阅读说明：本技术 一种交流地电位梯度电压信号测量装置 (Alternating current ground potential gradient voltage signal measuring device ) 是由 张军 诸海博 王松亭 张海军 常伟 徐海宁 袁峰 何方 张娜 于 2020-05-12 设计创作，主要内容包括：一种交流地电位梯度电压信号测量装置,输入分压电路的输入端与被测信号输出端相连接,而输入分压电路的输出端依次与差动放大电路,混频电路,模拟数字转换电路及单片机电路相连通；在单片机电路输出端与差动放大电路输入端之间还设置有一实现两路运算放大器进行差动放大及电路增益的增益调节电路；在单片机电路输出端与混频电路输入端之间还设有波形发生器电路。混频电路同时接收来自波形发生器电路信号,在其中进行混频处理,并将混频后的信号输出到模拟数字转换电路的输入端。模拟数字转换电路对输入信号进行数字化,输出数字量信号到单片机电路。单片机电路能够对波形发生器电路和增益调节电路进行控制。(The input end of an input voltage division circuit is connected with the output end of a detected signal, and the output end of the input voltage division circuit is sequentially communicated with a differential amplifying circuit, a mixing circuit, an analog-digital conversion circuit and a single chip microcomputer circuit; a gain adjusting circuit for realizing differential amplification and circuit gain of the two operational amplifiers is also arranged between the output end of the singlechip circuit and the input end of the differential amplifying circuit; and a waveform generator circuit is also arranged between the output end of the singlechip circuit and the input end of the mixing circuit. The mixing circuit simultaneously receives signals from the waveform generator circuit, performs mixing processing in the waveform generator circuit, and outputs the mixed signals to the input end of the analog-digital conversion circuit. The analog-digital conversion circuit digitizes the input signal and outputs a digital quantity signal to the singlechip circuit. The single chip circuit is capable of controlling the waveform generator circuit and the gain adjustment circuit.)

1. The utility model provides an alternating current ground potential gradient voltage signal measuring device, it includes power supply circuit, input bleeder circuit, its characterized in that: the input end of the input voltage division circuit is connected with the output end of the detected signal, and the output end of the input voltage division circuit is sequentially communicated with the differential amplifying circuit, the mixing circuit, the analog-digital conversion circuit and the singlechip circuit; a gain adjusting circuit for realizing differential amplification and circuit gain of the two operational amplifiers is also arranged between the output end of the singlechip circuit and the input end of the differential amplifying circuit; and a waveform generator circuit with signal frequency set by the singlechip circuit is also arranged between the output end of the singlechip circuit and the input end of the mixer circuit.

2. The ac ground potential gradient voltage signal measurement device according to claim 1, wherein: the waveform generator circuit outputs a sine carrier signal, and the frequency of the signal is set by the singlechip circuit.

3. The alternating-current ground potential gradient voltage signal measurement apparatus according to claim 1 or 2, characterized in that: the output frequency value of the waveform generator circuit is the sum or difference of the frequency of the detected signal and the preset intermediate frequency value.

4. The ac ground potential gradient voltage signal measurement device according to claim 1, wherein: the analog-digital converter used by the analog-digital conversion circuit is an audio analog-digital converter, and the sampling rate is integral multiple of the preset intermediate frequency.

5. The method of the alternating-current ground potential gradient voltage signal measurement device according to claim 1, characterized in that: the adopted singlechip circuit is an 8-bit, 16-bit or 32-bit singlechip.

6. The method of the alternating-current ground potential gradient voltage signal measurement device according to claim 1, characterized in that: sampling data is firstly subjected to a relevant average filtering algorithm to obtain a sampling value of an intermediate frequency signal period, and then discrete Fourier transform algorithm is used for processing the sampling point data to obtain an amplitude value of a detected signal.

Technical Field

The invention belongs to the technical field of electronic measurement, and particularly provides an alternating current ground potential gradient voltage signal measuring device and method, which are particularly used for measuring alternating current ground potential gradient voltage signals in cathode protection parameters of buried steel pipelines.

