CN116859126A - An AC impedance spectrum measurement system and method based on the dual-channel half-bridge method - Google Patents

Abstract

The invention discloses an AC impedance spectrum measurement system and method based on a dual-channel half-bridge method, which belongs to the technical field of measuring electrical variables and is used for impedance spectrum measurement. The system includes a frequency sweep signal generator, a collection card, a power supply, a host computer, Measurement system circuit, data acquisition module and data analysis calculation module; the method includes: connecting the impedance to be measured to the reverse end of the first reverse operational amplifier, and the host computer controls the frequency sweep signal generator to provide an excitation signal and apply it to the measurement system The input end of the circuit controls the acquisition card to obtain the inverting amplifier output of the first channel and the inverting amplifier output of the second channel in real time, and calculates the amplitude and phase of the impedance to be measured within the frequency sweep range. The AC impedance measuring device of the present invention measures accurately and achieves stable output of the signal ratio to be measured. The ratio error does not exceed 0.2%, and the measurement error of the resistance is controlled within 0.7%. The resonance period and impedance amplitude of the cable impedance spectrum measured by this device also meet the Theory and simulation derivation.

Description

An AC impedance spectrum measurement system and method based on the dual-channel half-bridge method

Technical field

The invention discloses an AC impedance spectrum measurement system and method based on a dual-channel half-bridge method, which belongs to the technical field of measuring electrical variables.

Background technique

As an inherent property of components, impedance is closely related to its performance. By measuring impedance, many other physical quantities can be indirectly measured quickly, such as pressure, temperature, vibration, etc. Therefore, impedance measurement is widely used in engineering and is currently common on the market. Most of the light-duty equipment is single-frequency or low-frequency AC impedance measurement. Instruments that can continuously measure the impedance spectrum in a wide frequency range are often bulky and expensive, ranging from hundreds of thousands. For application scenarios such as outdoor measurement and small laboratories, it is necessary to create a simple, high-precision and wide-frequency range impedance spectrum measuring instrument.

Contents of the invention

The purpose of the present invention is to provide an AC impedance spectrum measurement system and method based on the dual-channel half-bridge method to solve the problem in the prior art that the impedance measurement equipment for continuously measuring the impedance spectrum in a wide frequency range is bulky and expensive.

An AC impedance spectrum measurement system based on the dual-channel half-bridge method. The system hardware includes a frequency sweep signal generator, acquisition card, power supply, host computer and measurement system circuit. The system software includes a data acquisition module and a data analysis and calculation module;

The frequency sweep signal generator provides AC frequency sweep signals or single frequency signals. The signal end of the frequency sweep signal generator is connected to the measurement system circuit. The measurement system circuit is also connected to the CH0 end and CH1 end of the acquisition card. The USB end of the acquisition card passes through the host computer. Connect the USB end of the frequency sweep signal generator. The power supply is connected to the frequency sweep signal generator, the measurement system circuit and the acquisition card. The acquisition card obtains the required output signal in real time and calculates it to obtain the AC impedance;

The measurement system circuit includes dual measurement channels. The first channel receives the excitation signal and sends it to the device under test. The inverse operational amplifier of the first channel serves as the half-bridge arm for impedance measurement. The second channel receives the excitation signal and sends it to R _REF . The two-channel inverting operational amplifier is used as a reference circuit to eliminate the system nonlinear error of the measurement bridge. Both outputs of the dual-channel operational amplifier are sent to the acquisition card;

The data acquisition module extracts the signal amplitude, phase, and frequency information collected by the acquisition card, and the data analysis and calculation module automatically calculates the impedance value at a certain frequency or the AC impedance spectrum within a wide frequency range.

An AC impedance spectrum measurement method based on the dual-channel half-bridge method, using an AC impedance spectrum measurement system based on the dual-channel half-bridge method, including:

S1: Connect the impedance to be measured to the reverse end of the first inverting operational amplifier;

S2: The host computer controls the frequency sweep signal generator to provide an excitation signal that is applied to the input end of the measurement system circuit;

S3: The host computer controls the acquisition card to obtain the first inverting amplifier output U1 and the second inverting amplifier output U2 in real time;

S4: Calculate the impedance amplitude to be measured within the frequency sweep range and phase/> .

