RU2121336C1 - Method of measuring of electrodermal resistance - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: method is based on connection of series-connected calibrated fixed and variable resistors between measuring and first auxiliary electrodes, on measurement of voltage drop between measuring and second auxiliary electrodes and on calibrated fixed resistor at periodical variation of value of calibrated variable resistor, and on calculation of electrodermal resistance by obtained values of voltage drop and resistance of calibrated fixed resistor. Novelty is in periodical variation of value of calibrated variable resistor at preset frequency and in measurement of variable components of voltage drop. This made it possible to enhance measurement accuracy due to decrease in errors caused by effect of millivoltmeter input resistance and polarization potentials. EFFECT: enhanced measurement accuracy. 2 dwg

Description

 The invention relates to medicine and medical equipment and can be used in the diagnosis and treatment of diseases by electro-puncture methods.

 The reliability of diagnostic tests using electropuncture methods is largely determined by the accuracy of measuring the electrical resistance (EX).

 A known method of measuring the skin resistance of acupuncture points on.with. USSR N 1111760 A, class A 61 H 39/02, declared 05/28/82, which includes applying to the acupuncture point of the measuring and outside its indifferent and additional electrodes, measuring the difference in electric potentials between the measuring and indifferent electrodes, switching on a calibrated resistor between the measuring and additional electrodes, re-measuring the difference potentials between the measuring and indifferent electrodes when a calibrated resistor is connected, measuring the voltage drop across a calibrated resistor and calculating the electrical cutaneous about resistance by the values of the measured potential differences and voltage drops and the values of the calibrated resistor.

 The disadvantage of this method is the low accuracy of the measurement due to the influence of the final value of the input resistance of the millivoltmeter used in the implementation of the method, and the arbitrary choice of the indifferent and additional electrodes. With a certain combination of potential differences between the measuring and indifferent, as well as measuring and additional electrodes (if the potential difference between the measuring and indifferent electrodes is larger than the potential difference module between the measuring and additional electrodes), using the known method significant measurement errors are possible, reaching tens of percent even with a large input impedance of a millivoltmeter (100 MΩ or more). In addition, in the known method, a constant measuring current passes through the ECS TA when a calibrated resistor is connected, the value of which is determined by the potential difference between the measuring and indifferent electrodes and the resistance of the calibrated resistor. As a result of this, the polarization processes taking place both in biological tissues and at the interface between the electrode and the skin have an effect on the accuracy of the measurement of ECS. Polarization processes cause the appearance of polarization potentials that are included in the acupuncture point resistance measurement circuit, which leads to a change in the recorded potential differences and further reduces the accuracy of the measurement of electric skin resistance. The value of polarization potentials will depend on the measuring current, which is not standardized in the known method, the measurement time and the electrodes used.

 Thus, the main disadvantage of the known analogue method is the low accuracy of the measurement of electric resistance.

где
U₁ - разность потенциалов между измерительным и вторым дополнительным электродом при отключенном калиброванном резисторе;
U₂ - то же, при подключенном калиброванном резисторе;
U₃ - падение напряжения на калиброванном резисторе;
R - сопротивление калиброванного резистора.Closest to the invention according to the achieved result is a method of measuring the electric skin resistance of acupuncture points by AS USSR N 1683745 A1, cl. A 61 H 39/02, declared 11/17/88, including the application of a measuring electrode on the acupuncture point and outside of its two additional electrodes, determining the potential difference between the measuring and each of the additional electrodes and comparing them modulo, an additional electrode whose potential is relatively the measuring electrode is of greater importance modulo, called the first additional electrode, the inclusion of a calibrated resistor between the measuring and the first additional electrodes, measuring the potential difference between dy measuring and second additional electrodes and the voltage drop across a calibrated resistor, and calculating the value of the electric resistance R _TA acupuncture points according to the formula:

Where
U ₁ is the potential difference between the measuring and the second additional electrode with the calibrated resistor disconnected;
U ₂ - the same, when a calibrated resistor is connected;
U ₃ - voltage drop across a calibrated resistor;
R is the resistance of a calibrated resistor.

