AU2010203289B2 - An Egg Sensor - Google Patents

Abstract

An egg testing arrangement includes a variable frequency multivibrator 16.130 to the input of which electrodes 16.032, 16.034 attached to an egg are connected. The electrodes and the egg act as a capacitor, and the frequency of the multivibrator varies with the capacitance of the egg. A second multivibrator 16.134 with a fixed frequency can be used in conjunction with a digital bridge 16.132, 16.136, 16.138 to improve the sensitivity of the tester by determining thee difference between the frequencies of the first and second multivibrators. . FIGURE 6 FIGURE 7 6.018 6.020 6.014 7.003 8.042 8.040 8.0348.0 8.002 8.074 8.006

Description

10059 An Egg Sensor Field of the invention [001] This invention relates to method and device for analysing eggs. [002] The invention is particularly suited for providing an estimate of the age or condition of an egg. Background of the invention [003] Eggs have an air pocket, usually at the "big end", separated from the white by a membrane, and as the egg ages, the amount of water in the egg decreases through evaporation through the membrane and the shell which is porous. An equivalent volume of air is drawn in through the shell at the air pocket end. Thus, as the egg ages, it will reach a stage where it will float in water. This has been used as a rough indicator that the egg has passed its "use by date". The floatation test will depend on a number of factors such as the temperature of the egg and the water. The floatation test is a guide rather than an exact determinant of the condition of the egg. [004] A traditional method of analysing eggs is candling, in which a light is shone through the egg to provide a visual indication of the relative size of the air pocket in the egg and of the condition of the egg. [005] W007137786 describes a device for measuring the volume of water in a container by measuring the relative capacitance between a pair of electrodes in the container by applying a time varying signal to the electrodes, measuring a variable characteristic of capacitance, and computing the capacitance. Capacitance is proportional to the dielectric constant of the material between the plates or electrodes. Water has a dielectric constant substantially greater than that of air. [006] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. Summary of the invention [007] The present invention provides a method of testing eggs including using the capacitance of an uncracked egg under test to control the frequency of a multivibrator, measuring the frequency of the multivibrator and calculating the capacitance of the egg from the measured frequency. 1 10059 [008] The measured capacitance can be compared with a predetermined value or a range of predetermined values. [009] The present invention also provides an egg testing arrangement for an uncracked egg, having a variable frequency multivibrator whose frequency is responsive to a capacitance connected to its input, the capacitance including the capacitance of an egg under test. [010] The egg testing arrangement can include a second multivibrator having a fixed frequency, and a digital bridge connected to the outputs of the first and second multivibrators to determine the difference between the frequencies of the first and second multivibrators. [011] The egg testing arrangement can include an egg retaining device having a first electrode and a second electrode, the first and second electrodes being mounted on the retaining device so as to be proximate to or in contact with an egg when the egg is placed in the egg retaining device. [012] The retaining device can be made of a resilient material. [013] The first and second electrodes can be made of a conductive resilient material. [014] The conductive resilient material can be an electrically conductive rubber. [015] The electrically conductive rubber can be a silicone rubber. [016] The egg testing arrangement can include a source of alternating voltage, and capacitance measuring equipment. [017] The egg retaining device can be a cup shaped vessel. [018] The egg testing arrangement can include signal processing means to evaluate the capacitance measurements. [019] The egg testing arrangement can include a third electrode to measure electrical interference. [020] The signal processing means can be programmed to compensate for interference using signals from the third electrode. [021] The egg testing arrangement can include a memory storing a predetermined value or range of predetermined values of impedance. [022] The processing means can be programmed to evaluate the measured value against a predetermined value or range of predetermined values. 2 10059 [023] The present invention further provides an egg testing cup including a recess adapted to conform to the base of an egg, a sense electrode conforming to the base of the recess, a ground electrode located to be above the air pocket of an egg inserted in the cup, and a reference electrode adapted to be proximate the egg white of an egg under test [024] This invention utilizes the facts that the contents of an egg have a large proportion of water and that water has a dielectric constant substantially greater than that of air, as well as the fact that egg shells porous and the egg lining membranes are permeable. [025] According to an embodiment of the invention, there is provided a method of testing eggs including applying an electrical signal to the egg and measuring an electrical parameter including an electrical characteristic of the egg, and measuring a second electrical parameter, and processing the first and second measurements to obtain a measurement of the electrical characteristic of the egg. [026] The second electrical parameter can include a background electric characteristic. [027] The step of processing can include one or more of analysing; evaluating; comparing; subtracting. [028] According to an alternative embodiment of the invention, there is provided a method of testing eggs including using the capacitance of an egg under test to control the frequency of a multivibrator, measuring the frequency of the multivibrator and calculating the capacitance of the egg from the measured frequency. [029] The invention also contemplates embodiments of egg testing devices with various electrode configurations for applying an electrical signal to an egg. [030] The electrical property can be impedance. [031] The electrical property can include resistance. [032] The electrical property can be capacitance. [033] Alternatively, the capacitance can be compared with a reference capacitance or a range of reference capacitances. [034] Preferably, an alternating voltage is applied to the egg via a pair of electrodes. [035] The capacitance can be measures as a proportion of a reference value. [036] The capacitance can be measured using a balance bridge. [037] The capacitance can be measured using a digital balance bridge. 3 10059 [038] The measured capacitance can be compared with a predetermined value or a range of predetermined values. [039] The invention also provides an egg sensor adapted to implement the method. [040] The sensor can include an egg retaining device having a first electrode and a second electrode, the first and second electrodes being mounted on the retaining device so as to be proximate to or in contact with an egg when the egg is placed in the egg retaining device. [041] The retaining device can be made of a resilient material. (eg, WACKER

