CN106618569A - Measuring device and method for contact impedance between electrodes and skin - Google Patents

Abstract

The invention discloses a device and method for measuring contact impedance between electrodes and skin, including a processor, and a current source, a voltage measurement circuit, a display and an alarm all interacting with the processor; the current source and the voltage measurement circuit pass through The multi-way switch is connected to an electrode system composed of several electrodes that is close to the surface of the user's skin; the present invention can obtain the contact status between each electrode and the skin in real time by injecting excitation currents into different electrodes and selecting measurement electrodes. At the same time, the present invention calculates the contact impedance through the boundary voltage value and the excitation value, and judges the contact condition of the electrode according to the average value method and the threshold value method. This method has been proved by simulation experiments and calibration board tests that its method is superior to the existing measurement technology in terms of measurement speed and measurement accuracy, meets the requirements of real-time display of the contact status of each electrode during the electrical impedance detection process, and further improves the performance of electrical impedance measurement. System data quality.

Description

Device and method for measuring electrode-skin contact impedance

【Technical field】

The invention belongs to the field of medical monitoring and testing devices, and relates to a device for measuring contact impedance, in particular to a device and method for measuring electrode-skin contact impedance.

【Background technique】

Bioelectrodes are widely used in various fields of medical monitoring, such as ECG monitoring, extraction of EEG signals and electrical impedance tomography (EIT) systems, etc. The electrode signal is transmitted to the body surface through human tissue, and is obtained through electrode induction, rear-end signal amplification, voltage measurement circuit and processor processing. In the entire transmission path of electrode signals, human tissue is a good conductor, and its impedance varies from hundreds of ohms to tens of ohms according to different frequencies, while the electrode-skin contact impedance varies from tens of thousands of ohms to hundreds of ohms, so The electrode-skin contact impedance directly affects the quality of the electrode signal. If it can be measured accurately, it will provide an important basis for the design of ECG, EEG and electrical impedance measurement circuits and the improvement of bioelectrodes. At the same time, it is generally accepted that the magnitude of the contact impedance reflects the quality of the electrode-skin contact. Therefore, the real-time measurement of the contact impedance during the data acquisition process is helpful for us to grasp the contact status of the electrodes in real time.

At present, in terms of ECG, EEG, and EIT imaging, two-electrode method and four-electrode derivation method are mostly used for the measurement of electrode-skin contact impedance.

In the two-electrode method, two electrodes are used as excitation electrodes and measurement electrodes. The excitation ammeter is used as I, and the measured voltage difference is V. The contact resistance value Z is then calculated based on the boundary voltage difference equal to the product of the value of the contact resistance and the current I. The two-electrode method measures the contact impedance Z as the sum of the contact impedances on the two electrodes. The contact impedance measured by this method includes the transmission impedance component of the tissue between the electrodes, and the contact impedance values on the two electrodes cannot be distinguished, which is not conducive to the judgment of the actual contact effect of the electrodes.

The four-electrode derivation method is: the first step is to use the four-electrode method, that is, to separate the excitation electrode from the measurement electrode, and measure the transmission impedance component Z1 between the electrodes; the second step is to change one of the excitation electrodes to a certain value. A measurement electrode position, so that the electrode under test is used as both a measurement electrode and an excitation electrode, and the impedance value Z2 is measured under this condition, so that the contact impedance value Z=Z2-Z1 on the electrode can be estimated. Although this method overcomes the shortcomings of the two-electrode method to a certain extent and improves the measurement accuracy of the electrode-skin contact impedance, it sacrifices the measurement speed and reduces the monitoring efficiency of the machine because it needs to switch electrodes twice.

【Content of invention】

The object of the present invention is to overcome above-mentioned shortcoming of prior art, provide a kind of measuring device and method of contact impedance between electrode-skin, device is made up of electrode system, current source and voltmeter. The current source is connected to the electrode under test and its object electrode, and the current source is connected to the electrode under test and its adjacent electrodes. The processor is connected to the voltage source and the current source, calculates the size of the contact impedance, and displays the contact status of the electrodes and the skin on the display. The excitation current is injected into different excitation electrode pairs through the current source, the boundary voltage difference between the measurement electrodes is detected, and the demodulated data is calculated by the processor to obtain the contact impedance value, thereby obtaining the contact quality between the electrodes and the skin.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve:

