A three-selector high-impedance isolated topology scanning measurement system

Abstract

The application discloses a three-selector high-resistance isolation topological scanning measurement system and belongs to the technical field of multi-channel resistance measurement circuits. The first channel selector and the third channel selector are arranged to be responsible for symmetrically selecting the excitation and return flow channels respectively, and the second channel selector is arranged to introduce a high-resistance sampling branch at the series connection node of the standard resistance and the measured impedance. The application decouples the sampling node from the main current path, reduces the influence of the switch resistance change on the resistance value estimation result, and improves the measurement stability and temperature drift suppression capability while maintaining the multi-channel polling capability.

Description

Technical Field

[0001] This invention belongs to the field of multi-channel resistance measurement circuit technology, specifically relating to a three-selector topology channel selector that isolates measurement nodes through a high-impedance sampling branch. Background Technology

[0002] In multi-channel scanning measurements, the industry commonly employs a two-channel scanning circuit system, namely the DS-Board (Dual-Selector Board). For example... Figure 1 As shown, this DS-Board scheme uses two cascaded selectors in the main measurement circuit to select the channel under test. Channel selector 1 and channel selector 2 select the channel in the sensor under test. The excitation voltage of the constant voltage source is divided by a precision standard resistor and the selected channel under test. Then, the voltage at the series connection point between the precision standard resistor and the sensor under test is sampled by an analog-to-digital converter (ADC). While the structure of this scheme is relatively straightforward, an analog switch is inevitably connected in series in the measurement link of the impedance under test. Because the on-resistance of the analog switch fluctuates with temperature, supply voltage, and signal level, measurement errors manifest as channel-dependent bias and drift; these problems are more pronounced under high impedance or low current conditions.

[0003] According to the error model of the DS-Board scheme, in the ideal two-resistor voltage divider measurement, the measured resistance value It can be calculated from the sampling node voltage; however, in DS-Board, the front-end switching resistor located between the standard resistor and the impedance under test is used. and the tail-end switching resistor located between the measured impedance and ground. It will be directly included in the resistance estimation result as an additive term. ,Right now: Therefore, the temperature dependence of the switching resistor is approximately transmitted directly to the estimated value with unity gain, which is a major reason why DS-Board is prone to significant temperature drift. Although existing DS-Boards facilitate multi-channel polling, their series-connected topology in the main measurement circuit causes changes in the switch's internal resistance to be directly mapped to measurement deviations, which is detrimental to improving the consistency, temperature stability, and residual level of multi-channel measurements. Summary of the Invention

[0004] The purpose of this invention is to address the problems caused by the direct in-line input of the analog switch on-resistance into the main measurement circuit in DS-Board, which leads to channel-related bias, temperature drift, cross-channel inconsistency, and crosstalk. This invention proposes a three-selector high-impedance isolation measurement circuit system that decouples the sampling node from the main current path, reduces the impact of switch internal resistance changes on the resistance estimation results, and improves measurement stability and temperature drift suppression while maintaining multi-channel polling capability.

[0005] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a three-selector high-impedance isolation measurement circuit system, which includes: a precision standard resistor, a first channel selector, a second channel selector, a third channel selector, an analog-to-digital converter (ADC), a microcontroller (MCU), and a constant voltage source; The microcontroller MCU is electrically connected to the first channel selector, the second channel selector, the third channel selector, and the analog-to-digital converter ADC. The microcontroller (MCU) is used to select the object under test whose impedance needs to be measured, and the two ends of the object under test are respectively used as the excitation end and the return end; The input terminal of the first channel selector is connected to a constant voltage source, and its output terminal is connected to the excitation terminal of the currently selected test object under the control of the microcontroller MCU. The precision standard resistor is connected in series between the constant voltage source and the excitation terminal, so that the excitation voltage of the constant voltage source is applied to the excitation terminal after being divided by the precision standard resistor. The input terminal of the third channel selector is connected to the return terminal of the currently selected object under the control of the microcontroller MCU, and its output terminal is grounded, thereby closing the current path of the object under test; The input of the second channel selector is connected to the excitation terminal of the currently selected test object under the control of the microcontroller MCU, and its output is connected to the high-impedance input terminal of the analog-to-digital converter ADC. The analog-to-digital converter (ADC) samples the series node voltage between the precision standard resistor and the object under test and sends it to the microcontroller (MCU) to estimate the impedance of the currently selected object under test based on the voltage division relationship of the circuit.