ELASTOSIL

T M 3003/70A/B). [042] The first and second electrodes can be made of a conductive resilient material. [043] The conductive resilient material can be an electrically conductive rubber. [044] The electrically conductive rubber can be a silicone rubber (eg, WACKER

ELASTOSL

T M LR 3162 A/B). [045] The sensor can include a source of alternating voltage, and capacitance measuring equipment. [046] The capacitance measuring equipment can include a balance bridge. [047] The balance bridge can be a digital balance bridge. [048] The egg retaining device can be a cup shaped vessel. [049] The egg retaining device can be a "C" shaped device. [050] The "C" shaped device can have a tapering cross section to accommodate different sized eggs. [051] The sensor can include signal processing means to evaluate the capacitance measurements. [052] The sensor can include a third electrode to measure electrical interference. [053] The signal processing means can compensate for interference using signals from the third electrode. [054] The processing means can include a memory including a predetermined value or range of predetermined values of impedance. [055] The processing means can evaluate the measured value against a predetermined value or range of predetermined values. 4 10059 [056] The frequency can be in the range of 10 khz to 500 khz. [057] The frequency can be in the range of 50 khz to 200 khz. [058] The frequency can be of the order of 16kHz. [059] The invention also provides method of compiling data from egg tests, and correlating the data with condition information relating to the eggs. [060] The data can be derived from the above method. [061] The condition information can be derived from candling. [062] The data can be compiled from a combination of candling and impedance measurement. [063] The data and condition information can be tabulated. [064] The tabulated data can be used for comparison with actual test results. [065] An embodiment of the invention includes an egg testing arrangement having a variable frequency multivibrator whose frequency is responsive to a capacitance connected to its input, the capacitance including the capacitance of an egg under test. [066] The arrangement can include a second multivibrator having a fixed frequency and a digital bridge connected to the outputs of the first and second multivibrators to determine the difference between the frequencies of the first and second multivibrators. Brief description of the drawings [067] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [068] Figures 1 & 2 schematically represent the growth of the air pocket in an egg with age ; [069] Figures 3 & 4 illustrate schematically the placement of electrodes adapted to measure electrical characteristics of an egg according to an embodiment of the invention; [070] Figure 5 schematically illustrates electrodes adapted to accommodate different sized eggs according to an embodiment of the invention; [071] Figure 6 & 7 schematically illustrate an egg retaining device having electrodes as shown in Figure 5. [072] Figure 8A schematically illustrates a cup shaped egg retaining device with peripheral electrodes according to an embodiment of the invention. 5 10059 [073] Figure 8B schematically represents a section view of the test cup of Figure 8A with an egg inserted in the cup. [074] Figure 9 is a schematic illustration of an egg retaining device using the principles of the device shown in Figure 8. [075] Figure 10 is a schematic illustration of the underside of the device of Figure 9. [076] Figure 11 is a schematic illustration of an egg testing apparatus according to an embodiment of the invention. [077] Figures 12 & 13 illustrate an alternative electrode configuration according to an embodiment of the invention. [078] Figure 14 illustrates a measurement circuit according to an embodiment of the invention. In this arrangement, the measured capacitor is used to modulate the frequency of a multivibrator. [079] Figure 15 is a time diagram illustrating the operation of the arrangement of Figure 14. [080] Figure 16 is a block diagram illustrating a digital bridge used in an embodiment of the invention. [081] Figure 17 is a block schematic of a microcontroller arrangement according to an embodiment of the invention. [082] Figure 18 is a timing diagram illustrating the operation of the arrangement of Figure 16. [083] Figure 19 illustrates a further embodiment of the cup. [084] Figure 20 illustrates an alternative embodiment of the cup. [085] Figure 21 illustrates a progressive inversion of the cup of Figure 20. [086] The numbering convention used in the drawings is that the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements. [087] It is understood that, unless indicated otherwise, the drawings are intended to be illustrative rather than exact representations, and are not necessarily drawn to scale. The orientation of the drawings is chosen to illustrate the features of the objects shown, and does