Abstract:
A buoyant water conditioner has a pH measurement system with a pH sensor, a pH measurement circuit, a display for displaying measured pH values, and a processor. After immersing the sensor in water of known pH value, the processor performs a calibration routine in response to the operation of a calibration switch. If the calibration succeeds, the sensor is immersed in water of unknown pH value, and the processor performs a pH measurement routine when a start switch is operated. Both routines include a delay period during which no pH values are displayed. If the calibration is not successful, the calibration routine is repeated until it succeeds. The calibration and start switches are mounted on an upper surface of the water conditioner housing. The system is powered by a solar cell battery or a chemical battery.

Description:
CROSS-REFERENCE TO RELATED PATENT  
       [0001]     This invention is an improvement over the invention disclosed and claimed in commonly-owned U.S. Pat. No. 6,238,553 issued May 29, 2001 for “Buoyant Water Chlorinator With Temperature, pH measurement, and Chlorine Concentration Displays”.  
       BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to water chlorination units of the type used in pools and spas. More particularly, this invention relates to a measurement circuit with simple calibration for use with a buoyant water chlorinator unit which measures water temperature, water pH, and chlorine concentration.  
         [0003]     Water chlorination units are known which are used to supply chlorine to water in pools for water purification. Several such units are buoyant with an inner chamber providing a containment volume for the chlorination material, typically one or more solid pellets, with the containment volume having openings through the walls thereof so that the chlorination material can dissolve in the surrounding water.  
         [0004]     The buoyant water chlorinator disclosed and claimed in my U.S. Pat. No. 6,238,553 comprises a buoyant housing with a lower apertured chamber for holding chlorine material, such as solid tablets. A removable cover retains the chlorine material in place. A plurality of measurement systems, each microprocessor-based, is carried by the housing. Each system has an easily-readable display, preferably mounted on the periphery of an upper housing surface, each display preferably comprising a liquid crystal display (LCD). One measurement system comprises a temperature sensor, such as a thermistor, for measuring the temperature of the ambient water. Electrical temperature signals produced by this sensor are coupled to a microprocessor programmed to convert these signals to signals capable of driving the associated display. A second measurement system comprises a pH level sensor for measuring the pH level of the ambient water. Electrical signals produced by this sensor are coupled to a microprocessor programmed to convert these signals to signals capable of driving the associated display. The remaining measurement system comprises an oxidation reduction potential sensor in the form of a chlorine concentration sensor for measuring the chlorine concentration of the ambient water. Electrical signals produced by this sensor are coupled to a microprocessor programmed to convert these signals to signals capable of driving the associated display.  
         [0005]     Electrical power is supplied to each measurement system from a power source contained within the housing. One suitable power source is a solar cell battery mounted on the same surface as the displays. Another source is a battery installed in a battery compartment. Both types of power source may be included and either source may serve as the primary power source for all systems, with the remaining source reserved as a back-up source, or the two sources may both serve as primary sources for different systems.  
         [0006]     The invention is used by placing it in the body of water in a pool or spa and observing the display values at intervals chosen by the user. When the displays indicate that the pH or chlorine concentration values need to be adjusted and that chlorine material must be added to the chlorine chamber, the cover is removed, and the fresh material is dropped into the receptacle chamber.  
         [0007]     In order to provide accurate signals specifying the pH level of the ambient water, the pH measurement system must be initially calibrated, and the calibration should preferably be checked each time before taking a measurement. Known pH measurement systems do include calibration circuitry, but the technical expertise required to operate such circuitry is typically well beyond the capabilities of the normal consumer. What is needed is a pH measurement system for use with a consumer-oriented buoyant water chlorinator which requires no technical expertise to calibrate and operate in the measurement mode.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention comprises a low cost pH measurement system for use with a buoyant water chlorinator which requires only simple calibration steps well within the grasp of any technologically-disadvantaged consumer, but which provides accurate calibration and pH readings in use.  
         [0009]     From an apparatus standpoint, the invention comprises a pH measurement system for a buoyant water chlorinator, the measurement system having a pH sensor for generating signals representative of pH level of a liquid, such as pool or spa water, a pH measurement circuit for converting signals output by the pH sensor to voltage signals representative of pH level; a pH level display for displaying the value of the liquid pH, and a processor coupled to the pH measurement circuit and the pH level display for converting the voltage signals representative of pH level to pH level display driving signals. A manually operable calibration switch is coupled to the processor for initiating a calibration routine performed by the processor. A manually operable start switch is coupled to the processor for initiating a liquid sample measurement routine performed by the processor. The calibration and start switches are preferably mounted on the upper surface of the housing for the buoyant water chlorinator. Electrical power is provided to the sensor, the circuit, the processor and the display by a solar cell or a chemical battery.  