S3 includes:

;

;

is the signal amplitude change,/> It is the phase shift produced by the op amp itself when the I/V of the dual measurement channels are completely consistent,/> is the input signal amplitude,/> is the inverting amplifier feedback resistor,/> is the reference resistor at the input end of the second inverting amplifier,/> is the angular frequency of the input signal,/> is time,/> and/> are the phase shifts through the two measurement systems respectively.

S4 includes:

;

;

;

in, is the impedance to be measured,/> is the amplitude of DUT,/> is the phase of the DUT.

Compared with the existing technology, the present invention has the following beneficial effects: The present invention consists of a precision frequency sweep signal generator, a core measurement system using a dual-channel "half-bridge", etc., which can not only meet the accuracy requirements of the laboratory, but also is simple to operate; communicate The impedance measurement device is accurate and robust. The innovative measurement structure design of the dual-channel "half-bridge method" compensates the amplitude and phase of the signal to be measured, achieving a stable output of the signal ratio to be measured. The ratio error does not exceed 0.2%. The resistance The measurement error is controlled within 0.7%. The resonant period and impedance amplitude of the cable impedance spectrum measured by this device are also in line with the theoretical and simulation derivation.

Description of the drawings

Figure 1 is a block diagram of the circuit structure of the measurement system;

Figure 2 is the impedance amplitude spectrum of the system measurement station;

Figure 3 is the impedance phase spectrum of the system measurement station;

Figure 4 is the circuit structure of the dual measurement channel;

Figure 5 is an overall scheme diagram of the present invention;

Figure 6 is the DUT and Ratio of two outputs under the same conditions;

Figure 7 is the DUT and Phase difference between two outputs under the same conditions;

Figure 8 is The ratio of the two outputs under the conditions;

Figure 9 is The phase difference between the two outputs under the conditions;

Figure 10 is the result of 430Ω resistance measurement under the system of the present invention;

Figure 11 is the result of 560Ω resistance measurement under the system of the present invention;

Figure 12 is the result of 1100Ω resistance measurement under the system of the present invention;

Figure 13 is the result of 1300Ω resistance measurement under the system of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

An AC impedance spectrum measurement system based on the dual-channel half-bridge method. The system hardware includes a frequency sweep signal generator, acquisition card, power supply, host computer and measurement system circuit. The system software includes a data acquisition module and a data analysis and calculation module;

As shown in Figure 1, the sweep signal generator provides an AC sweep signal or a single frequency signal. The signal end of the sweep signal generator is connected to the measurement system circuit. The measurement system circuit is also connected to the CH0 and CH1 ends of the acquisition card. The USB of the acquisition card The end is connected to the USB end of the frequency sweep signal generator through the host computer. The power supply is connected to the frequency sweep signal generator, the measurement system circuit and the acquisition card. The acquisition card obtains the required output signal in real time and calculates it to obtain the AC impedance;

As shown in Figure 4, the measurement system circuit includes dual measurement channels. The first channel receives the excitation signal and sends it to the device under test. The inverse operational amplifier of the first channel serves as the half-bridge arm for impedance measurement. The second channel receives the excitation signal and sends it to the device under test. R _REF , the second inverting operational amplifier is used as a reference circuit to eliminate the system nonlinear error of the measurement bridge. Both outputs of the dual operational amplifier are sent to the acquisition card;

The data acquisition module extracts the signal amplitude, phase, and frequency information collected by the acquisition card, and the data analysis and calculation module automatically calculates the impedance value at a certain frequency or the AC impedance spectrum within a wide frequency range.

An AC impedance spectrum measurement method based on the dual-channel half-bridge method, using an AC impedance spectrum measurement system based on the dual-channel half-bridge method, including:

S1: Connect the impedance to be measured to the reverse end of the first inverting operational amplifier;

S2: The host computer controls the frequency sweep signal generator to provide an excitation signal that is applied to the input end of the measurement system circuit;

S3: The host computer controls the acquisition card to obtain the first inverting amplifier output U1 and the second inverting amplifier output U2 in real time;

S4: Calculate the impedance amplitude to be measured within the frequency sweep range and phase/> .