 The named method is selected as a prototype of the claimed method as coinciding with it by the maximum number of features.

 In the prototype method, by selecting an additional electrode to which a calibrated resistor should be connected, it is possible to increase the accuracy of measurements by significantly reducing the error component from the influence of the input resistance of the millivoltmeter.

 The disadvantage of this method is the lack of measurement accuracy.

где
Z₁ и Z₂ - сопротивления кожного покрова под первым и вторым дополнительными электродами;
R_вх - входное сопротивление милливольтметра.Due to the influence of the input resistance of the millivoltmeter, the measurement error by the known method is determined by the expression (1) given in the description of the copyright certificate:

Where
Z ₁ and Z ₂ - resistance of the skin under the first and second additional electrodes;
R _I - input resistance of a millivoltmeter.

For real resistance values with a large input resistance of a millivoltmeter (R _in = 100 MΩ), the measurement error of the prototype method is determined by units of percent. So at resistances: Z _TA = 50 kOhm; Z ₁ = Z ₂ = 300 kOhm; R = 500 kOhm the measurement error by the prototype method will be γ = 6%. When using a millivoltmeter with a lower input resistance, the measurement error will increase in proportion to a decrease in the input resistance, and with an input resistance R _I = 30 MΩ (which is quite realistic when using the method), the error will be γ = 20%.
In addition, in the prototype method, as well as in the analogue method, a constant measuring current passes through the ECS TA. As a result of this, the accuracy of measuring the EX when using the prototype method is also influenced by polarization processes, which lead to the appearance of polarization potentials that change the recorded potential differences, which further reduces the accuracy of the measurement of electric skin resistance. In this case, the value of polarization potentials will depend on the measuring current, which is not standardized in the known prototype method, on the measurement time and on the electrodes used.

 Thus, the disadvantages of the known methods are determined by the low accuracy of measuring the electric resistance.

 The aim of the invention is to improve the accuracy of measuring electric resistance.

 This goal is achieved by the fact that according to the method of measuring the electric skin resistance of acupuncture points, including applying a measuring and two additional electrodes to the acupuncture point, connecting a calibrated resistor with a known resistance between the measuring and one of the additional electrodes, measuring the potential difference between the measuring and second additional electrodes , measuring the voltage drop across a calibrated resistor and calculating the value of the electric the surrounding resistance of the acupuncture point between the measuring and the first additional electrodes include a calibrated resistor consisting of a series connection of constant and variable calibrated resistors, periodically changing the resistance of the variable calibrated resistor with a given frequency in the selected resistance range and measuring the variable components of the voltage drop between the measuring and the second additional electrodes and at a constant calibrated cut Store and from the values of the voltage drops and DC resistance of the calibrated resistor is determined electrodermal resistance acupuncture points.

 With this embodiment, the method of measuring the electrical resistance by periodically measuring the resistance of a variable calibrated resistor with a given frequency in the selected resistance range ensures the measurement of electrical resistance by an alternating measuring current, which eliminates measurement errors due to polarization potentials and the influence of the input resistance of a millivoltmeter, and therefore improves the accuracy measurements.

где
U₁ - амплитуда падения напряжения на постоянном калиброванном резисторе;
U₂ - амплитуда падения напряжения между измерительным и вторым дополнительным электродами;
R₀ - сопротивление постоянного калиброванного резистора.The method consists in the fact that a measuring electrode is applied to the studied skin in the area of the acupuncture point and two additional electrodes are placed outside it and fixed to the patient’s body. Between the measuring and the first additional electrode include a calibrated resistor, consisting of a series connection of constant and variable calibrated resistors with a resistance of 100 to 500 kOhm, periodically change the resistance of a variable calibrated resistor with a given frequency in a selected resistance range. Using a millivoltmeter of alternating current with a large input resistance (100 MΩ or more), the amplitudes of the voltage drops U ₁ are determined on a constant calibrated resistor and U ₂ between the measuring and the second additional electrodes. Then calculate the value of electric skin resistance Z _TA acupuncture points according to the formula:

Where
U ₁ - the amplitude of the voltage drop across a constant calibrated resistor;
U ₂ - the amplitude of the voltage drop between the measuring and the second additional electrodes;
R ₀ is the resistance of a constant calibrated resistor.

