RU2330608C2 - Method and device for diagnostics of tooth solid tissues state (bioobjects) - Google Patents

Abstract

FIELD: medicine; stomatology.

SUBSTANCE: method includes several stages. Preliminary stage implies that total dynamic range of resistance variation is divided into finite indexing (enumerated) number of dynamic subranges according to permissible reduced error of analog-to-digital conversion of measured resistance. Analog-to-digital conversion of measured tissue resistance is performed within found and evaluated subrage by two stages. The first stage implies that analog-to-digital conversion of measure resistance for fixed digit count is carried out bit-by-bit, by successive balancing, starting with high-order digit, referring relevant balancing reference resistive weight to each digit. Analog-to-digital conversion for the rest low-order digits within the same subrange is accompanied with correction of balancing up and down by discrete value corresponding to low-order digit weight. The device for measurement of tooth solid tissue resistance contains electrodes, reference voltage source, null device, low-pass filter, instrumental amplifier and digital measurement device with liquid crystal display. It also comprises reference voltage regulator, electrodes switch keys, resistive bridge, and voltage divider. Digital measurement device with liquid crystal display is designed as microprocessor system including microprocessor with attached keyboard, memory unit and interface scheme RS-232.

EFFECT: improved reliability and reproducibility of results at wide spread of rating indices for teeth of any types and for various patients.

4 cl, 2 dwg

Description

The invention “Method and device for measuring the resistance of hard tissues of teeth of bioobjects” relates to medicine and can be used in dentistry to measure the resistance of hard tissues of teeth of bioobjects in order to diagnose their condition both before and during treatment, and to monitor the results of treatment by means of a constant probe electric signal, as well as for measuring the resistance of tissues of other biological objects. There is a method in which to diagnose the state of tooth tissue, they act on the studied local area of the tooth with a constant electric probe signal, followed by measuring the current strength at the output of the studied local area of the tooth using passive and active electrodes and a measuring device. According to the magnitude of the measured current, the condition of the tissues of the teeth being examined is diagnosed (see, for example, A.S. No. 2239357, class A61B 5/05, "Method for the diagnosis of demineralization of permanent tooth enamel" authors Ramm N.L., Kiselnikova L.P. date publ. 2004.04.27, AS No. 1822747, class A61B 5/05 “Method for the diagnosis of caries.” Authors V.K. Leontyev, T. N. Zhorova, G. G. Ivanova and A. I. Ivanov, publication date June 23, 93 Bull. No. 23).

The closest in technical essence to the proposed method is A. with. No. 1822747, cl. АВВ 5/05 "Method for the diagnosis of caries." Authors V.K.Leontiev, T.N. Zhorova, G.G. Ivanova and A.I. Ivanov, date publ. 06/23/93. Bull. Number 23. According to the method, an active current of 100 μA at 3 V during teething is passed through the hard tissues of the tooth under study using active and passive electrodes, then after 4 and 5 months the condition of the tissues of the tooth being examined is diagnosed by a change in electrical conductivity.

However, the existing methods do not indicate a method for measuring current, but indicate normalizing current values at which a diagnosis is made. Using the standard method and device for measuring the current strength in the prototype due to the significant error in measuring the current (tenths and hundredths of a μA) and the dependence of the results of measuring the current strength on the stability of the voltage source forming the electrical probing signal, entails a low reliability of the diagnosis. The low reliability of the diagnosis is due to the large variability and, therefore, poor reproducibility of the measurement results. The use of standard devices, for example, an instrument of the type M-2001, indicated in the prototype, leads to the appearance of additional bias errors, including due to the appearance of the polarization effect in the contact between the active electrode and the studied biological object.

In addition, the error and instability of measuring the current strength of a small level significantly reduces the allowable dynamic range of measurement with a given error. Reducing the permissible dynamic range of measurement leads to a reduction in the diagnostic capabilities of various stages, types and forms of dental caries with acceptable reliability and to limiting the scope of the proposed method for the diagnosis of other biological objects.

It is known that a direct indicator of the state of tooth tissue is active resistance, which directly depends on pathological changes in the condition and structure of the tubules that make up the basis of dentin. See, for example, an article by Batyukov N.M., Ivanova G.G., Tikhonova E.P., Kasumova M.K., Mchedlidze T.Sh., Tikhonova E.P. “Systematic analysis of dental hard tissues based on optical, x-ray and electrical signals” - Institute of Dentistry, No. 1 (34), 2007, p.102-104. It has been established that the dynamic range of possible values in order to diagnose the measured active resistance (hereinafter simply referred to as resistance) of the state of hard tissues of the teeth of biological objects covers a value of 10 ⁸ with a permissible maximum current of the probing electric signal not exceeding 100 μA by 3 V at the lower boundary of the dynamic range of measured resistance. The minimum current of the probe signal is determined by the sensitivity of the technical device by which the resistance is measured at the upper boundary of the dynamic range. At the upper boundary of the dynamic range of 100 mOhm, with established restrictions on the upper limit of the voltage of the probing signal of 3 V, the decrease in the current passing through the studied local area of the tooth or other biological objects reaches values that are outside the sensitivity limit established even for modern digital measuring devices. In addition, the magnitude of the current becomes commensurate with the magnitude of the instability of the reference current source forming the probing electrical signal. The problem of measuring the magnitude of the resistance for the passage of current through the hard tissues of the teeth of biological objects, arises not only because of the finite sensitivity of the devices for measuring the high-resistance resistances of resistors, but also because of the influence of other factors, including the final value of the insulation resistance, for example, the insulation resistance of the printed circuit board, on which the electronic components of the circuit are installed during installation. In particular, when using a four-arm resistive bridge, in order to determine the imbalance of the bridge at 1 kOhm against the background of the measured resistance to the passage of the bioobject current at 5 · 10 ⁷ Ohms with the indicated parameters of the electric sounding signal, it is necessary that the null-organ included in the diagonal of the bridge, I would feel a signal of 3.6 · 10 ^-2 μV. Such a high sensitivity with a conventional circuitry solution is almost impossible to obtain even with the use of modern electronic components such as an instrument amplifier type INA 118 from BURR-BROWN Corporation and a zero-organ type LP311.

Therefore, under these conditions, the problem arises of finding methods and devices for direct digital measurement of the resistance of biological objects in a wide dynamic range with a given reduced measurement error.

Known methods for measuring the active resistance in digital form by using the delta-sigma ADC together with resistance bridges (see, for example, pages 373-379 of the book: “Pairing sensors and data input devices with IBM PC computers”: Transl. From English / Edited by W. Tompkins and J. Webster. - M .: Mir, 1992. - 592 s, ill., As well as the article "Features of the use of delta-sigma ADC together with resistance bridges in measuring devices." Pavel Vovk, " Chip News Ukraine ”, No. 2 (42), March 2005). The digital form of presentation of the measurement results leads to a decrease in the measurement error and to the expansion of the dynamic range of the measured value, including resistance.

However, in these methods, the measurement of resistance and its conversion into a digital code is carried out indirectly, that is, an electrical signal is converted into a digital code, which is proportional to the imbalance of the resistive bridge, which limits the allowable dynamic range of the desired resistance and the accuracy of its measurement. The decrease in the accuracy of digital resistance measurement by known methods and devices in a wide dynamic range (from tens of Ohms to 10 ⁸ Ohms and above) is also associated with the limitations of the probing current passing through the studied area of the biological object, which should not exceed 100 μA at the lower limit of the dynamic range. Under these conditions, the main factors leading to an increase in the error of digital measurement of the resistance of the studied local areas of biological objects, by known methods, cannot actually be sufficiently eliminated to conduct reliable diagnostics of the state of biological objects. When using known methods of digital measurement or analog-to-digital conversion of the resistance of biological objects, these main factors affecting the reliability of diagnostics should include, first of all, the influence of high-frequency noise; instability of the source of the electrical sounding signal; the presence of an in-phase signal (induction of a power network with a frequency of 50 Hz); offset and zero drift of analog elements (amplifiers). The most significant destabilizing factor is associated with the influence of high-frequency noise on the measurement results.