Background

Alternating current ground potential gradient (ACVG) voltage signals in cathode protection parameters of the buried steel pipeline can reflect the corrosion condition of the pipeline to a certain extent, so that the detection of the ACVG voltage signals is an important safety maintenance means and can achieve the purpose of preventing the corrosion in the bud. The signal is measured by a precision instrument, so that the accurate position of a damage point of an outer anticorrosive coating of the pipeline can be accurately found, quantitative analysis is carried out on the corrosion state, real and reliable basic data are provided for integrity management of the pipeline, the pipeline corrosion is controlled from the source, and a basis is provided for the anticorrosive work of the pipeline.

The AC ground potential gradient signal is a low-frequency AC voltage signal, which is sent by a special transmitter and the signal variation is detected along the pipeline by a measuring device. The ac ground potential gradient signals operate at frequencies varying from about 100Hz to several kHz, which are kept away from the local power frequency and its harmonic frequencies. For example, when the power frequency is 50Hz, the frequencies of 128Hz, 570Hz, 640Hz, 1280Hz and the like can be selected; further, when the power frequency is 60Hz, 96Hz, 512Hz, 570Hz, 1280Hz can be used. In actual use, different working frequencies are selected according to different test working conditions, the measurement accuracy of signals with higher frequencies is higher, the resolution is better, signals with lower frequencies can be transmitted for a longer distance, and the frequency range of the actual measured signals reaches about 100 Hz-200 kHz. The AC ground potential gradient signal magnitude is typically expressed in dB μ V, with 0dB representing a1 μ Vrms signal. In practice, μ V is usually omitted and is directly expressed in dB, for example 60dB for 1mVrms signals. Signals below 0dB are too weak and are generally considered to be disregarded as interfering signals.

In order to realize accurate measurement of the alternating-current ground potential gradient signal, the dynamic range of the measuring device is required to reach more than 140dB, the signal resolution is required to be better than 5dB, namely 1.78 mu Vrms, the two indexes directly reflect the measuring accuracy and sensitivity of the device, in addition, equal-accuracy measurement of any frequency signal of 100 Hz-200 kHz is required to be realized, and the measuring speed is required to be more than 2 times/second.

For the above requirements for measuring the alternating-current ground potential gradient voltage signal, the following relevant patent documents are consulted:

patent CN102707133 "an apparatus, system and method for measuring a variable frequency ac voltage" discloses a method comprising: the method comprises the steps that an edge detection module polls the rising edge or the falling edge of a square wave signal with the same period as the alternating current, and outputs a period change signal when the rising edge or the falling edge of the square wave signal is inquired, and a central processing circuit samples the voltage value of the alternating current according to a sampling time interval, stores and calculates the average value of all sampled voltage values. This method has the following disadvantages: 1. in the process of generating square wave signals by alternating current signals, random noise and zero drift of an edge detection circuit can influence the generation time of edges of the square wave signals, so that the sampling period of a single chip microcomputer changes and the accuracy of voltage sampling data is further influenced; 2. the edge detection module adopts a comparator circuit and cannot be used for edge identification detection of a mu V-level input signal; 3. the device outputs the average value of the alternating voltage in the sampling period instead of the effective value; 4. the measured signal is measured by a 10bit analog-to-digital converter (ADC) in the single chip microcomputer, and the dynamic range of about 60dB can be achieved.

Patent CN104655916 "a device and method for measuring effective value of alternating voltage" discloses a method, which is: converting an alternating current signal to be detected into a pulse signal by using a signal comparator, and measuring the period T of the pulse signal by using a processor; meanwhile, inputting the alternating current signal to be detected into a peak value detection circuit, measuring a peak value U of the alternating current signal to be detected by using a processor, and finally obtaining an effective value of the alternating current signal to be detected through calculation. This method has the following disadvantages: 1. in the process of generating square wave signals by alternating current signals, random noise and zero drift of an edge detection circuit can influence the generation time of edges of the square wave signals, so that the sampling period of a single chip microcomputer changes and the accuracy of voltage sampling data is further influenced; 2. the edge detection module adopts a voltage stabilizing diode as a reference voltage of a comparator, and input signals of a mu V level cannot be identified, so that the edge detection module cannot work normally; 3. an analog-digital converter (ADC) in the MSP430 single-chip microcomputer is used for measuring a measured signal, the resolution is only 16 bits at most, and the dynamic range of 140dB cannot be achieved. 4. The patent is limited to measuring power frequency voltage signals

