RU2121294C1 - Device for measuring of electrodermal resistance - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: device has two amplifiers, measuring and two passive electrodes, three electronic switches, comparator, two storage units, two multivibrators, commutator, two calibrated resistors, amplitude detector, controllable voltage divider, standard voltage source, and recorder. Introduction into device of commutator, two calibrated resistors, amplitude detector, controllable voltage divider, second multivibrator, and standard voltage source enabled measurement of electrodermal resistance on measuring alternating current at minium amplitude of the latter, which made it possible to enhance measurement accuracy due to elimination of errors caused by effect of polarization potentials and by variation of recorded parameters because of measuring current action. EFFECT: enhanced measurement accuracy. 2 dwg

Description

 The invention relates to medical equipment, and in particular to devices for measuring skin resistance at acupuncture points used in electropuncture diagnostic studies.

 The reliability of diagnostic studies largely depends on the errors in the measurement of electric skin resistance, which are mainly determined by the measurement methods and instruments used, and should not exceed the minimum recorded informative changes in the measured parameters. Considering the minimum recorded informative changes in electric skin resistance with electro-puncture diagnostic methods equal to 5 - 10% of the measured resistance value, we can determine the total permissible error in the measurement of electric skin resistance, which should not exceed for reliable assessment of the results of one percent in a wide range of possible values of electric skin resistance, defined by 10 - 500 kOhm (see Voll. R. Arbeitsrichlinien fur die Elektroakupunktur. - Hamburg, Blume, 1963).

 A device for measuring electric skin resistance by AS USSR N 1215202, class A 61 H 39/02, claimed 06/28/84, containing three electrodes, a current regulator connected to the first electrode, a recorder connected to the first and second electrodes, a differential amplifier whose output is connected to the third electrode, an inverting input connected to the second electrode, and a non-inverting one to the second output a current regulator, the third output of which is connected to the third input of the recorder.

 In the known device, the analogue, a measuring current of constant amplitude with values reaching units of microamperes is passed through the electric skin resistance, and the electric skin resistance is measured by the voltage drop at the desired resistance. In this case, a sufficiently large potential difference reaching several volts can be created in the studied area of the skin. As a result, a breakdown of the membranes of the skin cells is possible, as well as a violation of the intactness of the acupuncture points, and as a result of this, a mismatch of the obtained resistance values with the true values, which determines the measurement errors.

 Thus, the main disadvantage of the known device is an analogue is the lack of accuracy in measuring electric skin resistance.

 The closest in technical essence and the achieved result to the proposed technical solution is a device for searching acupuncture points by a.s. USSR N 1060185, class A 61 H 39/02, claimed 08/11/82, containing an amplifier, to the first input of which a measuring electrode is connected and the first output of a controlled resistor, the input of which is connected to the output of the matching unit, the first passive electrode connected to the input of the voltage follower, the second passive electrode connected to a common bus, the repeater voltage, the input of which is connected to the first passive electrode, the first electronic switch, the first output of which is connected to the output of the voltage follower and the second input of the amplifier, and the second output to the second output of the control a resistor, a second amplifier, a first and a second recorder, a second electronic key, a third amplifier, a first memory block, a comparator, a third electronic key and a second memory block, a multivibrator, two matching circuits and a trigger whose input is connected to the multivibrator output and the first the inputs of the matching circuits, the first output of which is connected to the input of the first electronic key and the second input of the second matching circuit, and the second output is connected to the second input of the first matching circuit, the output of which is connected to an ode of the second electronic key, the output of the amplifier is connected to the output of the second electronic key and through the second amplifier with the second input of the comparator, the output of the second memory block is connected to the input of the matching unit and the second registrar, the output of the second matching circuit is connected to the input of the third electronic key, and the first registrar is with the output of the first memory block.

 The named device is selected as a prototype of the claimed device as matching with it according to the maximum number of features.

 In the prototype device, the measurement of electric skin resistance is carried out at a minimum value of a constant measuring current, determined by the difference in electric skin potentials, electric skin resistances and the resistance of the controlled resistor, which reduces the measurement errors due to the influence of the measuring current on the skin condition. In this case, the use of a constant measuring current leads to the appearance of polarization potentials that change the recorded differences of the electrodermal potentials during the measurement tests, and, consequently, to the appearance of measurement errors determined both by the duration of the research process and by the electrodes used for measurement.