not necessarily represent the orientation of the objects in use. 6 10059 Detailed description of the embodiment or embodiments [088] The invention will be described with reference to an egg sensing device and a method of sensing an impedance characteristic of an egg as shown in the embodiments shown in the drawings. [089] The invention contemplates embodiments in which the configuration and location of the test electrodes differs. [090] In one embodiment, there are two test electrodes and both are located so as to always be adjacent the filled portion of the egg. [091] In another embodiment, there are two electrodes, and one is located to be always adjacent to the filled part of the egg, and the other is located to be adjacent the filled part of a new egg, and to be adjacent the air pocket in an older egg. [092] In a third embodiment, there are two electrodes, one being adjacent the filled part and the other always adjacent the air pocket. [093] In a further embodiment, there are more than two test electrodes, one always adjacent the filled part of the egg, another always adjacent the air pocket, and the or each additional electrode located at intermediate points relative to the air pocket as it grows with age. On the basis of the foregoing, various other configurations of electrode location can readily be envisaged by the person skilled in the technology without departing from the inventive concept. [094] In a still further embodiment, the third electrode can act as an emi (electromagnetic interference) detection electrode. [095] Figure 1 shows an egg 1.002 having a shell 1.010, the white 1.004, a membrane 1.008 containing the white, and an air or gas pocket 1.006. A line 1.012 indicates the base of the air pocket. In Figure 2, the air pocket 2.006 has expanded as indicated by the line 2.012 due to the loss of water from the egg liquid 2.004. [096] Figures 3 & 4 schematically illustrate an arrangement of electrodes relative to an egg according top a first embodiment of the invention. The egg is orientated with the small end at the bottom. The small end is in contact with a first electrode 3.014. A second electrode 3.016 is located near the top of the egg, ie, near the large end in a position where, while the egg is still usable, the liquid will still be close to or above the level of the contact. The electrodes 3.014 and 3.016 are arranged so, ignoring the shell and membrane, a measurement of the capacitance will always have liquid between the electrodes 3.014 and 3.016. 7 10059 [097] However, in Figure 4, the air pocket has increased in size so that the electrode 3.016 is no longer adjacent the liquid. As the liquid level drops below the electrode 3.016, the measured capacitance value will change in relation to the value when the electrode 3.016 was adjacent the liquid. This can be equated to having an air filled capacitor in series with a liquid filled capacitor. [098] To improve the accuracy of the measurement, a third reference electrode 3.018 can also be provided. Electrode 3.018 is located to contact the egg shell at a point where the liquid in the egg will be present while the egg remains sound. This can provide a reference measurement for comparison with the value measured at electrode 3.016. [099] Figure 5 illustrates a modification of the arrangement of Figures 3 & 4 which is adapted to accommodate differently sized eggs. The spacing of the electrodes 5.014 and 5.016 can be tapered to accommodate eggs of different sizes. [0100] Figure 6 illustrates an egg holder adapted to retain eggs of different sizes as illustrated at 7.002 and 7.003 in Figure 7 while measurements such as those described with reference to Figures 3 & 4 are made. The holder 6.020 has a substantially "C" shaped section which tapers to accommodate eggs of different sizes. The holder 6.020 includes the electrodes 6.014, 6.016, and 6.018 which act in the same manner as those described with reference to Figures 3 & 4. [0101] The embodiment shown in Figure 8A & 8B differs from the foregoing embodiments and the prior art in a number of ways. One difference is that the cup of Figure 8 is adapted to receive the egg with the air pocket of the egg at the bottom of the cup. [0102] Figure 8A schematically illustrates the electrodes of an egg tester according to a further embodiment of the invention. The tester is in the form of a cup 8.030 having electrodes on its inner wall. An egg 8.002 is shown before insertion into the cup. The egg is inserted with the air pocket located at the base of the cup. In this arrangement, the weight of the egg produces a contact force with the electrodes. This helps to reduce the air gap between the egg shell and the electrodes and provides reliable contact between the egg shell and the electrodes on the inner wall of the cup. The cup can be dimensioned so that when a large egg is inserted, it will make contact with the sensing electrode and with the common electrode and the reference electrode. [0103] A lower