Known bridge device for multi-point determination of the impedance characteristics of biological objects (AS No. 2104668, class 6 A61B 5/05, publ. 1998.02.20). This device in order to expand the functionality and improve the accuracy of measuring the impedance characteristics of biological objects contains: an alternating voltage generator; four-arm bridge measuring circuit formed by the first, second and third elements; first and second operational amplifier; a large-scale amplifier, the input of which is connected to the output of the second operational amplifier; an amplitude rectifier, the input of which is connected to the output of a large-scale amplifier; ADC, the input of which is connected to the output of the amplitude rectifier; a computing device, the input of which is connected to the output of the ADC; two multiplexers whose inputs of the same name are connected in parallel. The output of the first multiplexer is connected to the output of the second operational amplifier and the input of the scale amplifier, and the output of the second multiplexer is connected to the inverting input of the second operational amplifier and the output of the first element of the four-arm bridge measuring circuit. The first output of the computing device is connected to the control output of the first element, and the third output to the control input of the third element of the four-arm bridge measuring circuit. The fourth output of the computing device is connected to the control input of a large-scale amplifier, and the nth number of measuring electrodes are connected to the inputs of the multiplexers.

The disadvantage of this device is the use of an alternating electric sounding signal, which entails the need to use additional measurements for measuring the active component of the impedance of the biological object and, therefore, such elements of the device circuit as the generator and amplitude rectifier, which leads to an increase in the measurement error of the active component of the measurement error . In addition, the implementation in the bridge circuit of the known method of digital measurement of impedance, including the active component, is carried out indirectly, that is, the electrical signal is proportional to the imbalance of the resistive bridge, which leads to an additional decrease in the allowable dynamic range of the desired active resistance and its accuracy measurements. An increase in the number of electrodes to exclude the influence of skin impedance on the accuracy of digital measurement of the active component of the impedance when measuring the resistance of tooth tissues cannot be applied due to the impossibility of using the nth number of active electrodes.

The closest in technical essence to the proposed invention is the invention: "Device for measuring the active and capacitive components of the impedance of biological tissues" RU No. 2196404 C2, class. A61B 5/053, 01.20.2003, which relates to biophysics and medical technology and can be used in medicine for rapid diagnosis of various diseases and quantitatively assess the degree of pathological changes in tissues and organs. The device operates on a four-electrode circuit and consists of a sinusoidal voltage generator, a broadband amplifier with automatic gain control to maintain a measuring current of a given amplitude, a phase-sensitive difference meter of two voltages, a constant voltage amplifier, an indication unit, and feedback and control circuit blocks.

The disadvantage of this device, as well as the device for A.S. No. 2104668, is the use of an alternating electric sounding signal, which entails the need to use for measuring the active component of the impedance of the bioobject an additional analog conversion on the phase-sensitive meter of the voltage drop difference in the studied area of the biological object with subsequent amplification and analog-to-digital conversion of the obtained amplified voltage difference, which leads to a significant increase in the measurement error of the active component of the measurement error . Indeed, the advantage of digital measurement in this case is reduced only to the convenience of presenting the measurement results in digital form and does not affect the reduction of measurement error. In addition, the implementation in the proposed scheme of digital measurement of impedance, including the active component, is carried out indirectly, that is, an electrical signal that is proportional to the imbalance of the resistive bridge is converted to a digital code, which leads to an additional decrease in the allowable dynamic range of the desired active resistance and the accuracy of its measurement. This measurement scheme, moreover, does not eliminate the error component that arises due to the instability of the source of the probing electrical signal.

An increase in the number of electrodes to exclude the influence of skin impedance on the accuracy of digital measurement of the active component of the impedance when measuring the resistance of tooth tissues cannot be applied due to the difficulty of installing the corresponding number of electrodes on the tooth. It should also be noted that the influence of the electrical properties of the electrode - biological tissue interface has a significant effect on the measurement of the active component of the impedance in the case when the measured active component of the impedance is comparable in magnitude with the active component of the impedance of the electrode - biological tissue interface. The active resistance of tooth tissues to electric current, even if they are pathologically destroyed, significantly exceeds the corresponding component of the interface resistance, since when measuring the active component of tooth tissue resistance, the sharpened needle of a syringe filled with potassium chloride is used as the active electrode, which leads to a significant decrease in the active and reactive components of the impedance of the electrode - tooth tissue interface compared with the measured resistance.

Thus, these known methods and devices cannot provide digital measurement of tooth tissue resistance in the dynamic range from tens to 10 ⁸ Ohms with a maximum value of the probe signal current at the lower value of the dynamic resistance range of 100 μA, even when the probe electric signal voltage is more than recommended 3 V, but not exceeding the permissible voltage of 8-9 V. Moreover, the influence of the main circuitry factors on the error of the digital measurement of the resistance of the investigated local areas of the tooth by known methods and devices cannot be eliminated, at least for a time not exceeding a few seconds.

The claimed group of inventions is intended to solve the problem of reducing the error in measuring the resistance of hard tissues of teeth of bioobjects to an electrical signal and, thereby, helps to increase the reliability, reproducibility and reliability of diagnostics of the state of hard tissues of teeth of bioobjects, including when detecting early stages of caries. The claimed group of inventions will also be able to provide control of the state of tooth tissues by the magnitude of changes in their resistance during treatment and prevention through the use of a probing constant electrical signal with a low voltage level. In addition, the diagnostic capabilities and nomenclature of the studied biological objects are expanding due to an increase in the dynamic range of the measured resistance (up to 10 ⁸ and higher). This problem can be solved using the proposed method for digitally measuring the resistance of tooth tissues of biological objects to an electrical signal using a device that implements this method in the form of a portable microprocessor device. This device, in addition to directly presenting the results of measurements and diagnostics on its own liquid crystal display (LCD) in digital form, has additional functions for storing and transmitting the received information in digital form using standard methods on a top-level PC. The upper level PC can be used to fully automate and visualize the diagnostic process according to the measurement results, including in the form of tomographic images of the studied tooth area, as well as archiving the information obtained in the form of a database of the studied patients (see. "System analysis of hard tooth tissues on the basis of optical, x-ray and electrical signals ”- Institute of Dentistry, No. 1 (34), 2007, p.102-104).

The technical result of a method for measuring the resistance of hard tissues of teeth of bioobjects is to reduce the error in measuring the resistance of hard tissues of teeth of bioobjects with a wide range of standard parameters for any types of teeth in various patients, regardless of age, and expanding the dynamic range of measured resistances while maintaining the probing electric current in the specified limits signal. The consequence of this is the expansion of the functionality of diagnostics of the state of hard tissues of teeth of biological objects, including the detection of soft and hard tissues of biological objects at the early stages of inflammatory processes.

The technical result of the device for measuring the hard tissue of teeth of bioobjects is to increase its accuracy by directly measuring the digital resistance of the studied local area of the tooth and other bioobjects to electric current by eliminating the component errors associated with the influence of the polarization of the electrodes on the measurement results and the instability of the source of an alternating electrical probe signal . As a result, the measurement error in comparison with known devices can be reduced to fractions of a percent for a wide dynamic range of conversion of resistance into a digital binary code, covering 10 ⁸ , with the above parameters of the probing electric constant signal, with digital storage, indication and, if necessary , transferring the measurement results to the upper level PC. At the same time, the expansion of the dynamic range of digital measurements while maintaining a given reduced measurement error is achieved due to a slight increase in the measurement time, which falls within the time interval acceptable for diagnostics.

In order to achieve a technical result in the method of measuring hard tissue of teeth of biological objects when exposed to an electric constant signal through a passive and active electrodes, the full dynamic range of changes in the resistance of biological objects at the preliminary stage of the study is divided into a final indexable (numbered) number of dynamic subranges according to the permissible value of the reduced error of the analog digital conversion of measured resistance. Within each dynamic sub-range, majority and successively at discrete time instants through an interval multiple of 10 ms, the results of exposure to a constant electric probe signal determine the resistance of tissues to the corresponding dynamic sub-range, starting with a minimum index value of zero. Within the found and established sub-range, the analog-to-digital conversion of the measured tissue resistance is carried out in combination in the following two stages: majority and sequentially at discrete time instants over an interval multiple of 10 ms, for each fixed number of digits, the values of each category are determined by sequential balancing of the measured resistance, varying model resistance starting from the senior bit to some fixed intermediate bit. For the remaining part of the least significant bits at the second stage, the same sub-range is also performed majorityally through a time interval uniformly distributed in the range from a certain minimum value to a value of 20 ms by analog-to-digital conversion by sequential balancing of the measured tissue resistance, varying the model resistance with correction for a minor digit unit up or down side of the binary code obtained on the previous high-order bits. If it is established that the measured tissue resistance belongs to a dynamic subrange with a zero index, then within the first stage, for a fixed number of bits, the analog-to-digital conversion of the measured resistance by sequential balancing, starting from the highest level, is performed bitwise, assigning to each category the corresponding weight of the balancing model resistance , and for the remaining part of the least significant bits in the same subband perform analog-to-digital conversion with correction of balancing resistance up or down by a discrete value corresponding to the weight of the least significant bit. When establishing the ownership of the measured resistance of biological objects to a dynamic sub-range with an index exceeding the minimum zero value, the weight of the balancing model resistance is established for each discharge in the first and second stages of analog-to-digital conversion according to a nonlinear law determined by the value of the resulting resistance equal to the measured tissue resistance connected in parallel to set dynamic sub-band other than the weight of the bit and tracking equation veshivaniya set for dynamic subband with index zero.