 In addition, in the prototype device, the measurement of electric skin resistances is carried out according to the resistance values of the controlled resistor, which is changed in proportion to the electric skin resistance. In this case, the resistance value of the controlled resistor is determined by the control voltage supplied to the input of the matching device. A semiconductor transistor (bipolar or field) is used as a controlled resistor in the device, which has significant non-linearity in the change in resistance from the control voltage in a wide range of resistance changes. As a result of this, even when using a special linearizing matching device, considerable difficulties arise in obtaining a linear characteristic of resistance control, which is necessary for constructing high-precision measuring devices.

 This reduces the accuracy of measuring electric resistance when using a prototype device, and also introduces significant limitations while ensuring high repeatability of instrument parameters. At the same time, the difficulty of setting up the approximating links and the low repeatability of parameters during mass production of devices additionally determine the measurement errors of the electric skin resistance of the prototype device.

 Thus, the disadvantages of the known devices are determined by the insufficient accuracy of the measurement of electric resistance.

 The aim of the invention is to remedy these shortcomings.

 This goal is achieved by the fact that in the device for measuring electrical resistance, containing two amplifiers, a measuring electrode connected to the first input of the first amplifier, two passive electrodes, three electronic keys, a comparator, the output of which is connected through the first electronic key to the input of the first memory unit, the second memory unit, the first multivibrator and recorder, introduced a controlled voltage divider, the second multivibrator and switch, the first input of which is connected to the second passive electrode, d a calibrated resistor, an amplitude detector, the output of which is connected through a controlled voltage divider to the input of the second amplifier, a reference voltage source, while the second input of the switch is connected to the first outputs of the calibrated resistors and the output of the third electronic switch, the first input of which is connected to the output of the first multivibrator, and the second input is to the first passive electrode and the second output of the first calibrated resistor, the second output of the second calibrated resistor is connected to the first input of the first amplifier, the output of which is connected to the input of the amplitude detector, and the second input to the output of the switch, the third input of the switch is connected to the first output of the second multivibrator and the first input of the first electronic key, the output of the reference voltage source is connected to the first input of the comparator, the output of the first memory block is connected to the second input of the controlled voltage divider, the second output of the second multivibrator is connected to the first input of the second electronic switch, the second input of which is connected to the output of the second amplifier and the second input of the comparator, and the output through the second memory block is connected to the registrar.

 With this embodiment of the device for measuring the electrical resistance by introducing a switch, two calibrated resistors, an amplitude detector, a memory unit, a second multivibrator and a reference voltage source, it is possible to periodically change the value of the measurement current and measure the electrical resistance in alternating current of a given frequency, which improves accuracy measurements by eliminating component errors from polarization processes and ensuring linearity converting the measured resistance in the output voltage.

 The invention is illustrated by drawings, where in FIG. 1 shows a functional diagram of the proposed device, in FIG. 2 is a timing diagram explaining its operation.

 The device contains an object of study (skin site), presented in the form of a node 1 (equivalent circuit equivalent of a skin site), measuring electrode 2, first and second passive electrodes 3, 4, calibrated resistors 5, 6, third electronic switch 7, first amplifier 8, switch 9, first multivibrator 10, amplitude detector 11, controllable voltage divider 12, first memory unit 13, second electronic key 14, second amplifier 15, second memory unit 16, second multivibrator 17, reference voltage source 18, compara OR 19, a first electronic switch 20 and a recorder 21.

Scheme 1 skin substitution is presented in the form of a Schaeffer model without taking into account the small value of the resistance of subcutaneous tissues (see Macs Phillippe. 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 - (Al is the acupuncture point) and passive electrodes 3, 4 (at the indifferent points of the skin cover A ₂ and A ₃ ), respectively.

 The calibrated resistors 5 and 6 are designed to create a measuring current in the circuit between the electrodes 2, 3, the value of which periodically changes when the total resistance of the circuit, consisting of resistors 5, 6 connected in series, changes due to the periodic closure of the calibrated resistor 5 with the electronic key 7. calibrated resistors use the exact constant of the resistor type PTMN-0.5 with a resistance of 50 - 500 kOhm, selected depending on the given measurement range and the required value, measure nogo current.

 The third electronic switch 7 provides the ability to periodically change the total value of the electrical circuit resistance between the electrodes 2, 3 due to the closure and opening of the terminals of the calibrated resistor 5. The key is made on one element of the chip K176KT1.

 The first amplifier 8 is a differential DC amplifier with a large input resistance (100 MΩ or more) to exclude its influence on the measuring circuit and is designed to amplify the potential difference between its first and second inputs. The amplifier is made on two K140UD1208 microcircuits and one K154UD1 microcircuit in the form of a large-scale differential amplifier.

