Patent Application
20080264802
The present invention relates generally to a testing method for assaying precious metals.
There are various quantitative techniques to assay precious metals, in particular gold, including spectrometric, calorimetric and gravimetric techniques. One of the more commonly used technologies to assay gold is based on electro-chemistry. Unlike the other techniques which are generally too complex, expensive or bulky to be used by most jewelers, the electro-chemical technique provides an easy and relatively inexpensive solution to assay gold.
For example, in the teaching of Medvinsky et al. of U.S. Pat. No. 4,799,999, an electrochemical process is used whereby a specimen is wetted by a described electrolyte and a small current anodizes the surface of the specimen. An external electronic measuring instrument is then applied to the charged surface, and potential difference decay is observed, tracked and analysed by the external measuring instrument. This process, while capable of reporting accurate results, is limited to the lower end of the karatage scale, for example, at a range between 6 and 14-karat. The technique does not respond significantly to gold alloy of higher karatage, for example, between 14 and 24 karat.
In another teaching of Medvinsky of U.S. Pat. No. 5,218,303, an electro-chemistry method which involves driving a series of low electric current pulses through a specimen which is wetted by an electrolyte to form an electrolytic paste is disclosed. The method involves measuring the instantaneous conductance of the electrolytic paste and comparing and interpolating the measured conductance against an empirical table of conductance standards. Although this method is said to be capable of measuring gold alloy at higher purity of between 14 and 24 karat, this technique may not be sufficiently reliable to provide accurate measurement of gold in the low and mid range scale.
The accuracy of the various gold assay methods in the market is limited to measurement at either a low end or a high end of the karatage scale. While a gold assaying method may be used to measure gold of high purity, the same method may lose its sensitivity when applied to measure gold of low purity. The reverse is also true whereby a method for measuring low purity gold may not be suitable to measure gold of high purity.
It is therefore desirable to provide an electro-chemical method for fast and accurate assaying of gold that preferably covers the broad spectrum of the karatage scale.
In accordance with one aspect of the present invention, there is provided a method for assaying precious metals comprising the steps of:
The assay value may be karatage or some other value relating to the purity or the amount of precious metal in a specimen.
The assay value may be based on locality of an input current response of the specimen. The assay value may be found by comparing or interpolating the locality of the input current response against the localities of a list of current responses of known precious metal compositions, which may be stored in a look-up table.
Alternatively, the assay value may be based on a slope or peak value of an input current response of the specimen. The assay value may be found by comparing or interpolating the results of the assay, for example, a maximum slope and peak of the input current response against the maximum slopes and peaks of a list of current responses in a look-up table, the look-up table being determined based on empirical data for specimens of known karatage or the like.
Alternatively, the assay value may be based on an integration of the resulting current, and may be based on the electrical charge that flows through the cell during the ramp input. Preferably, the integration is over the whole of the ramp input period, although other periods during the ramp input may also be used. Other cell current characteristics, e.g. current values at certain times in the ramp input, may also be used to determine assay values.
In an alternative embodiment of the invention, the assay value may be found by comparing the results of the assay, e.g. total electrical charge flow, with values in a look-up table, the look-up table being determined based on empirical results for specimens of known karatage or the like. The assay value may be determined by interpolating the look-up table values, where necessary. Alternatively, the assay results could be input into an assay value formula that relates total electrical charge or the like to assay values and that is determined from empirical findings.
Preferably, the precious metals assay method comprises the step of driving a ramp input through the anode specimen to initiate an electrolytic reaction.
Preferably, the precious metals assay method comprises the step of driving a ramp input for a duration of between about 6 to about 8 seconds.
Preferably, the precious metals assay method includes a ramp input duration which is about 7 seconds.
Preferably, the precious metals assay method includes a ramp input which comprises a voltage in a triangular-shaped waveform.
Preferably, the precious metals assay method includes a ramp input having a peak which is in a range of between about 4.5V to about 5.0V.
Preferably, the precious metals assay method includes a ramp input having a peak of about 4.8V.