Patent CN105807128 "method and system for measuring ac voltage by using multi-period strategy for digital-to-analog conversion" discloses a method for measuring ac voltage by using multi-period strategy for digital-to-analog conversion, the scheme is: s1: equally dividing the detected sinusoidal voltage signals of P periods into N parts, wherein common divisor does not exist between P and N except 1, and generating a digital value of a step wave step; s2: inputting the N data into a DAC to generate a periodic step wave; s3: measuring the voltage value of the step wave; s4: carrying out differential sampling on the two waveforms; s5: and a segmented sampling mode is adopted during DFT operation, and only the step middle data is operated. This method has the following disadvantages: 1. additional errors can be brought by a digital-to-analog converter (DAC), and the testing precision is influenced; 2. the dynamic range of the DAC is limited, usually 16 bits, and the optimal dynamic range can only reach 96 dB; 3. the DAC needs stabilization time, only data in the middle time segment of the step are calculated during sampling, the data sampling rate is lowered invisibly, and the signal to noise ratio is not improved; 4. the DAC cannot output signals of the μ V level, and thus measurement of weak signals is not applicable.

Patent CN106353562 discloses a method for measuring weak nonlinear current-voltage characteristics by ac excitation, which comprises: exciting the to-be-measured element by adopting an alternating voltage signal, adjusting the frequency and amplitude of the exciting voltage signal, measuring the amplitude of each order of harmonic signal, calculating the coefficient of each item in the to-be-measured current-voltage relation according to the measurement data, and calculating the nonlinear current-voltage relation of the to-be-measured element according to the obtained coefficient. This method has the following disadvantages: 1. the alternating-current ground potential gradient signal is a passive signal, and the application of an alternating-current voltage excitation signal on the passive signal can influence the normal function of the transmitter; 2. the effective signal of the alternating-current ground potential gradient signal is a single frequency, and no harmonic component exists, so that the method for measuring the harmonic wave in the patent is not applicable; 3. the AC ground potential gradient signal is a linear signal, but is not a non-linear current-voltage characteristic signal described in the patent, so the method described in the patent is not applicable to AC ground potential gradient signal measurement.

Patent CN109444506 "a method for measuring and calculating voltage of ac system" discloses a method comprising: sampling an alternating voltage input signal of a collection point of each path of a cycle by using an AD (analog-to-digital) according to the alternating voltage frequency of an alternating current system by using a single chip microcomputer; calculating each harmonic effective value and angle of the corresponding acquisition point voltage by using FFT (fast Fourier transform) according to the alternating voltage input signal obtained by sampling; calculating each subharmonic effective value and angle of each path of voltage in the alternating current system through ohm's law according to each subharmonic effective value and angle of the collection point; and calculating the voltage value and angle required by each type of the alternating current system through a cosine theorem formula according to the effective value and angle of each subharmonic of each path of voltage. This method has the following disadvantages: 1. the input signal is alternating current system voltage, the amplitude is more than mV, and the measurement requirement of mu V level voltage cannot be met; 2. the measurement object of the method is the three-phase four-wire system alternating current system voltage, and the alternating current ground potential gradient signal is a single-path differential signal, so the method is not applicable.

Patent CN109444526 "a device for measuring ac voltage with variable frequency" discloses a device for measuring ac voltage with variable frequency, which comprises a housing, wherein a central processing module is arranged inside the housing, the central processing module is electrically connected with an analog-to-digital conversion module and an edge detection module, and the central processing module, the analog-to-digital conversion module and the edge detection module are electrically connected with a working power supply module; the working power supply module comprises a working power supply circuit, and in the device for measuring the alternating-current voltage with the variable frequency, the integrated circuit feeds back and collects the output voltage through the working power supply circuit, then controls the on-off of the second triode, realizes the stable output of the output voltage, and is matched with the energy storage circuit consisting of the third capacitor and the fourth capacitor to store energy for the output voltage, so that the voltage fluctuation is reduced, and the stable output of the voltage is further improved. This method has the following disadvantages: 1. random noise and zero drift of the edge detection circuit can influence the generation time of the edges of the square wave signals, so that the sampling period of the single chip microcomputer is changed, and the accuracy of voltage sampling data is further influenced; 2. the input signal described in this patent is an alternating current system voltage, the amplitude is above mV, and the measurement requirement of μ V-level voltage cannot be met. 3. This patent is limited to measuring power frequency voltage signals.