 Switch 9 is designed to switch the second input of the first amplifier 8 from the circuit of the second passive electrode 4 to the connection circuit of calibrated resistors 5, 6 when the control signal arrives at its third input from the first output of the second multivibrator 17. Switch 9 is made on two elements of the K176KT1 chip and one element microchips K176LN1.

The first multivibrator 10 is designed to generate a signal that periodically turns on the third electronic key 7. The pulse repetition period of the multivibrator 10 determines the frequency of the measuring signal F, at which the electrical skin resistance is measured and is selected to be large for the total transient time determined by the recharge of the capacitances of full electrical skin resistances at points A ₁ , A _{2 of the} skin when the calibrated resistor 5 is closed and opened. It is made on the K561LA7 chip.

 The amplitude detector 11 is designed to isolate voltages equal to the amplitude of the alternating voltage components generated at the output of amplifier 8. It is made on two K154UD1 microcircuits and KD522A diodes.

 The controlled voltage divider 12 is designed to change the input voltage of the second amplifier 15 according to the control voltage supplied from the output of the first memory unit 13. The controlled divider 12 is made according to the circuit of the voltage divider on a constant resistor and a controlled semiconductor resistance, which is used as a field transistor KP103M1.

 The first memory unit 13 is designed to store the output voltage of the comparator 19 supplied to the memory unit when the first electronic key 20 is turned on. It is made in the form of a storage capacitor.

 The second electronic key 14 is designed to connect the input of the second memory block 16 to the output of the second amplifier 15 at time when it is exposed to the first input of the control signal from the second output of the second multivibrator 17. The electronic key is made similar to the electronic key 7 on the element of the chip K176KT1.

 The second amplifier 15 is designed to amplify the DC voltage supplied to its input from the output of the controlled voltage divider 12. It is made in the form of a large-scale DC amplifier on a chip of type K154UD1.

 The second memory block 16 is designed to store the output voltage of the second amplifier 15 at times when the electronic switch 14 is turned on, proportional to the measured value of the electric skin resistance. The block is made similar to block 13 of the memory.

 Multivibrator 17 is designed to generate signals that control the operation of the first 20 and second 14 electronic keys and switch 9. The oscillation period of the multivibrator is selected at least twice as long as the signal period of the first multivibrator 10. Multivibrator 17 is made similarly to multivibrator 10 on the K176LE5 chip.

 The source 18 of the reference voltage is designed to generate a predetermined reference voltage supplied to the second input of the comparator 19. It is made on a Zener diode KS162A and a field-effect transistor KP103I.

 The comparator 19 is designed to compare the output voltage of the second amplifier 15 with the voltage of the reference voltage source 18. The comparator is made on a K154UD1 chip.

 The first electronic key 20 is designed to connect the output of the comparator 19 to the input of the first memory unit 13 when a control voltage is supplied from the first output of the multivibrator 17. It is made similar to the third electronic key 6.

 The registrar 21 is designed to register the measured value of the electric skin resistance. A pointer microammeter type M42103 was used as a recorder.

 A device for measuring electric resistance is as follows.

 The indifferent electrodes 3, 4 are fixed in the indifferent region of the skin 1, and the measuring electrode 2 is pressed by the contact surface to the skin in the studied area of the acupuncture point. The operation of the device is illustrated by the time diagram shown in FIG. 2.

где
R₁, R₂ - сопротивления калиброванных резисторов 5, 6.For each half of the output signal U _{17 of the} second multivibrator 17, the first multivibrator 10 performs at least one oscillation period, during which its output voltage U ₁₀ periodically turns the electronic key 7 on and off. When the electronic key 7 is turned off between points A ₁ , A ₂ calibrated connected in series resistors 5, 6, through which the source of EMF E _1, E ₂ in the chain of resistors 5, 6 will leak electrical current I _min, the value of which can be determined based on Ohm's law for the total circuit, considering current passing circuit:

Where
R ₁ , R ₂ - resistance calibrated resistors 5, 6.

(2)
При периодическом включении и выключении электронного ключа 7 по управляющему сигналу U₁₀ с частотой F также будет изменяться электрический ток I, проходящий в цепи между измерительным 2 и первым пассивным 3 электродами. При этом среднее значение тока I_o и его амплитуду ΔI можно найти:

(3)

(4)
Подставляя в выражения (3), (4) значения токов из выражений (1), (2), получим следующее:

В первую половину каждого периода изменения выходного напряжения U₁₇ второго мультивибратора 17 выходным сигналом с первого его выхода открывается первый электронный ключ 20 и включается коммутатор 9, подключая второй вход усилителя 8 к выводу калиброванного резистора 6.When the output voltage U _{10 of the} multivibrator 10 changes, the electronic key 7 opens and the conclusions of the calibrated register 5 are closed, which leads to a decrease in the total resistance in the current path between points A ₁ , A ₂ and to a corresponding increase in the flowing electric current to the value I _max :