A measuring device for electrode-skin contact impedance, including a processor, and a current source, a voltage measurement circuit, a display and an alarm all interacting with the processor; An electrode system consisting of several electrodes on the surface of the user's skin is connected; wherein,

The electrode system includes excitation electrodes and measurement electrodes;

The processor is used to control the selection of the excitation electrode and the measurement electrode, and calculate the contact impedance of the corresponding electrode according to the excitation current and the measured response voltage;

The current source is used to output a sinusoidal current signal of a specific frequency, and inject an excitation current to the excitation electrode through a multi-way switch under the control of the processor;

The voltage measurement circuit is used to collect the boundary voltage difference signal of the measuring electrode, perform gain amplification processing and analog-to-digital conversion on the collected signal, and then provide it to the processor;

The multi-way switch is connected with the electrode system, and the excitation current is accurately injected into the selected excitation electrode; at the same time, the multi-way switch is connected with the voltage measurement circuit, and the detected boundary voltage difference is selectively provided to the voltage measurement circuit;

The display is used to display the contact impedance and connection status of each electrode on the motor system in real time;

The alarm is used to sound when the processor detects that the electrode is in poor contact with the user's skin, prompting medical personnel to check the electrode.

The further improvement of the present invention is:

The voltage measuring circuit includes a plurality of amplifiers and a 16-bit analog-to-digital converter, and the output terminal of the analog-digital converter is connected with the input terminal of the processor.

A method for measuring contact impedance between electrodes-skin, comprising the following steps:

1) The processor selects the excitation electrode and the measurement electrode, the measured electrode is used as the positive electrode of the excitation electrode, and another reference electrode is used as the ground terminal of the excitation electrode;

2) The processor controls the multi-way switch to send the current source current I to the excitation electrode pair, and the voltage measurement circuit will measure the boundary voltage difference U1 between two adjacent electrodes through the multi-way switch, based on the value of the boundary voltage difference equal to the contact impedance and The product of the current I, the processor calculates the contact impedance value Z1 between the tested electrode and the skin;

3) The processor changes the excitation electrodes through the multi-way switch, and sends the current source current I to the changed excitation electrode pair, the voltage measurement circuit selects the corresponding measurement electrode through the multi-way switch, and obtains the voltage difference U2 between two adjacent electrodes , based on the boundary voltage difference being equal to the product of the value of the contact impedance and the current I, the processor calculates the transmission impedance component Z'; subtracts the transmission impedance Z' component from the contact impedance Z1 to obtain the value of the transmission impedance Z2;

4) The processor calculates the value of the contact impedance Z of the electrode under test through the contact impedance Z1 and the transmission impedance Z2, wherein: Z=Z1-Z2;

5) The processor judges the contact condition of the electrode under test according to the value of the contact impedance Z of the electrode under test. If the judgment result is that the electrode under test is in poor contact with the skin of the user, the processor sends an alarm command to the alarm, and at the same time The display shows the connection status of the corresponding electrode.

The further improvement of the present invention is:

In described step 5), the method for judging the contact condition of the tested electrode is as follows:

Calculate the average value of the electrode-skin contact impedance value measured on each electrode, and compare it with the measured electrode-skin contact impedance value Z; if the contact impedance value Z of the measured electrode is greater than twice the average value, the electrode is judged Poor contact with skin.

In described step 5), the method for judging the contact condition of the tested electrode is as follows:

Set the impedance upper limit threshold Zr at each frequency point, and compare the obtained contact impedance value Z on each electrode with the impedance upper limit threshold Zr value; if the contact impedance value Z is less than or equal to the impedance upper limit threshold Zr, the electrode contact condition is good; If the contact impedance value Z is greater than the upper impedance threshold Zr, the electrode contact condition is poor.

Compared with the prior art, the present invention has the following beneficial effects:

A device for measuring electrode-skin contact impedance provided by the present invention can obtain the contact status between each electrode and the skin in real time through the calculation of the processor by injecting excitation current into different electrodes and selecting the measurement electrode, and feedback it to the user in time. medical staff. At the same time, the electrode-skin contact impedance measurement method provided by the present invention calculates the contact impedance through the boundary voltage value and the excitation value, and judges the contact status of the electrode according to the average value method and the threshold value method. This method has been proved by simulation experiments and calibration board tests that its method is superior to the existing measurement technology in terms of measurement speed and measurement accuracy, meets the requirements of real-time display of the contact status of each electrode during the electrical impedance detection process, and further improves the performance of the electrical impedance based measurement. System data quality.