In summary, the current measurement device and method cannot meet the requirement of accurate measurement of the alternating current ground potential gradient signal.

Disclosure of Invention

The invention provides an alternating-current ground potential gradient voltage signal measuring device, aiming at solving the technical problem that the prior art can not realize accurate and rapid measurement on an alternating-current ground potential gradient voltage signal.

The purpose of the invention is realized by the following technical scheme:

the utility model provides an alternating current ground potential gradient voltage signal measuring device, it includes power supply circuit, input bleeder circuit, its characterized in that: the input end of the input voltage division circuit is connected with the output end of the detected signal, and the output end of the input voltage division circuit is sequentially communicated with the differential amplifying circuit, the mixing circuit, the analog-digital conversion circuit and the singlechip circuit; a gain adjusting circuit for realizing differential amplification and circuit gain of the two operational amplifiers is also arranged between the output end of the singlechip circuit and the input end of the differential amplifying circuit; and a waveform generator circuit with signal frequency set by the singlechip circuit is also arranged between the output end of the singlechip circuit and the input end of the mixer circuit. The signal to be measured enters the differential amplifying circuit after passing through the input voltage division circuit, and under the action of the gain adjusting circuit, the differential amplifying circuit amplifies the signal and outputs the signal to the frequency mixing circuit. The mixing circuit simultaneously receives signals from the waveform generator circuit, performs mixing processing in the waveform generator circuit, and outputs the mixed signals to the input end of the analog-digital conversion circuit. The analog-digital conversion circuit digitizes the input signal and outputs a digital quantity signal to the singlechip circuit. The single chip circuit is capable of controlling the waveform generator circuit and the gain adjustment circuit. The functions of each circuit are described below.

The input voltage division circuit can attenuate a signal to be detected, so that the amplitude of the signal can meet the requirement of the input range of the differential amplification circuit. The voltage range of the detected signal usually reaches 10Vrms (rms represents an effective value), and exceeds the working voltage range of a general circuit (5V or lower), and the direct input can cause the differential amplifying circuit to be saturated and not work normally.

The gain of the differential amplifier circuit is set by the gain adjusting circuit. The gain adjusting circuit receives a control signal of the singlechip and realizes the gain adjusting function of the differential amplifying circuit by switching the external gain resistor.

The waveform generator circuit part can output sine waveform signals, and the frequency of the output signals of the sine waveform signals is set by the single chip microcomputer. The output frequency value of the waveform generator circuit is the sum or difference of the frequency of the detected signal and the preset intermediate frequency value.

The frequency mixing circuit receives output signals of the differential amplifying circuit and the waveform generator circuit, outputs a signal of an intermediate frequency after frequency mixing processing, and the frequency value is not any integral multiple of the local power frequency so as to avoid interference.

The analog-digital converter (ADC) adopted by the analog-digital conversion circuit is an audio ADC (audio analog-digital converter), and the sampling rate is an integral multiple of the preset intermediate frequency. The sampling rate is integral multiple of the preset intermediate frequency, and the single sampling time of the ADC is integral multiple of the local power frequency period. And the data sampled by the ADC is sent to the single chip microcomputer circuit for storage.

The singlechip circuit adopted by the invention is an 8-bit, 16-bit or 32-bit singlechip; but not limited to, an STM32 series single chip microcomputer of an ARM inner core, an AVR inner core series single chip microcomputer and a PIC series single chip microcomputer.

The single chip microcomputer circuit controls a sampling period, when data acquisition of one sampling period is completed, the single chip microcomputer performs correlation average calculation on the sampling data to obtain voltage sampling data of an intermediate frequency signal period, and then Discrete Fourier Transform (DFT) algorithm is used for calculating the sampling data to obtain the amplitude of a detected signal.