If it is established majority and sequentially at discrete time instants after an interval multiple of 10 ms that the value of the measured resistance exceeds the selected dynamic subband, then, when switching to a dynamic subband with a large index, the value increases synchronously with an increase in the index, but within the specified limits, voltage of the electrical sounding signal.

When determining the dynamic sub-range index and during analog-to-digital conversion within the established dynamic sub-range, the polarity of the probe electric signal applied to the passive and active electrode is changed, each time during the transition from the balancing binary code from discharge to discharge.

To achieve a technical result, a device for measuring the resistance of hard tissues of teeth of biological objects containing electrodes, a voltage reference source, a zero-organ, a low-pass filter, an instrument amplifier and a digital measuring device with a liquid crystal display, a voltage reference regulator, electrode switching keys, and a resistive bridge are introduced , in the symmetrical shoulders of which are included a shunt voltage divider and reference resistors with resistances of the same nominal value, the divider is tense I constructed as a series-connected resistors and switches. A digital measuring device with a liquid crystal display is made in the form of a microprocessor system, which includes a microprocessor with a keyboard connected to it, a storage device and an RS-232 interface circuit. In this case, the first group of microprocessor outputs is connected to the control inputs of the reference voltage regulator, the input of which is connected to the output of the reference voltage source, and the output is connected to the first diagonal of the resistive bridge, the second diagonal of which is connected to the inputs of the instrument amplifier, the output of which is connected to the first through a low-pass filter the input of the zero-organ, the second input of which is connected to a common bus, and its information output is connected to the information input of the microprocessor. The second group of microprocessor outputs is connected to the control inputs of the switching keys of the electrodes, the inputs of which are connected to the electrodes, and the outputs are connected to the inputs of the shunt voltage divider, the control inputs of which are connected to the third group of outputs of the microprocessor. The fourth group of microprocessor outputs is connected to the control inputs of the voltage divider, and its fifth output is connected to the control input of the zero-organ.

The method is as follows. Based on preliminary studies, the maximum dynamic range of changes in the resistance of hard tissues of the teeth of biological objects (hereinafter referred to as tooth tissues) is determined. For tooth tissues, the maximum range of resistance changes is about 100 mOhm, and the minimum range can be from one to several tens of ohms. The magnitude of the dynamic range depends on the diameter of the active electrode. The larger the diameter of the active electrode, the smaller the dynamic range is shifted. However, the diameter of the active electrode is established from the need to study hard-to-reach fissure cavities of the tooth, which limits the diameter of the active electrode to tenths of 1 mm and leads to a shift in the dynamic range of the measured resistances upwards, that is, to the maximum value indicated. At a minimum, the diameter of the active electrode is limited by the diameter of the injection needle developed by the industry, comprising 0.3-0.45 mm.

For the accepted magnitude of the reduced error of digital resistance measurement based on calculation and preliminary experiment, the maximum dynamic range is divided into a number of dynamic subranges. Suppose that for a given reduced measurement error, an acceptable dynamic sub-range is set in the range from 0 to R ₀ kOhm. This dynamic subrange is assigned index 0. To measure the resistance of a biological object exceeding the resistance of the resistor (hereinafter simply referred to as resistance) equal to R ₀ , the measured resistance of the tooth tissues is shunted so that the next dynamic sub-range of the resulting resistance already with index 1 also fits into the dynamic sub-range with index 0, that is, it would have a lower bound R ₀ , and an upper bound - 2R ₀ . The values of shunt resistances for the formation of the m-th dynamic sub-range are determined by the maximum permissible measured resistance of tooth tissue R _xm in each sub-range, expressed through the resistance R ₀ in accordance with the equality R _xm = (1 + m) R ₀ , where m = entr [R _x / R ₀ ] (entr - operator for determining the integer part of the result of dividing the resistances indicated in brackets); R _{x (m-1} ) R _x R _xm ; R _x is the value of the measured resistance of the tooth tissue or simply the measured resistance. The parameter m shows how many times the integer number of times the measured resistance R _x exceeds the upper boundary of the dynamic subrange with index 0. For the further description, we express the shunt resistance through resistance R ₀ in the form of the product λ (m) · R ₀ . Then the resulting resistance belonging to the corresponding dynamic sub-range is formed by parallel connection of the measured resistance R _x and shunt resistance λ (m) · R ₀ . The value of the resulting resistance in parallel connected measured R _x and shunt λ (m) · R ₀ resistances are found in accordance with the formula

where parameter α takes values within the limits determined by the inequality 0≤α≤1, since the measured resistance R _x in the dynamic range with index m = 0,1, ..., can be represented as R _x = R ₀ (α + m )

Therefore, the values of the dimensionless function λ (m), which determine the value of the shunt resistance, are found from the above equality, provided that the maximum value of the resulting resistance for any value of the index m is set in accordance with the equality R _max = R ₀ at α = 1. In accordance with this equality, concrete values of the dimensionless function λ (m) are established

where, under the introduced restrictions on the maximum dynamic range of the measured resistance, they are limited, for example, by the following numerical values m = 0,1,2,3,4.

From the last equation it follows that at m = 0 the shunt resistance is infinity, in other words, the active and passive electrodes are connected directly, for example, to the arm of a four-arm resistive bridge without a shunt resistance. For m = 1,2,3,4 the resistance of the shunt R _W takes the values: 2R ₀ ; 1.5R ₀ ; 1.333R ₀ ; 1.25R ₀ , where for the dimensionless function λ (m) with m = 1,2,3,4 the following specific values of the function λ (m) are obtained: λ (1) = 2; λ (2) = 1.5; λ (3) = 1.333; λ (4) = 1.25.

The belonging of the measured resistance to the dynamic sub-range with the corresponding index m is determined sequentially in time and majority within the selected number of clock cycles of the shunted measured resistance R _xsh with the maximum value of the model compensating resistance R ₀ according to the majority of coincidence of the sign of the comparison results. If it is majority, that is, by the majority of coincidence of the signs of the results of comparison of R _xsh with the reference R ₀ resistance, the sign of the imbalance error is determined as positive, which corresponds to the condition R _xsh > R ₀ , then in this case we pass to the next dynamic order in the next order. If in the same way the majority sign is determined to be negative (for example, a null-organ for determining the sign of the difference in this case gives a signal corresponding to zero), then in this case the previous dynamic sub-range is left.

It should be noted to assess the advantages of the proposed method as follows. If we perform bitwise balancing of the measured resistance in the selected dynamic subband, regardless of its index, starting from the highest bit, by changing the balancing model resistance in each bit in accordance with the law of bitwise balancing, that is, changing the balancing resistance R _ESD in the i-th bit according to law 2 ⁱ · R for i = 1,2, ..., then the measured resistance R _x for the dynamic subband with index m> 0 is obtained in accordance with the equality

This equality determines the calibration characteristic, according to which the measured resistance R _x is associated with the balancing model resistance for any value of the index m. This nonlinear calibration characteristic is converted to a linear calibration characteristic only for the index m = 0. Indeed, when m = 0 the function λ ^-1 (m) = 0 and

R _x = R _0уp = α · R ₀ ,

а_i=1 или 0 и R=R₀/(2^N-1) R₀·2^-N (число двоичных разрядов в полученном в результате аналого-цифрового преобразования двоичном коде).Where

and _i = 1 or 0 and R = R ₀ / (2 ^N -1) R ₀ · 2 ^-N (the number of binary bits in the binary code obtained as a result of the analog-to-digital conversion).