         [0010]     The calibration routine includes a first delay period during which the voltage signals representative of pH level are not displayed on the pH level display. Similarly, the liquid sample measurement routine includes a second delay period during which the voltage signals representative of pH level are not displayed on the pH level display.  
         [0011]     The pH measurement circuit includes a plurality of operational amplifiers, a first resistance for setting the value of an isopotential voltage coupled to the amplifiers, a second resistance for setting the value of a calibration voltage coupled to the amplifiers, and a third variable resistance for adjustably setting the value of a slope voltage coupled to the amplifiers. The first and second resistances are preferably fixed value resistors.  
         [0012]     From a process standpoint, the invention comprises a method of measuring the pH value of water held by a confinement vessel, such as a pool or spa, the method comprising the steps of (a) providing a pH measurement system having a pH sensor for generating signals representative of pH level of water, a pH measurement circuit for converting signals output by the pH sensor to voltage signals representative of pH level; a pH level display for displaying the value of the water pH, a processor coupled to the pH measurement circuit and the pH level display for converting the voltage signals representative of pH level to pH level display driving signals, a manually operable calibration switch coupled to the processor for initiating a calibration routine performed by the processor, a manually operable start switch coupled to the processor for initiating a water sample measurement routine performed by the processor; and a source of electrical power for providing power to the sensor, the circuit, the processor and the display; (b) immersing the pH sensor in a water sample of known pH value; (c) applying electrical power to the sensor, the measurement circuit, the display, and the processor; (d) operating the calibration switch to initiate the calibration routine; (e) delaying the display of the voltage signals representative of pH level for a first delay period; (f) after the end of the first delay period, displaying the voltage signals representative of the pH level of the water sample; and (g) comparing the displayed pH level value with the known pH value.  
         [0013]     If the displayed pH level value does not match the known pH value, the calibration routine is repeated by removing power from the system; reapplying power to the system; and repeating steps (b) through (g) above.  
         [0014]     When the displayed pH level value matches the known pH value at the end of the calibration routine, a water sample measurement is performed by (h) immersing the pH sensor in water of unknown pH value; (i) applying electrical power to the sensor, the measurement circuit, the display, and the processor; (j) operating the start switch to initiate the liquid sample measurement routine; (k) delaying the display of the voltage signals representative of pH level for a second delay period; and (l) after the end of the second delay period, displaying the voltage signals representative of pH level of the water sample.  
         [0015]     The step (b) of immersing is usually preceded by the step of selecting a water sample of pH value lying at the mid-point of the expected range of pH values of the water.  
         [0016]     The steps (b) and (c); the steps (h) and (i); or all of them can be performed in reverse order by first applying electrical power to the system, and then immersing the sensor in the water.  
         [0017]     The invention enables a consumer/user who is not even moderately technically oriented or skilled to easily conduct accurate pH measurements on pool or spa water. Moreover, any water sample measurement can be initiated by the user in full confidence of the accuracy of the measurement to be obtained by virtue of the automatic calibration routine which is initiated by the mere press of a switch button.  
         [0018]     For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a schematic view of the preferred embodiment of the invention;  
         [0020]      FIG. 2  is a top plan view of the invention of  FIG. 1 ;  
         [0021]      FIG. 3  is a block diagram of the temperature measurement system of the invention;  
         [0022]      FIG. 4  is a block diagram of the pH measurement system of the invention;  
         [0023]      FIG. 5  is a block diagram of the chlorine concentration measurement system of the invention;  
         [0024]      FIG. 6  is a circuit schematic of the pH measurement circuit of the invention;  
         [0025]      FIG. 7  is a schematic diagram illustrating the factory calibration process for the invention;  
         [0026]      FIG. 8  is a schematic diagram illustrating the calibration check procedure; and  
         [0027]      FIG. 9  is a schematic diagram illustrating the pH measurement procedure. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Turning now to the drawings,  FIG. 1  is a schematic view illustrating the preferred embodiment of the invention. As seen in this FIG., the preferred embodiment includes a housing  11 , typically made from plastic material. Housing  11  has an upper sealed hollow space  12  to ensure buoyancy in water, and a lower wall portion  13  providing a hollow interior for receiving one or more water-soluble chlorine tablets (not shown). A plurality of adjustable openings  15  are distributed about the circumference of lower wall portion  13  to allow water to enter the hollow interior volume and leach chlorine from the tablets. A cover  16  is removably mounted to the top of housing  11 . To add more chlorine tablets, cover  16  is removed to expose the hollow lower interior.  