【Description of drawings】

Figure 1 is a device structure diagram of the electrode-skin contact impedance measurement system.

Fig. 2 is a flow chart of the electrode-skin contact impedance measurement system.

Fig. 3 is a schematic diagram of a rapid measurement method for contact impedance.

Figure 4 is a circuit schematic diagram of the calibration board.

FIG. 5 is a schematic diagram of an accurate measurement method of contact impedance.

【detailed description】

The present invention is described in further detail below in conjunction with accompanying drawing:

Referring to Fig. 1, the measuring device of the contact impedance between the electrode-skin of the present invention comprises a processor, and a current source, a voltage measurement circuit, a display and an alarm that all interact with the processor; The switch is connected to an electrode system composed of several electrodes that is close to the surface of the user's skin; wherein,

The electrode system includes excitation electrodes and measurement electrodes;

The processor is used to control the selection of the excitation electrode and the measurement electrode, and calculate the contact impedance of the corresponding electrode according to the excitation current and the measured response voltage;

The current source is used to output a sinusoidal current signal of a specific frequency, and inject an excitation current to the excitation electrode through a multi-way switch under the control of the processor;

The voltage measurement circuit is used to collect the boundary voltage difference signal of the measurement electrode, and perform gain amplification processing and analog-to-digital conversion on the collected signal, and then provide it to the processor; the voltage measurement circuit includes multiple amplifiers and a 16-bit analog-to-digital converter, the output of the analog-to-digital converter is connected to the input of the processor.

The multi-way switch is connected with the electrode system, and the excitation current is accurately injected into the selected excitation electrode; at the same time, the multi-way switch is connected with the voltage measurement circuit, and the detected boundary voltage difference is selectively provided to the voltage measurement circuit;

The display is used to display the contact impedance and connection status of each electrode on the motor system in real time;

The alarm is used to sound when the processor detects that the electrode is in poor contact with the user's skin, prompting medical personnel to check the electrode.

As shown in Figure 2, the present invention also discloses a method for measuring contact impedance between electrodes-skin, comprising the following steps:

1) The processor selects the excitation electrode and the measurement electrode, the measured electrode is used as the positive electrode of the excitation electrode, and another reference electrode is used as the ground terminal of the excitation electrode;

2) The processor controls the multi-way switch to send the output current of the current source to the positive ground terminal of the excitation electrode, and the voltage measurement circuit sends the measured boundary voltage value to the processor through the multi-way switch; the processor passes the excitation current and the boundary voltage value Calculate the value of contact impedance Z1 on the electrode under test;

3) The processor changes the excitation electrode through the multi-way switch, and the voltage measurement circuit sends the boundary voltage value to the processor through the multi-way switch; the processor calculates the value of the transmission impedance Z2 through the excitation current and the boundary voltage value;

4) The processor calculates the value of the contact impedance Z of the electrode under test through the contact impedance Z1 and the transmission impedance Z2;

5) The processor judges the contact condition of the electrode under test according to the value of the contact impedance Z of the electrode under test. If the judgment result is that the electrode under test is in poor contact with the skin of the user, the processor sends an alarm command to the alarm, and at the same time The display shows the connection status of the corresponding electrode.

Among them, the method of judging the contact condition of the electrode under test can adopt the following two methods:

1. Calculate the average value of the electrode-skin contact impedance value measured on each electrode, and compare it with the measured electrode-skin contact impedance value Z; if the contact impedance value Z of the measured electrode is greater than twice the average value, then judge The electrode is in poor contact with the skin.

2. Set the impedance upper limit threshold Zr at each frequency point, and compare the obtained contact impedance value Z on each electrode with the impedance upper limit threshold Zr value; if the contact impedance value Z is less than or equal to the impedance upper limit threshold Zr, the electrode contact status Good; if the contact impedance value Z is greater than the upper impedance threshold Zr, the electrode contact condition is poor.