According to the alternating-current ground potential gradient voltage signal measuring device and method provided by the invention, the requirement of alternating-current voltage input in the range of 1 mu Vrms-10 Vrms can be met by reasonably setting the parameters of the input voltage division circuit and the gain of the differential amplifying circuit, and the dynamic range reaches more than 140 dB. The waveform generator circuit outputs sine wave signals with stable amplitude and frequency, the range reaches more than 0 Hz-300 kHz, the signals and amplified voltage signals are subjected to frequency mixing processing in the frequency mixer, stable intermediate frequency signals are output, the intermediate frequency signals carry all information of the signals to be detected, the frequency spectrum migration of the signals to be detected is realized, the signal frequency is moderate, and the signal is suitable for being processed by an analog-digital converter. By reasonably setting the output frequency of the waveform generator circuit, the intermediate frequency signal can be ensured to be far away from the interference of power frequency and harmonic frequency thereof, and the frequency range of the detected signal can reach 10 Hz-20 kHz. . The audio ADC adopted in the analog-digital conversion circuit can reach the sampling rate of 48 kHz-768 kHz, intermediate frequency signals can be subjected to oversampling, and the measurement precision is improved through post-processing. The sampling period of the device is an integral multiple of the intermediate frequency signal period and the power frequency signal period, for example, 0.5 second, 0.4 second and the like can be taken, and the requirement of measuring rate can be met. In the data processing process of the single chip microcomputer, a correlation average filtering algorithm is adopted to carry out in-phase superposition average processing on useful intermediate frequency signals. In the process, the intermediate frequency signals with the same phase are strengthened, the random noise signals, the power frequency and harmonic interference signals with different phases are restrained, and the signal amplitude is greatly reduced. In the process, the amplitude of the signal of the non-intermediate frequency is further inhibited because the phase of the signal of the non-intermediate frequency is different from the phase of a conversion coefficient in the algorithm, and finally the output signal is intermediate frequency signal amplitude data with high signal-to-noise ratio, and the data and the amplitude of the detected signal are in a linear relation.

Compared with the prior art, the method can meet the measurement requirement of the alternating current ground potential gradient signal, and has remarkable advantages in the aspects of measurement precision, signal resolution and measurement speed.

Drawings

FIG. 1 is a block diagram of the circuit principle of the present invention;

FIG. 2 is a schematic diagram of the power input block of the present invention;

fig. 3 is a circuit schematic of an embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the accompanying drawings; due to the diversity of the measured signals, the frequencies of the signals are not limited to the frequencies exemplified in the examples, and therefore, other frequencies set by applying the same measurement principle also belong to the protection scope of the present invention.

Example 1

As shown in fig. 1 and 2, the power supply circuit of the alternating-current ground potential gradient voltage signal measuring device of the invention is input to a voltage dividing circuit; the input end of the input voltage division circuit is connected with the output end of the detected signal, and the output end of the input voltage division circuit is sequentially communicated with the differential amplifying circuit, the mixing circuit, the analog-digital conversion circuit and the singlechip circuit; a gain adjusting circuit for realizing differential amplification and circuit gain of the two operational amplifiers is also arranged between the output end of the singlechip circuit and the input end of the differential amplifying circuit; and a waveform generator circuit with signal frequency set by the singlechip circuit is also arranged between the output end of the singlechip circuit and the input end of the mixer circuit. The signal to be measured enters the differential amplifying circuit after passing through the input voltage division circuit, and under the action of the gain adjusting circuit, the differential amplifying circuit amplifies the signal and outputs the signal to the frequency mixing circuit. The mixing circuit simultaneously receives signals from the waveform generator circuit, performs mixing processing in the waveform generator circuit, and outputs the mixed signals to the input end of the analog-digital conversion circuit. The analog-digital conversion circuit digitizes the input signal and outputs a digital quantity signal to the singlechip circuit. The single chip circuit is capable of controlling the waveform generator circuit and the gain adjustment circuit.

Fig. 2 is a schematic circuit diagram of an embodiment of the apparatus according to the present invention, which includes the numbers, specifications and connection modes of the chips and peripheral components of each partial circuit, and the circuit is described in detail below.