In one embodiment, the ramp input may ramp up and then ramp down. The period of the ramp down may be equal to that of the ramp up period.
The ramp input may begin from a voltage corresponding to a steady state open circuit voltage measured across the electrolytic cell.
In accordance with a further aspect of the present invention, there is provided precious metal assaying apparatus comprising:
an anode and cathode for forming an electrolytic cell with a specimen that is to be assayed; and
electronic testing circuitry associated with the anode and cathode for determining an electrical characteristic of the cell;
wherein the circuitry comprises a driver for applying a ramp voltage to the cell, and a monitoring circuit for measuring the resulting current flowing through the cell during the application of the ramp voltage.
a shows a superimposed graph comprising regions for gold alloys of different karatages;
b to 4h show graphs depicting locality of different regions for gold alloys of different known karatages;
a shows a superimposed graph comprising current responses for gold alloys of various karatages over a ramp input;
b to 5g show graphs comprising individual current response for each gold alloy of different known karatage over a ramp input;
a shows a superimposed graph comprising current responses for gold alloys of various known karatages over the period of a ramp input;
b to 6g show graphs comprising individual current response for each gold alloy of different known karatage over the period of a ramp input;
The testing device 100 as shown in
The anode probe 103 may be coupled to a first surface of a specimen 106, e.g. a ring, to form an anode specimen. Coupling may, for example, be through a spring clip 108 of a specimen holder 101 or, alternatively, through a crocodile clip cable.
A controlled quantity of electrolytic gel 114 may be discharged onto a second surface of the specimen 106 through a nozzle 126 by rotating a knob 122 that actuates an actuator, such as for example a plunger of a gel dispenser, to dispense the electrolytic gel. The electrolytic gel is typically a mixture of acidic and salt solution, for example, 1.25% acid with 0.05% chloride salt. Preferably, hydrochloride acid is used although other types of acid such as sulfuric acid may also be used. The solution is further mixed with soft gel.
The cathode probe 112 should generally be positioned adjacent the nozzle 126, and configured so that in use, the cathode probe is able to make electrical contact with specimen 106 via electrolytic gel 114 dispensed from the nozzle 126.
The discharged electrolytic gel 114 creates a wet junction that physically and electrically links the second surface of the anode specimen to the cathode probe 112. The specimen 106, anode probe 103, electrolytic gel 114 and the cathode probe 112, when electrically interconnected, form an electrolytic cell 201 whose electrical characteristics may be analysed to assay the specimen 106.
The testing device 100 may take the form that for example is described in co-pending Singapore patent application no. 200507368-9, entitled “A Testing Device for Precious Metals” which is filed on 11 Nov. 2005, the contents of which are incorporated herein by reference in their entirety.
The circuit board 118 may be powered by either a DC inlet 202 or a 9-V battery 204 as shown in
The circuitry of the circuit board 118 may comprise for example, a microprocessor 250, a memory chip 265, a differential amplifier 240 and a voltage driver 215. Preferably, the circuitry is constructed of microchips or other small circuit components so that it may be easily integrated within the small and compact housing 110 that may be easily carried in one's hand.
The driver 215 is used to provide a controlled ramp input signal to the electrolytic cell 201. The driver 215 may comprise, for example, an IC based voltage generator. Alternatively, discrete components may be used to construct the driver 215. The driver 215 may be controlled by a plurality of input lines 222, 223 and 224, which are connected to driver 215 from the microprocessor 250.
For example, input lines 222 and 223 may carry command signals to selectively enable or disable the driver 215 and its output lines 220 and 227. Input line 224 may carry data information to control the generation of the ramp input signal. Typically, the data information from line 224 is an analog signal which is converted from the digital serial output of the microprocessor 250 through a D/A converter 226.
The first output line 220 of the driver 215 is connected to a relay L22. The relay L22 may be configured to selectively switch between connecting the electrolytic cell 201 to a line 230 of the microprocessor 250 through a normally closed switch 218. Alternatively, the relay L22 may switch the connection of the electrolytic cell 201 to the second output line 227 of the driver 215 through a normally open switch 212.