[0006] As a preferred embodiment of the first aspect above, the object under test is an electrode channel in a multi-electrode array sensor.

[0007] As a preferred embodiment of the first aspect, the microcontroller (MCU) polls and scans the electrode channels in the multi-electrode array sensor, sequentially selecting different electrode channels for impedance measurement.

[0008] As a preferred embodiment of the first aspect mentioned above, the first channel selector, the second channel selector, and the third channel selector are all preferably CD74HC4067 channel selectors.

[0009] As a preferred embodiment of the first aspect above, the analog-to-digital converter (ADC) is preferably the AD7606 model.

[0010] As a preferred embodiment of the first aspect, the microcontroller (MCU) performs median and mean mixed filtering on the acquired series node voltage signals to suppress acquisition noise.

[0011] As a preferred embodiment of the first aspect above, in the microcontroller MCU, the impedance of the currently selected object under test is... Estimate using the following formula: In the formula: The series node voltage between a precision standard resistor and the object under test, obtained by the analog-to-digital converter (ADC). This is the excitation voltage output by the constant voltage source; This refers to the resistance value of a precision standard resistor. and These are the pre-calibrated front-end and rear-end switching resistors, respectively.

[0012] As a preferred embodiment of the first aspect above, the front-end switching resistor and tail-end switch resistor The calibration method is as follows: Select at least two precision loads with known resistance values ​​as the objects under test, and connect the precision loads to the current path between the constant voltage source and the ground through the first channel selector and the third channel selector. The analog-to-digital converter (ADC) samples the series node voltage between the precision standard resistor and the precision load and sends it to the microcontroller (MCU). Using the resistance values ​​of all precision loads and the series node voltages as fitting data, the front-end switching resistor is obtained through fitting. and tail-end switch resistor The calibration value.

[0013] Compared with the prior art, the present invention has the following advantages: 1) This invention sets up a high-resistance sampling branch at the series node of the standard resistor and the impedance under test, functionally separating the second channel selector from the main current loop, so that the on-resistance of the second channel selector no longer enters the resistance estimation result in the form of an additional series voltage drop; compared with DS-Board, this topology directly reduces the sensitivity of the measurement result to changes in the internal resistance of the switch.

[0014] 2) The first and third channel selectors of this invention are responsible for the symmetrical selection of the excitation and return channels, respectively, and work with the second channel selector to sample the actual node voltage at high impedance. The TS-Board reconstructs the switch resistor drift, which was originally an additive term directly entering the measurement result in the DS-Board, into a form transmitted through the voltage divider gain factor; the front-end switch drift is attenuated by the square denominator term, and can be partially canceled when the front and rear switches drift in the same direction, thus having better temperature drift suppression capability. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the structure of a traditional two-channel scanning circuit system, DS-Board. Figure 2 This is a schematic diagram of the TS-Board high-impedance isolation measurement circuit system with three selectors according to the present invention. Figure 3 This is a schematic diagram of an exemplary piezoresistive thin-film sensor; Figure 4 The figure shows the experimental results of temperature drift comparison between DS-Board and TS-Board.

[0016] The following labels are used in the figure: 1. Precision standard resistor; 2. First channel selector; 3. Second channel selector; 4. Third channel selector; 5. Object under test; 6. Analog-to-digital converter (ADC); 7. Microcontroller (MCU); 8. Constant voltage source; 9. Ground. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0018] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0019] In the description of this invention, it should be understood that the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0020] like Figure 2 The diagram illustrates a preferred embodiment of a triple-selector high-impedance isolation measurement circuit system (Triple-Selector Board, TS-Board) according to the present invention. The TS-Board system includes: a precision standard resistor 1, a first channel selector 2, a second channel selector 3, a third channel selector 4, an analog-to-digital converter (ADC) 6, a microcontroller (MCU) 7, and a constant voltage source 8. This TS-Board system can be used to measure the channel impedance of different impedance channels in a multi-channel test object 5.

[0021] It should be noted that the object under test 5 of the TS-Board system can be any electronic component whose impedance needs to be measured.

[0022] The following section provides a detailed introduction to the specific connections and operating methods of each component in the TS-Board system.