electrode, the sensing electrode 8.032, is adapted to contact the end of an egg inserted into the cup. This electrode conforms to a lower portion of the cup. In use, the end of the egg with the air pocket is inserted into the cup, the egg having a substantially upright orientation when inserted in the cup. 8 10059 [0104] An intermediate second electrode, the common electrode 8.034, is located on the inside of the cup in a circular layout. The common electrode can be the ground electrode. The common electrode is in the shape of a horizontal arc and has a gap to permit a first connection lead 8.038 from the lower electrode 8.032 to be brought out to the rim of the cup for connection to the external test circuitry (not shown). A second connection lead 8.040 serves a similar purpose for the intermediate electrode 8.034. A third electrode, the reference electrode 8.036, likewise partially circumscribes the cup while providing a gap for the leads 8.038, 8.040. A third connection lead 8.042 connects the electrode 8.036 to the rim of the cup. In an alternative embodiment the connections to the electrodes can be brought out by way of through-holes in the wall of the cup. [0105] The sensing electrode 8.032, the ground electrode 8.034 and the reference 8.036 are located to be proximate to, or to contact an egg placed in the cup for testing. The sense electrode 8.032 is located so it is proximate the air pocket of the egg under test. The ground electrode 8.034 is located so it will normally be above the air pocket. The reference electrode 8.036 located so it is always adjacent to the liquid contents of the egg. Its function is described below. [0106] As shown in Figure 8B, the electric field 8.072 between the sense electrode 8.032 and the ground electrode 8.034 passes through the air pocket 8.006 and will normally also pass through some egg white. The electric field line 8.074 between the reference electrode 8.036 and the ground electrode 8.034 passes through the egg white, but not through the air pocket. [0107] The dielectric constant of water is many times greater than that of air. Thus proportional changes in the volume of water will have several times greater effect than proportional changes in the volume of air. [0108] Also, the preferred path of the electric field lines will, be through the path with the least impedance. Hence, for the reference electric field lines the greater proportion of the electric field will pass through the egg white. Similarly, because the sense electric field path includes a proportion of egg white, the preferred path will also be through the egg white and the air pocket. [0109] The air pocket 8.006 can be considered as the initial air pocket when the egg is first tested. After the lapse of a number of days, the air pocket will expand as indicated by the dashed line air pocket 8.007. As can be seen, the electric field line 8.072 now passes through a greater length of air than when the smaller initial air pocket 8.006 was present. This path can still contain a proportion of egg white, but this will be a smaller proportion than that of the initial test. Hence, with the air pocket 8.007, there will be a change in capacitance 9 10059 between the sense electrode and the ground electrode compared with that of the air pocket 8.006. On the other hand, the electric field line 8.074 between the reference electrode 8.036 and the ground electrode 8.034 passes through the same length of egg white as on the first test occasion. The change in the dielectric constant of the egg white between the initial state and the second state may be considered as negligible for present purposes. [0110] A further electrical environment sensing electrode (not shown) can also be provided, so that stray electrical impulses or electromagnetic interference (emi) can be eliminated from the measured signal. Placing the environmental sensing electrode close to the test electrodes ensures that it detects similar emi influences to the measurement electrodes. However, the environmental electrode is located so that it does not measure the egg capacitance. A single environmental electrode can be used for a plurality of cups. The emi electrode signal, properly scaled, is deducted from the sensing electrode measurements by the microcontroller to correct these readings. [0111] Figure 9 is a schematic view of a test cup embodying the electrodes of Figure 8. The cup 9.030 is mounted on or formed integrally with a mounting plate 9.050 to provide a unitary moulded receptacle. A raised rim 9.044 is formed at the upper edge of the cup. The conductive neoprene leads 9.038, 9.040, 9.042 can extend up to the top of the rim, or even across the rim and down the outer wall of the rim. This can be used to facilitate connection to external electrical leads which can be provided with resilient connectors to contact the conductive neoprene leads. The leads connect electrically with associated electrodes 9.032, 9.034, and 9.036 respectively. The