(2)
When the electronic key 7 is turned on and off periodically by the control signal U ₁₀ with a frequency F, the electric current I passing in the circuit between the measuring 2 and the first passive 3 electrodes will also change. In this case, the average value of current I _o and its amplitude ΔI can be found:

(3)

(4)
Substituting the values of currents from expressions (1), (2) into expressions (3), (4), we obtain the following:

In the first half of each period of the change in the output voltage U _{17 of the} second multivibrator 17, the output from the first output opens the first electronic key 20 and turns on the switch 9, connecting the second input of the amplifier 8 to the output of the calibrated resistor 6.

During the second half of each period of the output voltage from the second output signal U ₁₇ multivibrator 17 opens a second electronic switch 14.

Усилителем 8 приложенное падение напряжения усиливается в K_у1 раз (напряжение U₈ - фиг. 2), где K_у1 - коэффициент усиления 8, и с помощью амплитудного детектора 11 на его выходе выделяется постоянное напряжение U₁₁, равное амплитуде выходного напряжения усилителя 8:
U₁₁= K_y1ΔIR₂. (8)
Это напряжение проходит через управляемый делитель 12 напряжений и второй усилитель 15, на выходе которого формируется напряжение U_15-1, равное (при условии, что коэффициент передачи амплитудного детектора равен 1):
U_15-1= K_y1K(U)K_y2ΔU₁,
где
K(U) - коэффициент передачи управляемого делителя 12 напряжений; K_у2 - коэффициент усиления второго усилителя 15.In the first half of the periods of the change in the output voltage U _{17 of the} second multivibrator 17 between the inputs of the first amplifier 8, the voltage drop U ₁ on the calibrated resistor 6 is affected by both the constant I _o and the variable ΔI of the components of the current flowing in the circuit between points A ₁ , A ₂ whose variable component ΔU ₁ is equal to:

By amplifier 8, the applied voltage drop is amplified by K _y1 times (voltage U ₈ - Fig. 2), where K _y1 is the gain 8, and with the help of an amplitude detector 11, a constant voltage U ₁₁ equal to the amplitude of the output voltage of amplifier 8 is extracted at its output:
U ₁₁ = K _y1 ΔIR ₂ . (eight)
This voltage passes through a controlled voltage divider 12 and a second amplifier 15, at the output of which a voltage U _15-1 is formed equal to (provided that the gain of the amplitude detector is 1):
U _15-1 = K _y1 K (U) K _y2 ΔU ₁ ,
Where
K (U) is the transmission coefficient of the controlled voltage divider 12; K _y2 - gain of the second amplifier 15.

The voltage U _{15-1 is} applied to the first input of the comparator 19 and compared with the voltage U _{0 of the} source 18 of the reference voltage applied to the second input of the comparator 19. A voltage is _generated proportionally to the voltage difference U _у15-1 and U ₀ at the output of the comparator 19, which is in the first half the period of the signal of the second multivibrator 17 through the open electronic key 20 will be applied to the input of the first memory unit 13, memorized in it. From the output of the first memory unit 13, the voltage will affect the input of the controlled voltage divider 12, changing its transmission coefficient K (U). The change in the output voltage of the comparator 19 and the transfer coefficient K (U) of the controlled voltage divider 12 will occur until the output voltage U _{15-1 of the} second amplifier 15 becomes equal to the voltage U ₀ . The duration of the output voltage period of the second multivibrator 17 is chosen so that the process of establishing the equality of voltages U _у15-1 = U ₀ ends in one half of the operation period of the multivibrator 17.

After the transition process, expression (9) can be rewritten in the form:
U _15-1 = K _y1 K (U) K _y2 ΔU ₁ = U ₀ ;
or
K = K _y1 K (U) K _y2 = U ₀ / ΔU ₁ ;
Where
K is the total transmission coefficient of the amplifier channel, consisting of a first amplifier 8 connected in series, an amplitude detector 11, a controlled voltage divider 12, and a second amplifier 17.

In the second half of the periods of operation of the first multivibrator 17, the switch 9 is set to its initial state, in which the second input of the amplifier 8 is connected to the second passive electrode 4 (point A ₃ ) and the potential difference U _{1-3 is} applied to the inputs of the first amplifier 8 (Fig. 2) points A ₁ , A ₃ , changing due to changes in the voltage drop across the variable resistance Z _x when the current changes in different halves of the periods of the first multivibrator 10.