[0023] The aforementioned microcontroller MCU7 is electrically connected to the first channel selector 2, the second channel selector 3, the third channel selector 4, and the analog-to-digital converter ADC6. The microcontroller MCU7 is used to select the object under test 5 whose impedance needs to be measured, with the two ends of the object under test 5 serving as the excitation end and the return end, respectively. Specifically, the first channel selector 2, the second channel selector 3, and the third channel selector 4 can switch the object under test 5 connected to the conduction circuit under the control of the microcontroller MCU7. The end of the object under test 5 that receives the input current is called the excitation end, and the end that receives the output current is called the return end. The analog-to-digital converter ADC6 can transmit the acquired signal value to the microcontroller MCU7 for signal processing and calculation.

[0024] The specific models of the first channel selector 2, the second channel selector 3, the third channel selector 4, and the analog-to-digital converter ADC6 can be selected according to actual needs. In the embodiments of the present invention, the first channel selector 2, the second channel selector 3, and the third channel selector 4 are preferably CD74HC4067 channel selectors. The analog-to-digital converter ADC6 is preferably AD7606.

[0025] The input terminal of the first channel selector 2 is connected to the constant voltage source 8, and its output terminal is connected to the excitation terminal of the currently selected test object 5 under the control of the microcontroller MCU7. The precision standard resistor 1 is connected in series between the constant voltage source 8 and the excitation terminal, so that the excitation voltage of the constant voltage source 8 is applied to the excitation terminal after being divided by the precision standard resistor 1.

[0026] It should be noted that the aforementioned precision standard resistor 1 must be connected in series between the constant voltage source 8 and the excitation terminal of the currently selected test object 5, but the specific position can be adjusted appropriately. A recommended method is to connect the precision standard resistor 1 in series between the constant voltage source 8 and the input terminal of the first channel selector 2. Thus, the current from the constant voltage source 8 first passes through the precision standard resistor 1 before being input to the test object 5 connected to the output terminal of the first channel selector 2. The output terminal of the first channel selector 2 can reuse the precision standard resistor 1 when switching the connected test object 5. Of course, theoretically, the precision standard resistor 1 can also be connected in series with the output terminal of the first channel selector 2. Thus, when the current from the constant voltage source 8 is output from the output terminal of the first channel selector 2, it is divided by the precision standard resistor 1 before being applied to the test object 5.

[0027] The input terminal of the third channel selector 4 is connected to the return terminal of the currently selected test object 5 under the control of the microcontroller MCU7, and its output terminal is connected to the ground terminal 9, thereby closing the current path of the test object 5.

[0028] The input terminal of the second channel selector 3 is connected to the excitation terminal of the currently selected test object 5 under the control of the microcontroller MCU7, and its output terminal is connected to the high-impedance input terminal of the analog-to-digital converter ADC6.

[0029] It should be noted that the specific model of the analog-to-digital converter ADC6 can be selected according to actual needs, but it should have a high-impedance input terminal. The specific impedance can be determined based on the actual impedance of the precision standard resistor 1 and the measured object 5. The impedance of the high-impedance input terminal should be much higher than the actual impedance of the precision standard resistor 1 and the measured object 5, preferably two orders of magnitude higher or more.

[0030] The input connection point of the aforementioned analog-to-digital converter (ADC6) is a series connection between the precision standard resistor 1 and the object under test (DUT) 5. Therefore, the ADC6 can introduce the voltage of this series connection into the sampling link, sample the voltage of this series connection in real time, and send it to the microcontroller (MCU7) for estimating the impedance of the currently selected DUT 5 based on the voltage division relationship of the circuit. Since this sampling branch is a high-impedance branch, the sampling current is negligible. Therefore, the on-resistance of the second channel selector 3 will not be directly mapped to the resistance estimation result as an additional series voltage drop.

[0031] In this TS-Board system, the first channel selector 2 and the third channel selector 4 are located in the excitation path and return path of the circuit, respectively, and symmetrically perform channel selection. The second channel selector 3 only undertakes the node voltage reading function and does not undertake the main current transmission function. This topology allows the measurement node to be sampled in a high-impedance manner, thereby avoiding the problem of "the sampling switch resistor directly entering the measurement result" in the DS-Board. At the same time, the symmetrical selection of the excitation path and the return path also helps to reduce cross-channel errors and signal crosstalk.

[0032] The TS-Board system is particularly suitable for test objects 5, which are multi-electrode array sensors. Multi-electrode array sensors have a series of different electrode channels, each of which has a different impedance. Each electrode channel can be used as the test object 5 in this invention.