The power supply circuit of the present example includes U1, U2, C8, C10, CD1, C11 to C16. The power circuit of the embodiment receives 5.5-15V DC power input and outputs 5.0V and 3.3V DC power for other circuits of the embodiment. U1 and U2 in the power circuit are DC voltage stabilizing chips of the power circuit part, and respectively output 5V and 3.3V DC voltage for other circuits. The U1 adopts LDO chip LP2985-50 to provide 5.0V working power supply for other circuits, and the name of the electric node signal is VCC 50. The U2 adopts LDO chip LP2985-33 to provide 3.3V working power supply for other circuits, and the name of the electric node signal is VCC 33. According to different schemes adopted by specific embodiments, different power supply requirements exist, and the power supply requirements can be adjusted according to actual requirements. The power supply negative electrode of the power supply circuit of this example is GND. Pin 1 of U1 and U2 is the power input pin, which is connected to the input power VPP, and the voltage range of VPP is 5.5V-15V. Pin 3 of U1 and U2 are enable pins and are connected to respective pin 1. Pin 2 of U1 and U2 are power ground pins that are connected to the device's power Ground (GND) signal. Pin 4 of U1 and U2 are decoupling pins, which are connected to decoupling capacitors C8, C10, respectively, to GND. Pin 5 of U1 and U2 are respective regulated voltage output pins. In the peripheral components of U1 and U2, CD1, C11 and C12 are filter capacitors of the voltage signal VPP at the input terminals of U1 and U2, C13, C14, C15 and C16 are filter capacitors of the voltage output pin 5 of U1, and C17-C24 are filter capacitors of the voltage output pin of U1 of U2.

The input voltage division circuit comprises C5, C7, R1, R5, R3 and R4, and forms an AC-coupled input voltage division circuit for attenuating the input signals VP1 and VP2 to proper amplitudes for the differential amplification circuit. The VBIAS signal of the resistor divider circuit is a reference potential point, taken from pin 5 of analog-to-digital converter (ADC) chip U7, at a voltage of about 1.5V. C28 and C29 are decoupling capacitances for the VBIAS signal. The input C5 and C7 in the voltage divider circuit are DC blocking capacitors for isolating DC signals, which are equivalent to paths for AC signals. . IN the input voltage division circuit, one group is R1 and R3, and the other group is R5 and R4, so as to form 2 groups of series resistance voltage division networks, which divide the input voltage VP1 and VP2 respectively, and the divided voltage nodes are IN1 and IN2, which are respectively connected with the 3 pin and the 5 pin of the amplifier U3.

The differential amplifying circuit comprises U3, R2 and R6, wherein U3 is a low noise operational amplifier (TLC 2272). U3 contains two independent operational amplifiers U3A and U3B, and power part U3C of U3 contains pin 8 and pin 4, and pin 8 connects power VCC50, and pin 4 connects GND. The non-inverting input pins of U3 are pin 3 and pin 5, which are connected to voltage nodes IN1 and IN2, respectively. The output pins of U3 are pin 1 and pin 7. A resistor R2 is connected between the pin 3 of the U3A and the pin 1, and a resistor R6 is connected between the pin 6 of the U3B and the pin 7. The electrical node signal name at pin 2 of U3 is AC1GA, and the electrical node signal name at pin 6 of U3 is AC1 GB.

The gain adjusting circuit comprises U4 and RG 1-RG 4, wherein U4 is an analog switch chip, the model is TMUX1109, the analog switch chip is an analog switch chip with extremely low leakage current, and RG 1-RG 4 are gain resistors. In the figure, U4 includes two parts, U4A and U4C. In U4C, pin 16 and pin 1 are both gating control pins and are connected with a general purpose input/output pin (GPIO) of the singlechip U8; pin 2 is an enable pin to connect to VCC 33; pin 15 and pin 3 are power pins, connected to GND. In U4A, pins 4, 5, 6, and 7 are strobe pins, and pin 8 is a common pin. Through control signals MUXA0 and MUXA1 on the gating control pins, an electric signal path can be formed between one gating pin and the common pin, namely a bidirectional signal path between pin 4/pin 8, pin 5/pin 8, pin 6/pin 8 or pin 7/pin 8 can be formed, and the practical effect is that one of RG 1-RG 4 is selected to be connected between an electric node AC1GA and an AC1GB node, and the resistance is set to be RGx. U3 combines with peripheral elements R2, R6, RGx to form a differential amplifier circuit, the gain of the amplifier is 1+ (R2+ R6)/RGx, wherein R2 and R6 have the same resistance value, and the gain of the amplifier changes when RGx changes. According to actual requirements, the RG 1-RG 4 take proper resistance values, and the level of the MUXA0 and the level of the MUXA1 are controlled to switch the RG 1-RG 4, so that the step adjustment of the gain of the differential amplifier circuit can be realized.