electrodes can also be formed of conductive neoprene. [0112] The electrodes 9.034 and 9.036 form arcs around the cup, leaving a gap through which leads 9.038 and 9.040 can be fed out to a connector and attached to the test apparatus together with the lead 9.042 from the reference electrode 9.036. [0113] In one embodiment, only two electrodes, eg, 9.032 and 9.034 are utilized to measure the capacitance of an egg. The third electrode, 9.036 can be provided as a reference electrode. [0114] While the cup and electrodes of this embodiment are made of neoprene rubber, other suitable materials can be used without departing from the inventive concept. [0115] Figure 10 is an underside view of the cup of Figure 9 showing partial views of the electrodes and associated leads in dashed outline. [0116] Figure 11 is a block schematic illustration of an egg testing arrangement according to an embodiment of the invention. The arrangement includes a receptacle as described in Figure 9. The receptacle includes a cup 11.030 and mounting plate 11.050 formed as a single piece moulding. Conductive electrodes 11.032, 11.034, and 11.036 are 10 10059 connected by their associated leads 11.066, 11.068, 11.070 to test equipment 11.011. The test equipment can include a microcontroller with a microprocessor 11.060, analog-to-digital converters (ADC) 11.064, 11.080, and signal generator 11.062. [0117] The arrangement of Figure 11 can be referred to as a driven tester because a signal is applied between the sensing electrode and the ground electrode via lines 11.066 and 11.068. [0118] This arrangement is adapted to measure the changes in capacitance due to changes in the air pocket in the egg. A signal of known frequency is applied to the sensing and ground electrodes 11.032, 11.034 and the capacitance is measured via the ADC 11.064 and the processor 11.060. Similarly, the reference electrode 11.036 is connected to an ADC 11.080 and fed to the processor for calculation of the capacitances. [0119] However, because the sensed signals can be relatively small, amplification may also be required before the signals are applied to the ADCs. In addition, the ADC conversion can introduce errors. [0120] Further, the capacitance of the egg can be small compared with the capacitance of the leads and electrodes, and the change of capacitance of the egg is small compared with the capacitance of the egg. [0121] Figure 14 illustrates a measurement circuit according to another embodiment of the invention, and its operation is illustrated by reference to the timing diagram of Figure 15. [0122] In this arrangement, the measured capacitance of the air pocket segment of the egg is used to modulate the frequency of a multivibrator. A multivibrator can be used for accurate and inexpensive electrodes capacitance measurement. A Schmidt trigger 14.104 has an RC timing arrangement including feedback resistor 14.106 and capacitor 14.108 connected to the input of the Schmidt trigger 14.104. Capacitor 14.108 can be provided to stabilize the multivibrator operation where the measured capacitance is low. In addition, the sensor electrode is connected to the input of the Schmidt trigger 14.104 in parallel with capacitor 14.108. Because resistor 14.106 and capacitor 14.108 are fixed, the rise time of the input signal for the multivibrator varies with the change in the sensed capacitance from the sensing electrode. Thus the output frequency varies in dependence on the measured capacitance value from the sense electrode and this frequency can be readily measured by a microcontroller. The output of the multivibrator can be fed into the second Schmidt trigger 14.118 and thence to digital counter 14.114. The counter output is used to determine the elapsed time from the initiation of the counting sequence for a predetermined number of pulses from the multivibrator as described with reference to Figure 15.. 11 10059 [0123] As shown in Figure 15, the measuring sequence is initiated by the RESET signal from the microcontroller. This initiates a counter 14.114 and a timer in the microcontroller. The counter is set to count a specified number of pulses, eg, 16 from the Schmidt trigger 14.118, which is determined by the input capacitance connected to the multivibrator incorporating Schmidt trigger 14.104 . When the specified number of pulses has been counted, the elapsed time is noted, and this provides an indication of the frequency of the multivibrator, which, in turn is an indication of the capacitance at the input of the multivibrator. [0124] The microcontroller can be programmed to generate interrupts every 1 ms. Within this interrupt period the microcontroller can be programmed to generate the RESET signal to reset counter 14.114 and also to trigger the initial multivibrator state. In this case, there is no need to measure distance between pulses edges but just end of 16 pulses counting. Another one advantage of this arrangement is possibility to lock electrode multivibrator to reduce