.

3. A device as defined in claim 1, wherein the measurements of transmission of ultraviolet light include a first measurement of transmission of ultraviolet light and a second measurement of transmission of ultraviolet light, and wherein the optical absorption analyzer further comprises: i. the light source for emitting ultraviolet light at the specific wavelength; ii. a first detector for making the first measurement of transmission of ultraviolet light from said light source through the sample of water; iii. a second detector for making the second measurement of transmission of ultraviolet light, wherein the second measurement is taken prior to the ultraviolet light travelling through the sample of water.

4. A device as defined in claim 3, wherein said light source is a first light source and wherein said specific wavelength is a first specific wavelength, said optical absorption analyzer further comprising a second light source for emitting light at a second specific wavelength different from the first specific wavelength, wherein: a. the first detector is used for making a first measurement of transmission of light from the second light source through the sample of water; b. the second detector is used for making a second measurement of transmission of light from said second light source, wherein the second measurement is taken prior to the light from said second light source travelling through the sample of water; c. the processing unit is configured to derive the concentration of the specific halogen by processing at least: i. results of the first and the second measurements of transmission of light from said second light source; and ii. the results of the first and the second measurements of transmission of light from said first light source.

5. A device as defined in claim 4, wherein said optical absorption analyzer further comprises a beam splitter module for directing: i. a first part of ultraviolet light generated by said first light source toward the first detector through the sample of water; ii. a second part of ultraviolet light generated by said first light source toward the second detector; iii. a first part of light generated by said second light source toward the first detector through the sample of water; and iv. a second part of light generated by said second light source toward the second detector.

6. A device as defined in claim 4, wherein said second specific wavelength at which said second light source emits light is between about 450 nm and 1100 nm.

7. A device as defined in claim 6, wherein said second specific wavelength at which said second light source emits light is between about 475 nm and 550 nm.

8. A device as defined in claim 4, wherein the first light source and the second light source are modulated light sources.

9. A device as defined in claim 4, wherein the first light source and the second light source are configured to emit light according to sinusoidal light patterns.

10. A device as defined in claim 9, wherein the first light source is modulated at a first frequency and the second light source is modulated at a second frequency, wherein the first frequency is different from the second frequency and wherein said processing unit is configured for deriving the concentration of the specific halogen at least in part based on a frequency distribution associated with: a. the results of the first and the second measurements of the transmission of light from said first light source; and b. the results of the first and the second measurements of the transmission of light from said second light source.

11. A device as defined in claim 10, wherein the first frequency of the first light source is between 420 and 580 Hz.

12. A device as defined in claim 11, wherein the second frequency of the second light source is between 540 and 600 Hz.

13. A device as defined in claim 3, wherein said optical absorption analyzer further comprises: i. a beam splitter module for directing: ii. a first part of ultraviolet light generated by said light source toward the first detector through the sample of water; and iii. a second part of ultraviolet light generated by said light source toward the second detector.

14. A device as defined in claim 1, wherein said optical absorption analyzer further comprises a temperature sensor for generating a signal conveying water temperature information for the sample of water, said processing unit being configured for deriving the concentration of the specific halogen at least in part by processing the results of the measurements of transmission of ultraviolet light and of the water temperature information.

15. A device as defined in claim 1, wherein the specific halogen whose concentration is being monitored is selected from the group consisting of chlorine and bromine.

16. A device as defined in claim 15, wherein the specific halogen whose concentration is being monitored is bromine.

17. A device as defined in claim 16, wherein the specific wavelength at which said light source emits light is between about 280 nm and 380 nm.

18. A device as defined in claim 17, wherein the specific wavelength at which said light source emits light is between about 300 nm and 360 nm.

19. A device as defined in claim 18, wherein the specific wavelength at which said light source emits light is about 310 nm.

20. A device as defined in claim 1, wherein said upper portion includes a display screen in electronic communication with the processing unit of said optical absorption analyzer for displaying information derived from the derived concentration of the specific halogen.

21. A device as defined in claim 1, further comprising an antenna for transmitting the signal conveying the derived concentration of the specific halogen to a remote device, said remote device including a display for conveying the derived concentration of the specific halogen.

22. A device as defined in claim 21, wherein said remote device is a smart phone.

23. A device as defined in claim 1, wherein said device is configured to transmit the signal conveying the derived concentration of the specific halogen to a processing module external to the device over a wireless link, said processing module external to the device being configured for using the derived concentration of the specific halogen to control generation of the specific halogen to detect at least one of an excess and an insufficiency of the specific halogen in the water.

24. A device as defined in claim 23, wherein said processing module external to the device being configured for controlling generation of the specific halogen by controlling operation of an electrolytic cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A detailed description of the embodiments of the present invention is provided herein below, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagram of a bathing unit system incorporating a water analysis device for monitoring a concentration of a specific halogen in water in accordance with a specific example of implementation;

(3) FIGS. 2A and 2B are diagrams of a water analysis device suitable for use in a bathing unit system of the type shown in FIG. 1, wherein the water analysis device is configured in accordance with a free-standing type of implementation;

(4) FIG. 3 shows a water analysis device of the type shown in FIGS. 2A and 2B positioned to float on a body of water, the device including an optical absorption analyzer in accordance with a first specific implementation;

(5) FIG. 4 is a functional block diagram of a water analysis device suitable for use in a bathing unit system of the type shown in FIG. 1, wherein the water analysis device is configured in accordance with an in-line type of implementation and includes an optical absorption analyzer similar to that shown in FIG. 3;

(6) FIG. 5A is a functional block diagram showing transmission of a signal by the optical absorption analyzer of the device of FIG. 3 or the optical absorption analyzer of FIG. 4 to a remote computing device;

(7) FIG. 5B is functional block diagram showing transmission of a signal by the optical absorption analyzer of the device of FIG. 3 or the optical absorption analyzer of FIG. 4 to a controller of the bathing unit system of FIG. 1;

(8) FIG. 5C is a functional block diagram showing transmission of a signal by the optical absorption analyzer of the device of FIG. 3 to a user interface part of the device of FIG. 3;

(9) FIG. 6 shows a functional block diagram of a bathing unit system including a water circulation path in which a water analysis device of the type shown in FIG. 4 has been positioned in-line in accordance with a non-limiting implementation of the invention;

(10) FIG. 7 is a diagram of a first variant of the in-line type of water analysis device shown in FIG. 4, wherein the water analysis device includes an optical absorption analyzer in accordance with a second specific implementation;

(11) FIG. 8 is a diagram of a second variant of the in-line type of water analysis device shown in FIG. 4, wherein the water analysis device includes an optical absorption analyzer in accordance with a third specific implementation;

(12) FIG. 9 is a diagram of a third variant of the in-line type of water analysis device shown in FIG. 4, wherein the water analysis device includes an optical absorption analyzer in accordance with a fourth specific implementation;

(13) FIG. 10 is a block diagram, showing some functional modules of a processing unit that may be used in connection with the water analysis device shown in FIGS. 3, 4, 7, 8 and 9 in accordance with non-limiting examples of implementation of the invention;

(14) FIG. 11 shows a functional diagram of components of a water analysis device using alternating light sources in accordance with a variant of implementation of the water analysis device shown in FIG. 9;

(15) FIGS. 12A and 12 B show graph of a frequency domain representation of light signals received at detector of the device of FIG. 9 and implemented in accordance with the variant depicted in FIG. 11;

(16) FIG. 13 shows a simplified representation of a user interface device of the device of FIG. 3 in accordance with a non-limiting example of implementation;

(17) FIG. 14 shows an example of an embodiment in which the device of FIG. 3 is part of a communication network according to a non-limiting example;

(18) FIGS. 15A and 15B show different examples of shapes of a space in a lower portion of a housing of the device of FIG. 3 in which a sample of water is received;

(19) FIG. 16 shows an example of a lookup table that may be stored in a memory of a processing unit of the water analysis devices of the type shown in FIGS. 3, 7, 8 and 9 and/or in a memory of a bathing unit controller of the type depicted in FIG. 1;

(20) FIG. 17 shows an example of an embodiment of a water analysis device in which a power source comprises a solar panel in accordance with a non-limiting example of implementation; and

(21) FIG. 18 shows a non-limiting example of a physical embodiment of the water analysis device of FIGS. 4, 7, 8 and 9.