[0033] For example, in the invention patent application number CN202510188539.2, an angle recognition method and device for data enhancement of thin film bending sensors are disclosed. The piezoresistive thin film sensor involved is composed of a first carbon fiber plate, a first adhesive layer, a polyimide film, a second adhesive layer, and a second carbon fiber plate. Both the first and second carbon fiber plates are broken at the pivot position, but each carbon fiber plate is interlocked on both sides of the break position by edge serrations. The polyimide film is laser-etched to form a microstructure etching pattern symmetrical about the pivot axis. A series of metal electrodes are arranged around the edge of the microstructure etching pattern, and each metal electrode is connected to an adapter base for connecting external circuits through a wire. The microstructure etching pattern and all metal electrodes are completely covered by a carbon nanotube film to form a piezoresistive thin film sensor. This piezoresistive thin-film sensor can be considered a typical multi-electrode array sensor of this invention. It features a microstructure etching pattern symmetrically etched around the axis of rotation at the bending position of the thin film, with a series of metal electrodes arranged around the edge of the microstructure etching pattern. Any two metal electrodes can be considered as an electrode channel, and each electrode channel can be considered as the object under test 5 of the TS-Board system of this invention. When the piezoresistive thin-film sensor bends, the impedance of different electrode channels changes. It is necessary to detect the impedance values ​​of all electrode channels and input them into the neural network model to estimate the bending angle.

[0034] Therefore, the microcontroller MCU7 in the TS-Board system can poll and scan all electrode channels in the multi-electrode array sensor according to a preset polling order, and control the three channel selectors to select different electrode channels in sequence for impedance measurement.

[0035] Taking the aforementioned piezoresistive thin-film sensor as an example, the working process of the TS-Board system of this invention is as follows: First, the microcontroller MCU7 controls three channel selectors to select the electrode channel formed by any two metal electrodes in the piezoresistive thin-film sensor. The first channel selector 2 selects one of the metal electrodes connected to the electrode channel as the excitation terminal; the third channel selector 4 selects the other metal electrode connected to the electrode channel as the return terminal. The excitation current output by the constant voltage source 8 flows sequentially through the precision standard resistor 1, the selected electrode channel, and then to the ground terminal 9, thereby forming a complete current loop. Since the first channel selector 2 and the third channel selector 4 exist in this complete current loop, both of which have switching resistances that cannot be completely ignored, they are respectively denoted as the front-end switching resistances. and tail-end switch resistor The second channel selector 3 sends the actual series node voltage between the precision standard resistor 1 and the excitation terminal of the selected electrode channel to the high-impedance input terminal of the analog-to-digital converter ADC6 for sampling; then, the microcontroller MCU7 reads the ADC sampling value and calculates the resistance value corresponding to the current measured electrode channel based on the voltage divider relationship.

[0036] For all electrode channels in a piezoresistive thin-film sensor, the microcontroller MCU7 can sequentially control three channel selectors to complete a polling scan. Specifically, the first channel selector 2 and the third channel selector 4 are sequentially connected to all possible metal electrode pairings. Each metal electrode pairing is considered as one electrode channel, and the impedance measurement results of each electrode channel can be output through polling scan. For example... Figure 3 As shown, in an exemplary piezoresistive thin-film sensor, 16 metal electrodes are arranged around the edge of the microstructure etching pattern, with equal spacing between them. These 16 metal electrodes are numbered from 0 to 15, resulting in 120 pairs of metal electrode combinations. By polling the 16 electrodes in a preset sequence, the ADC sampling values ​​for each of the 120 electrode channels can be obtained, representing the series node voltages between the 120 precision standard resistors and the excitation terminals of the electrode channels.

[0037] In an ideal voltage divider model that neglects the switching resistor of the channel selector, when a precision standard resistor 1 and an electrode channel with impedance are connected in series in the conducting circuit between the constant voltage source and the ground terminal, the resistance value of the electrode channel is... The estimation formula is: , in This is the excitation voltage of the constant voltage source. The resistance value is the value of the precision standard resistor connected in series. This is the sampling voltage at the connection node between the series precision standard resistor and the electrode channel.

[0038] And for Figure 1 For the DS-Board system shown, the resistance of the electrode channels is... The estimation formula becomes: This indicates that the switched resistors in the DS-Board system are directly incorporated into the measurement results in an additive manner.

[0039] For the present invention Figure 2 The TS-Board system shown has its ADC sampling point located at the actual connection point between the series precision standard resistor and the channel under test, and is read through a high-impedance branch. Therefore, the resistance value of the electrode channel is... The estimation formula can be written as: , in: .