electromagnetic radiation. [0125] This arrangement work well in case of a sufficiently large capacitance change but if the changes are small, the measurements may not be sufficiently accurate. [0126] According to a further embodiment of the invention, digital bridge measurement, rather than analogue form, can be used to improve accuracy. In this method differences between the reference electrode signal and the sensing electrode signal are determined by a digital bridge as shown in Figure 16. [0127] In the arrangement shown in Figure 16, the same multivibrator arrangement as shown in Figure 14 can be used. The multivibrator 16.130 is connected to the counter/divider 16.132 with a division factor of, for example, 28 (256). In this case on the counter output we will have sum of input 256 pulses and sum of small changes of each pulse. Finally we "multiply" one pulse change on 256 for more precise measurement. [0128] A disadvantage of this multiplication is a long total pulse because relative changes are still the same. To avoid this a similar multivibrator 16.134 is used but with constant reference capacitor CREF . This multivibrator is adapted to operate on a frequency close to that of the measurement multivibrator 16.130 and is connected to the similar counter 16.136. As a result, output signals of the reference and measurement "arms of the digital bridge" will be close and the differences of these two signals can be measured with help of XOR logic cell. [0129] The sense electrode 16.032 and the ground electrode 16.034 are connected to inputs of multivibrator 16.130 which drives counter 16.132. The reference electrode is 12 10059 connected to t the input of a second multivibrator 16.134 which drives a second counter 16.136. [0130] The outputs of the counters 16.132 and 16.136 are applied to the inputs of an XOR logic block 16.138 which determined the difference in time for the two counters to supply a predetermined number, say 256, of pulses. Thus the output of the XOR gate is a measure of the difference between the frequencies of the multivibrators 16.130 and 16.134. This difference in frequency changes with time as the size of the air pocket increases. [0131] Figure 18 is a timing diagram illustrating the operation of the arrangement of Figure 16. [0132] In the timing diagram of Figure 18, the reference multivibrator 16.136 has a slightly longer pulse period than the sensing multivibrator 16.132 and thus the reference counter takes longer to reach the designated count of 256 pulses. Thus the XOR gate 16.138 produces the output pulse shown in the bottom time diagram of Figure 18 initiated by the 2 5 6 th pulse from the sensing multivibrator and terminated by the 2 5 6 th pulse of the reference multivibrator. The length of this XOR output pulse is an indication of the difference between the multivibrator frequencies. Thus, when calibrated, this can be used to provide a measure of the current capacitance of the egg. [0133] This arrangement has one more advantage. Together with reference constant capacitor, a reference electrode 16.036 can also be used. This electrode should be located in the same area with measurement electrode but not exactly in the same position - it should not sense signal but sense electromagnetic environment. In this case external electromagnetic fields will have same influence on both "digital bridge arms" and will eliminated or significantly reduced (in case not absolutely equal influence on electrodes) because the output signal is the difference between the input signals. In addition, short spikes will be completely eliminated because both counters should count same number of spikes. [0134] This arrangement has a number of advantages. Most microcontrollers have timers and additional functionality for measurement. [0135] The microcontroller can be programmed to count pulses from multivibrator output in fixed period of time or handle interrupts for pulses period measurement. [0136] The counting period can be set to 20 ms or any multiply by 20 ms. In case of the pulses period measurement it is possible to make a number measurements within 20 ms and calculate average value. Using multiples of 20 ms it is possible to "digitally filter" 50 Hz noise without any extra hardware elements for analogue filtering. 