(22) It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

(23) In the drawings, the embodiments of the invention are illustrated by way of examples. It is to be expressly understood that the description and drawings are only for the purpose of illustration and are an aid for understanding. They are not intended to be a definition of the limits of the invention.

DETAILED DESCRIPTION

(24) The description below is directed to specific implementations and uses of embodiments of the invention in the context of bathing units. It is to be understood that the term bathing unit, as used for the purposes of the present description, refers to spas/swim-spas, whirlpools, hot tubs, bath tubs, therapeutic baths and swimming pools and any other type of unit having a water receptacle holding water in which a halogen has been dissolved. Moreover, it is to be appreciated that while specific embodiments of the invention have been described for using in the context of bathing units, the person skilled in the art will appreciate in view of the present description that alterative embodiments may be configured for use in an environment including a body of water other than a bathing unit in which measurement of a concentration of halogen may be of interest.

(25) FIG. 1 illustrates a block diagram of a bathing unit system 100 incorporating a water analysis device 500 in accordance with a specific example of implementation. The bathing unit system 100 includes a bathing unit receptacle 102 for holding water 104, water inlets 110 (only one is shown) which will typically be connected to respective jets, water outlets 108 (only one is shown) and a circulation system 106 including a flow conduit for removing and returning water from and to the receptacle 102 through the water inlets and water outlets. The circulation system 106 depicted is shown as having a single flow conduit for the purpose of simplicity, however, the person skilled in the art will appreciate that practical implementations of the bathing unit system 100 may include multiple flow conduits interconnecting water inlets and water outlets of the receptacle 102. A heating module 116, a water pump 112 and a filter 124 are shown positioned within the circulation system 106. It should be understood that the bathing unit 100 may include more or fewer bathing unit components that may be positioned in various suitable positions in the circulation system. The bathing unit system 100 may further include a sanitizing system 130 for sanitizing the water 104 in the receptacle 102. In some embodiments, the sanitizing system 130 may comprise an electrolytic cell 135 configured to release a free halogen in the water of the bathing unit 100.

(26) A bathing unit controller 122 controls the settings of the components of the bathing unit system 100 including the settings of the heating module 116, the water pump 112, the filter 124 and/or the sanitizing system 130. The controller 122 receives electrical power from an electric power source (not shown) and controls the distribution of power supplied to the various bathing unit components on the basis of control signals originating from various sensors, program instructions and/or user commands in order to cause desired operational settings to be implemented. Some manners in which the bathing unit controller 122 may be configured and used to control the bathing unit components for the regulation of the operation of the bathing unit system 100 are generally known in the art and are not critical to the invention and as such will not be described in further detail here.

(27) As depicted in FIG. 1, a water analysis device 500 may be used in connection with the bathing unit system 100. More specifically, the water analysis device 500 is configured to monitor a concentration of a specific halogen H in the water of the bathing unit system 100 to assist in maintaining such concentration within a desired operational range. To that end, the water analysis device 500 comprises an optical absorption analyzer 150 and a housing 502 within which the optical absorption analyzer 150 is disposed. The halogen H whose concentration is monitored may be any suitable halogen. For instance, in this embodiment, the halogen H is bromine. However, in other embodiments, the specific halogen H may be chlorine or any other suitable halogen. It is noted that in this description, the term halogen may also refer to chemical species containing halogens rather than pure elements, for instance hypochlorous and/or hypobromous acid.

(28) The water analysis device 500 may be embodied in different types of configurations.

(29) Standalone Configuration of Water Analysis Device 500

(30) In a first type of configuration, shown in FIGS. 2A, 2B and 3, the water analysis device 500 is a standalone device configured to be disposed in the water 104 contained in the receptacle 102 of the bathing unit system 100 of FIG. 1. The water analysis device 500 is a standalone device in that it is structurally separate from the other components of the bathing unit 100 (e.g., the circulation system 106). More specifically, in this embodiment, the housing 502 is configured to float atop the water 104 held in the receptacle 102 such that an upper part of the housing 502 remains above a level of the water 104 and a lower part of the device is submersed below the water level when the analysis device 500 is disposed in the receptacle 102. In this specific example of implementation, the housing 502 comprises a lower portion 512 configured for being at least partially submerged in water during use and an upper portion 514 configured for extending at least partially above the water 104 held in the receptacle 102 during use. This may be achieved for example by ensuring that the housing 502 has a density that is less than a density of the water 104 in the receptacle.

(31) The lower portion 512 of the housing 502 comprises a pair of opposing walls 508 510 which in use extend into the water 104 of the receptacle and which define a space 504 there between where water can circulate. The walls 508 510 include opposing windows 516 518 spaced apart by a distance D.sub.W and which are made of a material permeable to ultraviolet light such as, for example, quartz, suitable types of optical glass, plastic (e.g., cellulose diacetate, polyethylene, acrylic, polyester, etc.) or any other suitable material.

(32) In the specific example of implementation depicted in FIGS. 2A 2B and 3, the housing 502 is configured such that the space 504 of the lower portion 512 of the housing 502 is substantially U-shaped. However, the space 504 defined by the walls 508 510 of the housing 502 may be shaped differently in other examples. For instance, in other examples, the space 504 defined by the walls 508, 510 may be V-shaped, cylindrical, or may have any other suitable shape. FIGS. 15A and 15B show yet other non-limiting configurations that may be formed by the walls 508 510 of the housing 502. For instance, FIG. 15A shows a specific example of implementation in which the lower portion 512 of the housing 502 comprises a pair of projections 515 517 projecting from a bottom surface 519 of the housing 502 and which define the walls 508 510. In this example, the projections 515 517 extend longitudinally along a substantial portion of a width W.sub.H of the housing 502. Notably, the projections 515 517 extend substantially from one side of a periphery of the housing 502 to an opposite side of the periphery of the housing 502. FIG. 15B shows another specific example of implementation in which the projections 515 517 extend longitudinally along a limited portion of the width W.sub.H of the housing 502. For example, in some cases, a ratio of a length L.sub.P of each projection 515 517 over the width W.sub.H of the housing 502 may be no more than 80%, in some cases no more than 70%, in some cases no more than 50%, and in some cases even less. The projections 515 517 may contain components of the optical absorption analyzer 150, including but not limited to the light source 152 and the detector 156.

(33) While the embodiment depicted in FIG. 3 shows a standalone device configured to float on the water 104, in alternative implementations (not shown in the figures) the standalone device may be entirely submerged in the water during use (e.g., by being anchored to a structure of the receptacle 102 or by having a sufficiently high density). In such cases, both the lower and upper portions 512, 514 of the housing 502 may be submerged in the water. In some cases, the water analysis device 500 may even be configured to be disposed at a bottom of the receptacle 102.

(34) Optionally, with reference to FIGS. 2A and 13, the upper portion 514 of the housing 502 may comprise a user interface device 524 configured for outputting information to a user and, in some cases, receiving inputs from the user. For instance, in the example of implementation depicted in FIG. 13, the user interface device 524 is configured to display information related to results obtained by the optical absorption analyzer 150. To that end, the user interface device 524 comprises a display 526 (e.g., a screen) which may convey one or more information elements related to results obtained by the optical absorption analyzer 150 related to a concentration of a specific halogen in the water. In some implementations, the user interface device 524 may comprise user data entry module 527 for receiving inputs from the user (shown schematically in FIG. 10) which may comprise user operable controls such as a keyboard, key pads, buttons, touch sensitive screen or any other suitable form of user data entry device. In some cases, the data entry module 527 may be integrated within the display, for example in cases where the display 526 is a touch screen display.

(35) The water analysis device 500 may also comprise a power source 165 for powering the various components of the water analysis device 500, including the optical absorption analyzer 150. This may be particularly useful in embodiments in which the water analysis device 500 is a standalone device. In the embodiment depicted in FIG. 3, the power source 165 is shown as comprising a battery 167 (e.g., a lithium-ion battery). In a variant shown in FIG. 17, the power source 165 of the water analysis device 500 may comprise a solar panel 600 for recharging the battery 167. More specifically, in accordance with a specific example of implementation, the solar panel 600 may be disposed on part of the upper portion 514 of the housing 500 to receive sunlight which may be converted into an electrical input for the battery 167 of the power source 165. It is to be appreciated that while examples of power sources 165 for the water analysis device 500 have been described, many other suitable ways for providing power to the water analysis device 500 may be contemplated, including for example through a connection to standard wiring, directly or through the bathing unit controller 122 (shown in FIG. 1).