When using, for example, to compare the measured resistance R _x and R _{0у of a} four- _armed resistive bridge for index m> 0, an unrecoverable bias error arises, the value of which is determined by the magnitude of the unbalance voltage of the four-armed resistive bridge due to the passage of current through the shunt resistance. This bias error is determined for β = α from the equality

where β = R _0yp / R ₀ ; R _0yp is the value of the balancing model resistance; δ = R ₀₁ / R ₀ ;

α = R _x / R ₀ ; R ₀₁ - values of equal reference resistances, complementing the balancing and measured resistances to a full four-arm resistive bridge, which are selected from the condition R ₀₁ = 3V / 10 ^-4 A. The specified bias error cannot be eliminated by the majority method of balancing with subsequent correction of the conversion result by a follow-up transformation . Since the above calibration characteristic nonlinearly expresses the measured resistance R _x through its reference analog R _0уp for indices m = 1,2, ..., this nonlinear dependence leads to the appearance of an additional methodological component of the measurement error R _x not taken into account.

To eliminate the nonlinear component of the error due to the additional introduction of dynamic subranges, by shunting the measured resistance R _x in accordance with the proposed method, the following steps are performed.

Initially, the majority of the measured resistance of tooth tissues to the dynamic sub-range with the corresponding index m is determined.

In the selected dynamic sub-range, successively in time and majority in majority of coincidences of the results of comparing the shunted measured resistance R _xsh with the model compensating resistance at each i-th discharge of balancing the shunted measured resistance R _{xsh with the} model balancing (compensating) resistance (hereinafter simply as model resistance) R _0уpi determine the sign of the difference (error) of the deviation R _xsh from the reference R _0pi resistance. By the sign of the difference between the shunted measured and exemplary resistances, bitwise and majorityly, starting from the highest bit and to the specified bit of the binary code N _c , compensation is made for the value of this difference. If it is majority, that is, for the majority of coincidence of the signs of comparison of the measured resistance R _xh with the model R _0pi resistance, the sign of the imbalance error is determined as positive at each balancing cycle, then the model balancing resistance is increased compared to the established model resulting resistance on the previous measures of majority balancing. In this case, the binary code in the i-th category is attributed to one. If, in the same way, the majority sign is determined to be negative (for example, the null-organ for determining the difference sign in this case gives a signal corresponding to zero), then the value of the model resistance set for the i-th discharge is turned off and the resulting model resistance set on the model divider is set on the previous measures of majority balance, and in the i-th bit of the binary code set to zero.

If the index is m> 0, then, in contrast to the usual linear bitwise balancing algorithm for m = 0, bitwise compensation of the difference between the shunted measured R _xsh and the model resistance for the ith balancing step is performed nonlinearly in accordance with the binary code β _i , the value of which is set a priori and equivalent to resistance

As a result, the difference between the resulting balancing and measured resistance R _x is determined, for example, by the imbalance value of the four-armed resistive bridge arising in its diagonal in the form of a differential voltage

; δ=R₀₁/R₀; i=1,2,...N_c; α=R_x/R₀; N_c - число старших разрядов в искомом двоичном коде, для которого осуществляется поразрядное уравновешивание; a_i=1 или 0 в зависимости от мажоритарного результата сравнения зашунтированного измеряемого R_хш и образцового сопротивлений для i-го такта уравновешивания.Where

; δ = R ₀₁ / R ₀ ; i = 1,2, ... N _c ; α = R _x / R ₀ ; N _c is the number of high order bits in the desired binary code for which bitwise balancing is performed; a _i = 1 or 0, depending on the majority result of comparing the shunted measured R _xh and the reference resistances for the i-th balancing cycle.

Using, according to the proposed method, bitwise compensation of the difference between the measured and sample resistance for the i-th balancing step is carried out nonlinearly in accordance with the binary code, which sets the value R _0pi For the remaining part of the least significant bits N _m = NN _c , the code is formed in the following mode, that is, according to the sign of error, also determined by majority, deviations of the measured from the model resistance obtained on the previous steps of balancing i = 1,2, ..., N _c . Moreover, the binary code obtained at the previous N _c temporary majority clock cycles Δt _{m is} corrected for a lower-order unit in a greater or lesser direction in accordance with the proposed method. The majority time cycle Δt _m is equal to the sum kΔt of ordinary elementary comparison cycles Δt, and the majority parameter k corresponds to the number of comparison cycles for a given majority choice of comparison results. The number of majority Δt _m cycles of correction of the remaining lower digits corresponds to Δt _m · 2 ^Nm . The majority parameters for the higher and lower digits can be different, and their values must be an odd number and allowed for the lower digits k = 1, and for higher digits the parameter k is recommended to be chosen equal to 3 or even 5.

An analysis of the error of the deviation of the measured from the reference balancing resistance, in particular, obtained in the diagonal of the four-armed resistive bridge, in the form of a voltage or current difference, shows that with an increase in the index of the selected subband, the unbalance value of the bridge decreases inversely with the square of the index of the selected subband, which results in a decrease in the sensitivity of the corresponding equipment that implements the method. This is due to the fact that part of the current from the reference voltage source branches off from the electrodes into a shunt resistance circuit. To compensate for the decrease in sensitivity of the corresponding equipment in the method, when switching to a resistance measurement range with a large index, the output voltage is increased depending on the index value from the reference voltage source by an amount not exceeding the maximum permissible norm of 8 V.

When diagnosing biological objects by means of a constant probing electric signal by the value of the measured resistance, a significant effect on the error in measuring the resistance and, therefore, on the reliability of diagnostics has a polarization effect, the elimination of which is possible in this case only by periodic polarity reversal of the probing constant electric signal. Therefore, in the proposed method, when converting synchronously with the clock of analog-to-digital conversion, the polarity of the constant probing electrical signal is changed by switching the passive and active electrodes.

The majority choice for parameter k, which is equal to 3, increases the reliability of the determined bit of the binary code by about 1.5 times, and the choice of a time cycle of 10 ms helps to suppress network interference by about the same amount and, as the experiment shows, even by a larger number time. This is due to the fact that the period of network interference is 20 ms, and a time cycle of 10 ms corresponds to their samples, equal in magnitude and opposite in sign. Network interference can be substantially suppressed up to 100-120 dB by circuit methods, for example, by using an instrument amplifier and filters, nevertheless, this type of interference, combined with the intrinsic noise of electronic components due to the low level of the useful signal, has an unacceptable effect on the case in question error of analog-to-digital conversion (digital resistance measurement). Especially dangerous is the effect of the total network and random interference on the determination of the higher bits of the binary code, which leads to a significant and unrecoverable by the usual methods of bitwise balancing of the error (including bias error) of the digital resistance measurement and, therefore, a significant decrease in the reliability and reproducibility of the results of medical diagnostics of the state of tooth tissues . Therefore, the nonlinear correction of the results of analog-to-digital conversion proposed for the method for the selected number of low-order bits in the follow-up mode allows us to additionally correct both the systematic component of the conversion error and suppress the noise that forms the random component of the error. Moreover, the efficiency of suppressing the random component of the error is quite high.

Figure 1 presents the structural diagram of a device for measuring the resistance of hard tissues of teeth that implements the proposed method. Figure 2 presents the simulation results and an example of a program part of the algorithm with a nonlinear change in the weight of the balancing resistance in the dynamic range with the index m = 2, as well as a graph of the values converted randomly to digital binary code when shunted input resistance is simulated in this dynamic subband.

A diagram of a device for diagnosing the state of tooth tissues consists of elements and blocks having the following notation: 1 - source of reference voltage; 2 - voltage reference regulator; 3 - four-arm resistive bridge; 4 - exemplary, equal to each other, resistors R ₀₁ included in the symmetrical shoulders of the four-arm resistive bridge; 5 and 6 - active and passive electrodes, respectively; 7 - keys for switching electrodes; 8 - shunt voltage divider, consisting of 8 ₁ , ..., 8 _m series-connected switching keys of the voltage divider and shunt resistors: 2R ₀ ; 1,5R ₀ ; ... (1 + 1 / m) R ₀ ; 9 - code-controlled voltage divider (hereinafter simply: voltage divider), consisting of 9 ₀ , ..., 9 _N-1 series-connected keys and resistors with values that vary by a factor of two R, that is, from 2 ° R to 2 ^{N- 1} R, the sum of which is equal to R ₀ ; 10 - instrumental amplifier; 11 - low-pass filter; 12 - zero organ; 13 - microprocessor system, consisting of 14 - microprocessor; 15 - control keyboard; 16 - liquid crystal display (LCD); 17 - memory device with sequential recording and reading; 18 is a diagram of an RS-232 interface.