13 10059 [0137] Short HF spikes can influence only on one counting period, resulting in low errors rate in normal environment especially after extra averaging due to slow signal changes. [0138] Frequency can be measured with good precision in wide dynamic range (because of 16 bit counter) comparing with analogue output and ADC. [0139] Also this method obviates the need for analogue circuit adjustment. [0140] The cost of this measurement method is lower compared with other methods. [0141] Figure 17 is a block diagram of a microcontroller arrangement adapted for use in an embodiment of the present invention. The microcontroller 17.090 is connected to the capacitance to digital converters 17.086, 17.092 such as those described above with reference to Figures 14 to 16 and Figure 18. The first capacitance to digital converter 17.086 can be connected to an array of sensing electrodes of a plurality of test cups, and the second capacitance to digital converter 17.092 can be connected to the corresponding array of reference electrodes. The controller 17.090 is adapted to read the electrodes individually via the multiplexor arrangements 17.094, 17.096. Thus the arrangement of Figure 17 can be used to test a plurality of eggs in a short period of time. [0142] Figures 12 & 13 illustrate an alternative electrode arrangement in which a pair of electrodes is used to measure both the capacitance of the air pocket and the egg liquid in series. The egg 12.002 has an air pocket 12.006 above the egg white 12.004. A top electrode 12.022 is adapted to fit over the top of the egg and make contact therewith. The electrode is sufficiently resilient to deform to the shape fo the egg. A bottom electrode 12.024 likewise is adapted to conform to the bottom of the egg. In this arrangement, the capacitance of the air pocket is in series with the capacitance of the egg white between the electrodes 12.022 and 12.024. The capacitance Cs of series connected capacitors C1 & C2 is given by the formula: Cs = (Cl * C2) / (C1 + C2) [0143] Figure 19 illustrates a cup according to an embodiment of the invention in which the electrodes are adapted to make contact with eggs of differing sizes. The measuring electrode is of similar configuration to that shown in Figure 8B, but the common electrode 19.034 and the reference electrode 19.036 are adapted to resiliently contact eggs of varying sizes. these electrodes project from the inner wall of the cup and are made of resilient material, and are conductive. The electrodes 19.034 and 19.036 are adapted to deflect when an egg is inserted into the cup so a small egg will contact the measuring electrode 10.032 as well as the projecting electrodes, while when a large egg is inserted, the projecting electrodes will deflect sufficiently to permit the large egg also to contact the 14 10059 measuring electrode 19.032 while also being in contact with the projecting electrodes. The projecting electrodes can have any suitable cross-section. In the illustrated embodiment, the projecting electrodes have a triangular cross-section and are cantilevered from the wall of the cup. [0144] Figures 20 and 21 illustrate an alternative embodiment of the sensing cup 20.030 in which the cup is initially inverted with the electrodes 20.032, 20.032, 20.034 on the underside and "within" the inverted cup. In this arrangement the egg is applied to the top of the dome formed by the inverted cup and presses downward so that the cup, which is highly pliable, inverts as shown in Figure 21 in stages [A] to [G]. Stage [A] shows the inverted cup 21.030 with the electrodes 21.032, 21.034, 21.036 on the inside of the cup. At stage [B], the top of the cup is depressed by the user pressing an egg against the top of the inverted cup forming a depression 21.202 which grows progressively as the egg is further pressed downwards. At some stage, such as stage [E], the cup may reach a toggle point where further downward will cause the cup to toggle to a configuration as exemplified at stage [G] in which the cup now presents an upward facing recess with an egg 21.002 therein. The toggle point will occur at some point after the depression passes the plane of the rim of the cup. [0145] The cup is so dimensioned, and the material of the cup is sufficiently pliable so that the electrodes are held against the side of the egg by the resilient force of the cup material. the cup can be dimensioned to accommodate eggs of differing sizes while maintaining the wall of the cup in contact with the egg. [0146] The electrodes in this embodiment are on the outside of the cup when the egg is inserted. However, we have found that, provided the wall of the cup is sufficiently thin to allow it to be readily inverted, eg, of the order of 7mm or less, the relative measurement is not affected by the interposition of the cup wall between the egg and the electrodes. [0147] As shown in Figure 21, the rim of the cup may be provided with a rim 21.204 which can facilitate the progressive inversion of the cup and reduce stress at the interface of the cup 21.030 and the support plate 21.050. [0148] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated. [0149] In this specification, terms indicating orientation or direction, such as "up", "down", "vertical", "horizontal", "left", "right" "upright", "transverse" etc. are not intended to be 15 10059 absolute terms unless the context requires or indicates otherwise. These terms will normally refer to orientations shown in the drawings. [0150] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [0151] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [0152] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein. 16