(36) In-Line Configuration of Water Analysis Device 500

(37) In a second type of configuration, shown in FIGS. 4, 6, 7, 8 and 9, the water analysis device 500 may be integrated within a circulation system 106 of the bathing unit system 100 along with one or more other components of the bathing unit 100, as shown for example in FIG. 6. More specifically, in such second type of configuration, the housing 502 of the water analysis device 500 may include a chamber forming a space 504 for holding a sample of water, wherein the chamber is in fluid communication with circulation piping 164 of the circulation system 106 of the bathing unit 100 such that water from the receptacle 102 is circulated through the space 504, notably via an inlet 900 of the water analysis device 500 through which water enters the space 504 and an outlet 902 of the water analysis device 500 through which water exits the space 504, as shown in FIG. 18. The chamber may be generally tubular in shape and includes walls 508 510 having opposing windows 516 518 made of a material permeable to ultraviolet light such as, for example, quartz, suitable types of optical glass or any other suitable material.

(38) Now that we have described some examples of physical configurations of the water analysis device 500, we will now describe some different manners in which this device operates to monitor halogen levels in water, include some different configurations of the optical absorption analyzer 150. It is to be appreciated that the while various examples of the optical absorption analyzer 150 may be described with reference to either the standalone configuration or the in-line configuration of the water analysis device 500, these examples may be used interchangeably with one or the other configurations in alternative implementations.

(39) Optical Absorption Analyzer

(40) As mentioned above, the optical absorption analyzer 150 of the water analysis device 500 is configured to monitor a concentration of one or more specific halogens (H) in the water of the bathing unit 100.

(41) In the embodiment shown in FIGS. 3 and 4, the optical absorption analyzer 150 comprises a (first) light source 152 configured to emit a beam of light 154 and a detector 156. In use, the beam of light 154 emitted by the light source 152 is directed towards a sample of water 158 obtained from water in the bathing unit 100. Specifically, the beam of light 154 travels through the window 516 of the housing 502, through the sample of water 158 contained in the space 504 defined by the housing 502 and through the window 518 of the housing 502. The detector 156 is positioned to receive the beam of light 154 after it has travelled through the sample of water 158 in order to make a measurement of light received from the light source 152. As will be discussed in more detail below, by using a light source 152 emitting light at a selected specific wavelength that is chosen based on a specific halogen H that is of interest, an estimate of the concentration of the halogen H in the water of the bathing unit 100 can be derived from the measurement made by the detector 156.

(42) The light source 152 may comprise any of a variety of types of light-emitting members. In this specific example of implementation, the light source 152 comprises a light-emitting diode (LED). However, the light source 152 may comprise any other type of light-emitting member in other examples, such as an incandescent bulb, a discharge lamp, a laser, or any other suitable type of light-emitting member. As most light-emitting members emit light in a diverging manner (i.e., light rays emitted by the light-emitting member may diverge from one another), the light source 152 may also comprise one or more optical elements (not shown) such as lenses or concave mirrors which are configured to collimate the light rays emitted by the light-emitting member to direct the light rays towards the sample of water 158. In this example, where the light-emitting member is an LED, the optical element of the light source 152 may constitute a plastic body encapsulating the LED and which is domed to collimate the light rays emitted by the LED.

(43) As noted above, the type of light-emitting member comprised by the light source 152 (e.g., incandescent bulb, laser, LED, etc.) may be chosen in accordance with the specific halogen H that is to be monitored by the optical absorption analyzer 150. More specifically, the light-emitting member of the light source 152 is chosen such that a wavelength of the beam of light 154 emitted by the light source 152 is absorbed by the specific halogen H that is of interest. In this example, where the halogen H being monitored is bromine, the wavelength at which the light source 152 emits light would be in the ultraviolet part of the spectrum between 280 nm and 380 nm. In some examples, the wavelength at which the light source 152 emits light may be between 300 nm and 360 nm. In a non-limiting practical implementation, the wavelength at which the light source 152 emits light is about 310 nm. For some non-limiting example of implementations, light source 152 may be implemented by using an off-the-shelf device such as UV LED device model No. UVLED-UV310R50 commercialized by BYTECH Electronics Co., Ltd. however other suitable types of commercially available light sources may be used in other alternative implementations. In accordance with another non-limiting practical implementation, the wavelength at which the light source 152 emits light may be about 330 nm.

(44) The detector 156 is a photodetector configured to sense light. To that end, the detector 156 comprises a light-sensing surface 157 that substantially faces the light source 152 to receive the beam of light 154 emitted by the light source 152. More particularly, the light-sensing surface 157 of the detector 156 converts light photons into current. For instance, in this example, the detector 156 is a photoelectric sensor such as a photodiode. The detector 156 may be any other suitable type of sensor capable of sensing light in other embodiments (e.g., a phototransistor). For some non-limiting example of implementations, detector 156 may be implemented by using by using an off-the-shelf device such as 4.8 mm Semi-Lens Silicon PIN photodiode model No. PD438C/S46 commercialized by Everlight however other suitable types of commercially available photodiodes may be used in other alternative implementations.

(45) The optical absorption analyzer 150 also comprises a processing unit 162 configured to process data related to operation of the optical absorption analyzer 150. For instance, the processing unit 162 is configured to process a signal transmitted to the processing unit 162 by the detector 156. Notably, the signal received by the processing unit 162 from the detector 156 is representative of the measurement of ultraviolet light sensed by the detector 156. In a manner that will be explained in more detail below, the processing unit 162 is programmed for deriving an estimate of the concentration of the halogen H present in the sample of water 158 based at least in part by processing the measurement of ultraviolet light sensed by the detector 156.

(46) The concentration of the halogen H may be derived by Equation 1 (also known as the Beer-Lambert equation) reproduced below:

(47) $\begin{array}{cc}\log \left(\frac{{}_e^i}{{}_e^t}\right)=\mathrm{.Math.}\mathrm{cl}& \left(\mathrm{Equation}1\right)\end{array}$
In Equation 1 above, .sub.e.sup.i is a radiant flux incident on the sample of water 158 and .sub.e.sup.t is a radiant flux transmitted through the sample of water 158. The molar attenuation coefficient is a property of the halogen H while c is a molar concentration of the halogen H in the sample of water 158 under study. Finally l is the optical pathlength of the beam of light 154 (i.e., a distance the beam of light 154 travels from the light source 152 to the detector 156 in the sample of water 158). Thus, using Equation 1, the processing unit 162 can derive the molar concentration c of a specific halogen H in the sample of water 158.

(48) It is noted that the optical pathlength l of the beam of light 154 is determined by the distance D.sub.W between the windows 516, 518. Notably, the optical pathlength l of the beam of light 154 can be optimized by adjusting the distance D.sub.W. For instance, if the distance D.sub.W between the windows 516, 518 is made too small, the sample of water 158 may be too small to contain an appreciable concentration of the halogen H. Moreover, if the distance D.sub.W between the windows 516, 518 is made too great, the sample of water 158 may contain too many impurities (e.g., dirt, air bubbles, etc.) which may affect the accuracy of the derived concentration of halogen H.

(49) Optionally, in some embodiments, as shown in FIG. 3, the optical absorption analyzer 150 may be configured to gather water temperature information relating to the water of the bathing unit 100. To that end, in this example of implementation, the optical absorption analyzer 150 comprises a temperature probe 180 for sensing the temperature of the water of the bathing unit 100. More specifically, in such embodiments, the temperature probe 180 makes a measurement of the temperature of the water and releases a signal conveying the recorded water temperature information to the processing unit 162. This may allow the processing unit 162 to use the water temperature information when deriving the concentration of the halogen H to compensate for effects that may be attributable to variations in water temperature rather than those that may be attributable to actual concentration of the halogen H.

