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You are an expert at summarizing long articles. Proceed to summarize the following text: 
RELATED APPLICATION 
       [0001]    This application is a divisional of and claims priority to U.S. Utility patent application Ser. No. 12/257,861, entitled “CHLORINATOR FOR PORTABLE SPAS,” filed on Oct. 24, 2008. The contents of that application are incorporated expressly by reference herein, as if fully set forth and full Paris Convention Priority is hereby expressly claimed. 
     
    
     FIELD OF INVENTION 
       [0002]    This disclosure relates to water purification particularly with respect to water containing vessels such as spas, hot tubs, whirlpools, pools and the like and to a chlorinator or oxidizer generator suitable for such purpose. 
       RELATED ART 
       [0003]    Portable spas have become quite popular as a result of their ease of use and multiplicity of features such as varied jet and seating configurations. Maintaining appropriate water chemistry and sanitation is of course important to enhancing the spa user experience. 
       SUMMARY 
       [0004]    The following is a summary of various features, aspects, and advantages realizable according to various illustrative embodiments of the invention. It is provided as an introduction to assist those skilled in the art to more rapidly assimilate the detailed discussion which ensues and does not and is not intended in any way to limit the scope of the claims which are appended hereto in order to particularly point out the invention. 
         [0005]    An illustrative embodiment of a portable spa chlorinator includes a housing having a fluid inlet at a first end, which leads to a chamber within the housing. A lid is attachable to a second end of the housing to close the chamber. First and second pairs of electrodes are attached to the lid so as to be suspended within the chamber when the lid is attached to the housing. When an appropriate voltage is applied, the electrodes interact with the fluid pumped through the chamber to generate various oxidizing agents. 
         [0006]    In one embodiment, each electrode of the first and second pairs comprises a doped diamond surface, wherein the dopant may be, for example, boron. In one illustrative embodiment, the doped diamond surface resides on a substrate, while in another the doped diamond surface comprises the surface of a whole diamond electrode. In the former illustrative embodiment, the substrate may be selected from one of the group including titanium, niobium, silicon, platinum, or stainless steel. The electrodes may be solid metal plates or a mesh, the latter providing increased surface area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a chlorinator according to an illustrative embodiment. 
           [0008]      FIG. 2  is an exploded perspective view of the chlorinator of  FIG. 1 . 
           [0009]      FIG. 3  is an exploded perspective view of an electrode assembly illustrated in  FIG. 2 . 
           [0010]      FIG. 4  is a schematic side view of a diamond doped electrode according to an illustrative embodiment. 
           [0011]      FIG. 5 . is a side schematic view of a chlorinator installed in the fluid circulation line of a portable spa. 
           [0012]      FIG. 6  is a partial perspective view of an illustrative embodiment of a lid and mesh electrode assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A chlorinator  11  according to a illustrative embodiment is shown in  FIGS. 1-3 . The chlorinator  11  includes a housing  13 , a lid  21 , and a cap  31 . The housing  13  is preferably a unitarily molded polyvinyl chloride (PVC) part with an integrally molded, barbed fluid outlet  15  at one end and an integrally molded flange  155  at the opposite end. In the illustrative embodiment, the housing  13  has a generally rectangular cross-section with rounded corners, e.g.  14 , arcing through ninety degrees, and is adapted to be plumbed into the circulation line of a portable spa. 
         [0014]    The lid  21  is also preferably a unitarily molded PVC part having a rim  22  whose contour conforms in shape to that of the rim  16  of the housing flange  155 . Four self-threading screws  24  attach the lid  21  to the flange  155 . An integrally molded, barbed fluid inlet  23  protrudes from the base  24  of the lid  21  and provides a fluid inlet to the housing  13 . As seen in  FIG. 2 , an o-ring  41  is inserted in a circular receiving channel  43  in the housing  13  to provide a watertight seal between the housing  13  and the lid  21 . 
         [0015]    The cap  31  is also preferably a unitarily molded PVC part and is attached to the lid  21  by a screw  26 . The edge  32  of the cap  31  fits flush against a mounting surface  35  of a raised (mesa) area  37  of the lid  21  and against an axially projecting perimeter edge or lip  40  of a second raised area  41 . The cap  31  is fastened into place against surface  35  by the screw  26 , which threads into a raised boss  39  portion of the lid  21 . Electrical leads  205 ,  207  enter through apertures at each side of the cap  31 . 
