CN111090006A - Small resistance measuring device based on weak signal - Google Patents
Small resistance measuring device based on weak signal Download PDFInfo
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- CN111090006A CN111090006A CN201811237425.9A CN201811237425A CN111090006A CN 111090006 A CN111090006 A CN 111090006A CN 201811237425 A CN201811237425 A CN 201811237425A CN 111090006 A CN111090006 A CN 111090006A
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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- G—PHYSICS
- G01—MEASURING; TESTING
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Abstract
The application discloses small resistance measuring device based on weak signal includes: the signal generating module is used for generating a sinusoidal signal with known frequency and known peak value by the RC bridge type oscillating circuit; the measuring circuit module is used for obtaining sinusoidal signals at two ends of the resistor to be measured according to the sinusoidal signals; the lock-in amplifier module is used for completing multiplication operation of sinusoidal signals at two ends of the resistor to be tested and a reference signal to obtain a direct current signal; the processing module is used for carrying out ADC (analog to digital converter) conversion on the direct current signal to obtain a digital quantity, matching the digital quantity with the digital quantity corresponding to the current range, and calculating the resistance value of the resistor to be measured if matching is successful; and the range conversion module is used for automatically switching the range gear when the digital quantity is not matched with the digital quantity corresponding to the current range gear. The method and the device can extract weak sinusoidal voltage signals at two ends of the resistor to be tested, can judge whether the resistance value of the current resistor to be tested is matched with the range gear, and can automatically complete switching of the range gear when the resistance value is not matched with the range gear.
Description
Technical Field
The application relates to the technical field of resistance measurement, in particular to a small resistance measuring device based on weak signals.
Background
At present, the traditional methods for measuring the resistance mainly include a voltammetry method, an equivalent substitution method, a bridge method and the like, and when the small resistance is measured, a larger error is easy to exist. In addition, when the traditional universal meter is used for measuring the resistance, the range gear needs to be manually selected, and the operation is complex.
Disclosure of Invention
In view of this, the present application provides a small resistance measurement device based on a weak signal, which can perform effective ac amplification according to different range steps to which the resistance of the measured resistance belongs, and can implement automatic switching of the range steps.
The application provides a small resistance measuring device based on weak signal includes:
the signal generating module is used for generating a sinusoidal signal with known frequency and known peak value by the RC bridge type oscillating circuit;
the measuring circuit module is used for obtaining sinusoidal signals at two ends of the resistor to be measured according to the sinusoidal signals;
the lock-in amplifier module is used for completing multiplication operation of the sinusoidal signals at the two ends of the resistor to be tested and the reference signal to obtain a direct current signal;
the processing module is used for carrying out ADC (analog to digital converter) conversion on the direct current signal to obtain a digital quantity, matching the digital quantity with the digital quantity corresponding to the current range, and calculating the resistance value of the resistor to be measured if matching is successful;
and the range conversion module is used for automatically switching the range gear when the digital quantity is not matched with the digital quantity corresponding to the current range gear.
Preferably, the signal generating module comprises an RC bridge oscillating circuit.
Preferably, the measurement circuit module includes: a reference resistance and the resistance to be measured, wherein:
one end of the reference resistor is connected with the output end of the RC bridge type oscillation circuit, and the other end of the reference resistor is connected with the input end of the lock-in amplifier module and one end of the resistor to be tested;
one end of the resistor to be tested is connected with one end of the reference resistor, and the other end of the resistor to be tested is grounded.
Preferably, the lock-in amplifier module comprises a phase-sensitive detection chip AD 630.
Preferably, the phase-sensitive detection chip AD630 includes: the device comprises an alternating current amplifying circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a trigger shaping circuit, a phase shifter circuit, a square wave driving circuit, a low-pass filter and a direct current amplifier.
Preferably, the processing module comprises an STM32 single chip microcomputer.
Preferably, the range conversion module includes: relay, triode and diode.
Preferably, the apparatus further comprises: and the display circuit is used for displaying the resistance to be tested.
Preferably, the display circuit includes: an LCD display.
Preferably, the band-pass filter circuit includes: filtering chip UFA 42.