(50) Furthermore, optionally, in some embodiments, the optical absorption analyzer 150 may be configured to gather water acidity/basicity information related to the water of the bathing unit 100. To that end, the optical absorption analyzer 150 may comprise a pH (PH) probe 182 for sensing the water acidity/basicity level of the water of the bathing unit 100. More specifically, in such embodiments, the PH probe 182 makes a measurement of the acidity/basicity level of the water and releases a signal conveying the recorded water acidity/basicity information to the processing unit 162. This may allow the processing unit 162 to use the water acidity/basicity information when deriving the concentration of the halogen H to compensate for effects that may be attributable to variations in water acidity/basicity rather than those that may be attributable to actual concentration of the halogen H.

(51) Once the processing unit 162 has derived an estimate of the concentration c of the halogen H in the sample of water 158, the optical absorption analyzer 150 releases a signal S.sub.c conveying the derived estimate of the concentration of the halogen H present in the sample of water 158. The signal S.sub.c released by the optical absorption analyzer 150 can be transmitted to one or more entities and used in various ways.

(52) In some embodiments, as shown in FIG. 5A, the signal S.sub.c released by the optical absorption analyzer 150 may be transmitted to a device 532 remote from the water analysis device 500 via a communication link 125 (e.g., a wired or wireless communication link). For instance, as shown in FIG. 3, the water analysis device 500 may optionally comprise an antenna 535 and suitable hardware/software modules for transmitting the signal S.sub.c to a remote device 532. The remote device 532 may include a display module and may be configured to display information conveying results obtained by the optical absorption analyzer 150. Notably, the remote device 532 may comprise a processing unit (not shown) and a display 534 for displaying information derived from the derived concentration of the specific halogen H. The remote device 532 may be embodied in any device suitable for a user to interact with. For instance, the remote device 532 may be a personal computing device or the bathing unit controller 122 of the bathing unit 100 (as shown in FIGS. 1 and 5B). The remote device 532 may alternatively be any other suitable type of device in other examples (e.g., desktop computer, a laptop, a tablet, a smart watch, a personal digital assistant (PDA), or any other suitable computing device etc.).

(53) In some implementations, for example of the type shown in FIG. 5B, the signal S.sub.c released by the optical absorption analyzer 150 may be transmitted to the controller 122 of the bathing unit 100. In practical implementations, the communication link 125 between the optical absorption analyzer 150 and the controller 122 may be wire-line or wireless. In such a configuration, the controller 122 may be programmed to cause an action to be performed in dependence of the derived concentration of the halogen H. More specifically, in this example, the controller 122 may compare the derived concentration of the halogen H with a recommended range of concentration of the halogen H to determine if an action is to be taken. For instance, the controller 122 may comprise a memory (not shown) in which is stored recommended ranges of concentrations of respective halogens. This may be implemented as a lookup table 155 stored in the memory of the controller 122, an example of which is shown in FIG. 16. For example, the lookup table 155 may include recommended upper and lower limits of the concentration of the specific halogen H (e.g., H.sub.1, H.sub.2, H.sub.3) such as a lower limit of 3 ppm and an upper limit of 5 ppm for bromine. The controller 122 may thus access the data stored in its memory and compare the derived concentration of the halogen H with the recommended range of concentration of the halogen H stored in its memory. Based on the comparison, the controller 122 determines if the derived concentration of the halogen H is greater, less than, or within the recommended range of concentration of the halogen H. The controller 122 may be programmed to implement an action at least partly dependent on its determination of where the derived concentration of the halogen H falls relative to the recommended range of concentration of the halogen H.

(54) For instance, the controller 122 may derive control signals for conveying messages to the user of the bathing unit 100 in order to allow the user adjust the concentration of the halogen H in the water of the bathing unit 100. For example, if the controller 122 determines that the derived concentration of the halogen H is lower than the recommended range of concentration of the halogen H, the controller 122 may convey a message instructing the user to take steps to increase the halogen H in the water of the bathing unit 100. If the controller 122 determines that the derived concentration of the halogen H is greater than the recommended range of concentration of the halogen H, the controller 122 may convey a message instructing the user to limit (e.g., stop) adding halogen H to the water, or in some cases, to add water to the bathing unit 100.

(55) In addition, or alternatively, the controller 122 may derive control signals for controlling operation of one or more devices of the bathing unit 100 in order to adjust the concentration of the halogen H in the water of the bathing unit 100. For example, if the controller 122 determines that the derived concentration of the halogen H is lower than the recommended range of concentration of the halogen H, the controller 122 may derive a control signal to cause an electrolytic cell 132 of the sanitizing system 130 to increase an input of the halogen H into the water of the bathing unit 100. If the controller 122 determines that the derived concentration of the halogen H is greater than the recommended range of concentration of the halogen H, the controller 122 may derive a control signal to cause the electrolytic cell 135 of the sanitizing system 130 to decrease an input of the halogen H into the water of the bathing unit 100 (e.g., to stop or reduce the generation of halogen H by a sanitizing device). This may allow the halogen H to evaporate from the water and thus reduce the concentration of the halogen H. Alternatively or additionally, the controller 122 may derive a control signal configured to control one or more valves (not shown) of the bathing unit 100 to add water into the circulation system 106 of the bathing unit 100 such as to reduce the concentration of the halogen H. For example, in such cases, the bathing unit 100 may also comprise a water outlet (e.g., a drain) through which water from the bathing unit 100 may be expelled and new water (i.e., water free of the halogen H) may be added via opening of the one or more valves, thus allowing a reduction of the concentration of the halogen H in the water of the bathing unit 100. The controller 122 may also store the derived concentration of the halogen H in its memory in a log of derived concentrations of the halogen H for future reference. In the event that the controller 122 determines that the derived concentration of the halogen H is within the recommended range of concentration of the halogen H, the controller 122 may store the derived concentration of the halogen H in its memory and not take any action to modify the concentration of the halogen H in the water of the bathing unit 100.

(56) The transmittal of the signal S.sub.c to the controller 122 to cause an adjustment of an input of the halogen H into the water of the bathing unit 100 and/or to cause an adjustment of an input of water into the bathing unit 100 may thus create a closed loop feedback system where the concentration of the halogen H is continuously derived by the processing unit 162 of the optical absorption analyzer 150 and then adjusted in consequence with the derived concentration of the halogen H.

(57) FIG. 6 shows a block diagram of a water flow path in which the water analysis device 500 is in-line with the circulation system 106 of the bathing unit 100 (as shown in FIG. 4). As shown, the water of the bathing unit 100 is monitored by the water analysis device 500 to monitor the concentration of the halogen H in the water, after which the water flows onwards in the circulation system 106 to be effected by the sanitizing system 130 on the basis of the concentration of the halogen H determined by the water analysis device 500 which, as discussed above, may increase or decrease the input of halogen H into the water based on the derived concentration of the halogen H. From there, the water flows into the receptacle 102 where the water is exposed to an environment of the receptacle 102 such that impurities may or may not be introduced into the water. The water then flows through the filter 124 where some impurities contained in the water may be removed, and then through the pump 112 where the water is pumped to circulate through the circulation system 106. The water then returns to the water analysis device 500 where the concentration of the halogen H in the water is monitored and the process restarts.

(58) Alternatively or additionally, as shown in FIG. 5C, the signal S.sub.c released by the optical absorption analyzer 150 may be transmitted to the user interface device 524 of the device 150 with which the processing unit 162 is in electronic communication via a connection 127 (e.g., a wired or wireless connection). The user interface device 524 is configured to display information derived from the derived concentration of the halogen H. For example, the display 526 of the user interface device 524 displays a plurality of information elements 528, 530 derived from the derived concentration of the halogen H. For instance, in this example of implementation, a first information element 528 may consist of the derived concentration of the halogen H (e.g., 3.5 ppm) and a second information element 530 may consist of a status of the concentration of the halogen H relative to the recommended range of concentrations of the halogen H. The status of the concentration of the halogen H may be conveyed to the user in various ways. For example, in some cases, the second information element 530 may be a color (e.g., red, yellow, green, etc.), a symbol (e.g., an exclamation mark), a word (e.g., LOW, OK, HIGH), or any other suitable graphical element to convey to the user whether the derived concentration is below, within or above the recommend range of concentrations of the halogen. The information elements 528, 530 displayed by the display 526 are determined by the processing unit 162 at least in part on the basis of the derived concentration of the halogen H. For example, the processing unit 162 may store a lookup table similar to the lookup table 155 in its memory (not shown) in order to determine whether the derived concentration is outside of or within the recommended range of concentration of the halogen H and the processing unit determines the information elements 528, 530 to be displayed on that basis (e.g., red if the concentration of the halogen H is too low).