When the relay L22 is activated by the driver 215, through for example setting line 220 to high by controlling the command lines 222 and 223, the normally open switch 212 is closed. This connects the output 227 of the driver 215 to the electrolytic cell 201. The activation of relay L22 also simultaneously disconnects the normally closed switch 218 and thereby decouples the electrolytic cell 201 from its connection to line 230 of the microprocessor 250. When connected to the electrolytic cell 201, the microprocessor 250 may instruct the driver 215 to generate and provide a controlled ramp input signal to the cell through the output line 227.
When the relay L22 is deactivated by the driver 215 through for example setting line 220 to low by controlling the command lines 222 and 223, the normally open switch 212 is disconnected, thereby disconnecting the output 227 of the driver 215 from the electrolytic cell 201. The deactivation of relay L22 also restores the switch 218 to its normally closed position, thereby connecting the electrolytic cell 201 to line 230 of the microprocessor 250.
A current measuring resistor R10 is connected in series to the electrolytic cell 201 and current passing through the resistor R10 is amplified by the differential amplifier 240. A first end of the resistor R10 may be inputted to an inverting terminal of the differential amplifier 240 while a second end of the resistor R10 may be inputted to a non-inverting terminal of the differential amplifier 240. The output 243 of the differential amplifier 240 may be connected to a first A/D converter ADC1 of the microprocessor 250.
When a new measurement cycle is initiated by, for example, pushing a reset switch 203, the microprocessor 250 may begin the cycle by disabling the relay L22 and thereby connecting the electrolytic cell 201 to the microprocessor 250.
The microprocessor 250 will detect an initial steady state open circuit voltage Vinit across the electrolytic cell 201 through line 230. The line 230 connects the anode probe 103 of the electrolytic cell 201 to an A/D converter ADC2 of the microprocessor 250. Depending on the design of the electrical circuitry, the cathode probe 112 may be connected to a reference voltage or to an analog ground.
If the cathode probe 112 is connected to a reference voltage, the open circuit voltage of the electrolytic cell 201 may be determined by, for example, offsetting the measured voltage of the anode probe 103 from the reference voltage. If the cathode probe 112 is connected to an analog ground, the voltage of the anode probe 103 is read directly as the open circuit voltage of the electrolytic cell 201.
Upon detecting a steady state open circuit voltage Vinit as shown in
The ramp input signal which is preferably a triangular-shaped waveform voltage is generated by the driver 215 from an initial value of Vinit and ramps-up to reach a peak voltage Vpeak within a ramping period of T2 seconds. A ramp input of other shapes, such as for example a curve may also be used. The peak voltage Vpeak may vary and is limited by the equation Vpeak=Vref+2.2V. Preferably, Vpeak ranges between 4.5V to about 5.0V. In this embodiment, the peak voltage Vpeak is set around 4.8V.
The voltage causes an electrolytic reaction within the electrolytic cell 201, which may be an oxidation or reduction of alloyed metals of the specimen 106. The reaction releases free ions into the electrolytic gel 114 which results in increased conductivity of the electrolytic gel. These free ions are released by impurities from gold alloy of specimen 106. Gold is slightly oxidized due to its stability in the reactivity series. However, the main contributor of the free ions is from the impurities of the gold alloy. A higher amount of gold in the alloy specimen 106 would result in lower conductivity through the electrolytic gel.
The duration of ramp input T2 may vary but is preferred to be between about 5 to about 8 seconds and even more preferably, at about 7 seconds. The short exposure time of the specimen 106 to the acidic electrolyte advantageously ensures that no destruction or damage is caused to the specimen during measurement.
At the end of T2, the ramp input signal is cut-off. The microprocessor 250 may then issue a command to deactivate the relay L22 and to restore the connection of the electrolytic cell 201 from the driver 215 to line 230 of the microprocessor 250.