         [0016]    As noted above, in the illustrative embodiment, the housing  13 , lid  21  and caps  31  are unitarily molded plastic parts. It should be understood that, in other embodiments, these parts could be fabricated as an assembly of sub-components. Additionally, such parts could be fabricated of materials other than PVC, for example, such as ABS, Luran, Teflon, PTFE or Kynar. 
         [0017]      FIGS. 2 and 3  depict an electrode or cell assembly  51 . The assembly  51  includes a first pair of electrodes  53 ,  55  and a second pair of electrodes  57 ,  59 . Each of the four electrodes  53 ,  55 ,  57 ,  59  lie parallel to one another in respective horizontal planes in the illustrative embodiment. 
         [0018]    As shown in  FIGS. 2 and 3 , the two inner electrodes  57 ,  59  and two outer electrodes  53 ,  55  are held in position by four bolts  60 ,  61 ,  62 ,  63 , which pass through respective sets of co-linear holes, one set being, for example, the four holes  125 ,  127 ,  129 ,  130 . The four bolts  60 ,  61 ,  62 ,  63  further pass through suitable spacers, respectively  91 ,  95 ,  105 ;  85 ,  98 ,  101 ;  93 ,  97 ,  107 ; and  87 ,  83 ,  103  and thread into suitable respective nuts  113 ,  111 ,  115 ,  109 . The bolts  60 ,  61 ,  62 ,  63  and their associated spacers and nuts are preferably fabricated of a suitable plastic, such as, for example, PVDF (Kynar). 
         [0019]    The two inner electrodes  57 ,  59  are connected to a voltage of a first polarity by a first supply electrode  71 . The first supply electrode  71  is attached to the two inner plates  57 ,  59  by a bolt  67 . The bolt  67  passes through respective oblong apertures  131 ,  133  in L-shaped mounting sections  82  of the electrodes  57 ,  59 , then through a hole  132  in the electrode  71 , and then threads into a nut  68 . 
         [0020]    The two outer electrodes  53 ,  55  are connected to a source of voltage opposite in polarity to that applied to the inner electrodes  57 ,  59 . That voltage is supplied by a second supply electrode  73 , which is attached to the outer electrodes  57 ,  59  by a bolt  65 . The bolt  65  passes through oblong apertures  135 ,  137  in L-shaped mounting sections  82  of the electrodes  53 ,  55 , then through a hole  136  in the second supply electrode  73  and then threads into a nut  109 . The bolts  65 ,  67  and supply electrodes  71 ,  73  are fabricated of conductive material such as, for example, titanium or platinum. 
         [0021]    The projecting shafts  72 ,  74  of the respective supply electrodes  71 ,  73  pass through respective holes in the lid  21  leading to respective wells  38 ,  36  and are fastened to the lid  21  by respective locking nuts  121 ,  123  and sealed against respective O-rings  117 ,  119 , which may be, for example, viton o-rings. The o-rings  117 ,  119  provide a watertight seal and, together with o-ring  41  insure that fluid does not escape or leak out of the housing  13 . 
         [0022]    Respective locking nuts  25  hold the ring terminals  201 ,  203  of the respective supply leads  205 ,  207  to the supply electrodes  71 ,  73 . Attachment of the cap  31  then covers the wells  36 ,  38 , the electrical leads  205 ,  207  and the supply electrode shafts  72 ,  74 . 
         [0023]    Thus, the electrode assembly  51  is attached to the lid  21  and is suspended within the housing  13  when the lid  21  is attached to the housing by the screws  24 . The interior of the housing  13  forms a chamber  157  wherein hydroxyl radicals are generated when power is supplied to the electrodes  71 ,  73  via the leads  205 ,  207 . 