A device for measuring the resistance of hard tissues of teeth of biological objects that implements the proposed method contains: a source of 1 voltage reference; voltage regulator 2; four shoulders 3 resistive bridge; exemplary 4, equal to each other resistors R ₀₁ included in the symmetrical shoulders of the four-arm 3 resistive bridge; active 5 and passive 6 electrodes connected to the first and second information inputs of the keys 7 of the switching electrodes, respectively; shunting 8 voltage divider (hereinafter simply: shunting voltage divider), consisting of 8 ₁ , ..., 8 _m series-connected switching keys of the voltage divider and shunt resistors: 2R ₀ ; 1,5R ₀ ; ... (1 + 1 / m) R ₀ ; a voltage divider 9, consisting of 9 ₀ , ..., 9 _N-1 series-connected keys and balancing model resistors with values that vary multiple by two R, that is, from 2 ° R to 2 ^N-1 R, the sum of which is R ₀ ; instrumental amplifier 10; low pass filter 11; null organ 12; microprocessor 13 system, consisting of microprocessor 14, control keyboard 15, LCD 16, memory device 17 with sequential recording and reading; circuit 18 of the RS-232 interface. The source 1 of the reference voltage through a regulator 2 of the reference voltage coupled to the first diagonal chetyrehplechego 3 resistive bridge, including a first two symmetrical arms exemplary 4 are equal between a resistor R _01, while the second two symmetrical arms - the active 5 and passive 6 electrodes, connected to the arm of the four-arm 3 resistive bridge through the keys 7 of the electrode switching, the outputs of which, in the same arm, are connected in parallel to the shunt 8 voltage divider, consisting of 8 ₁ , ..., 8 _m connected in series to for switching voltage divider and shunt resistors: 2R ₀ ; 1,5R ₀ ; ... (1 + 1 / m) R ₀ . The second diagonal of the four-arm 3 resistive bridge is connected to the first and second input of the instrumental 10 of the amplifier, respectively, the output of which through a low-pass filter 11 is connected to the first input of the zero-organ 12, the second input of which is connected to a common bus. The information output of the zero-organ 12 is connected to the input of the same name microprocessor 13 of the system. The control inputs of the reference voltage regulator 2, the electrodes switching keys 7, the shunting 8 voltage divider and the voltage divider 9 are connected respectively to the first, second, third and fourth groups of digital outputs of the microprocessor 13 system, and the control input of the zero-organ 12 is connected to the fifth control digital output microprocessor 13 system. The corresponding inputs and outputs of the control keyboard 15, LCD 16, memory 17 devices with sequential recording and reading, circuit RS 18 interface is standardly connected to the inputs and outputs of the microprocessor 14. Other digital outputs of the microprocessor 14 and the information input are connected to the first, second, third and fourth groups of digital outputs of microprocessor 13 of the system, as well as the fifth control digital output of the same system and its information input, respectively.

A device for measuring the resistance of hard tissues of teeth of bioobjects works as follows.

Previously, in accordance with the proposed method, a control program is recorded in a non-volatile memory device integrated in the microprocessor 14 (for example, executed on a large integrated circuit such as AT89 SI 51E D2-3CU31IM). The control program implements the algorithm below, according to which the following actions and settings are performed in the device for diagnosing the state of tooth tissue of biological objects in the following sequence.

When the device is turned on, that is, when the power is connected, at the digital outputs of the first, second, third and fourth groups, as well as at the fifth control digital outputs of the microprocessor 13 of the system, the following initial control binary codes are set in accordance with the control program:

- on the first group of digital control outputs of the microprocessor 13 of the system, a binary code is set, according to which the minimum allowable voltage, for example, 3 V, is set at the output of the reference voltage regulator 2;

- a binary code is set on the second group of digital control outputs of the microprocessor 13 system, in accordance with which the electrode switching keys 7 are set, for example, to a state in which the active 5 electrode is connected to the output of the voltage regulator 2 and the input of the reference resistor 4 R ₀₁ - passive 6 electrode;

- a binary code is set on the third group of digital control outputs of the microprocessor 13 system, according to which, in the shunt 8 voltage divider, consisting of 8 ₁ , ..., 8 _m series-connected switching keys of the voltage divider and shunt resistors, all series-connected switching keys the voltage divider is in the open state, disconnecting the series-connected resistors with ratings 2R ₀ , 1,5R ₀ , ..., (1 + 1 / m) R ₀ from the active 5 and passive 6 electrodes;

- a binary code is set on the fourth group of digital control outputs of the microprocessor 13 system, according to which in the voltage divider 9, all 9 ₀ , ..., 9 _N-1 series-connected keys connect balancing reference resistances with ratings from 2 ⁰ R to 2 ^N-1 R to the output of the voltage regulator 2 and to the diagonal of the bridge on the one hand, and to the model 4 resistor R ₀₁ , on the other hand;

- from the fifth control digital output of the microprocessor 13 of the system to the zero-organ 12 receives a constant locking signal.

The listed initial state of the control binary codes in accordance with the proposed method sets the operation mode of the device, in accordance with which it is determined whether the measured resistance R _x belongs to the desired dynamic sub-range. The initial state is recorded in the form of the corresponding values of the program parameters in the storage device of the microprocessor 14, which is part of the microprocessor 13 of the system.

Before measuring the resistance of tooth tissues, a passive electrode 6, which is recommended to use a viewing mirror, is placed in the oral cavity. The active electrode 5, made, for example, in the form of a single syringe filled with calcium chloride with a blunt needle, is placed in the local, for example, in the fissure region of the tooth. As a result of the contact between the electrode and the studied area of the tooth, the working arm of the four-arm 3 resistive bridge is closed. The signal that determines the imbalance of the four-arm 3 resistive bridge due to inconsistencies of the measured R _x and the voltage of the resulting balancing model resistance originally installed in the divider 9 is fed to the first and second inputs of the instrument amplifier 10 from the second diagonal of the four-arm 3 resistive bridge. The output differential signal through the filter low frequencies 11 is fed to the information input of the zero-organ 12. To measure the active resistance of the studied local area of the tooth is not it is necessary to apply a start signal or a “start” signal to the microprocessor 14 by pressing the “start” button. The start button is not shown in FIG. 1, since it is an integral part of the control keyboard 15, its technical implementation does not affect the operation of the device as a whole. However, for the convenience of operation of the device, the "start" button can be duplicated on the remote control in the form of a special "clip" connected to a single syringe forming an electrode 5.

According to the “start” signal, the device, in accordance with the control program recorded a priori in the memory of the microprocessor 14, enters the measurement mode. In the measurement mode, through the fifth control digital output of the microprocessor 13 of the system, a pulse gating signal with a period of 10 ms and a duty cycle of at least 1000 is supplied to the control input of the null organ 12 from the corresponding output of the microprocessor 14. According to this gating pulse signal from the information output zero body 12 is read every 10 ms information signal corresponding to "unit" or "zero". The information signal “one” corresponds to an event in which the measured resistance R _x exceeds the initially set maximum exemplary balancing resistance at the 9 voltage divider in the symmetrical arm of the four-arm 3 resistive bridge, and “zero” - to the opposite event. To increase the reliability, the decision on the output information signal of the zero-organ 12 about the state of the control code of the voltage divider 9 is carried out majority. This means that the output information signal of the null-organ 12 is considered reliable according to the results of the analysis of multi-cycle comparison of the signals taken from the diagonal of the four-arm 3 resistive bridge arriving at the first and second input of the null-organ 12 depending on the a priori established majority basis. The majority basis determines the choice of the state of the information signal from the output of the null organ 12 from three to two or from five to three, which corresponds to the decision during the majority measure on the reliability of the output information signal of the null organ 12 according to two or three coinciding events out of three possible or five alternative ones appearing at the output of the null organ 12 in the form of signals corresponding to unity or zero. The majority time cycle (hereinafter simply the majority cycle) is equal to the total duration of the strobe pulse repetition periods, the number of which corresponds to the majority basis. In this case, after each majority clock cycle, the direction of the current of the probing electric signal changes due to the sequential switching of the contacts of the keys 7 of the switching electrodes according to the digital control signal from the first group of digital outputs of the microprocessor 13 of the system to the control inputs of the keys 7 of the electrode switching. Moreover, the switching time of the contacts of the keys 7 of the switching electrodes, as well as the time of establishing the voltage at the output of the regulator 2 of the reference voltage, is set much less than 10 ms, therefore, the transients associated with switching the contacts of the keys 7 of the switching of the electrodes and with the change of voltage at the output of the controller 2 of the voltage , do not affect the operation of the device as a whole.