 The invention is illustrated by drawings. In FIG. 1 shows a functional diagram of a specific implementation of the proposed method; in FIG. 2 - equivalent circuit measuring circuits of electric current when measuring voltage drops in the proposed method.

 According to the proposed method, in the form of a node 1, an equivalent circuit diagram of a skin site is presented, a measuring electrode 2, first and second additional electrodes 3, 4, a calibrated resistor 5, a variable calibrated resistor 6, a constant calibrated resistor 7, a switch 8 and an AC millivoltmeter 9.

Scheme 1 substitution of the skin is presented in the form of a Schaeffer model (see Macs Phillippe. The study of human skin impedance for low-frequency currents. - These. Dat. Ing. Univ. Nancy, 1973. - 96 p.), Where E ₁ , E ₂ and E ₃ are the electrodermal potentials, and Z _x , Z ₁ and Z ₂ are the electrodermal resistances at the points of the measuring electrode 2 - (A1 is the acupuncture point) and additional electrodes 3, 4 (at the indifferent points of the skin A ₂ and A ₃ ), respectively .

где
R - сопротивление калиброванного резистора 5.Additional electrodes 3, 4 are fixed in the selected indifferent area of the skin, and measuring electrode 2 is attached to the acupuncture point. Then, a calibrated resistor 5 is connected between the measuring electrode 2 and the first additional electrode 3, consisting of a series-connected variable calibrated resistor 6 and a constant calibrated resistor 7. In this case, an electric current I will flow through the electric circuit between the measuring electrode 2 and the first additional electrode 3, which can be determined based on Ohm's law for a complete circuit, considering the current path:

Where
R is the resistance of the calibrated resistor 5.

With a periodic change in the resistance of the calibrated resistor 5 to the selected value 2ΔR by changing the resistance of the variable resistor 6 with a frequency F in the range from
R _max = R _cp + ΔR = R ₀ + 2ΔR
before
R _min = R _cp -ΔR = R ₀ ,
Where
R _cp = R ₀ + ΔR is the average value of the calibrated resistor 5, R ₀ is the resistance of a constant calibrated resistor 7, 2ΔR is the resistance of a variable calibrated resistor 6, the current I will periodically change in the range from I _max to I _min . The frequency F of the periodic variation of the variable calibrated resistor is chosen equal to the frequency of the variable measuring signal depending on the conditions of experimental studies (for example, F = 100 Hz).

Соответственно, минимальное значение протекающего тока I_min, будет соответствовать максимальному значению сопротивления калиброванного резистора 5:

Таким образом при периодическом изменении сопротивления калиброванного резистора 5 с частотой F также будет изменяться электрический ток I, проходящий в цепи между измерительным 2 и первым дополнительным 3 электродами. При этом, среднее значение тока I₀ и его амплитуду ΔI можно найти:

Подставляя в выражения (5), (6) значения токов из выражений (3), (4) получим следующее:

Изменяющийся ток в анализируемой цепи можно рассматривать как сумму двух токов: постоянного I₀ и переменного с амплитудой ΔI. Этот ток будет замыкаться через сопротивление точки акупунктуры Z_x.The maximum current value I _max will correspond to the minimum resistance R _{min of the} calibrated resistor 5:

Accordingly, the minimum value of the flowing current I _min will correspond to the maximum value of the resistance of the calibrated resistor 5:

Thus, with a periodic change in the resistance of the calibrated resistor 5 with a frequency F, the electric current I passing in the circuit between the measuring 2 and the first additional 3 electrodes will also change. Moreover, the average current value I ₀ and its amplitude ΔI can be found:

Substituting the values of currents from expressions (3), (4) into expressions (5), (6), we obtain the following:

The changing current in the analyzed circuit can be considered as the sum of two currents: constant I ₀ and variable with an amplitude ΔI. This current will be shorted through the resistance of the acupuncture point Z _x .