Claims (20)

1. A method of testing eggs including using the capacitance of an uncracked egg under test to control the frequency of a multivibrator, measuring the frequency of the multivibrator and calculating the capacitance of the egg from the measured frequency.

2. A method as claimed in claim 1, wherein the measured capacitance is compared with a predetermined value or a range of predetermined values.

3. An egg testing arrangement for an uncracked egg, having a variable frequency multivibrator whose frequency is responsive to a capacitance connected to its input, the capacitance including the capacitance of an egg under test.

4. An egg testing arrangement as claimed in claim 3, including a second multivibrator having a fixed frequency, and a digital bridge connected to the outputs of the first and second multivibrators to determine the difference between the frequencies of the first and second multivibrators.

5. An egg testing arrangement as claimed in claim 3 or claim 4, including an egg retaining device having a first electrode and a second electrode, the first and second electrodes being mounted on the retaining device so as to be proximate to or in contact with an egg when the egg is placed in the egg retaining device.

6. An egg testing arrangement as claimed in claim 5, wherein the retaining device is made of a resilient material.

7. An egg testing arrangement as claimed in claim 5, wherein the first and second electrodes are made of a conductive resilient material.

8. An egg testing arrangement as claimed in claim 7, wherein the conductive resilient material is an electrically conductive rubber.

9. An egg testing arrangement as claimed in claim 8, wherein the electrically conductive rubber is a silicone rubber.

10. An egg testing arrangement as claimed in any one of claims 3 to 9, including a source of alternating voltage, and capacitance measuring equipment.

11. An egg testing arrangement as claimed in any one of claims 3 to 10, wherein the egg retaining device is a cup shaped vessel.

12. An egg testing arrangement as claimed in any one of claims 3 to 11, including signal processing means to evaluate the capacitance measurements. 17 10059

13. An egg testing arrangement as claimed in any one of claims 3 to 12, including a third electrode to measure electrical interference.

14. An egg testing arrangement as claimed in any one of claims 3 to 13, wherein the signal processing means is programmed to compensate for interference using signals from the third electrode.

15. An egg testing arrangement as claimed in any one of claims 3 to 14, including a memory storing a predetermined value or range of predetermined values of impedance.

16. An egg testing arrangement as claimed in any one of claims 3to 15, wherein the processing means is programmed to evaluate the measured value against a predetermined value or range of predetermined values.

17. An egg testing cup including a recess adapted to conform to the base of an egg, a sense electrode conforming to the base of the recess, a ground electrode located to be above the air pocket of an egg inserted in the cup, and a reference electrode adapted to be proximate the egg white of an egg under test.

18. A method of testing eggs substantially as herein described with reference to the accompanying drawings.

19. An egg testing arrangement substantially as herein described with reference to the accompanying drawings.

20. An egg testing cup substantially as herein described with reference to the accompanying drawings. 18