During the ramping period T2, a resulting current passing through the resistor R10 is amplified by the differential amplifier 240. The magnitude of the resulting current is dependent on the level of free ions discharged by the non-gold alloy metals in the specimen 106 during the ramp input T2. The analog resulting current from the differential amplifier 240 are inputted into the ADC1 of the microprocessor 250 and is converted into digital values.
The digitized resulting current samples are used by the microprocessor 250 to determine an assay value for the specimen 106.
In one embodiment of the invention, the current samples are processed by the microprocessor 250 to map out a current response for the test specimen 106 over the voltage ramp input.
The locality of the current response is compared to a list of regions stored in a look-up table. Each region in the look-up table is assigned a corresponding value, which may for example, reflects the purity of a precious metal such as gold. As shown in
The locality information related to each region and a corresponding karatage value may be arranged in an empirical look-up table and may be stored in the memory chip 265 which may be downloaded into the microprocessor 250 during power-up.
The purity of the specimen 106 may be determined by, for example, comparing the locality of the current response formed by the current samples of the measured specimen 106 against the localities of the list of regions provided in the look-up table. If the current samples of the current response are concentrated within one of the listed regions, a match is found and the corresponding value of the matched region is read out. The assay value may then be transmitted to an electronic display 270, such as for example, a LCD for read out.
Alternatively, the assay value of the specimen 106 may also be determined by interpolating the location of the current response situated between two listed regions in the look-up table to obtain a corresponding assay value if a match is not found. For example, an assay value of the specimen 106 which is located between the region of 9K and 12K may be determined through interpolation.
The look-up table may be created by collating the current samples of various specimens of known purity over the voltage ramp input. The region of a known specimen may be mapped out by taking the area between the upper and lower bands of the current response of the known specimen. The region may then be adjusted further to fine tune the accuracy of the mapping through experimentation. The karatage value of the known specimen is assigned to this region. This process is repeated in the same manner for different specimens of known compositions to form the look-up table.
In another alternative embodiment of the invention, other input characteristics of the current response from the test specimen 106 over the voltage ramp input are determined by the microprocessor 250. These input characteristics may include, for example, the slope (preferably a maximum slope) and peak (preferably a maximum turning point) of the current response. These input characteristics are compared to a set of recorded characteristics for known alloy compositions in an empirical look-up table, as shown for example in Table 1, which may be stored in the memory chip 265.
The look-up table may be created by collating the characteristics of current responses of various specimens of known purity over the voltage ramp input as shown for example by the graphs in
The microprocessor may also perform an interpolation between two nearest available values in the look-up table if an exact measured input characteristic is not found in the table.
In yet another alternative embodiment of the invention, the current samples are used by the microprocessor to work out an area beneath a current curve over the period T2 of the ramp input.
The calculated area represents the total electrical charges of the resulting current during the period T2 of the ramp input signal. The calculated area is compared to a set of electrical charges for known alloy compositions in an empirical look-up table, as shown for example in Table 2, which may be stored in the memory chip 265.
The look-up table may be created by collating the data of electrical charges of different samples of known purity for the duration of the ramp input, as shown for example in
The microprocessor 250 may compare the electrical charge of a measured specimen against the look-up table to find a corresponding value which may, for example, reflect the purity of gold in the specimen 106. The microprocessor may also perform an interpolation between two nearest available values in the look-up table if an exact measured input value is not found in the range listed in the table. The corresponding value or the interpolated value may then be transmitted to an electronic display 270, such as for example a LCD for read out.
In another alternative embodiment of the invention, the ramp input may be ramped down from Vpeak to Vinit over a period of T3 as shown in
Some electrical connections which are known in the prior art have been omitted in these drawings for clarity.
While the invention has been particularly shown and described with reference to various embodiments, it will be recognized by those skilled in the art that modifications and changes may be made to the present invention without departing from the spirit and scope thereof. The scope of the invention should therefore be determined not with reference to the above description but with reference to the appended claims along with their full scope of equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200508244-1 | Dec 2005 | SG | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SG06/00397 | 12/20/2006 | WO | 00 | 8/16/2007 |