(59) In some non-limiting implementations, the signal S.sub.c released by the processing unit 162 may be transmitted exclusively to the user interface device 524. That is, the signal S.sub.c released by the processing unit 162 may be transmitted exclusively locally to the water analysis device 500 such that the signal S.sub.c is not transmitted to the controller 122 of the bathing unit 100 or any other remote device 532.

(60) Alternatively, as shown in FIG. 14, the water analysis device 500 may be part of a communication network 550 in which the water analysis device 500 can communicate with one or more other devices connected to the communication network 550. The communication network 550 may be a wired or wireless communication network. In the example depicted in FIG. 14, the communication network 550 is a (home) Wi-Fi network established by a router 552. More specifically, in this example of implementation, the water analysis device 500 communicates with a plurality of remote devices 532, including for example a smart phone and a laptop via respective wireless links 554, 556 established through the Wi-Fi network.

(61) Alternatively still, the water analysis device 500 may communicate over a communication link (wireline or wireless) established directly one or more other devices, without the need for a WiFi network.

(62) While embodiments of the optical absorption analyzer 150 have been described above, it will be appreciated that the configurations shown can be modified to account for additional factors and improve precision when deriving the concentration of the halogen H and/or to improve or otherwise facilitate deriving the concentration of the halogen H.

(63) Some variants of the optical absorption analyzer 150 will now be described.

(64) Reference Measurement of Light Emitted by the Light Source

(65) In a first variant, the optical absorption analyzer 150 may be configured to make a measurement of the beam of light 154 emitted by the light source 152 before the light has travelled through the sample of water 158. This additional measurement serves as a reference measurement to allow the determination of the concentration of the halogen H to allow the processing unit 162 compensate for effects that may be attributable to variations in the ultraviolet light emitted by the light source 152 and/or received by the detector 156 rather than those that may be attributable to actual concentration of the halogen H. For example, such variations of the ultraviolet light emitted by the light source 152 and/or received by the detector 156 may be due to variations in the manufacturing of the light source 152, or the power source 165 and/or variations that occur over time as the light source 152 and/or the power source 165 age.

(66) For instance, FIG. 7 shows a specific example of implementation in which an optical absorption analyzer 150 is configured substantially similarly to the optical absorption analyzer 150 depicted in FIGS. 3 and 4, with the exception that the optical absorption analyzer 150 comprises a second detector 202 in addition to the (first) detector 156. In this case, the second detector 202 is configured to make a reference measurement of the ultraviolet light emitted by the (first) light source 152 and may thus also be referred to as a reference detector 202.

(67) More specifically, in use, the first detector 156 records a first measurement of ultraviolet light received from the light source 152 after the beam of light 154 has travelled through the sample of water 158 and the second detector 202 records a second measurement of ultraviolet light received from the light source 152 prior to the beam of light 154 having travelled through the sample of water 158. In other words, the second detector 202 receives the beam of light 154 in an unmodified state (i.e., without the beam of light 154 having travelled through the sample of water 158 and interacted with its chemical constituents). To that end, the second detector 202 is positioned on a same side of the sample of water 158 as the light source 152 such that the beam of light 154 does not traverse the sample of water 158 to reach the second detector 202. More particularly, in this embodiment, the second detector 202 is positioned such that its light-sensing surface 203 faces a direction transversal to the beam of light 154. In other words, the light-sensing surface 203 of the second detector 202 faces a direction transversal (e.g., generally perpendicular) to a direction faced by the light-sensing surface 157 of the first detector 156.

(68) Moreover, in this embodiment, the optical absorption analyzer 150 comprises a beam splitter module 200 for directing a first portion 170 of the beam of light 154 toward the first detector 156 and a second portion 172 of the beam of light 154 toward the second detector 202. In other words, the beam splitter module 200 directs a first part of ultraviolet light generated by the light source 152 toward the first detector 156 and a second part of ultraviolet light generated by the light source 152 toward the second detector 202. In this example, the first and second portions 170, 172 of the beam of light 154 respectively directed to the first and second detectors 156, 202 are substantially equal to one another (i.e., the amount of light directed to the first and second detectors 156, 202 is similar). However, in other examples, the beam splitter module 200 may be configured to split the beam of light 154 such that a given one of the first and second portions 170, 172 of the beam of light 154 is greater than the other one of the first and second portions 170, 172 of the beam of light 154. For example, in some cases, the first portion 170 of the beam of light 154 that is directed to the first detector 156 may be greater than the second portion 172 of the beam of light 154 that is directed to the second detector 202. This may be helpful to ensure that an adequate amount of light reaches the first detector 156 which may be further from the light source 152 than the second detector 202.

(69) In some specific practical implementations, the beam splitter module 200 may comprise a semi-transparent body to allow the first portion 170 of the beam of light 154 to be transmitted through to the first detector 156 and the second portion 172 of the beam of light 154 to be reflected to the second detector 202.

(70) In other embodiments, as shown in FIG. 8, rather than the beam of light 154 being directed to the second detector 202 by a beam splitter module 200, the second detector 202 may be configured to receive light directly from the light source 152. For instance, the second detector 202 may be positioned to receive a portion 175 of the light emitted by the light source 152 that is outside of a cone of light collimated and directed to the sample of water 158. To that end, in such embodiments, the second detector 202 is positioned such that its light-sensing surface 203 faces the light source 152. For example, the light-sensing surface 203 of the second detector 202 may face the same direction as the light-sensing surface 157 of the first detector 156.

(71) With the configurations of the optical absorption analyzer 150 described above with reference to FIGS. 7 and 8, the processing unit 162 can derive an estimate of the concentration of the halogen H at least in part by processing results of the first and second measurements effected by the first and second detectors 156, 202 respectively. More specifically, based on the reference measurement of the light source 162 effected at the second detector 202, the processing unit 162 can calculate calibration coefficients that account for the variations in the power of the light source 152 and which may thus improve accuracy of the derived concentration of the halogen H.

(72) More specifically, the radiant flux .sub.e.sup.i incident on the sample of water 158 can be measured using the signal S.sub.R.sup.A recorded by the second detector 202 while the transmitted radiant flux .sub.e.sup.t (i.e., the radiant flux received at the first detector 156) can be measured using the signal S.sub.A.sup.A recorded by the first detector 156. The first and second detector chains have their own specific response functions R.sub.R and R.sub.A, such that the recorded signals S.sub.R.sup.A, S.sub.A.sup.A are given by Equations 2 and 3 reproduced below:
S.sub.R.sup.A=R.sub.R.sub.e.sup.i(Equation 2)
S.sub.A.sup.A=R.sub.A.sub.e.sup.t(Equation 3)

(73) Replacing Equations 2 and 3 into Equation 1 results in Equation 4 reproduced below:

(74) $\begin{array}{cc}\log \left(\frac{\frac{S_R^A}{R_R}}{\frac{S_A^A}{R_A}}\right)=\mathrm{.Math.}\mathrm{cl}& \left(\mathrm{Equation}4\right)\end{array}$

(75) Similar to what was described above, the optical absorption analyzer 150 derives an estimate of the concentration c of the halogen H. To do so, Equation 4 can be transformed into Equations 5 and 6, shown below, where and are calibration coefficients:

(76) $\begin{array}{cc}c=\frac{1}{\mathrm{.Math.}l}\log \left(\frac{\frac{S_R^A}{R_R}}{\frac{S_A^A}{R_A}}\right)& \left(\mathrm{Equation}5\right)\\ c=\log \left(\frac{S_R^A}{S_A^A}\right)& \left(\mathrm{Equation}6\right)\end{array}$

(77) The calibration coefficient is defined as a ratio of the first detector chain response R.sub.A over the reference detector chain response R.sub.R as given by Equation 7 shown below:

(78) $\begin{array}{cc}=\frac{R_A}{R_R}& \left(\mathrm{Equation}7\right)\end{array}$

(79) The calibration coefficient can be measured by using a sample of water containing no target halogen (i.e., the concentration c of the halogen H=0) in which case Equation 6 transforms into Equation 8 shown below:

(80) $\begin{array}{cc}0=\log \left(\frac{S_R^A}{S_A^A}\right)& \left(\mathrm{Equation}8\right)\end{array}$

(81) Equation 8 can be solved to obtain Equations 9 and 10 shown below:

(82) $\begin{array}{cc}1=\frac{S_R^A}{S_A^A}& \left(\mathrm{Equation}9\right)\\ =\frac{S_A^A}{S_R^A}& \left(\mathrm{Equation}10\right)\end{array}$

(83) Using Equation 10, the calibration coefficient can be calculated as a ratio of the detector signal S.sub.A.sup.A over the detector signal S.sub.R.sup.A, when the concentration c of the halogen H is null (in other words no halogen in the water). Meanwhile, the calibration coefficient in Equation 6 can be calculated by using an etalon sample (i.e., a sample having standard known properties) with a known concentration c of the halogen H (c=c.sub.0, as measured by other methods, such as for example using a Bromine titration test kit). As such, Equation 6 can be transformed into Equation 11 as shown below:

(84) $\begin{array}{cc}=\frac{c_0}{\log \left(\frac{S_R^A}{S_A^A}\right)}& \left(\mathrm{Equation}11\right)\end{array}$

(85) In other words, Equation 11 can be used to calculate the calibration coefficient using the calibration coefficient , and the detector signals S.sub.R.sup.A, S.sub.A.sup.A measured with the etalon sample.

(86) Using Multiple Light Sources of Different Wavelengths

(87) In another variant, the optical absorption analyzer may be configured to make a measurement of light emitted at a wavelength that the halogen H does not substantially absorb in addition to the measurement made to gauge the light emitted by the light source 152 whose wavelength the halogen H substantially absorbs. This may allow the determination of the concentration of the halogen H to compensate for effects that may be attributable to impurities in an optical path between the light source 152 and the first detector 156 rather than those that may be attributable to actual concentration of the halogen H in the sample of water 158. For example, such impurities may be due to sand particles in the sample of water 158 and/or particles having adhered to the windows 516, 518 between the light source 152 and the first detector 156.

(88) For instance, FIG. 9 shows a specific example of implementation in which an optical absorption analyzer 150 is configured substantially similarly to the optical absorption analyzer 150 depicted in FIG. 7, with the exception that the optical absorption analyzer 150 comprises a second light source 204 in addition to the (first) light source 152. The second light source 204 emits a beam of light 174 that is received by the first detector 156 for measurement of the light emitted by the second light source 204. The beam of light 174 emitted by the second light source 204 has a wavelength that is different from the wavelength of the beam of light 154 emitted by the first light source 152. Specifically, the wavelength of the beam of light 174 emitted by the second light source 204 is such that the beam of light 174 is substantially not absorbed by the halogen H. That is, the wavelength of the beam of light 174 is generally unaffected by the concentration of the halogen H in the sample of water 158. As the second light source 204 is used as a reference, the second light source may be referred to as a reference light source. In this embodiment, the wavelength of the beam of light 174 may emit light in the visible or near-infrared range of the spectrum (e.g., about 400 nm to 1100 nm) rather than in the ultraviolet range. For instance, in some cases, the wavelength of the beam of light 174 may be between about 450 nm and 600 nm, in some cases between about 475 nm and 550 nm, and in some cases about 500 nm.

(89) In this example of implementation, the first detector 156 records a first measurement of ultraviolet light received from the first light source 152 and the second detector 202 records a second measurement of ultraviolet light received from the first light source 152 prior to the beam of light 154 having travelled through the sample of water 158. The first detector 156 then records a first measurement of light received from the second light source 204 and the second detector 202 records a second measurement of light received from the second light source 204 prior to the beam of light 174 having travelled through the sample of water 158 (i.e., without the beam of light 174 having traversed the sample of water 158 and interacted with its chemical constituents). As such, in this example, the same first detector 156 is used for making the first measurements of transmission of light from the first and second light sources 152, 204, and the same second detector 202 is used for making the second measurements of transmission of light from the first and second light sources 152, 204 prior to the light of the respective light sources travelling through the sample of water 158.

(90) In this example of implementation, the first and second light sources 152, 204 are sequentially turned ON and OFF to allow the detectors 202 and 156 to make their respective measurements. More specifically, the first light source 152 is turned ON (i.e., to emit light) for a period of time and then turned OFF (i.e., to cease emitting light) to allow the second light source 204 to be turned ON for a period of time and then turned OFF. With this cycled approach the optical absorption analyzer 150 can be referred to as a sequential two-wavelength analyzer. In order to derive an estimate of the concentration of the halogen, the processing unit in FIG. 9 may make use of Equations 1 to 11, which also apply to the second light source 204 albeit with a new molar attenuation coefficient and new calibration coefficients and , all three variables being selected for the wavelength of the second light source 204.

(91) The second light source 204 is positioned on the same side of the sample of water 158 as the light source 152 such that the beam of light 174 has to traverse the sample of water 158 to reach the second detector 202. More particularly, in this embodiment, the second light source 204 is positioned such to face a direction transversal (e.g., generally perpendicular) to a direction faced by the first light source 152.

(92) Thus, in order to direct the beam of light 174 emitted by the second light source 204 to the first detector 156, the beam splitter module 200, in addition to being configured to split the beam of light 154 emitted by the first light source 152, is configured to split the beam of light 174 emitted by the second light source 204. Notably, the beam splitter module 200 directs a first portion 176 of the beam of light 174 towards the first detector 156 and a second portion 178 of the beam of light 174 towards the second detector 202. In this example, the first and second portions 176, 178 of the beam of light 174 respectively directed to the first and second detectors 156, 202 are substantially equal to one another (i.e., the amount of light directed to the first and second detectors 156, 202 is similar). However, in other examples, the beam splitter module 200 may be configured to split the beam of light 174 such that a given one of the first and second portions 176, 178 of the beam of light 154 is greater than the other one of the first and second portions 176, 178 of the beam of light 154. For example, in some cases, the first portion 176 of the beam of light 174 that is directed to the first detector 156 may be greater than the second portion 178 of the beam of light 154 that is directed to the second detector 202.

(93) With the configuration of the optical absorption analyzer 150 described above, the processing unit 162 can derive the concentration of the halogen H at least in part by processing results of the first and second measurements of transmission of light from the first light source 152 and the first and second measurements of transmission of light from the second light source 204. More specifically, based on the measurements of the light received from the second light source 204, the processing unit 162 can calculate a calibration coefficient that accounts for the impurities and whose inclusion in calculating the concentration of the halogen H may thus improve an accuracy of the derived concentration of the halogen H. This calibration coefficient may thus be referred to as an interference coefficient in some cases.

(94) Notably, according to the principles of optical absorption, when two chemical species (labeled 1 and 2) are present in the sample of water 158, the Beer-Lambert equation becomes Equation 12 for the first light source 152 and Equation 13 for the second light source 204, as shown below:

(95) $\begin{array}{cc}\log \left(\frac{\frac{S_R^A}{R_R}}{\frac{S_A^A}{R_A}}\right)={\mathrm{.Math.}}_1^A{c}_1{l}_1^A+{\mathrm{.Math.}}_2^A{c}_2{l}_2^A& \left(\mathrm{Equation}12\right)\\ \log \left(\frac{\frac{S_R^R}{R_R}}{\frac{S_A^R}{R_A}}\right)={\mathrm{.Math.}}_1^R{c}_1{l}_1^R+{\mathrm{.Math.}}_2^R{c}_2{l}_2^R& \left(\mathrm{Equation}13\right)\end{array}$

(96) Equation 14, reproduced below, is obtained by subtracting Equation 13 from Equation 12:

(97) $\begin{array}{cc}\log \left(\frac{\frac{S_R^A}{R_R}}{\frac{S_A^A}{R_A}}\right)-\log \left(\frac{\frac{S_R^R}{R_R}}{\frac{S_A^R}{R_A}}\right)={\mathrm{.Math.}}_1^A{c}_1{l}_1+{\mathrm{.Math.}}_2^A{c}_2{l}_2-\left({\mathrm{.Math.}}_1^R{c}_1{l}_1+{\mathrm{.Math.}}_2^R{c}_2{l}_2\right)& (\mathrm{Equation}14\end{array}$