[0040] Compared to the DS-Board, the front-end switching resistor in the TS-Board of this invention... Instead of being directly included in the estimation result as an additive bias term, it is mapped into the result through the voltage divider gain factor.

[0041] Furthermore, differentiating the temperature in the estimation formula for the TS-Board system reveals that the front-end switch drift in the TS-Board is due to... Enter and be subject to The denominator term decays; and when and When both types of drift increase with rising temperature, their contributions can partially cancel each other out. This cancellation effect does not exist in the DS-Board's dual-selector series topology because the DS-Board's switching drift enters the estimation result as a purely additive term.

[0042] Therefore, this invention improves the dual-selector main circuit series structure of the DS-Board into a three-channel selector structure of the TS-Board. A high-resistance sampling branch is introduced at the actual series node of the standard resistor and the measured impedance. The second channel selector only handles node voltage reading and no longer handles main current transmission; therefore, its on-resistance will not directly enter the resistance estimation result in the form of additive bias. The first and third channel selectors symmetrically select the excitation path and return path, respectively. Furthermore, the remaining series switching terms in the TS-Board enter the result through a voltage divider gain factor. The front-end switch drift is attenuated by the square denominator term and, under certain conditions, partially cancels out the tail-end drift, significantly different from the purely additive drift mechanism of the DS-Board. The TS-Board can achieve significantly better temperature drift and residual control levels than the DS-Board.

[0043] Furthermore, in the embodiments of the present invention, referring to conventional ADC signal acquisition optimization methods, the microcontroller MCU7 performs median and mean mixed filtering on the acquired series node voltage signals to suppress acquisition noise. When the ADC is AD7606, it can achieve 8-channel synchronous sampling. Therefore, preferably, after each channel selection is completed, a channel selector is used to simultaneously acquire 8 instantaneous samples, and a median and mean mixed filtering is performed at the MCU end using a sliding window of length 10 to suppress acquisition noise and improve measurement stability.

[0044] Based on the principle description of the TS-Board system described above, an impedance estimation program can be built into the microcontroller MCU7 to estimate the impedance of the currently selected object under test 5. Estimate using the following formula: In the formula: The series node voltage between the precision standard resistor 1 and the object under test 5, as measured by the analog-to-digital converter ADC6; This is the excitation voltage output by the constant voltage source 8; This is the resistance value of precision standard resistor 1; and These are the pre-calibrated front-end and rear-end switching resistors, respectively.

[0045] It is important to note the front-end switching resistor. and tail-end switch resistor The calibration method can be performed in advance using a precision load with a known resistance value as the object under test. The specific procedure is as follows: First, select at least two precision loads with known resistance values ​​as the test objects 5 in the above TS-Board system, and connect the precision loads to the current path between the constant voltage source 8 and the ground terminal 9 through the first channel selector 2 and the third channel selector 4. The analog-to-digital converter ADC6 samples the series node voltage between the precision standard resistor 1 and the precision load and sends it to the microcontroller MCU7. Then, using the resistance values ​​of all precision loads and the series node voltages as fitting data, the front-end switching resistor is obtained. and tail-end switch resistor The calibration value.

[0046] To achieve the minimum amount of data required for fitting, at least two precision loads with known resistance values ​​are needed, although theoretically more is better. Additionally, due to the front-end switching resistors... and tail-end switch resistor In practice, the calibration process is affected by temperature T, therefore it is best to conduct the calibration within the actual operating temperature range of the object under test (5). Theoretically, it is best to obtain fitting data at each different operating temperature T and then calibrate the corresponding front-end switching resistor. and tail-end switch resistor However, the aforementioned analysis has demonstrated that the drift of the front-end switch is attenuated by the square denominator term, and can be partially canceled out when the front and rear switches drift in the same direction. Therefore, when the accuracy requirement is not high, calibration tests can be carried out at room temperature (e.g., 28°C) or other operating temperatures to obtain fitting data, and then the front-end and rear-end switch resistors can be calibrated and extended to other operating temperatures.