S3 includes:

;

;

is the signal amplitude change,/> It is the phase shift produced by the op amp itself when the I/V of the dual measurement channels are completely consistent,/> is the input signal amplitude,/> is the inverting amplifier feedback resistor,/> is the reference resistor at the input end of the second inverting amplifier,/> is the angular frequency of the input signal,/> is time,/> and/> are the phase shifts through the two measurement systems respectively.

S4 includes:

;

;

;

in, is the impedance to be measured,/> is the amplitude of DUT,/> is the phase of the DUT.

The main control system of the present invention uses the STM32F103RCT6 microcontroller designed by ST Company as the control core of the entire system, and has rich I/O interfaces to meet the design needs of this system. It mainly includes three aspects: controlling the digital frequency synthesizer to generate sweep signals; communicating with the host computer, executing the commands sent by the host computer and returning to the working status of the microcontroller; controlling the acquisition card, and setting acquisition card related parameters through the host computer.

As shown in Figure 5, the human-computer interaction interface includes signal acquisition, signal processing, and data transmission and reception. The excitation system includes the control part, the signal generation with AD9959 as the core, the voltage amplification with AD8099 as the core, and the power amplification part with THS3091 as the core. The voltage amplification and power method sections are collectively referred to as signal conditioning. AD9959 generates frequency sweep signals, and the amplitude, phase and frequency interval are controlled by STM32; in order to make the signal output of this module more stable, two 9th-order Butterworth low-pass filters are designed at the signal output end to remove high-frequency noise. The AD8099 chip has ultra-low noise, ultra-low distortion, high slew rate and high gain bandwidth product, and the offset voltage is less than 0.5mV. Considering the gain bandwidth product of the chip, the signal amplitude amplification part is composed of two AD8099 chips cascaded and some peripheral circuit components, so that the high-frequency signal has sufficient amplitude. The THS3091 chip is a current feedback operational amplifier with low distortion and high slew rate. In order to flexibly change the input impedance according to needs, a π-type impedance network is designed before the input pin of the operational amplifier. The power amplifier module uses a total of four THS3091 chips. Two chips are used as a group to form a channel. There are two channels in total. Each channel can provide a maximum drive current of 500mA. Whether it is welded through a 0Ω resistor or not, the chip's Whether connected in parallel or not, if this resistor is soldered, it can provide a driving current of 1A.

The measurement system uses OPA818 as the measurement bridge of the "half-bridge method". OPA818 is a voltage feedback operational amplifier with low noise, low distortion, ultra-high slew rate and high gain bandwidth product. The measurement structure uses a dual-channel operational amplifier, in which the first operational amplifier serves as the "half-bridge" bridge arm for impedance measurement, and the second operational amplifier serves as the reference circuit to eliminate the system nonlinear error of the measurement bridge.

When dual-channel I/V is used as a measurement circuit, the circuit structure is consistent, and the measurement system chip also has consistent characteristics. According to the calculation formula, it can be seen that when the dual-channel I/V is completely consistent, the amplifier gain error and phase shift can be eliminated. During calculation, the amplitude attenuation and phase difference will be compensated, which improves the accuracy of impedance measurement. Although there is still an error in the phase when the circuit is not completely consistent, the measurement error is much smaller than the traditional "half-bridge method".