(98) If the first light source 152 and the second light source 204 are collinear, the optical pathlengths for their beams can be considered to be equal, as expressed in Equations 15 and 16 below:
l.sub.1.sup.A=l.sub.1.sup.R=l.sub.1(Equation 15)
l.sub.2.sup.A=l.sub.2.sup.R=l.sub.2(Equation 16)

(99) The optical pathlength l.sub.1 (for the first light source 152) is kept distinct from the optical pathlength l.sub.2 (for the second light source 204) to cover cases for example where the chemical species 2 is deposited on the windows 516, 518 as a thin layer and chemical species 1 is present throughout the volume of the sample of water 158. By combining Equations 14, 15 and 16, Equations 17 and 18 are obtained as shown below:

(100) 0$\begin{array}{cc}\log \left(\frac{\frac{S_R^A}{R_R}}{\frac{S_A^A}{R_A}}\frac{\frac{S_A^R}{R_A}}{\frac{S_R^R}{R_R}}\right)=c_1{l}_1\left({\mathrm{.Math.}}_1^A-{\mathrm{.Math.}}_1^R\right)+c_2{l}_2\left({\mathrm{.Math.}}_2^A-{\mathrm{.Math.}}_2^R\right)& \left(\mathrm{Equation}17\right)\\ \log \left(\frac{S_R^A{S}_A^R}{S_A^A{S}_R^R}\right)=c_1{l}_1{}_1+c_2{l}_2{}_2& \left(\mathrm{Equation}18\right)\end{array}$

(101) In Equations 17 and 18, .sub.1 and .sub.2 are the effective molar attenuation coefficients as defined in Equations 19 and 20 shown below:
.sub.1=.sub.1.sup.A.sub.1.sup.R(Equation 19)
.sub.2=.sub.2.sup.A.sub.2.sup.R(Equation 20)

(102) The second light source 204 can be chosen to emit wavelengths so that the molar attenuation coefficient of the second interfering chemical species is substantially the same as for the first light source 152.

(103) A granular opaque inhomogeneous contaminant such as dirt can cause this type of progressive decrease of transmission affecting wavelengths of light emitted by the first and second light sources 152, 204 in a similar manner. One can also find a wavelength for the second light source 204 so that a film of matter reduces the light intensity in a manner similar to the wavelength of the light beam 154 emitted by the first light source 152. When this happens, .sub.2=0, as can be seen in Equation 21 below:
.sub.2=.sub.2.sup.A.sub.2.sup.R=0(Equation 21)

(104) To illustrate the above, let us say that we have an interfering species in the optical path between the first light source 153 and the detector 156. If this species is interfering, it means that it absorbs at the wavelength at which the first light source 152 is emitting light, the same wavelength used to measure the concentration of the specific halogen H. If only one wavelength is used, the presence of this interfering species in the optical path will reduce the intensity of the wavelength received at the detector 156 and the optical absorption analyzer will think that a greater concentration of halogen H is present in the water.

(105) By choosing the wavelength of the second light source 204 so the interfering species absorbs the same amount at the wavelength of the second light source 204 and at wavelength of the first light source 152, a simplification occurs as can be seen by equations 19 and 20 above and the information provided by the second light source 204 allows us to compensate for this interfering absorption in order to derive an estimate of the concentration of halogen H where the effects of the interfering species have been compensated.

(106) One example is dirt accumulating on the window. Assume that each grain of dirt is 100% absorbing at all wavelengths (opaque). The transmittance of the window will be given only by the percentage of surface covered by this opaque material. Another example would be a material that attenuates all wavelengths by the same ratio, a neutral absorber. In both of these examples Equation 21 holds.

(107) A specific non-limiting way to achieve the condition in equation 21 is to choose the wavelength of the second light source 204 to be as close as possible to the wavelength of the first light source 152, while being away from the maximum absorption wavelength of the halogen H.

(108) Equation 22, reproduced below, can be obtained by replacing Equation 21 in Equation 18:

(109) $\begin{array}{cc}{c}_1={}_1\log \left(\frac{S_R^A{S}_A^R}{S_A^A{S}_R^R}\right)& \left(\mathrm{Equation}22\right)\end{array}$

(110) Equation 22 contains a calibration coefficient .sub.1 that can be calculated using an etalon sample with a known concentration of the halogen H (c.sub.1=c.sub.0), as measured by another method. In this case, the calibration coefficient .sub.1 (which we can also refer to as the interference coefficient) can be obtained by Equation 23 shown below:

(111) $\begin{array}{cc}{}_1=\frac{c_1}{\log \left(\frac{S_R^A{S}_A^R}{S_A^A{S}_R^R}\right)}& \left(\mathrm{Equation}23\right)\end{array}$

(112) The ideal optical absorption analyzer 150 would be configured such that the halogen H absorbs strongly at the wavelengths of the light emitted by the first light source 152 and not at all, or in practice significantly less, at the wavelengths of the light emitted by the second light source 204. In this ideal optical absorption analyzer 150, the second light source 204 is chosen so there is negligible absorption by the halogen H at the wavelength of the light emitted by the second light source 204. If this is not possible, the optical absorption analyzer 150 will still produce a usable result as long as the absorption of light by the halogen H is sufficiently different at the wavelength of the light emitted by the first light source 152 and at the wavelength of the light emitted by the second light source 204.

(113) Optionally, in some embodiments, the water analysis device 500 may use the interference-related information (e.g., the interference coefficient .sub.1) to inform the user of a cleanliness status of the water and the windows 516, 518 of the housing 502.

(114) More specifically, in some embodiments, the processing unit 162 of the water analysis device 500 may be configured to transmit to the user interface device 524 of the water analysis device 500, and/or the remote device 532 to which the water analysis device 500 is connected, the interference-related information gathered from monitoring the sample of water 158. For instance, in addition to the derived concentration of the halogen H, the signal S.sub.C transmitted by the processing unit 162 to the user interface device 524 and/or the remote device 532 may include the interference-related information. In turn, the user interface device 524 and/or the remote device 532 may display information derived from the interference-related information received in the signal S.sub.C. For instance, in a specific example of implementation, as shown in FIG. 13, the display 526 of the user interface device 524 may display a third information element 531 derived from the interference-related information. For example, the third information element 531 may consist of a cleanliness status of the water and/or of the windows 516, 518 of the housing 502 which may be expressed graphically or numerically in any suitable way. In this example, the cleanliness status is expressed as a rating on a given scale (e.g., 1/10, 2/10, 3/10, etc.) to inform the user of the cleanliness of the water of the bathing unit 100 and/or of the windows 516, 518 of the housing 502. This may be advantageous for the user to take action, if necessary, based on the cleanliness status displayed by the user interface device 524 and/or the remote device 532. For example, the user may be compelled to clean the windows 516, 518 of the housing 502 and/or verify the functionality of the filter 124 of the bathing unit 100.

(115) Using Light Sources of Different Wavelengths and Operating them at Different Frequencies

(116) In some variants, the first and second lights sources 152, 204 of the optical absorption analyzer 150 depicted in FIG. 9 may be continuously left ON and may be operated according to an intermittent (e.g., periodic) light pattern (e.g., with a variable modulation), such as for example, but without being limited to, a sinusoidal light pattern or a square wave light pattern. Advantageously, keeping the first and second light sources 152, 204 ON and operating them according to an intermittent light pattern may present a number of advantages including reducing transition effects caused by activating/deactivating the light sources 152, 204.

(117) In order to achieve this, the first and second light sources 152, 204 may be operated at different frequencies. For instance, the first light source 152 emits light at a first frequency F.sub.1 and the second light source 204 emits light at a second frequency F.sub.2 different from the first frequency F.sub.1. Preferably, the first and second frequencies F.sub.1 and F.sub.2 are selected so that they are not harmonics of one another. In this embodiment, the optical absorption analyzer 150 may be configured to derive the concentration of the specific halogen H at least in part based on a frequency distribution associated with the results of the first and the second measurements of the transmission of light from the first light source 152 and the results of the first and the second measurements of the transmission of light from the second light source 204. Advantageously, by selecting certain first and second frequencies, effects of some external sources of interference may be reduced on the measurements of the transmission of light from the first and second light sources 152, 204. External sources of interference may include, for example but without being limited to, changes in ambient light (for example due to the time of day, the amount of sun, the type of light, clouds, etc.) as well as the presence of electrical/electronic EM fields (typically caused by the electrical grid60 Hz, 120 Hz and harmonics (240 Hz, 480 Hz, etc.)).