         [0029]     Arranged about the upper peripheral surface  17  of housing  11  are three liquid crystal (LCD) displays  20 - 22 . Display  20  is a water temperature display and is electrically coupled to a microprocessor-based temperature processing unit  30  shown in  FIG. 3 , which receives water temperature measurement signals from a temperature sensor  31 . Display  21  is a pH level display and is electrically coupled to a microprocessor-based pH level processing unit  32  shown in  FIG. 4 , which receives pH level signals from a pH electrode  33 . Display  22  is an oxidation reduction (ORP) display and is electrically coupled to a microprocessor-based chlorine concentration processing unit  34 , which receives signals from an oxidation reduction potential sensor  35 .  
         [0030]     With reference to  FIG. 2 , mounted on upper peripheral surface  17  are three manually operable switches  25 - 27 . In the preferred embodiment, switch  25  is a push button toggle switch, while switches  26  and  27  are push button momentary contact switches; however, other switch types can be used, if desired. Switch  25  is a main power switch: operation of this switch applies power to the three measuring circuits described below. Switch  26  is a calibration switch: operation of this switch enables automatic calibration of the pH measurement circuit. Switch  27  is a start switch: operation of this switch enables the pH measurement circuit to commence pH measurement of the water in which the chlorinator is suspended. Electrical power is supplied to the displays  20 - 22 , sensors  31 ,  33 , and  35 , and processing units  30 ,  32 , and  34  by one or more solar cells  37  mounted on the upper peripheral surface  17  of housing  11 . An alternate source consisting of a battery (not shown) mounted in an appropriate portion of housing  11  is also provided.  
         [0031]      FIG. 3  is a block diagram of the water temperature measurement system described above. As seen in this FIG., remote temperature sensor  31 , which may comprise any one of a number of commercially available devices capable of generating signals representative of the temperature of the water with which the unit  31  comes in contact (such as a thermistor), has an output electrically coupled to the microprocessor unit  30 . Microprocessor unit  30  may comprise any known microprocessor capable of receiving the signals from sensor  31  and converting these signals to signals capable of operating display  20 . One such microprocessor is a type 16F877 available from Microchip corporation. The display output of microprocessor unit  30  is electrically coupled to the display input terminals of display  20 , which displays temperature value in the form of integers plus an indication of the scale employed (i.e., Fahrenheit, Celsius, or some other scale).  
         [0032]      FIG. 4  is a block diagram of the pH measurement system described above. As seen in this FIG., remote pH electrode  33  has a signal output electrically coupled to a pH measurement circuit  40  described below. The output of circuit  40  is coupled to a microprocessor unit  32 . Electrode  33  may comprise any one of a number of commercially available sensors capable of generating electrical signals representative of the pH level of water with which the electrode  33  comes in contact (such as the sensor component incorporated into the series H-58800 pH meters available from ATI-Orion Research, Inc.). Microprocessor unit  32  may comprise the same type of unit as microprocessor unit  30 , with different programming to convert the pH input signals to signals capable of operating display  21 . The display output of microprocessor  32  is electrically coupled to the display input terminals of display  21 , which displays pH values in the normal form of an integer, a decimal point and another integer.  
         [0033]      FIG. 5  is a block diagram of the ORP chlorine concentration system described above. As seen in this FIG., chlorine sensor  35  has a signal output electrically coupled to microprocessor  34 . Sensor  35  may comprise any one of a number of known sensors capable of generating signals representative of the ORP (usually in millivolts) of water with which sensor  35  comes in contact. The ORP is related to chlorine concentration in a known manner. Microprocessor unit  34  may comprise the same type of unit as microprocessor unit  30 , with different programming to convert the ORP signals supplied by sensor  35  to signals capable of operating display  22 . The display output of microprocessor unit  34  is coupled to the input terminals of display  22 , which displays ORP in the form of three integers and the legend “mv”.  
         [0034]     As illustrated in  FIGS. 3-5 , each unit is electrically powered by either solar cells  37 , a battery  39 , or a combination of the two. More specifically, if one or two of the systems shown in  FIGS. 3-5  draws substantially more power than the others, either the solar cells  37  or the battery  39  may be dedicated to the unit(s) with a higher power consumption, with the remaining power source shared among all three systems. In the alternative, one of the two power sources (e.g., solar cells  37 ) may serve as the principal power source for all three units, and the other source used as a back-up source.  
         [0035]      FIG. 6  is a circuit schematic of the pH measurement circuit  40  of the invention. As seen in this FIG., a voltage signal from pH sensor electrode  33  is coupled to one input of a conventional quad op amplifier  41 . Amplifier  41  is preferably a commercially available type LF 347 JFET device. Supply voltage from sources  37 ,  39  is applied to input terminals  43 ,  44  of power switch  25 . A pair of resistors  45 ,  46  provides an isopotential voltage of appropriate level to amplifier  41  via conductor  47 . Another pair of resistors  48 ,  49  provides a calibration voltage of appropriate level to amplifier  41  via conductor  51 . A single adjustment potentiometer  52  provides a slope adjustment capability for amplifier  41 . The voltage on output terminal  53  is coupled to the voltage measurement input of microprocessor  32 .  