[0047] In this embodiment, Figure 3Taking the piezoresistive thin-film sensor shown as an example, the performance of the DS-Board and TS-Board systems was experimentally verified. Under the power supply condition of a constant voltage source 8 with an excitation voltage controlled at 5 V, a temperature drift comparison experiment was conducted on the DS-Board and TS-Board. Six precision loads of 200, 400, 680, 800, 1000, and 1200 Ω were selected as the test objects 5 for testing. Data at 28℃ was used as a benchmark, and two-point linear calibration was performed using two anchor loads of 200 Ω and 1200 Ω. The experimental results are as follows... Figure 4 As shown, the average temperature coefficient of the TS-Board at the board level decreased from 1.0338 Ω / ℃ of the DS-Board to 0.0740 Ω / ℃, a decrease of 92.8%. After excluding the anchor point load, the average absolute residual at the intermediate load point decreased from 2.518 Ω to 0.360 Ω, indicating that the TS-Board not only significantly reduced the temperature drift, but also effectively suppressed the load-related error that remained after the two-point linear calibration.

[0048] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A three-selector high-impedance isolation measurement circuit system, characterized in that, include: Precision standard resistor (1), first channel selector (2), second channel selector (3), third channel selector (4), analog-to-digital converter (ADC) (6), microcontroller (MCU) (7), and constant voltage source (8); The microcontroller MCU (7) is electrically connected to the first channel selector (2), the second channel selector (3), the third channel selector (4), and the analog-to-digital converter ADC (6), respectively. The microcontroller MCU (7) is used to select the object under test (5) whose impedance needs to be measured, and the two ends of the object under test (5) are respectively used as the excitation end and the return end; The input terminal of the first channel selector (2) is connected to the constant voltage source (8), and its output terminal is connected to the excitation terminal of the currently selected test object (5) under the control of the microcontroller MCU (7). The precision standard resistor (1) is connected in series between the constant voltage source (8) and the excitation terminal, so that the excitation voltage of the constant voltage source (8) is applied to the excitation terminal after being divided by the precision standard resistor (1). The input terminal of the third channel selector (4) is connected to the return terminal of the currently selected test object (5) under the control of the microcontroller MCU (7), and its output terminal is grounded, thereby closing the current path of the test object (5). The input terminal of the second channel selector (3) is connected to the excitation terminal of the currently selected test object (5) under the control of the microcontroller MCU (7), and its output terminal is connected to the high-impedance input terminal of the analog-to-digital converter ADC (6). The analog-to-digital converter (ADC) (6) samples the series node voltage between the precision standard resistor (1) and the object under test (5) and sends it to the microcontroller (MCU) (7) to estimate the impedance of the currently selected object under test (5) based on the voltage division relationship of the circuit.

2. The three-selector high-impedance isolation measurement circuit system as described in claim 1, characterized in that, The object under test (5) is the electrode channel in the multi-electrode array sensor.

3. The three-selector high-impedance isolation measurement circuit system as described in claim 2, characterized in that, The microcontroller MCU (7) polls and scans the electrode channels in the multi-electrode array sensor, and sequentially selects different electrode channels for impedance measurement.

4. The three-selector high-impedance isolation measurement circuit system as described in claim 1, characterized in that, The first channel selector (2), the second channel selector (3) and the third channel selector (4) are preferably CD74HC4067 channel selectors.

5. The three-selector high-impedance isolation measurement circuit system as described in claim 1, characterized in that, The analog-to-digital converter (ADC) (6) is preferably of model AD7606.

6. The three-selector high-impedance isolation measurement circuit system as described in claim 1, characterized in that, The microcontroller MCU (7) performs median and mean mixed filtering on the acquired series node voltage signals to suppress acquisition noise.

7. The three-selector high-impedance isolation measurement circuit system as described in claim 1, characterized in that, In the microcontroller MCU (7), the impedance of the currently selected test object (5) Estimate using the following formula: In the formula: The series node voltage between the precision standard resistor (1) and the object under test (5) is measured by the analog-to-digital converter (ADC) (6); The excitation voltage output by the constant voltage source (8); The resistance value of the precision standard resistor (1); and These are the pre-calibrated front-end and rear-end switching resistors, respectively.

8. The three-selector high-impedance isolation measurement circuit system as described in claim 7, characterized in that, The front-end switching resistor and tail-end switch resistor The calibration method is as follows: Select at least two precision loads with known resistance values ​​as the test object (5), and connect the precision loads to the current path between the constant voltage source (8) and the ground terminal (9) through the first channel selector (2) and the third channel selector (4). The analog-to-digital converter (ADC) (6) samples the series node voltage between the precision standard resistor (1) and the precision load and sends it to the microcontroller (MCU) (7). Using the resistance values ​​of all precision loads and the series node voltages as fitting data, the front-end switching resistor is obtained through fitting. and tail-end switch resistor The calibration value.

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