         [0024]    In one embodiment, the electrodes  53 ,  55 ,  57 ,  59  are rectangular in shape and each comprise a boron doped synthetic diamond electrode tailored to flow rate. As illustrated in  FIG. 4 , such electrodes may be formed, for example, by chemical vapor deposition (CVD) of a very thin coating  203  of boron or nitrogen doped diamond onto a niobium substrate  205 . Such electrodes may be fabricated, for example, by Adamant, Chauxde-Fords, Switzerland. Other substrate materials may be used such as titanium, silicon, platinum or stainless steel. Embodiments may also be constructed of self-supporting diamond without using a substrate, such as may be obtained, for example, from Advanced Oxidation, Cornwall, U.K. In various embodiments, the substrates may either be solid plates or mesh, the latter providing increased surface area.  FIG. 6  illustrates an embodiment employing mesh electrodes  209 . 
         [0025]    In operation of illustrative embodiments in an illustrative portable spa environment, a chlorinator  11  is installed in the circulation line  156  of a portable spa  158  as shown in  FIG. 5 . A constant current mode of operation of the device  11  may be employed. In such case, a selected current flow through each electrode pair  57 ,  59 ;  53 ,  55  in the range of 1-5 amps, for example, 2 amps, may be used with a floating voltage across each electrode pair of 5-24 volts. In such embodiments, flow rates through the cell  11  may range from ½ gallon to 5 gallons per minute with a salt (NaCl) level in the spa water of from 500 ppm to 3500 ppm (target 1,000 to 2,000 ppm). Electronically, a constant current AC/DC transformer supplying 1 to 4.5 amps at 5 to 24 volts D.C. may be used along with a microcontroller to control activation of the cell  11 . 
         [0026]    In such embodiments, hydroxyl radicals are generated directly off the electrode plates  53 ,  55 ,  57 ,  59 . The hydroxyl radicals then oxidize organic waste in the process water or react with water and dissolved salts to produce various oxidizers. These include but are not limited to, ozone (O3), hydrogen peroxide (H2O2), sodium hypochlorite (NaHOCl/OCl), chlorine dioxide (ClO2), sodium persulfates (NaHSO5) and sodium percarbonate (Na 2 CO 3 ). This broad spectrum of oxidizers is capable of neutralizing organic and other contaminants which may be present. 
         [0027]    The design of the housing  13  is preferably such as to provide adequate mixing and turbulence of the process stream and the generated hydroxyl radicals. Flow through the cell  11  is optimized to allow for the self cleaning of the cell generated by polarity reversing and sloughing of the formed scale layers. Vapor lock is prevented in the cell  11  though either maintaining flow when the cell  11  is mounted horizontally with inlet  23  located on the top as shown in  FIG. 1  or by mounting the cell  11  vertically with water entering the inlet  23  from the bottom. 
         [0028]    A chlorine generator system according to an illustrative embodiment may operate in an open-loop mode using scheduled and timed generation of chlorine. The length and interval of daily generation is typically a function of the spa size, bather load, and water salinity. In such a system, the cell  11  may produce a constant stream of 0.1 to 0.60 ppm (parts per million) chlorine in a 4 gpm flow (2 Amp &amp; 1000 to 2000 ppm salt). To maintain the chlorine level in the water, the cell  11  must operate longer for a large spa than for a small spa. Additionally the cell  11  must run longer with a higher expected bather load. The salt level has a strong direct relationship to the quantity of chlorine produced. 
         [0029]    In an illustrative open loop system the user inputs three variables to the system at start-up. The first is the spa size (SPA). A size code may be used (e.g. 1-8). The anticipated use level, (USE) (1-5) is the second variable. Use level “(1)” corresponds to minimal use and vacation mode. A higher level should be entered if more bathing is expected. The user preferably adjusts the use level over the course of use. The third start-up variable input is the water hardness (Hd). This parameter controls the polarity reversal cycle timing used to clean the electrodes. 
         [0030]    As an additional input feature, a manual chlorine addition (Add) command may be implemented. This command instructs the system to generate enough chlorine to add 2 ppm to the spa. This chlorine Add temporarily overrides scheduled operation times. 
         [0031]    The manual Add command dictates that the system run for a length of time sufficient to add 2 ppm Chlorine. The amount of time needed to bring the water to 2 ppm is highly dependent on the amount of bather load in the water. A standard 24 hour dose or longer may be needed to completely bring the water up. In one implementation of the Add command, the system switches from 2 amps to 4-4.5 amps to rapidly generate chlorine. One run cycle every six hours may be used to maintain uniform around the clock treatment. 