The waveform generator circuit portion includes U6, C25, C26, C27, and C6. U6 is a waveform generator chip of Direct Digital Synthesis (DDS) type, model AD9833, which has a frequency resolution of 28bit, and when the clock frequency is 2.5MHz, the frequency resolution of the output signal reaches 0.01 Hz. The communication port of the U6 comprises FSYNC, FSCLK and FDATA which are connected with GPIO of the singlechip; pin 5 of U6 is a clock signal input terminal connected to the timer output terminal (pin 13) of the single chip. Pin 10 of U6 is the output terminal, which is connected to pin 6 of U5. Pin 2 of U6 is the positive power supply pin and is connected to VCC 33. Pin 4 and pin 9 of U6 are power supply negative terminals and are connected to GND. Pin 1 of U6 is connected to capacitor C25 to GND, and pin 3 of U6 is connected to capacitors C26 and C27 to GND.

The mixer circuit includes U5, C2, and C3. U5 is a mixer chip, model SA 612. The signal input pins 1, 2 of U5 are connected to pin 1 and pin 7 of U3 through capacitors C2, C3, respectively. The signal output pins 4 and 5 of the U5 are connected to the signal input terminal pin 6 and the pin 7 of the U7 through coupling capacitors C1 and C4, respectively. Pin 8 of U5 is the positive power supply pin and is connected to VCC 50. Pin 3 of U5 is the negative terminal of the power supply and is connected to GND. Pin 6 of U5 is a carrier signal input pin and is connected to pin 10 of U6 through coupling capacitor C6.

The analog-digital conversion circuit comprises U7, C1, C4, C10, C31-C34, C28 and C29. U7 is an analog-to-digital converter (ADC) chip, model TLV320ADC 5140. Pin 1 and pin 19 of U7 are power pins to which a 3.3V power supply VCC33 is connected. Pin 4 and pin 25 of U7 are the negative power supply pins, connected to GND. Pin 2 of U7 is the internal analog circuit regulator pin, with capacitors C31 and C32 to GND. Pin 24 of U7 is the internal digital circuit regulator pin, connecting capacitors C33 and C34 to GND. Pin 3 of U7 is the reference voltage pin, which is connected to capacitor C30 to GND. Pin 5 of U7 is a bias voltage output pin, which is connected to capacitors C28 and C29 to GND, and the node signal is also referred to as VBIAS, which is also used as the reference potential of the aforementioned input voltage divider circuit, and the voltage is about 1.5V. Pin 14 of U7 is the run control pin, which is connected to VCC 33. Pin 20 of U7 is a clock input pin and is connected to pin 13 of the single chip U8. Pins 15 to 18 of the U7 are communication pins and are connected to pins 17 to 20 of the single chip microcomputer U8, respectively. Pins 21 to 23 of the U7 are data output pins and are connected to pins 7 to 9 of the single chip microcomputer U8, respectively. Pin 6 and pin 7 of U7 are analog voltage input pins and are connected to output pin 4 and pin 5 of U5 through coupling capacitors C1 and C4, respectively.

The single chip microcomputer circuit comprises U8, C9, Y1, CX1 and CX 2. U8 is a single chip microcomputer chip, and the model is the singlechip of ARM kernel, and the model is STM32F030F 4. Pin 5 and pin 16 of U8 are the positive power supply pins and are connected to VCC 33. Pin 15 of U8 is the negative terminal of the power supply, connected to GND. Pin 1 of U8 is connected to GND. And the pin 2 and the pin 3 of the U8 are crystal oscillator pins and are connected to two ends of a crystal oscillator Y1, the other two pins are respectively connected with capacitors CX1 and CX2 to GND to form a crystal oscillator circuit, and the frequency of Y1 is 11.0592 MHz. The pin 4 of the U8 is a reset input pin, and the other end of the connecting capacitor C9 and C9 is connected with GND. Pin 14 of U8 is connected to pin 16 of U4 and pin 6 of U8 is connected to pin 1 of U4. Pins 7 through 9 of U8 receive pins 21 through 23, respectively, of U7. Pins 10 through 12 of U8 receive pins 8 through 6, respectively, of U6. Pins 17 through 20 of U8 receive pins 18 through 15 of U7, respectively. Pin 13 of U8 is connected to pin 20 of U7 and pin 5 of U6.

The above is the circuit connection situation, and the following is a description of the signal processing in the actual operation.

