Abstract:
A precious metal testing apparatus determines the percentage content of precious metal in a specimen being tested by detecting the change in the rate of current flow through a resistive layer formed on the specimen by an application of a corrosive electrolyte on the specimen. The electrical circuit forms a fixed resistance circuit and a variable resistance circuit due to the formation of a growing resistive layer on the specimen such that the flow of current through the variable resistance circuit decreases as the flow of current through the fixed resistance circuit increase. The detection of the rate of change in current flow as a result of the increasing growth of the resistive layer can be compared to a look-up table that provides a corresponding percentage of precious metal in the specimen. Calibration of the testing apparatus can be accomplished with a specimen of known purity of the precious metal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims domestic priority on U.S. Provisional Patent Application Ser. No. 61/653,587, filed on May 31, 2012, the content of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to an apparatus for testing the purity of precious metals, and, more particularly, to a testing apparatus that identifies the silver content in a specimen being tested by the apparatus. 
     A precious metal testing apparatus is shown in U.S. Pat. No. 5,888,362, issued to Lloyd V. Fegan, Jr., on Mar. 30, 1999. This testing apparatus provides a portable device that can provide accurate analysis of the quality of the precious metal, particularly gold and platinum, being tested by utilizing a hand-held probe having an electrode embedded in an electrolyte contained within a reservoir formed in the probe. The testing apparatus generates a galvanic current through the metal being tested from a battery, the strength of the current being proportionate to the quality of the precious metal being tested. In the Fegan patent, a meter circuit measures the extent of galvanic action of dissimilar metals in the presence of an electrolyte, one of the metals being the sample being tested for quality. Thus, the invention is useful for testing the metal content of gold coins, art objects jewelry, and the like, by reason that the probe can simply be touched against the object being tested to provide a reading representing the quality of the precious metal in the object. 
     The hand-held probe in the aforementioned precious metal testing apparatus is typically in the form of a pen having a fibrous tip from which a small amount of electrolyte is deposited onto the object being tested. The meter attached to the probe continuously measures the strength of the galvanic current and compares the result with a known point of reference for the type of precious metal being tested, whereby the percentage of precious metal within the object being tested will be known. This measurement process by the meter and pen is completed within a few hundredths of a second, thus providing an efficient manner in which the quality of precious metal can be determined. However, even though the measurement process is fast, the strengths of the galvanic reaction when reacted with gold or platinum are very weak. 
     The Fegan gold testing apparatus, however, is not very effective in testing for the content of silver in an object. Silver is highly conductive and the current from the pen probe easily passes through the silver specimen causing the needle to bottom out. Other known methods of testing for silver involves exposing the silver (AG) samples to a chemical test. The concentration (i.e. the purity) of the silver in the specimen is the based on a visual inspection of the chemical reaction reflecting a change in color of the exposed chemical. Such visual inspection tests can be somewhat subjective and the accuracy of the test is dependent on the experience of the person conducting the chemical test. 
     It would be desirable to provide an electronic apparatus that would provide an accurate and efficient testing of a specimen to be able to determine the concentration of the silver content within the sample. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a testing apparatus operable in conjunction with precious metals to determine the percentage of content of the precious metal in the object being tested. 
     It is another object of this invention to provide a precious metal testing apparatus that can be utilized to test a precious metal other than gold. 
     It is a feature of this invention that the percentage content of silver can be determined in a sample being tested. 
     It is another feature of this invention that the calculation of the percentage content of precious metal in a sample being tested is based on a measurement of the rate of change of current or voltage through the test specimen as a resistive layer is established between the probe and the specimen being tested. 
     It is an advantage of this invention that the test probe causes the formation of a resistive layer on the sample being tested which changes the rate at which current flows from the probe through the sample being tested to the monitor displaying the test results. 
     It is another advantage of this invention that the growth of the resistive layer is a function of the percentage content of precious metal within the specimen being tested. 
     It is still another feature of this invention that the changes in the rate of current flowing from the probe through the resistive layer on the specimen being tested can be detected and compared with a look-up table that provides a corresponding percentage content of precious metal present in the specimen being tested. 
     It is another advantage of this invention that the probe carries a supply of an electrolyte that corrodes the precious metal being tested in a selected specimen. 
     It is yet another feature of this invention that the probe carries a supply of a saturated solution of ammonium chloride that forms silver oxide from corrosion of the silver content in a specimen being tested. 
     It is yet another advantage of this invention that the layer of silver oxide created by the application of an electrolyte to cause corrosion in the specimen being tested impedes the flow of current through the specimen. 
     It is still another object of this invention to provide an electrical circuit that utilizes Kirchhoff&#39;s law to determine the changes in the rate of current flow through the resistive layer growing on a specimen containing precious metal being tested. 