         [0032]    In one embodiment, salt is measured each time the unit  11  generates chlorine as well as when requested by the user. The system measures the salt level of the water by means of measuring the voltage across the cell  11 . The voltage reading is then compared against allowable limits. The salt concentration is normalized, and displayed on the user interface. A voltage higher than specified returns a low salt error and a voltage less than specified returns a high salt error. 
         [0033]    If there is a low salt condition, an error may be sent to the spa controls, triggering a “water care” icon to flash. The unit  11  may be allowed to continue to generate chlorine in this condition. The spa controls or controller will boost available voltage to a regulated limit to automatically compensate for low salt or conductivity situations. If there is a high salt condition, an error will be sent to the spa controls, again triggering the water care icon to flash. In this case, the unit  11  will not generate chlorine until the salt level has been corrected. 
         [0034]    To prevent mineral scale on the electrodes  53 ,  55 ,  57 ,  59 , polarity reversal may be used. The time period of the reversal is a function of water hardness and is preferably made adjustable to a user input hardness reading. Rapid cycling of the electrodes will cause premature electrode failure. Therefore a dead band in the cycle may be implemented to allow the electrodes to discharge prior to the polarity reversal. The dead band interval may be, for example, a minimum of 20 seconds. 
         [0035]    At either initial start-up or at a maintenance event, the spa water should be manually balanced. Once the spa water has been balanced it should be super chlorinated (5 ppm). Super chlorination prepares the system for operation and immediate spa usage by cleaning the spa after a period of nonuse. After super chlorination, salt is added to the water. The spa control system may operate such that the water care icon is blinking to indicate that the salt level is low and/or the unit has not been initialized or programmed. Salt should be added slowly into the filter compartment while all of the jets are operating. The jets should operate an additional 10 minutes after the salt is fully added. An example of a target salt concentration is 1000 ppm. High demand users can add up to 2000 ppm salt, which will lower the hours required to generate chlorine and therefore lower the USE level. A salt level reading is preferably taken every time the unit begins a generation cycle to ensure proper salt levels at start-up and during the time between water changes. 
         [0036]    Typical operation of an illustrative system preferably requires a weekly chlorine and water quality check to ensure that the system is working correctly. Although the user is not required to enter the chlorine concentration, the value is needed to determine the use level. Over the course of the first month, the user may determine their Use Level by taking a reading of the water before they enter the spa. If the chorine level is low, e.g., “1” or less, the user will want to increase the use level by one to increase the output. If the user finds that the chlorine level is 5 or higher, the user will want to drop the use level by one and retest in a few days or a week. If the bather load is predictable, the use level may only need occasional adjustments. 
         [0037]    If the bather load is sporadic, the user may want to perform a manual addition. In such case, the user may enter the spa control menu and confirm an addition (Add). The addition operation turns the system on immediately and operates the specified amount of time determined to elevate the chlorine level by 2 ppm (this depends on bather load and time and cannot be guaranteed). If the water is overly polluted such that the actual bather load far exceeded the anticipated bather load, a manual dichlor/MPS dose may be used and is compatible with the system. 
         [0038]    Typically, the spa will require a monthly manual shock with MPS or dichlor to eliminate any accumulated waste. The oxidizer level should be brought to and held at 5 ppm while all jets configurations and pumps are operated for 30 minutes each. It is important to monitor pH at this time as well to ensure that the water remains balanced. 
         [0039]    Over time the water level in spa typically drops from evaporation or splash out. When fresh water is added to the spa, it is important to rebalance the water and monitor the salt concentration. The system may employ a conductivity sensor to determine the amount of salt in the water and whether it is too high or too low. A water care icon may be arranged to blink to indicate that the salt is low and that more salt is needed. Salt should be added in 0.25 lb (100 g) increments to ensure that it is not over dosed. 
         [0040]    While the apparatus and method have been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims.

Summary:
An oxidizer generating apparatus having a housing with a fluid inlet at a first end, the inlet leading to a chamber, and a lid attachable to a second end of the housing for closing the chamber. First and second pairs of electrodes are attached to the lid so as to suspend them within the chamber in position to generate chlorine and/or other oxidants from fluid pumped through the housing.