The impedance amplitude spectrum and impedance phase spectrum of the system measurement station are shown in Figure 2 and Figure 3 respectively. Figure 2 is a comparison chart of the measured and simulated input impedance phase spectrum of a terminal short-circuit cable with a length of 100m. The phase error is within the measurement margin. Meets the measurement requirements; Figure 3 is a comparison chart of the measured and simulated input impedance amplitude spectrum of a terminal short-circuit cable with a length of 100m. The resonance period and amplitude of the amplitude spectrum are consistent with the simulated values, meeting the measurement requirements; the present invention uses two symmetrical I /V conversion circuit improves the traditional "half-bridge method". When calculating impedance, the accuracy and stability of the ratio of the two outputs have a great impact on the impedance measurement. DUT and The ratio of the two outputs under the same conditions is shown in Figure 6. It can be seen that the measured values are consistent with the theoretical formula derivation; DUT and/> The phase difference between the two outputs under the same conditions is shown in Figure 7. Since the two inverting amplifier circuits are consistent, the phase difference should be close to 0. It can be seen that the measured value is consistent with the theoretical formula derivation;/> The ratio of the two outputs under the conditions is shown in Figure 8,/> The phase difference between the two outputs under the conditions is shown in Figure 9. The system output is measured and the phase difference between the first and second channels is obtained. Since the circuit characteristics of the two inverting amplifiers are consistent, no additional capacitance and inductance characteristic components are introduced. , the phase difference should be close to 0, it can be seen that the measured value conforms to the theoretical formula derivation.

According to the method of the present invention, resistances with different resistance values are measured under frequency sweep conditions, and a measurement curve of the resistance within a wide frequency range is drawn. The measurement results of 430Ω, 560Ω, 1100Ω, and 1300Ω resistance are shown in Figure 10, Figure 11, Figure 12, and Figure 13 respectively. The corresponding errors do not exceed 0.2%, 0.7%, 0.6%, and 0.6%.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments. The recorded technical solutions may be modified, or some or all of the technical features may be equivalently replaced, but these modifications or substitutions shall not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of each embodiment of the present invention.

Claims (4)

1. An AC impedance spectrum measurement system based on the dual-channel half-bridge method, characterized in that the system hardware includes a frequency sweep signal generator, acquisition card, power supply, host computer and measurement system circuit, and the system software includes a data acquisition module, data Analysis and calculation module; The frequency sweep signal generator provides AC frequency sweep signals or single frequency signals. The signal end of the frequency sweep signal generator is connected to the measurement system circuit. The measurement system circuit is also connected to the CH0 end and CH1 end of the acquisition card. The USB end of the acquisition card passes through the host computer. Connect the USB end of the frequency sweep signal generator. The power supply is connected to the frequency sweep signal generator, the measurement system circuit and the acquisition card. The acquisition card obtains the required output signal in real time and calculates it to obtain the AC impedance; The measurement system circuit includes dual measurement channels. The first channel receives the excitation signal and sends it to the device under test. The inverse operational amplifier of the first channel serves as the half-bridge arm for impedance measurement. The second channel receives the excitation signal and sends it to R _REF . The two-channel inverting operational amplifier is used as a reference circuit to eliminate the system nonlinear error of the measurement bridge. Both outputs of the dual-channel operational amplifier are sent to the acquisition card; The data acquisition module extracts the signal amplitude, phase, and frequency information collected by the acquisition card, and the data analysis and calculation module automatically calculates the impedance value at a certain frequency or the AC impedance spectrum within a wide frequency range. 2. An AC impedance spectrum measurement method based on the dual-channel half-bridge method, using the AC impedance spectrum measurement system based on the dual-channel half-bridge method according to claim 1, which is characterized in that it includes: S1: Connect the impedance to be measured to the reverse end of the first inverting operational amplifier; S2: The host computer controls the frequency sweep signal generator to provide an excitation signal that is applied to the input end of the measurement system circuit; S3: The host computer controls the acquisition card to obtain the first inverting amplifier output U1 and the second inverting amplifier output U2 in real time; S4: Calculate the impedance amplitude to be measured within the frequency sweep range and phase/> . 3. A kind of AC impedance spectrum measurement method based on dual-channel half-bridge method according to claim 2, characterized in that, S3 includes: ; ; is the signal amplitude change,/> It is the phase shift produced by the op amp itself when the I/V of the dual measurement channels are completely consistent,/> is the input signal amplitude,/> is the inverting amplifier feedback resistor,/> is the reference resistor at the input end of the second inverting amplifier, is the angular frequency of the input signal,/> is time,/> and/> are the phase shifts through the two measurement systems respectively. 4. A kind of AC impedance spectrum measurement method based on dual-channel half-bridge method according to claim 2, characterized in that, S4 includes: ; ; ; in, is the impedance to be measured,/> is the amplitude of DUT,/> is the phase of the DUT.