 In this case, the electronic switch 20 is closed, and the gain K of the amplifier channel remains equal to the value set in the first half of the period of operation of the second multivibrator 17.

Проходя через усилительный канал (8, 12, 15) и амплитудный детектор 11 пропорционально напряжению ΔU₂ на выходе второго усилителя 15 сформируется напряжение U_15-2, равное:
U_15-2= KΔU₂= K_y1K(U)K_y2ΔU₂= (U₀/ΔU₁)ΔU₂. (12)
Это напряжение через открытый второй электронный ключ 14 будет воздействовать на вход второго блока 16 памяти, запоминаясь в нем.The variable component of the change in the potential difference U _1-3 will be determined by the voltage drop ΔU ₂ from the variable component of the current ΔI on the measured resistance Z _x , i.e.:

Passing through the amplification channel (8, 12, 15) and the amplitude detector 11 in proportion to the voltage ΔU ₂ at the output of the second amplifier 15, a voltage U _15-2 is formed equal to:
U _15-2 = KΔU ₂ = K _y1 K (U) K _y2 ΔU ₂ = (U ₀ / ΔU ₁ ) ΔU ₂ . (12)
This voltage through the open second electronic switch 14 will affect the input of the second memory unit 16, memorized in it.

Substituting the values ΔU ₁ and ΔU ₂ from expressions (7), (11) into expression (11), we can write for the output voltage U ₁₆ of the memory unit 16:
U ₁₆ = (U ₀ / R ₂ ) Z _x , (13)
which at constant values of U ₀ and R _{2 is} proportional to the measured resistance Z _x .

By the value of the voltage U ₁₆ with the help of the registrar 21 will be provided registration of the measured value of the electric skin resistance Z _x . Moreover, as can be seen from expression (13), the device linearly converts the measured resistance Z _x into the output voltage U ₁₆ with a conversion coefficient equal to U ₀ / R ₂ . This allows for accurate measurement of electrical resistance. Moreover, by changing the ratio U ₀ / R ₂ it is possible to change the measurement ranges, realizing the possibility of constructing multi-range measuring instruments with linear measurement slags, which allow to obtain high measurement accuracy due to minimal measurement errors on the recorder scale.

Since the electric skin resistance in some limits depends on the value of the measuring current, the device can be changed within certain limits by changing the values of the calibrated resistors 5, 6 to ensure measurements at a single value of the measuring current. When changing the resistance value R _{1, the} values of the constant (1) and variable (2) of the measuring current components will change, and the recorded value will not change. It is also possible to change the value of the measuring current components in the device by changing the resistance R _{2 of the} calibrated resistor 5 while simultaneously proportionally changing the voltage U _{0 of the} reference voltage source so that the ratio U ₀ / R ₂ remains constant. In this case, the value of the electric skin resistance recorded by the recorder 21 will also not change. And this further improves the accuracy of measurements by eliminating errors from the nonlinearity of the measured electric skin resistance when choosing a constant value of the measuring current.

 Thus, in the device for measuring electric skin resistance, the accuracy of measuring electric skin resistance is increased in a wide range of recorded resistance values due to the linear conversion of the measured resistance to the output voltage and the use of an alternating measuring current with a minimum amplitude, which eliminates the effect of polarization processes and conversion parameters on the measurement results links of the device, providing high reliability of the results.

Claims (1)

 A device for measuring electrical resistance, containing two amplifiers, a measuring electrode connected to the first input of the first amplifier, two passive electrodes, three electronic keys, a comparator, the output of which is connected through the first electronic key to the input of the first memory unit, the second memory unit, the first multivibrator and a recorder, characterized in that a controlled voltage divider, a second multivibrator and a switch are introduced into it, the first input of which is connected to the second passive electrode, two calibers a resistor, an amplitude detector, the output of which is connected through a controlled voltage divider to the input of the second amplifier, a reference voltage source, while the second input of the switch is connected to the first outputs of the calibrated resistors and the output of the third electronic switch, the first input of which is connected to the output of the first multivibrator, and the second input - to the first passive electrode and the second output of the first calibrated resistor, the second output of the second calibrated resistor is connected to the first input of the first amplifier, you the path of which is connected to the input of the amplitude detector, and the second input to the output of the switch, the third input of the switch is connected to the first output of the second multivibrator and the first input of the first electronic key, the output of the reference voltage source is connected to the first input of the comparator, the output of the first memory block is connected to the second input controlled voltage divider, the second output of the second multivibrator is connected to the first input of the second electronic switch, the second input of which is connected to the output of the second amplifier and the second input row comparator, and output via the second memory unit is connected with the registrar.

Images