After the first majority measure, two alternative events are possible. Suppose that the first event corresponds to the fact that R _x exceeds the initial maximum value of the model balancing resistance installed in the symmetrical arm of the four-arm 3 resistive bridge on 9 voltage divider. In this case, during the transition to the next majority clock cycle, the model balancing resistances initially set on the 9 voltage divider remain unchanged. According to the control code coming from the first and third groups of digital outputs of the microprocessor 13 of the system, the reference voltage at the output of the reference voltage regulator 2 increases more than 3 V, for example, by k V, that is, a voltage equal to (3 + k) V is established, and shunt resistance 2R _{0 is} connected in parallel with active 5 and passive 6 electrodes. The connection of the shunt resistance 2R ₀ defines a dynamic subrange with index m = 1. In the second majority cycle, after connecting the shunt resistance 2R _{0, the} information output signal of the zero-organ 12, previously amplified on the instrumental 10 amplifier and passed through the low-pass filter 11, is again majority-analyzed. If it is decided that the measured resistance R _x exceeds the dynamic sub-range with the following in order of the index value, the above-described process for determining the measured resistance R _x belonging to the dynamic followed subband value and Dex continues until the last of the maximum value of the index. If it is established that the measured resistance R _x exceeds the dynamic subrange and with the maximum index, the measurement process stops and a message appears on the LCD 16.

All intermediate values of binary codes are generated and stored in the memory of the microprocessor 14 in accordance with the control program that implements the above-described first stage of the combined analog-to-digital conversion algorithm.

If, for a dynamic subrange with a zero index, an information output signal of a zero-organ 12 appears, corresponding to such an alternative event, when R _x majority does not exceed the maximum Ro exemplary balancing resistance installed in the symmetrical arm of the four-arm 3 resistive bridge on the voltage divider 9, then the operating mode device changes as follows. On the voltage divider 9, in accordance with the control code coming from the fourth group of digital outputs of the microprocessor 13 system, all initially set exemplary balancing resistances from 2 ⁰ R to 2 ^N-2 R are disconnected, that is, shunted by the corresponding short-circuited key contacts from 9 ₀ to 9 _N-2 , except for the resistance of the highest category 2 ^N-1 R.

As before, in order to increase the reliability, the decision on the output information signal of the null-organ 12 on the further change of the control code of the voltage divider 9 is carried out majority-wise and the following two alternative events are possible after the first majority-cycle. The first event corresponds to the fact that R _x exceeds the initial exemplary balancing resistance 2 ^N-1 R installed in the symmetrical arm of the four-arm 3 resistive bridge on the voltage divider 9. In this case, when moving to the next majority measure, this resistance remains unchanged until the end of the conversion process. An alternative event corresponds to the fact that R _x does not exceed the initial value of the model balancing resistance 2 ^N-1 R installed in the symmetrical arm of the four-arm 2 resistive bridge on the voltage divider 9. When carrying out an alternative event, the resistance 2 ^N-1 R is disconnected, that is, it is shunted by the corresponding short-circuited key 9 of the voltage divider. Further, irrespective of the decision-making results at the first majority cycle, when switching to the second majority cycle in accordance with the control code set on the 4th group of digital outputs of the microprocessor 13 system, an exemplary balancing resistance 2 ^N-2 R is connected by switching the corresponding key contacts 9 _N-2 . In the second majority cycle, the decision to save or disable the resistor 2 ^N-2 R is carried out similarly to the method described above. After each majority cycle on the second group of digital control outputs of the microprocessor 13 system, the binary code is inverted synchronously with the beginning of the next majority cycle, and, in accordance with this, the contacts of the electrode switching keys 7 are set to the opposite state. Periodic inversion of the control code of the keys 7 for switching the electrodes leads to the fact that the active 5 or passive 6 electrodes are alternately connected to the output of the reference voltage regulator 2, and vice versa, then the passive 6 and then the active 5 electrodes are connected to the input of the reference resistor 4 R ₀₁ . Due to this, the direction of the current flowing through the active 5 and passive 6 electrodes changes, and the effect of the polarization effect on the results of digital measurement of the desired resistance R _{x is} practically eliminated.

After completing the second majority cycle, four combinations of the state of the keys and, therefore, the resistance values on the voltage divider 9 are possible:

- all keys remained in a closed state, which corresponds to a zero initial code;

- the high-order key is open, and the rest all the keys remain closed, which corresponds to a code that, in addition to the high-order digit, which is equal to one, all other digits remain at zero;

- the key following the high order is open, and the rest all the keys remain closed, which corresponds to a code that, except for the next high order, equal to one, all other digits remain at zero;

- the key of the senior and the following after the senior digit is open, and the rest all the keys remain closed, which corresponds to a code that, in addition to two high order bits equal to one, all other bits remain at zero.

As a result of the above steps, when determining the remaining bits of the code a _i from i = 1 to N _c inclusive, a control binary code is generated at the output of the fourth group of digital outputs of the microprocessor 13 system. This code corresponds to such a combination of key states 9 ₀ , ..., 9 _Nc-1 in 9 voltage divider, which determines the result of converting the measured resistance R _x into a binary code of the form

where a _i = 1, if the key 9 _i in the voltage divider 9 is in the open state and a _i = 0 for the opposite case, for j = 1,2, ..., N _c , in the dynamic sub-range with the index m = 0. In the dynamic range with index 0, the resistance R _x is measured in the range from zero to a maximum value equal to R (2 ^Nc -1). All intermediate values of binary codes and the code β _Nc obtained on the N _c clock cycle are generated and stored in the memory of the microprocessor 14 using a control program that implements the above-described stage of the combined analog-to-digital conversion algorithm.

In accordance with the proposed method, in order to reduce the error at the second stage of the combined analog-to-digital conversion algorithm, starting from the N _c +1 discharge, the mode of balancing the measured resistance changes. A sign for changing the balancing mode is only the discharge number N _c . In this case, the transition to a new conversion mode (stage) is carried out by a conditional transition, when the number of majority cycles on the microprocessor 14 software counter reaches the value of N _c . In accordance with the new balancing mode, the following actions are performed according to the signal of the microprocessor 14 software counter:

1) all the keys in the divider 9 initially remain in the state that was achieved before the execution of N _{c the} majority balance beat inclusively;

2) on N _c + 1-st majority stroke of balancing to the binary code β _Nc obtained on previous N _c majority _strokes , which is stored in the memory of microprocessor 14, one is added or subtracted by the output information signal of the zero-organ 12 determined by majority, 1;

3) in accordance with the resulting binary code received after each majority clock step coming from the 4th group of control digital outputs of the microprocessor system 13, the state of the keys 9 ₀ , ..., 9 _N-1 in the voltage divider 9 changes;

4) at the next N _c + 2nd majoritarian beat of balancing to the binary code obtained at the previous N _c + 1 majoritarian beat at the output information signal of the zero-organ 12, the unit is added or subtracted again and the conditions of paragraph (3) are satisfied.

Performing the above steps when determining the remaining bits of the code 2 ^N-Nc times, the result is a combination of the states of the keys 9 ₀ , ..., 9 _N-1 in the voltage divider 9, which corresponds to the result of converting the measured resistance R _x into binary code in dynamic sub-range from zero to a maximum value equal to R (2 ^N -1) = R ₀ . All intermediate values of binary codes, as well as during conversion to the first N _{c of} majority cycles, are generated and stored in the memory of microprocessor 14 in accordance with a program that implements the second stage of the above combined analog-to-digital conversion algorithm.