When the current passes through the resistance of the acupuncture point Z _{x, a} voltage drop will be created on the resistance both from the constant I ₀ and from the variable ΔI components.

Переключая милливольтметр 9 с помощью коммутатора 8 к постоянному калиброванному резистору 7 можно измерить падение напряжения U₁ от переменной составляющей тока на постоянном калиброванном резисторе 7, которое можно получить, вычисляя падения напряжений на постоянном калиброванном резисторе 7 при минимальном U_imax и максимальном U_imin значениях калиброванного резистора 5:

Т. к. сопротивление постоянного R₀ и переменного 2ΔR калиброванных резисторов известны, то по напряжению U₁ можно определить значение переменной составляющей тока ΔI, протекающего по контуру между точками A₁ и A₂ при периодическом изменении сопротивления переменного калиброванного резистора 6:

И на основании выражений (9), (11) можно определить сопротивление Z_ТА точки акупунктуры:

Предлагаемый способ повышает точность измерения электрокожного сопротивления точек акупунктуры за счет исключения влияния на результат поляризационных процессов. Выражения (9) - (12) показывают, что регистрируемое по способу сопротивление точки акупунктуры не зависит от суммарной контурной электродвижущей силы (E₁ - E₂) в цепи прохождения тока между измерительным 2 и первым дополнительным 3 электродами, а следовательно, ее изменение за счет поляризационных потенциалов не влияет на определяемое по способу сопротивление точки акупунктуры.If using a millivoltmeter 9 of alternating current to measure the voltage drop between the points A ₁ and A _{3 of the} location of measuring 2 and the second additional 4 electrodes, then the millivoltmeter 9 will record the following voltage value:

By switching the millivoltmeter 9 using the switch 8 to a constant calibrated resistor 7, it is possible to measure the voltage drop U ₁ from the alternating current component on the constant calibrated resistor 7, which can be obtained by calculating the voltage drops on the constant calibrated resistor 7 with a minimum U _imax and maximum U _imin values of the calibrated resistor 5:

Since the resistance of the constant R ₀ and variable 2ΔR calibrated resistors are known, the voltage U ₁ can be used to determine the value of the variable component of the current ΔI flowing along the circuit between points A ₁ and A ₂ with a periodic change in the resistance of the variable calibrated resistor 6:

And on the basis of expressions (9), (11), it is possible to determine the resistance Z _{TA of} the acupuncture point:

The proposed method improves the accuracy of measuring the electric resistance of acupuncture points by eliminating the influence on the result of polarization processes. Expressions (9) - (12) show that the acupuncture point resistance recorded by the method does not depend on the total contour electromotive force (E ₁ - E ₂ ) in the current path between the measuring 2 and the first additional 3 electrodes, and therefore, its change after the account of polarization potentials does not affect the resistance of the acupuncture point determined by the method.

 In addition, in the proposed method, the measurement error from the shunting effect of the input resistance used in the implementation of the AC millivoltmeter 9 method is significantly reduced.

To assess the measurement error due to the influence of the input resistance R _I millivoltmeter 9, we consider the equivalent circuit of the passage of electric current when measuring voltage drops.

In FIG. 2a shows an equivalent circuit of the measuring circuit when measuring voltage U ₁ , FIG. 2b - when measuring voltage U ₂ .