     It is a further feature of this invention that the detection circuit in the tester establishes a portion of the circuit that has a fixed value resistance and a portion of the circuit that forms a variable resistance due to the formation of the resistive layer on the specimen being tested. 
     It is further advantage of this invention that the increase in the variable resistance portion of the electrical circuit due to the growth in the formation of the resistive layer from the corrosion of the precious metal in the specimen being tested results in a decrease in the current through the variable resistance portion of the circuit and a corresponding increase in the current flowing through the fixed resistance portion of the electrical circuit. 
     It is still a further feature of this invention that the testing apparatus can be calibrated using a sample having a known content of precious metal being tested. 
     It is still a further advantage of this invention that the sample having a known content of precious metal can be a specimen formed of sterling silver. 
     It is another feature of this invention that the display for the testing apparatus can provide an LED indication of several parameters, including the status of the testing apparatus, such as power on, ready for testing, battery status, the ability of the testing apparatus to conduct subsequent tests, and the number of tests that can be conducted before another calibration is required. 
     It is still another feature of this invention that the LED display can also provide an indication of the percentage of precious metal content in the specimen being tested. 
     It is yet another feature of this invention that the microprocessor in the testing apparatus terminates power to the probe after conducting a test of a specimen. 
     It is yet another advantage of this invention that the termination of power to the probe after completing a test of a specimen allows the accumulated charge within the probe to be dissipated before providing an indication of the apparatus being ready to conduct another test. 
     It is a further object of this invention to utilize the rate of change of the flow of current through a specimen being tested due to the increasing growth of a resistive layer created by the application of a corrosive electrolyte on the specimen where the growth of the resistive layer is proportional to the percentage content of a precious metal within the specimen, to ascertain through comparison with a look-up table comparing various rates of change in current flow corresponding to percentage content of precious metal the percentage of precious metal content within the specimen being tested. 
     It is still a further object of this invention to provide4 a method of testing a specimen containing a percentage content of precious metal involving an evaluation of the rate of change in the flow of electrical current through the specimen where a resistive layer is growing as a result of an application of a corrosive electrolyte on the specimen and where the growth of the resistive layer is proportionate to the percentage content of the precious metal within the specimen. 
     It is a further feature of this invention that the method of testing by analyzing the rate of change of electrical current flowing through a specimen having a resistive layer growing thereon is particularly adapted for use in testing silver content in a specimen containing a percentage content of silver. 
     These and other objects, features and advantages can be accomplished according to the instant invention by providing a precious metal testing apparatus that determines the percentage content of precious metal in a specimen being tested by determining the change in the rate of current flow through a resistive layer formed on the specimen being tested by the application of a corrosive electrolyte on the specimen. The electrical circuit forms a fixed resistance circuit and a variable resistance circuit due to the formation of a growing resistive layer on the specimen such that the flow of current through the variable resistance circuit decreases as the flow of current through the fixed resistance circuit increase. The detection of the rate of change in current flow as a result of the increasing growth of the resistive layer can be compared to a look-up table that provides a corresponding percentage of precious metal in the specimen. Calibration of the testing apparatus can be accomplished with a specimen of known purity of the precious metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a schematic diagram of a testing apparatus incorporating the principles of the instant invention and including a pen probe electrically coupled to a meter to test the concentration of silver within the specimen being tested; 
         FIG. 2  is a vertical cross-sectional view of a pen probe forming a part of the testing apparatus incorporating the principles of the instant invention; 
         FIG. 3  is a schematic view of the electronic circuit forming the apparatus measuring the purity of silver in a test specimen; 
         FIG. 4  is a schematic view of the electronic circuit depicted in  FIG. 3  but modified to show the operative principle of the instant invention; 
         FIG. 4A  is a schematic representation of the variable resistance network depicted in  FIG. 4 ; and 
         FIG. 5  is a photograph of a prototype of the testing apparatus in operation testing the concentration of silver content in a test specimen on the pan of the test apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1-3 , a testing apparatus for analyzing the concentration or purity of silver within a specimen being tested can best be seen. This testing apparatus  10  incorporates the principles of the instant invention. 
     In general, the testing apparatus  10  is used to analyze the concentration of silver, but is believed to be operable in conjunction with testing the content of gold or possibly other precious metals, such as platinum, and is based on measuring the rate of change of current or voltage shift through the test specimen as a resistive layer is established between the probe and the specimen being tested. 