(118) In some specific practical applications, the first and second frequencies F.sub.1, F.sub.2 may be chosen so that they are not harmonics of one another and so that they are not harmonic of signals that are considered noise (e.g. electrical/electronic signals). In a specific non-limiting example of implementation, the first frequency F.sub.1 is greater than the second frequency F.sub.2. For instance, the first frequency F.sub.1 may be between 420 and 580 Hz, such as for example about 450 Hz. Furthermore, the second frequency F.sub.2 may be above 350 Hz, such as for example between 350 Hz and 200 kHz, in some cases between 400 Hz and 1 kHz, in some cases between 500 Hz and 800 Hz, in some cases between 540 Hz and 600 Hz, such as for example about 570 Hz.

(119) In this embodiment, the signals produced by the light received at the first and second detectors 156, 202 are composed of a superposition of the signals produced by light emitted by each of the first and second light sources 152, 204. The amplitude of the signals recorded at the first and second detectors 156, 202 can be derived by applying a Fourier transform demodulation to obtain a frequency domain representation of the signals recorded at the first and second detectors 156, 202. The signals produced by the light of the first and second light sources 152, 204 have amplitudes A.sub.1, A.sub.2 (which may correspond to the signals S.sub.R.sup.A, S.sub.R.sup.R in equation 22 above). FIG. 12A depicts a frequency domain representation of signals received at the first detector 156, and shows that the signal recorded at the first detector 156 has peak amplitudes A.sub.1, A.sub.2 which are smaller than the original amplitudes A.sub.1, A.sub.2 (shown in FIG. 12B) measured at the second detector 202. This variation in amplitude may be attributed to an absorption of light by the halogen H and by impurities contained in the sample of water 158. The maximum amplitudes A.sub.1, A.sub.2 (which may correspond to the signals S.sub.A.sup.A, S.sub.A.sup.R in equation 22 above) forming the peaks of the signal, or the area of the peaks may be used. In this example, the greater amplitude A.sub.2 corresponds to the light received from the second light source 204 at the first detector 156 at the second frequency F.sub.2 and the smaller amplitude A.sub.1 corresponds to the light received from the first light source 152 at the first detector 156 at the first frequency F.sub.1.

(120) FIG. 12B depicts the frequency domain representation of the signals received at the second detector 202, and shows that the signal recorded at the second detector 202 has peak amplitudes A.sub.1, A.sub.2 which are approximately equal to one another in this example. Using A.sub.1, A.sub.2 A.sub.1, A.sub.2 in equation 22, an estimate of the concentration of halogen H in the sample of water 158 can be derived.

(121) In specific implementations, the first and second signals are modulated in order to shift these signals away from interfering signals. Choosing two distinct frequencies for the two sources allows us to operate them simultaneously, removing the need to various timed sequences (source 152 ON, source 204 OFF, etc. . . . ). Demodulation (Fourier transform) allows separating the signals from interfering influences occurring at other frequencies. In specific implementation, the first and second frequencies of modulation of the light sources may be chosen at frequencies where minimal amounts of interference exist.

(122) alternatively, the first and second frequencies of the light sources may be chosen to be sufficiently high so that a high pass filter may in some cases be used to filter out effects of changes in ambient light, which would typically be at relatively low frequencies (e.g., such as the passage of a cloud). In addition, a suitable filter, such as a band-pass filter, may be used to filter out effects of the electrical/electronic signals (e.g., by discriminating against selected frequencies such as 60 Hz, 120 Hz and harmonics) without hindering the first and second frequencies F.sub.1, F.sub.2 of the first and second light sources 152, 204. In such cases, the first and second frequencies F.sub.1, F.sub.2 of the light sources 152, 204 may be chosen not to correspond to a harmonic of the electrical/electronic signals.

(123) Processing Unit 162

(124) FIG. 10 depicts a functional block diagram of processing unit 162 in accordance with a specific embodiment. In this embodiment, the processing unit 162 of the optical absorption analyzer 150, 150 and 150 comprises a controller 700 configured to receive inputs from and issue outputs to other modules of the processing unit 162 and entities outside of the processing unit 162. For example, the controller 700 is in communication with a light source driver 702 of the processing unit 162 that is configured to send a signal to one or more light sources 704 (e.g., first and second light sources 152, 204) of the optical absorption analyzer 150, 150, 150 to actuate/deactivate the one or more light sources 704. The processing unit 162 also comprises a current to voltage converter 710 in communication with one or more detectors 706 (e.g., first and second detectors 156, 202) and configured to produce a voltage proportional to a current received from the signal transmitted to the processing unit 162 by the detectors 706. The current to voltage converter 710 is in communication with an analog to digital converter 712 which converts the analog signal produced by the current to voltage converter 710 into a digital signal. The digital signal produced by the analog to digital converter 712 is then transmitted to a data processing module 714 of the processing unit 162, where the data contained in the digital signal transmitted to the data processing module 714 is processed. For example, the data processing module 714 may be configured to derive an estimate of the concentration of the halogen H in the manner described above.

(125) The controller 700 comprises a memory (not shown) for storing data therein. More specifically, the memory 165 may store data related to operation of the water analysis device 500. For example, this may include operational parameters of the optical absorption analyzer 150 and/or reference data related to one or more halogens which can be monitored by the water analysis device 500. For example, the lookup table previously discussed, similar to the lookup table 155 depicted in FIG. 16, may be stored in the memory of the controller 700. Other data related to operation of the water analysis device 500 may also be stored in the memory of the controller 700. For example, data related to the wavelength associated with the different light sources, frequencies at which the light sources can be operated and other such data is stored in the memory of the controller 700.

(126) The controller 700 also receives inputs from and issue outputs to entities outside of the processing unit 162. For instance, the controller 700 may be in communication with a temperature probe 180 to receive the signal conveying the temperature of the water. Moreover, the controller 700 may be in communication with the user interface device 524, including the display 526 and the data entry module 527. This may be useful to allow a user to provide information related to operation of the water analysis device 500 into the processing unit 162. For example, this may include making a selection of the halogen H which is intended to be monitored by the water analysis device 500. As another example, this may allow connecting the device 500 to the communication network 550 (e.g., entering a password to a Wi-Fi network).

(127) In embodiments where the water analysis device 500 is part of the communication network 550, as depicted in FIG. 14, the controller 700 may interface with the communication network 550 via a communication module 752. The communication module 752 may be for example a receiver, transmitter or transceiver that allows the processing unit 162 to communicate with the communication network 550.

(128) The embodiments described above are intended to be exemplary only.

(129) It will be apparent to the person skilled in the art in light of the specification that many variations are possible. For example, while embodiments of devices described in the present application including a processor programmed for deriving the concentration of a specific halogen by processing various measurements of light transmission obtained by photo-detectors of the apparatus, it is to be appreciated that such computations need not occur in the device 500 itself but may in some implementations be implemented by processors located remotely from the device 500, including processors that may be located at the bathing unit controller 122 or in the cloud. In such cases measurements of light transmission, once obtained by the photo-detectors, would be transmitted to the remote location including one or more processor programmed for implementing some of the processing functionality, including some of the computations, described in the present application.

(130) It will also be understood by those of skill in the art that throughout the present specification, the term a used before a term encompasses embodiments containing one or more to what the term refers. It will also be understood by those of skill in the art that throughout the present specification, the term comprising, which is synonymous with including, containing, or characterized by, is inclusive or open-ended and does not exclude additional, un-recited elements or method steps.

(131) Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the case of conflict, the present document, including definitions will control.

(132) As used in the present disclosure, the terms around, about or approximately shall generally mean within the error margin generally accepted in the art. Hence, numerical quantities given herein generally include such error margin such that the terms around, about or approximately can be inferred if not expressly stated.

(133) Although various embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art in light of the present description that numerous modifications and variations can be made. The scope of the invention is defined more particularly in the appended claims.