Principle of the present invention:

System Structure and Composition

The invention is used for measuring and judging the contact quality between the electrode and the skin, so that medical personnel can know the contact status between the electrode and the skin in real time during the electrical impedance measurement process. As shown in Fig. 1, the device structure diagram of the measurement system of the present invention includes a processor, a display, a current source, a voltage measurement circuit, a multi-way switch and an electrode system, etc. The processor is connected with a current source, a voltage measuring circuit, a display and an alarm, and the current source injects a current signal to the excitation electrode through a multi-way switch under the control of the controller. After the current signal passes through the human body tissue, it is detected by the voltage measurement circuit through the multi-way switch, and the voltage measurement circuit converts the detected boundary voltage difference into a digital signal and provides it to the processor. The processor calculates and obtains the contact impedance value on the measured electrode through the excitation current value and the obtained boundary voltage value. The processor compares the contact impedance values on each electrode by means of an average method and a threshold method to determine the contact status of each electrode with the skin. The processor displays the calculated results on the monitor, and when a poor contact of a specific electrode is detected, an alarm sounds to prompt medical personnel.

Contact Impedance Measurement Method and Effect

Figure 2 is a schematic diagram of the measurement of contact impedance. The following takes the 16-electrode system as an example to introduce the measurement process of contact impedance in detail:

First, the processor selects a measurement method for contact impedance.

When performing fast measurement of contact impedance (as shown in Figure 3), the processor sends the current source current I to the excitation electrode pair through a multi-way switch, and the voltage measurement circuit selects the measurement electrode through a multi-way switch to obtain the voltage between two adjacent electrodes. The boundary voltage difference U1 is based on the product of the boundary voltage difference equal to the value of the contact impedance and the current I, and the contact impedance value Z1 between the electrode under test and the skin is calculated.

Use the calibration board (as shown in Figure 4) to simulate the head impedance, connect an external 1K resistor to simulate the contact impedance, and change the position of the excitation electrode. The measurement results are shown in the following table:

The results show that the measurement error of the electrode-skin contact impedance is the smallest when the adjacent electrode of the tested electrode is used as the excitation electrode. Therefore, in the specific implementation, we choose the adjacent electrode of the measured electrode as the excitation electrode to measure the contact impedance.

When the rapid measurement of the contact impedance is performed, the transmission impedance component in the measured contact impedance is further measured on the basis of the rapid measurement of the contact impedance. As shown in Figure 5, the multi-way switch sends the current source current I to the excitation electrode pair, and the voltage measurement circuit selects the measurement electrode through the multi-way switch to obtain the voltage difference U2 between two adjacent electrodes, based on the fact that the boundary voltage difference is equal to the contact impedance The value is multiplied by the current I to calculate the transmission impedance component Z'.

Finally, subtract the transmission impedance Z' component from the contact impedance Z1 to accurately measure the value of the transmission impedance Z2.

Use the calibration board model to simulate, connect an external 1K resistor to simulate the contact impedance, and change the position of the excitation electrode. The measurement results are shown in the following table:

The results show that the accuracy of the accurate measurement method of contact impedance is better than that of the fast measurement method, and the error of the measured contact impedance is the smallest when the adjacent electrode of the measured electrode is used as the excitation electrode. Therefore, in the accurate measurement method of contact impedance, the excitation method should choose adjacent excitation.

Method accuracy comparison test: select the two-electrode method, the fast measurement method and the accurate measurement method to measure the contact impedance on the same electrode, and compare the accuracy of the three methods. The excitation electrode is selected as the adjacent electrode of the measured electrode. The measurement results are shown in the table below:

The results show that the measurement accuracy of the accurate measurement method of contact impedance proposed in this paper is obviously better than that of the two-electrode method, and has a measurement accuracy not lower than that of the four-electrode derivation method without sacrificing the measurement speed. Although the accurate measurement method of contact impedance proposed in this paper has some influence on the measurement speed (the measurement speed is equal to that of the four-electrode derivation method), it has the smallest measurement error, and its measurement accuracy is obviously better than that of the two-electrode method and the four-electrode derivation method .

Poor electrode contact discrimination method to determine the electrode-skin contact status: For the obtained electrode-skin contact impedance values (Z1, Z2, Z3,..., Z16), use the average method and threshold method to determine whether the electrode is in good contact. Calculate the mean value Zm of the contact resistance on the 16 electrodes, and compare the value of the contact resistance on a specific electrode with twice the mean value. If the contact impedance value between the specific electrode and the skin is greater than or equal to twice the average value of the contact impedance between all electrodes and the skin, it is considered that the contact condition of the specific electrode is poor, and the monitor will prompt the monitor to check the electrode;

In order to make up for the judgment defect of the average method in the case of poor contact of most electrodes, an upper impedance threshold Zr is set at each frequency point. If the contact impedance value between a specific electrode and the skin is greater than the upper threshold, the specific electrode is considered to be in poor contact. and displayed on the display.