     An exemplary embodiment of the pen probe  11  forming part of the testing apparatus  10  is shown in  FIG. 2 , which is a cross-sectional view of the exemplary hand-held pen probe  11 . The pen probe  11  is preferably formed with a generally cylindrical body  12 , which can be made of plastic or other substantially electrically non-conductive material. A top cap  13  is coupled to an electrical wire  14  fitted with a jack  15  to facilitate a detachable electrical connection of the pen probe  11  to the circuitry  30  within the meter  20 . The end of pen probe  11 , which is placed into contact with the specimen to be tested, is formed as a fiber tip  16  that is in communication with a reservoir  17  containing a supply of electrolyte, such as a saturated solution of ammonium chloride, or other solutions that will be operable to form a resistive layer on the specimen being tested. 
     The fiber tip  16  is preferably provided with a thin platinum wire  18 , which is preferably embedded into the fiber tip  16  and extends into the reservoir  17 . A second thin platinum connecting wire  19  couples the platinum wire  18  to the wire  14  at the top cap  13  of the pen probe  11 . The wires  18 ,  19  provide for the passage of electrical current into the electrolyte which is absorbed into the fiber tip  16  and is deposited onto the specimen being tested. The testing apparatus  10  further includes a meter  20  including a housing  21  in which is mounted a printed circuit board  22  including a port  23  to which the jack  15  can be detachably connected. Also electrically connected to the circuitry  22  is a test pad  25  that is preferably formed as a copper pour having a surface coating of gold. 
     The meter  20  is also constructed with a light-emitting diode (LED) indicator bar  24  that reflects the results of the testing of the sample, as will be discussed in greater detail below. In addition, the housing  21  supports a calibration switch  26  that is operable to initiate the calibration procedure, as will also be described in greater detail below. The housing  21  can also support other LEDs that reflect the status of the operation of the testing apparatus  10 , such as a ready light  27 , a power-on light, a battery status light, etc. The meter  20  can also have a three position on/off switch  29  that is movable to an off position, an external power position, and a battery power position. The housing  21  also supports a port  28  for connection to a source of external power, such as 110 VAC electrical current through the use of an adapter (not shown). 
     The electronic circuitry  30  is reflected in the schematic diagram of  FIG. 3 . Either a battery (not shown) or a source of external electrical power connected through the port  28  provides an electrical current I net  into the circuitry  30 . The current I net  reaches the node  32  and is divided into a first current flow I pan  and a second current flow I sense . With the silver specimen S placed on the test pan  25  and the probe  11  touching the silver specimen S a circuit is completed for the passage of I pan  and I sense  to ground  33 . Because the initial resistance of the silver specimen S is minimal, the current I pan  is substantially greater than the current I sense  which must pass through the diode D 1 , diode D 2  and the resister R 25  to reach ground  33 . 
     As the probe  11  touches the silver specimen S, the electrolyte in the probe  11  deposits on the silver specimen S and starts corroding the adjacent surface of the silver specimen S by forming silver oxide between the fiber tip  16  and the silver specimen S. The layer of silver oxide is a resistive layer that impedes the flow of electrical current. Thus, as the layer of silver oxide increases, the current I pan  decreases and, due to Kirchhoff&#39;s law, the current I sense  increases. The principle is demonstrated in  FIGS. 4 and 4A . Essentially, the pan  25 , silver specimen S and probe  11  form a variable resistance R 1  due to the growing layer of silver oxide between the probe  11  and the silver specimen S. The portion of the circuitry  30  between the node  2  and the ground  33 , which includes the diode D 1 , the resister R 25  and the diode D 2 , is a fixed value resistance. As the variable resistance R 1  increases with the building of the silver oxide layer, the current I pan  decreases, resulting in the current I sense  increasing. 
     A prototype of the testing apparatus  10  is depicted in  FIG. 5  where the fiber tip  16  of the probe  11  is in contact with the silver specimen S, seated on the pan  25 . The LED indicator bar  24  is divided into four sets of LEDs, although in the commercial embodiment all four sets of lights will not likely be required. In the first set  36  of LEDs, the lights cycle as the tests, as described in greater detail below are conducted. The first set  36  of LEDs provide an indication that the testing is being conducted. The second set  37  of LEDs provides an indication of the charge remaining in the pen probe  11  with the second set  37  of LEDs providing a visual indication of the status of the pen probe  11  as far as conducting a subsequent test. Associated with the second set  37  of lights is the ready light  27  that provides a reinforcement of the status of the pen probe  11  to conduct another test. 
     The third set  38  of LEDs is the concentration indicator with each respective LED indicating a different concentration or purity of silver in the silver specimen S. For example, the LED at one end could indicate 99.99% silver content, the next LED 95% silver content, the next LED 92.5% silver content (which is sterling silver), the next LED 90% and the last LED perhaps less than 80% silver. Between the second set  37  and the third set  38  of LEDs, a red LED could be used to provide an indication that no silver content was found during the test. The fourth set  39  of LEDs could be used to provide a count down of tests before a new calibration of the apparatus  10  is required. 