         [0036]     The circuit of  FIG. 6  is a simplified modification of the pH measurement circuit disclosed in the technical publication entitled “A Low-Cost pH Meter for the Classroom” authored by David L. Harris et al found in the Journal of Chemical Education, Volume 69, Number 7, July, 1992, the disclosure of which is hereby incorporated by reference. The circuit shown in this technical publication employs three adjustment potentiometers: one for adjusting the isopotential voltage; one for the calibration voltage; and one for the slope adjustment. In contrast, the circuit of  FIG. 6  incorporates only one adjustment potentiometer  52  for slope adjustment.  
         [0037]     The circuit of  FIG. 6  is initially calibrated at the factory in the following manner illustrated in  FIG. 7 . With display  21  connected to microprocessor  32 , pH sensor electrode  33  is initially immersed in a buffer solution of known pH—7.0 in the process illustrated in  FIG. 7 —and allowed to equilibrate for a preselected period of time. Potentiometer  52  is adjusted as necessary until display  21  displays the correct known pH value of the buffer solution. Next, pH sensor electrode  33  is immersed in a second buffer solution of different known vaule—7.4 in  FIG. 7 —and the value displayed by display  21  is observed. Potentiometer  52  is adjusted as necessary until display  21  displays the correct known pH value of the second buffer solution. If adjustment was found necessary for the measurement of the second buffer solution, the process is repeated until the best fit between the two value readings is obtained. Since the range of pH values normally encountered in swimming pools and spas is normally quite small—in the range from about 7.2 to about 7.8—adjustment of the slope by means of potentiometer  52  will typically provide a linear range for the measurement circuit  40  for the values of interest to swimming pool and spa users.  
         [0038]     Once factory calibration is complete, the unit is ready for use by the consumer. With reference to  FIG. 8 , the user initially immerses the pH sensor electrode  33  in a buffer solution of known pH value—preferably 7.5 (the mid-range value for swimming pools and spas)—and operates the calibrate switch  26 . Operation of the calibrate switch  26  starts a calibration program routine in microprocessor  32  which provides an initial delay period (thirty seconds in the preferred embodiment) before measuring the value of the voltage output from pH measurement circuit  40 . After the delay period, microprocessor  32  measures the output voltage, and causes display  21  to display the corresponding pH value. The user then observes this value on display  21 . If the displayed pH value matches the known value of the buffer solution (7.5), the unit is ready for a water sample measurement. If the display is incorrect, the user is instructed to operate power switch  25  a first time to turn off the circuit  40 , and to operate power switch  25  a second time to turn the power back on. This is followed by repeating the calibration procedure by operating calibration switch  26  and observing the displayed pH value with pH sensor electrode  33  still immersed in the 7.5 pH buffer solution. Any variance between the pH value displayed at the end of the calibration procedure will normally be due to circuit drift due to ambient conditions. In practice, any such variance will quickly disappear and the correct pH calibration value will be displayed.  
         [0039]     After the automatic calibration procedure is successfully completed, a water sample measurement is obtained by the user by the procedure illustrated in  FIG. 9 . The user immerses the pH sensor electrode  33  in a water sample (usually by immersing the electrode in the water immediately adjacent the chlorinator unit) and operates the start switch  27 . Operation of the start switch  27  starts a sample measurement program routine in microprocessor  32  which provides an initial delay period (fifteen seconds in the preferred embodiment) before measuring the value of the voltage output from pH measurement circuit  40 . After the delay period, microprocessor  32  measures the output voltage, and causes display  21  to display the corresponding pH value. The user then observes this value on display  21 . If this value lies within the acceptable range (7.4 to 7.6 in the preferred embodiment) nothing further need be done. If this measured value lies outside the acceptable range, the user then can take corrective action, usually by adding more chlorine to the chlorinator unit.  
         [0040]     As will now be apparent, the invention provides a simple procedure for the consumer/user to check the accuracy of the pH measurement circuit and to measure the pH value of the water in the user&#39;s pool or spa. The user need only operate a single switch  26  to check the calibration of the measurement circuit  40 , and another switch  27  to take a water sample measurement. This eliminates the technical complexity of operating known pH measurement circuits, while ensuring the accuracy of water sample measurements. In addition, the calibration circuitry of the invention is relatively simple and thus can be manufactured at minimum cost.  
         [0041]     Although the above provides a full and complete disclosure of the preferred embodiments of the invention, various modifications, alternate constructions and equivalents will occur to those skilled in the art. For example, although the invention has been described with reference to specific electronic components, other types of such components can be utilized, as desired. Moreover, different delay periods for the calibration and the water sample measurement routines can be incorporated into the invention. Therefore, the above should not be construed as limiting the invention, which is defined by the appended claims.