Suppose that the measured resistance R _x is in the subrange with index m> 0, in accordance with which the following actions are performed:

- a binary code is set on the first group of digital control outputs, according to which a voltage exceeding 3 V is set at the output of the voltage regulator 2, for example, at k V, that is, a voltage equal to (3 + k) V is set, where, for example , k = 1,2, ..., m;

- a binary code is set on the third group of digital control outputs, according to which in the shunt divider 8 voltage, consisting of 8 ₁ , ..., 8 _m series-connected switching keys of the voltage divider and shunt resistors, all series-connected switching keys of the voltage divider are installed in open state, except for the key 8 _k , as a result of which a resistor with a value of λ (m) R ₀ = (1 + m) R ₀ / m, (m = 1, 2, ...) is connected in series with the four shoulders 3 resistive bridge parallel to the active 5 and passive 6 electrodes, and the rest of the resistors connected in series with the corresponding keys remain disconnected;

- set to zero the initial control code supplied to the voltage divider 9, from the output of the fourth group of digital outputs of the microprocessor 13 system;

- based on the result of comparing the resistance R _xsh with a zero value, a control code is set that is supplied to the voltage divider 9 from the output of the fourth group of digital outputs of the microprocessor 13 of the system, corresponding to the resistance value determined by the formula

to determine R _0ypi (m) from the need to measure the resistance R _xh in the dynamic subband with index m> 0.

Next, the device repeats the actions in accordance with the description of the operation of the device in the dynamic subband with index 0, except for certain changes associated with the type of control code that is supplied to the voltage divider 9 from the output of the fourth group of digital outputs of the microprocessor 13 of the system. A change in the nonlinear function that describes the change in the control code of the voltage supplied to the inputs of the voltage divider 9 and, consequently, the change in the balancing model resistance, leads to a qualitative change, according to the proposed method, of the principle of balancing the measured resistance R _x in comparison with known methods and devices of analog-to-digital conversion.

In order to algorithmically describe the overall operation of a device that implements, in accordance with the proposed method, a combined algorithm for analog-to-digital conversion of the measured resistance R _x (digital measurement of R _x ), we describe its operation in the form of the following related system of algorithms. In accordance with the presented system of algorithms, a control program is implemented that is written a priori in the non-volatile memory of the microprocessor 14, which is part of the microprocessor 13 of the system. The microprocessor 13 system performs the function of a multifunctional control unit in the device, including the formation and implementation of: control signals from the control keyboard 15; recording and reading functions of both service information and measurement results from a storage device 17 with sequential recording and reading; additional function of indication of measurement results on LCD 16; data transmission through circuit 18 of the RS-232 interface on the upper level PC.

The first stage of the operation of the device is presented in the form of the following algorithm describing the operation of the device at the preliminary stage of determining the index of the dynamic subband to which the measured resistance R _x belongs:

wherein R _shj [(j) Δt _m] - the value of the shunt resistance for the m-th subband dynamic at j = m; Δt _m is the time majority interval multiple of 10 ms; R ₀₁ - the specified model resistance included in the symmetrical shoulders of the four shoulders of the 3 resistive bridge; R _0urmax (jΔt _m ) is the resistance defining the upper boundary of the dynamic subband for j = m;

- напряжение, характеризующее чувствительность четырехплечего 3 резистивного моста при m=1,2,...;

- voltage characterizing the sensitivity of the four shoulders of the 3 resistive bridge at m = 1,2, ...;

R _{0 urmax} (jΔt _m ) = R ₀ ; U _m = U ₀ + ΔU · m is the change in the initial voltage U ₀ at the output of the voltage regulator 2, depending on the index of the dynamic sub-range at m = 1,2, ...; R ₀₁ - exemplary 4 resistance;

- усиленный сигнал разбалансировки моста на выходе инструментального усилителя 10 с коэффициентом усиления К_у;

- amplified signal imbalance of the bridge at the output of the instrumental amplifier 10 with a gain of K _y ;

- сигнал разбалансировки моста, после усиления инструментальным усилителем 10 и фильтрации, на выходе фильтра 11 нижних частот с функцией фильтрации ψ[...];

- the bridge unbalance signal, after amplification by instrumental amplifier 10 and filtering, at the output of the low-pass filter 11 with the filtering function ψ [...];

- a function that describes the signal at the output of the zero-organ 12;

- мажоритарная функция принимающая значение 1, если мажоритарно выполняется условие R_хшm-R_{0урмакс}(jΔt_м)≥0 и ноль - в противоположном случае, реализуемая программно в микропроцессоре 14.

- the majority function assuming the value 1, if the condition R _хшm -R _0urmax (jΔt _m ) ≥0 is satisfied majority and zero - in the opposite case, implemented programmatically in microprocessor 14.

As can be seen from the preliminary stage of the combined algorithm, the belonging of the measured resistance R _{x to the} corresponding dynamic subband is determined by the value of the majority function equal to 1, which provides the transition function from the dynamic subband with a lower index to the dynamic subband with a large index.

If it is established that R _x belongs to a dynamic sub-range with index 0, then the program recorded in the microprocessor 14 and the control sequence of the output control digital signals of the microprocessor 13 of the system received at the control inputs of the above described elements of the device (reference voltage regulator 2, electrode switching keys 7, shunting 8 voltage divider, voltage divider 9 and null-organ 12), the next second and third stages of the combined analog-to-digital conversion algorithm are implemented.

For the second and third stages with m = 0, the corresponding record of the combined algorithm is represented as

- напряжение, характеризующее чувствительность четырехплечего 3 резистивного моста при m=0.Where

is the voltage characterizing the sensitivity of the four-arm 3 resistive bridge at m = 0.

At these stages, in contrast to the preliminary stage of operation of the device, the measured resistance R _x is converted to digital binary code by a combined analog-to-digital conversion algorithm. At the first stage, bitwise balancing is performed for the higher digits and at the second stage, the following balancing is performed for the lower digits with a majority decision on the value of each bit in the conversion process. For a dynamic subrange with index 0, the shunt resistances in the shunt 8 voltage divider are disabled.

If it is established that R _x belongs to a dynamic subband with an index exceeding zero, then in accordance with the control program, the following modified combined analog-to-digital conversion algorithm is implemented.

The corresponding modified combined algorithm that determines the operation of the control program recorded in the memory of microprocessor 14, which controls the sequence of output control digital signals of microprocessor 13 of the system, has the form

- напряжение, характеризующее чувствительность четырехплечего 3 резистивного моста для i-го разряда уравновешивающего двоичного кода; U_m=U₀+ΔU·m - изменение исходного напряжения U₀ на выходе регулятора 2 опорного напряжения в зависимости от индекса динамического поддиапазона; R₀₁ - образцовое 4 сопротивление; К_у и ψ[...] - коэффициент усиления К_у инструментального усилителя 10 и передаточная функция фильтра 11 нижних частот;Where

- voltage characterizing the sensitivity of the four-arm 3 resistive bridge for the i-th category of the balancing binary code; U _m = U ₀ + ΔU · m is the change in the initial voltage U ₀ at the output of the voltage regulator 2, depending on the index of the dynamic sub-range; R ₀₁ - exemplary 4 resistance; K _y and ψ [...] is the gain K of _the instrumental amplifier 10 and the transfer function of the low-pass filter 11;

- изменение уравновешивающего сопротивления для динамического поддиапазона с индексом m>0 при изменении номера разряда i от 1 до N_c в зависимости от изменения двоичного кода

- change in the resistance to dynamic equilibration subband with index m> 0 when changing the discharge rooms i from 1 to N _c, depending on the binary code changes

j = 1 + m, ..., m + N _c is the number of the majority balance beat;

- изменение уравновешивающего сопротивления для динамического поддиапазона с индексом m>0 при изменении номера разряда i от N_c+1 до N в зависимости от изменения двоичного кода

- a change in the balancing resistance for the dynamic subband with index m> 0 when the discharge number i changes from N _c +1 to N depending on the binary code change

j = m + 1 + N _c , ..., m + N _c +2 ^N-Nc is the number of the majority balance beat;

- значение результирующего измеряемого сопротивления зашунтированного сопротивлением λ(m)·R₀;

- the value of the resulting measured resistance shunted by the resistance λ (m) · R ₀ ;

- мажоритарная функция, принимающая значение 1, если мажоритарно выполняется условие

и ноль - в противоположном случае;

- majority function taking the value 1, if the condition is satisfied majority

and zero - in the opposite case;

- мажоритарная функция, принимающая значение 1, если мажоритарно выполняется условие

и -1 - в противоположном случае.