     Referring again to  FIG. 1 , the ADC 1  and ADC 2  sensors provide a reading of the current I sense  on opposite sides of the resister R 25 . The test procedure operates to take a predetermined number of readings by the sensors ADC 1  and ADC 2  which are sent to the microprocessor  40  which calculates the rate of increase in the current I sense . The average rate of increase over the predetermined number of readings being taken is then compared to a calibration sample to derive the silver content within the specimen S being tested. The basic principle in making this derivation is that the higher the silver content in the silver specimen S, the faster the silver oxide layer grows from the deposit of electrolyte from the pen probe  11 . Therefore, the faster the rate of increase in the I sense  current, the greater the percentage of silver in the specimen S. Preferably, the apparatus  10  will take eight readings of the current I sense  before the testing of the specimen S is completed. 
     Presently, calibration of the apparatus  10  is desired after every four or five tests of specimens S. Calibration is conducted by utilizing a known silver content test specimen S, such as a 92.5% sterling silver specimen. The calibration button  26  is pressed to begin the calibration sequence so that the apparatus  10  knows to save the test results in the microprocessor  40  for comparison with the subsequent tests of the unknown silver specimens S. Thus, the count down set  39  of LEDs provides a visual indication as to how many unknown test specimens can be tested before a re-calibration of the apparatus  10  is needed. Built into the microprocessor  40  can be a block on further testing of unknown specimens S once the count down has diminished to zero, unless a calibration sequence is conducted. 
     Once a test of a silver specimen S has been conducted, the pen probe  11  has to be discharged of residual current, i.e. cooled down, before another test can be conducted. Presently, that cool down period is approximately 6-8 seconds, which can be programmed also into the microprocessor  40  to prevent any testing unless the cool down period has expired and the ready light  27  is illuminated. Thus, the power supply to the pen probe  11  is preferably modulated between on and off by the microprocessor  40  with the power being turned off for the cool down period. 
     In operation, the apparatus  10  is powered on through either an internal battery (not shown) or by a connection to a AC power source to provide, preferably, a 3.3 volt connection at the power input point  28 . First, the apparatus  10  must be calibrated by depressing the calibration button  26  and placing a known silver content specimen S, such as a sterling silver (92.5% silver content) specimen, on the pan  25 . The fiber tip  16  of the pen probe  11  is then pressed against the known specimen S to deposit electrolyte on the specimen S while the current I pan  is passed through the pan  25 , silver specimen S and pen probe  11 . The apparatus  10  takes preferably eight readings of the current I sense  to determine a rate of change of the current I sense , which is proportional to the rate of growth of the silver oxide layer forming on the known silver specimen S due to the chemical reaction with the electrolyte. Once the eight readings have been completed, the microprocessor  40  stores the average rate of change in current I sense  as the calibration sample for future comparisons. 
     Once calibrated, the pen probe  11  is passed through a cool down period by the microprocessor  40  turning the power off, before the apparatus  10  is ready to conduct a test of an unknown specimen S. When the ready light  27  is illuminated, the unknown silver content specimen S is placed onto the pan  25  and the fiber tip of the pen probe  11  is placed against the specimen S to deposit electrolyte thereon. As with the calibration procedure, the apparatus  10  takes eight readings of the I sense  current and calculates an average rate of increase in the current I sense  over the eight readings. Because the rate of growth of the silver oxide layer is proportional to the concentration of silver in the unknown test specimen S, the rate of increase in the current I sense  will be reflective of the purity of the silver specimen. The rate of increase in the current I sense  is then compared to the calibration reading stored in the microprocessor  40  and the purity of the silver is derived. 
     After the test of the unknown silver content specimen S has been completed, the microprocessor  40  again shuts off the power to the pen probe  11  so that the accumulated charge therein can be dissipated and the pen probe  11  cooled down. After the requisite cool down period, the microprocessor  40  illuminates the ready light  27  and another test of an unknown silver content specimen S can be conducted as described above. For each test of an unknown silver content specimen S, the count down LED set  39  is manipulated until ultimately reaching zero, whereupon a new calibration of the apparatus  10  is to be conducted, as described above, to enable another series of testing of unknown silver content specimens. 
     One skilled in the art will recognize that this principle of comparing the rate of increase, as opposed to simply measuring a voltage generated, of the growth of a resistive layer being formed on a test specimen can be extended to any precious metal specimen that can grow a resistive layer. Thus, while the preferred embodiment of the instant invention is described above with respect to testing for the purity of silver in an unknown silver content specimen, the same principle can be used to test for other precious metals, including gold. 
     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.