Statistical table of thresholds at each frequency

The above content is only to illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solutions according to the technical ideas proposed in the present invention shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (5)

1. An electrode-skin contact impedance measuring device is characterized by comprising a processor, a current source, a voltage measuring circuit, a display and an alarm, wherein the current source, the voltage measuring circuit, the display and the alarm are all interacted with the processor; the current source and the voltage measuring circuit are connected with an electrode system which is tightly attached to the skin surface of a user and consists of a plurality of electrodes through a multi-way switch; wherein,

the electrode system comprises an excitation electrode and a measuring electrode;

the processor is used for controlling the selection of the excitation electrode and the measuring electrode and calculating the contact impedance of the corresponding electrode according to the excitation current and the measured response voltage;

the current source is used for outputting a sinusoidal current signal with specific frequency and injecting exciting current to the exciting electrode through the multi-way switch under the control of the processor;

the voltage measuring circuit is used for acquiring boundary voltage difference signals of the measuring electrodes, performing gain amplification processing and analog-to-digital conversion on the acquired signals and then providing the signals to the processor;

the multi-way switch is connected with the electrode system and accurately injects excitation current into the selected excitation electrode; meanwhile, the multi-way switch is connected with the voltage measuring circuit and selectively provides the detected boundary voltage difference to the voltage measuring circuit;

the display is used for displaying the contact impedance and the connection condition of each electrode on the motor system in real time;

the alarm is used for sounding when the processor detects that the electrode is in poor contact with the skin of a user, and prompts medical staff to check the electrode.

2. The electrode-to-skin contact impedance measurement device of claim 1, wherein the voltage measurement circuit comprises a plurality of amplifiers and a 16-bit analog-to-digital converter, an output of the analog-to-digital converter being coupled to an input of the processor.

3. A method for measuring the contact impedance between an electrode and the skin using the measuring device according to claim 1 or 2, comprising the steps of:

1) the processor selects an exciting electrode and a measuring electrode, the electrode to be measured is used as the positive electrode of the exciting electrode, and a reference electrode is taken as the ground end of the exciting electrode;

2) the processor controls the multi-way switch to send current source current I to the excitation electrode pair, the voltage measuring circuit measures boundary voltage difference U1 between two adjacent electrodes through the multi-way switch, and the processor calculates to obtain a contact impedance value Z1 between the electrode to be measured and the skin based on the product of the boundary voltage difference equal to the contact impedance value and the current I;

3) the processor changes the excitation electrodes through the multi-way switch, sends current source current I to the excitation electrode pairs after the change, the voltage measuring circuit selects corresponding measuring electrodes through the multi-way switch to obtain voltage difference U2 between two adjacent electrodes, and the processor calculates and obtains transmission impedance component Z' based on the product of the value of the boundary voltage difference equal to contact impedance and the current I; subtracting the component of the transmission impedance Z' from the contact impedance Z1 to obtain a value of the transmission impedance Z2;

4) and the processor calculates the value of the contact impedance Z of the measured electrode through the contact impedance Z1 and the transmission impedance Z2, wherein: z is Z1-Z2;

5) the processor judges the contact condition of the electrode to be detected according to the contact impedance Z value of the electrode to be detected, and if the judgment result shows that the contact condition of the electrode to be detected and the skin of a user is poor, the processor sends an alarm instruction to the alarm and simultaneously displays the connection condition of the corresponding electrode on the display.

4. The method for measuring the contact impedance between the electrode and the skin as claimed in claim 3, wherein in the step 5), the method for determining the contact condition of the electrode to be measured is as follows:

averaging the electrode-skin contact impedance values measured on each electrode, and comparing the average with the measured electrode-skin contact impedance value Z; and if the contact impedance value Z of the measured electrode is more than 2 times of the mean value, judging that the contact condition of the electrode and the skin is poor.

5. The method for measuring the contact impedance between the electrode and the skin as claimed in claim 3, wherein in the step 5), the method for determining the contact condition of the electrode to be measured is as follows:

setting an impedance upper limit threshold Zr at each frequency point, and comparing the obtained contact impedance value Z on each electrode with the impedance upper limit threshold Zr; if the contact impedance value Z is less than or equal to the impedance upper limit threshold value Zr, the electrode contact condition is good; if the contact impedance value Z is larger than the impedance upper limit threshold Zr, the electrode contact condition is poor.