- majority function taking the value 1, if the condition is satisfied majority

and -1 in the opposite case.

As follows from the presented last stage of the modified combined algorithm, in contrast to the conventional bitwise balancing algorithm and the tracking conversion algorithm, in this algorithm, the code is corrected in accordance with the proposed method according to the sign of the mismatch error of the nonlinearly converted measured and balancing value. The implementation of this algorithm is based on the microprocessor 14. When implementing the considered analog-to-digital conversion algorithm, the balancing resistance for the dynamic subband with index m> 0 is changed using the binary control code, which comes from the fourth group of digital outputs of the microprocessor system 13 to the control inputs of the voltage divider 9 . This binary code is generated in accordance with the control program that implements the presented algorithm in the microprocessor 14. The value of the control code supplied to the control inputs of the voltage divider 9 is different from the binary code obtained by conventional bitwise balancing, or is calculated in accordance with the formula

in the current balance beat, or is calculated a priori and written to the non-volatile memory 17 with sequential recording and reading. In both cases, the code-to-code conversion function is implemented. Modern non-volatile memory devices with sequential write and read, for example, Atmel firms have a capacity of 4 MB and allow you to record data on 18 or more bit binary code and thereby serve as a code-to-code converter.

Thus, the present invention, due to the implementation of the combined analog-to-digital conversion algorithm with the majority setting of the binary digits and the implementation of the nonlinear balancing function of the measured resistance, significantly expands the dynamic range of the digital measurement of the resistance of biological objects while maintaining a given relative conversion error.

Indeed, as a result of digital measurement, the desired resistance appears in the idea

- есть результат преобразования в m-ом выбранном динамическом поддиапазоне. Полная погрешность цифрового измерения, независимо от m-ого выбранного динамическом поддиапазона, складывается из двух составляющих. Первая составляющая - это погрешность выбора динамического поддиапазона и вторая составляющая - это погрешность аналого-цифрового преобразования в выбранном динамическом поддиапазоне. Причем в соответствии с предложенным способом благодаря мажоритарному анализу результатов сравнения измеряемого и уравновешивающего сопротивления, нелинейному комбинированному аналого-цифровому преобразованию входного сопротивления в динамическом поддиапазона с индексом m>0, а также использованию для усиления ошибки разбалансировки четырехплечего 3 резистивного моста инструментального 10 усилителя, фильтра 11 нижних частот и согласованному увеличению источника питания четырехплечего 3 резистивного моста за счет введения регулятора 2 опорного напряжения, увеличение первой и второй составляющей погрешности за счет снижения чувствительности моста при увеличении измеряемого сопротивления сводится к минимуму. Слабая зависимость результирующей погрешности цифрового измерения искомого сопротивления от выбранного динамического поддиапазона существенно расширяет общий динамический диапазон измерения искомого сопротивления диагностируемых биообъектов и повышает надежность их диагностики. Синхронное с аналого-цифровым преобразованием изменение полярности зондирующего сигнала, приложенного к активному и пассивному электродам, устраняет погрешность поляризации.where m is the index of the selected dynamic subband, and the binary code

- there is the result of the conversion in the mth selected dynamic subband. The total error of the digital measurement, regardless of the m-th selected dynamic sub-range, consists of two components. The first component is the error of the choice of the dynamic subband and the second component is the error of the analog-to-digital conversion in the selected dynamic subband. Moreover, in accordance with the proposed method, due to the majority analysis of the results of comparison of the measured and balancing impedances, the nonlinear combined analog-to-digital conversion of the input impedance in the dynamic sub-band with the index m> 0, as well as the use of instrumental amplifier 10, filter 11 low frequencies and a coordinated increase in the power supply of the four-arm 3 resistive bridge due to the introduction of a regulator and 2 reference voltages, an increase in the first and second component of the error due to a decrease in the sensitivity of the bridge with an increase in the measured resistance is minimized. The weak dependence of the resulting error of digital measurement of the required resistance on the selected dynamic sub-range significantly expands the overall dynamic range of measurement of the desired resistance of the diagnosed biological objects and increases the reliability of their diagnosis. Synchronous with analog-to-digital conversion, a change in the polarity of the probe signal applied to the active and passive electrodes eliminates the polarization error.

Claims (4)

1. A method of measuring the resistance of hard tissues of teeth of biological objects when exposed to teeth by an electric constant signal using a passive and active electrodes, characterized in that the full dynamic range of resistance changes at the preliminary stage is divided into a final indexed (numbered) number of dynamic subranges according to the permissible value of the reduced error of the analog -digital conversion of the measured resistance; within each dynamic subband, majority and sequentially at discrete time instants through an interval multiple of 10 ms, according to the results of exposure to a constant electric probe signal, the resistance of tissues to the corresponding dynamic subrange is determined, starting with a minimum index value of zero; within the found and established sub-range, the analog-to-digital conversion of the measured tissue resistance is carried out in combination in the following two stages: majority and sequentially at discrete time instants over an interval multiple of 10 ms, for each fixed number of bits, the values of each category are determined by sequential balancing of the measured resistance, varying model resistance starting from the senior bit to some fixed intermediate bit; and for the remaining part of the least significant bits at the second stage in the same sub-range, they also perform majority over a time interval uniformly distributed in the range from a certain minimum value to a value of 20 ms by analog-to-digital conversion by sequential balancing of the measured tissue resistance, varying model resistance with a correction of one the lower order to the greater or lower side of the binary code received on the previous high-order bits; if the affiliation of the measured tissue resistance to a dynamic subrange with a zero index is established, then within it, at the first stage for a fixed number of digits, the analog-to-digital conversion of the measured resistance by sequential balancing, starting from the highest level, is performed bitwise, assigning to each category the corresponding balancing weight reference resistance, and for the remaining part of the least significant bits in the same sub-band perform analog-to-digital conversion with correction of balancing resistance up or down by a discrete value corresponding to the weight of the least significant bit; when establishing the affiliation of the measured resistance of biological objects to a dynamic sub-range with an index exceeding the minimum zero value, the weight of the balancing model resistance is established for each discharge in the first and second stages of analog-to-digital conversion according to a nonlinear law determined by the value of the change in the resulting resistance equal to the measured tissue resistance connected in parallel and fixed shunt model resistance in the set dynamics sub-band other than the weight of the bitwise and tracking balancing set for the dynamic sub-band with a zero index. 2. The method according to claim 1, characterized in that, if it is majority and sequentially at discrete time instants after an interval multiple of 10 ms, it is established that the measured resistance value exceeds the selected dynamic subband, then when switching to a dynamic subband with a large index synchronously with an increase in the index is changed upward, but within the specified limits, the voltage value of the electrical sounding signal. 3. The method according to claim 1, characterized in that when determining the index of the dynamic subband and during analog-to-digital conversion within the established dynamic sub-range, the polarity of the probe electric signal applied to the passive and active electrodes is changed, each time when switching in a balancing binary code from discharge to discharge. 4. A device for measuring the resistance of hard tissues of teeth of biological objects, containing electrodes, a reference voltage source, a zero-organ, a low-pass filter, an instrument amplifier and a digital measuring device with a liquid crystal display, characterized in that a reference voltage regulator, electrode switching keys are inserted into it , a resistive bridge, in the symmetrical shoulders of which are included a shunt voltage divider and reference resistors with resistances of the same nominal value, a voltage divider is made in the form of series-connected resistors and keys, and the digital measuring device with a liquid crystal display is made in the form of a microprocessor system, including a microprocessor with a keyboard connected to it, a memory device and an RS-232 interface circuit, while the first group of microprocessor outputs is connected to the control the inputs of the reference voltage regulator, the input of which is connected to the output of the reference voltage source, and the output is connected to the first diagonal of the resistive bridge, the second diagonal which is connected to the inputs of the instrumental amplifier, the output of which through the low-pass filter is connected to the first input of the zero-organ, the second input of which is connected to the common bus, and its information output is connected to the information input of the microprocessor, the second group of outputs of the microprocessor is connected to the control inputs of the switching keys electrodes, the inputs of which are connected to the electrodes, and the outputs are connected to the inputs of the shunt voltage divider, the control inputs of which are connected to the third group of micro outputs otsessora, the fourth group of outputs of which is connected to the control inputs of the voltage divider, and its fifth output - to the control input of the zero-body.

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