The measured signal is an alternating current signal with a certain frequency, after the input signal is amplified by the input voltage division circuit and the differential amplification circuit, the amplitude of the input signal is preferably more than 1mV, otherwise, the gain resistance of U3 in the differential amplifier circuit is adjusted by the gain adjustment circuit so as to adjust the gain of the amplifier. The frequency of the signal under test is set to Fin, which in this example is assumed to be 128 Hz.

After the single chip microcomputer is started, an MCLK signal is output through a timer interface, the frequency of the MCLK signal is selected according to the working characteristic parameters of U6 and U7, the frequency value is generally between 1MHz and 25MHz, and in the example, 12.288MHz is taken. After the MCLK signal is asserted, U8 sends a frequency setting command to U6 causing U6 to output a carrier signal Fc, in this example 628 Hz. The frequency of Fc is Fc = Fin + Fb, which is a predetermined intermediate frequency signal, typically several hundred Hz to several kHz, in this example 480 Hz. 480Hz is positioned between the power frequency of 50Hz and the harmonic frequency thereof, so the interference of the power frequency and the harmonic frequency thereof can be effectively avoided.

In U5, the ac signal amplified by U3 and the carrier signal from U6 are mixed, and two kinds of frequency signals are output, one of which is 480Hz and is the difference frequency between the carrier signal frequency and the input signal frequency, and the other of which is 756Hz and is the sum frequency between the carrier signal frequency and the input signal frequency, and only the 480Hz signal may be processed in the subsequent processing. The mixed signal enters the signal input pin 6 and the signal input pin 7 of the U7 through the ac coupling capacitors C1 and C4, respectively.

The singlechip U8 sets the sampling rate of U7 to be 48kHz, which is 100 times of the intermediate frequency. The sampling rate may be set to other values, but is guaranteed to be an integer multiple of the intermediate frequency for subsequent correlation averaging calculations. In addition, the sampling time Ts preset in this example is 0.5s to achieve a data refresh rate of about 2 times per second. In order to effectively eliminate power frequency and harmonic interference thereof in the correlation average calculation, Ts is an integral multiple of the power frequency signal period, in the example, the power frequency is 50Hz, the period is 20ms, and the time duration of Ts is 0.5s which is 25 times of the power frequency period, so that the requirements are met.

The data out pin of U7 sends the analog to digital conversion results during sampling to U8, and the data is stored in the buffer of U8. In this example, data of 24000 points is stored for 0.5s, and the data is usually stored in an array form, and is set as data [1..24000] in this example. After the end of this sampling, U8 suspends the reception of data and starts the data processing. The data processing mainly comprises two steps of correlation average calculation and Discrete Fourier Transform (DFT), and the specific implementation process is as follows:

1. an average value array avg [1..100] was prepared.

2. Dividing data [1..24000] data into one group of 100 points, and totaling 240 groups, namely a1 st group G1[1..100] corresponds to the data [1..100], a 2 nd group G2[1..100] corresponds to the data [101..200], and so on, and a 240 th group G240[1..100] corresponds to the data [23901..24000 ].

3. The data for each group of identical positions from G1 to G240 were averaged and the results were stored in avg [1..100 ]. For example: avg [1] = (G1 [1] + G2[1] + … + G240[1 ])/240, and in general, avg [ n ] = (G1 [ n ] + G2[ n ] + … + G240[ n ])/240, n ranges from 1 to 100.

4. After the processing, data of one signal period of the 480Hz intermediate frequency signal is obtained, the data totals 100 points and is stored in a plurality of groups avg [1..100 ]. The sampling rate of the data is Fs =48kHz, and a single-point DFT (discrete fourier transform) is performed with the above data. According to the DFT principle, the frequency resolution of the conversion is Fs/100, which is just 480Hz, so that the amplitude information of the intermediate frequency signal can be obtained through one time of DFT. The amplitude information of the intermediate frequency signal and the amplitude information of the measured signal are in a linear proportional relationship, so that the amplitude information of the measured signal can be obtained after the processing.

When the measured signal frequency needs to take other values due to measurement, the carrier signal frequency Fc needs to be synchronously adjusted, so that the output intermediate frequency signal frequency Fb is kept constant, and thus, data processing programs and parameters performed in U8 do not need to be changed.

Numerous modifications may be made by those skilled in the art without departing from the scope and spirit of the invention. The above description is only a preferred and practical embodiment of the present invention, and should not be taken as limiting the scope of the present invention. All equivalent variations using the contents of the present specification and drawings are included in the right of the present invention.