И напряжение U_{i пост} от протекающего постоянного тока I'_i, будет равно:

Переменную составляющую падения напряжения U₁ при изменении сопротивления переменного калиброванного резистора 6 можно будет представить в виде:
U₁= U_{1 пост max}-U_{1 пост max}/2,
или

При измерении падения напряжения U₂ милливольтметр 9 подключается к точкам A₁, A₃ (фиг. 2б).When measuring voltage U _{1, the} input resistance R _{I of the} millivoltmeter 9 is connected in parallel with the constant calibrated resistor 7. With a large input resistance of the millivoltmeter 9 (R _I >> R ₀ ), the current I ' _i flowing in the circuit can be written as:

And the voltage U _{i post} from the flowing direct current I ' _i will be equal to:

The variable component of the voltage drop U ₁ when changing the resistance of a variable calibrated resistor 6 can be represented in the form:
U ₁ = U _{1 post max} -U _{1 post max} / 2,
or

When measuring the voltage drop U ₂ millivoltmeter 9 is connected to the points A ₁ , A ₃ (Fig. 2B).

(17)
Подставляя выражение (17) в выражение (16), и преобразовывая относительно I₃ получим:

Пренебрегая в выражении (18) из условий: R_вх >> Z₂, R_вх(Z_x + Z₁ + R) >> Z_x(Z₁ + Z₂ + R), соответствующими значениями для тока I₃ запишем:

Падение напряжения от постоянного тока между точками A₁ и A₃ - U_{2 пост} можно найти из произведения:

или

Преобразовывая выражение (20) (прибавляя к обеим частям уравнения значение Z_x(E₁ - E₂)/(Z_x + Z₁ + R) получим:

Переменную составляющую напряжения U₂ можно определить в виде:

Подставляя в выражение (22) соответствующие значения, полученные на основании выражения (21) при изменении сопротивления калиброванного резистора 5 в пределах от R₀ до R₀+2ΔR получим следующее:

По значениям напряжений U₁, U₂ и сопротивления R₀ определяем сопротивление точки акупунктуры, используя выражения (14) и (23):

Выражение (24) показывает, что с учетом принятых допущений на погрешность измерения не влияет входное сопротивление милливольтметра 9. При этом погрешность измерения за cчет шунтирующего действия входного сопротивления милливольтметра 9 определяется сделанными при выводе выражения (24) допущениями, анализ которых показывает, что погрешность измерения за счет входного сопротивления милливольтметра определяется выражением (25), полученным на основании выражения (18) путем определения процентного соотношения выражений, пренебрегаемых при выводе формулы погрешности измерения:

И для реальных значений сопротивлений при сопротивлениях: Z_ТА = 50 кОм; Z₁ = Z₂ = 300 кОм; R = 500 кОм; R_вх = МОм погрешность измерения по предлагаемому способу будет составлять

0,35%.To determine the voltage U _{2 we} use the method of loop currents. Choosing the direction of the currents in the circuits I and II and asking contour currents I ₁ and I ₃ you can write the equation:
(Z _x + Z ₁ + R) I ₁ - (Z ₁ + R) I ₃ = E ₁ - E ₂ (15)
- (Z ₁ + R) I ₁ + (Z ₁ + Z ₂ + R + R _in ) I ₃ = E ₂ - E ₃ (16)
Adding the expression (- Z _x I ₁ ) to both sides of equation (16) and adding the resulting equation with equation (15) for current I ₁ we get:

(17)
Substituting expression (17) into expression (16), and transforming with respect to I ₃ we obtain:

Neglecting in expression (18) from the conditions: R _in >> Z ₂ , R _in (Z _x + Z ₁ + R) >> Z _x (Z ₁ + Z ₂ + R), we write the corresponding values for current I ₃ :

The voltage drop from DC between points A ₁ and A ₃ - U _{2 post} can be found from the product:

or

Transforming the expression (20) (adding to both sides of the equation the value Z _x (E ₁ - E ₂ ) / (Z _x + Z ₁ + R) we obtain:

The variable voltage component U ₂ can be defined as:

Substituting in the expression (22) the corresponding values obtained on the basis of the expression (21) when changing the resistance of the calibrated resistor 5 in the range from R ₀ to R ₀ + 2ΔR we get the following:

Using the values of voltages U ₁ , U ₂ and resistance R _{0, we} determine the resistance of the acupuncture point using expressions (14) and (23):

Expression (24) shows that, taking into account the assumptions made, the input resistance of the millivoltmeter 9 does not affect the measurement error. Moreover, the measurement error due to the shunt action of the input resistance of the millivoltmeter 9 is determined by the assumptions made when deriving expression (24), the analysis of which shows that the measurement error due to the input resistance of a millivoltmeter, it is determined by expression (25) obtained on the basis of expression (18) by determining the percentage of the expressions neglected when measurement error ode formula:

And for real values of resistances at resistances: Z _TA = 50 kOhm; Z ₁ = Z ₂ = 300 kOhm; R = 500 kΩ; R _I = MOhm measurement error by the proposed method will be

0.35%.

1,2% (в способе-прототипе при аналогичных условиях погрешность измерения может достигать

20%), что вполне приемлемо для любых диагностических систем, использующих методы электропунктуры. При этом в предлагаемом способе не требуется проводить функциональный выбор дополнительных электродов, что сокращает время измерений. Кроме того исключение погрешностей от поляризационных процессов в отличие от способа-прототипа при использовании предлагаемого способа позволяет получать высокую точность измерения при выборе любого типа электродов и неограниченном времени проведения диагностических исследований, что позволяет на основе предлагаемого способа реализовать системы для долговременного контроля за состоянием пациентов в специализированных диагностических комплексах.Thus, the proposed method provides a measurement with minimal error from the shunt action of the input resistance of the millivoltmeter 9, significantly less than the measurement error when using the prototype method. This allows you to use for the implementation of the proposed method millivoltmeter 9 with a lower input resistance, which simplifies and cheapens the hardware implementation of the proposed method. So when using a millivoltmeter 9 with an input resistance R _I = 30 MΩ and above the combination of resistances, the measurement error due to the shunting action of the millivoltmeter will be

1.2% (in the prototype method under similar conditions, the measurement error can reach

20%), which is quite acceptable for any diagnostic systems using electropuncture methods. Moreover, the proposed method does not require a functional selection of additional electrodes, which reduces the measurement time. In addition, the exclusion of errors from polarization processes, unlike the prototype method, when using the proposed method allows to obtain high measurement accuracy when choosing any type of electrodes and unlimited time for diagnostic studies, which allows us to implement systems for long-term monitoring of patients in specialized diagnostic complexes.

 Thus, the proposed method provides high accuracy in measuring the electrical resistance and can be widely used to create instruments for diagnostic systems using diagnostic methods for electrical resistance, for example, when implementing electro-puncture methods.

Claims (1)

A method for measuring the skin electrode resistance of acupuncture points, including applying a measuring and two additional electrodes to the acupuncture point, connecting a calibrated resistor with a known resistance between the measuring and one of the additional electrodes, measuring the potential difference between the measuring and the second additional electrodes, measuring the voltage drop across the calibrated resistor and calculating, according to the measurement results, the values of electric skin resistance of the acupuncture point, excellent In order to increase the measurement accuracy, between the measuring and the first additional electrodes it includes a calibrated resistor, consisting of a series connection of constant and variable calibrated resistors, additionally periodically vary the resistance of the variable calibrated resistor with a given frequency in the selected resistance range and measure the variable components voltage drops between the measuring and second additional electrodes and at constant calibres the resistor and the value of the voltage drop and the resistance of the constant calibrated resistor calculate the value of the electric skin resistance Z _TA acupuncture points according to the formula
Z _TA = R ₀ U ₂ / U ₁ ,
where U ₁ - the amplitude of the voltage drop across a constant calibrated resistor;
U ₂ - the amplitude of the voltage drop between the measuring and the second indifferent electrode;
R ₀ is the resistance of a constant calibrated resistor.

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