To sum up, the application discloses little resistance measurement device based on weak signal includes: the signal generating module is used for generating a sinusoidal signal with known frequency and known peak value by the RC bridge type oscillating circuit; the measuring circuit module is used for obtaining sinusoidal signals at two ends of the resistor to be measured according to the sinusoidal signals; the lock-in amplifier module is used for completing multiplication operation of sinusoidal signals at two ends of the resistor to be tested and a reference signal to obtain a direct current signal; the processing module is used for carrying out ADC (analog to digital converter) conversion on the direct current signal to obtain a digital quantity, matching the digital quantity with the digital quantity corresponding to the current range, and calculating the resistance value of the resistor to be measured if matching is successful; and the range conversion module is used for automatically switching the range gear when the digital quantity is not matched with the digital quantity corresponding to the current range gear. The method and the device can extract weak sinusoidal voltage signals at two ends of the resistor to be tested, can judge whether the resistance value of the current resistor to be tested is matched with the range gear, and can automatically complete switching of the range gear when the resistance value is not matched with the range gear.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an embodiment 1 of a weak signal-based small resistance measurement apparatus disclosed in the present application;
fig. 2 is a schematic structural diagram of an embodiment 2 of a weak signal-based small resistance measurement apparatus disclosed in the present application;
fig. 3 is a circuit topology diagram of an ac amplifying circuit disclosed in the present application;
FIG. 4 is a circuit topology diagram of a bandpass filter circuit as disclosed herein;
FIG. 5 is a circuit topology diagram of a phase sensitive detector circuit disclosed herein;
FIG. 6 is a circuit topology diagram of a trigger shaping circuit disclosed herein;
FIG. 7 is a circuit topology diagram of a phase shifter circuit disclosed herein;
FIG. 8 is a circuit topology diagram of a square wave drive circuit as disclosed herein;
FIG. 9 is a circuit topology of a low pass filter as disclosed herein;
fig. 10 is a circuit topology diagram of a span conversion module as disclosed herein.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
As shown in fig. 1, which is a schematic structural diagram of an embodiment 1 of a weak signal-based small resistance measurement apparatus disclosed in the present application, the apparatus may include:
a signal generating module 101, configured to generate a sinusoidal signal with a known frequency and a known peak value by using an RC bridge oscillating circuit;
the measuring circuit module 102 is used for obtaining sinusoidal signals at two ends of the resistor to be measured according to the sinusoidal signals;
the lock-in amplifier module 103 is used for completing multiplication operation of the sinusoidal signals at the two ends of the resistor to be tested and the reference signal to obtain a direct current signal;
the processing module 104 is configured to perform ADC conversion on the direct current signal to obtain a digital quantity, match the digital quantity with a digital quantity corresponding to the current range, and if matching is successful, calculate a resistance value of the resistor to be measured;
and the range conversion module 105 is used for automatically switching the range gear when the digital quantity is not matched with the digital quantity corresponding to the current range gear.
The working principle of the small resistance measuring device based on the weak signal disclosed by the embodiment is as follows: when the resistance of the resistor to be measured needs to be measured, the signal generation module 101 provides a sinusoidal signal with known frequency and known peak value, and after voltage division is performed by the reference resistor in the measurement circuit module 102, sinusoidal signals at two ends of the resistor to be measured are obtained and are used as input signals of the lock-in amplifier module 103.
The lock-in amplifier module 103 performs multiplication on the input sinusoidal signals at two ends of the resistor to be measured and the other input reference signal, obtains a direct current signal and a plurality of alternating current signals, which are proportional to the amplitude of the sinusoidal signals at two ends of the resistor to be measured, by using the same-frequency and same-phase correlation of the two signals, and then obtains the direct current signal after filtering, which is used as the input signal of the processing module 104.
After receiving the input signal, the processing module 104 performs ADC conversion on the dc signal to obtain a digital quantity, and matches the digital quantity corresponding to the current range, if matching is successful, the resistance value of the resistor to be measured is calculated by backstepping, and if matching is failed, the processing module 104 controls the range conversion module 105, and changes the amplification factor of the ac amplifier in the lock-in amplifier module 103 through the range conversion module 105, so as to finally realize automatic switching of the range.
In summary, the embodiment can extract the weak sinusoidal voltage signals at the two ends of the resistor to be tested, and can determine whether the resistance value of the current resistor to be tested is matched with the range, and when the resistance value is not matched with the range, the switching of the range can be automatically completed.
As shown in fig. 2, which is a schematic structural diagram of an embodiment 2 of a weak signal-based small resistance measurement apparatus disclosed in the present application, the apparatus may include: the circuit comprises an RC (resistor-capacitor) bridge type oscillation circuit 201, a reference resistor R0, a resistor Rx to be tested, a lock-in amplifier module 202, an STM32 single chip microcomputer 203, a measuring range conversion module 204 and a display circuit 205; wherein:
one end of the reference resistor R0 is connected to the output end of the RC bridge oscillating circuit 201, and the other end is connected to the input end of the lock-in amplifier module 202 and one end of the resistor Rx to be measured;
one end of the resistor Rx to be tested is connected with one end of the reference resistor R0, and the other end of the resistor Rx to be tested is grounded;
the lock-in amplifier module includes phase-sensitive detection chip AD630, and phase-sensitive detection chip AD630 includes: the device comprises an alternating current amplifying circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a trigger shaping circuit, a phase shifter circuit, a square wave driving circuit, a low-pass filter and a direct current amplifier;
the range conversion module 204 includes: relay, triode and diode.
The working principle of the small resistance measuring device based on the weak signal disclosed by the embodiment is as follows: when the resistance of the resistor to be measured needs to be measured, the RC bridge oscillation circuit 201 generates a sinusoidal signal with a frequency of 1KHz and a peak value of 700mV, the reference resistor R0 adopts a precision resistor of 2 kilo-ohms, and the current flowing through the resistor Rx to be measured meets the ohm law, because the input impedance of the rear-stage module is nearly infinite and is far greater than the resistance value of the resistor Rx to be measured, the current flowing through the reference resistor R0 is approximately equal to the current flowing through the resistor Rx to be measured, and thus the formula (1) is met:
the resistance value of the resistor Rx to be tested meets the formula (2):
since U0 and R0 are known, it can be known from formula (2) that the resistance of Rx can be obtained by extracting the voltage UR at two ends of the resistor to be measured only by using the lock-in amplifier.
Specifically, the principle of the lock-in amplifier module 202 extracting the weak sinusoidal voltage signals at the two ends of the resistor Rx to be detected is as follows:
the lock-in amplifier is designed based on the phase-sensitive detection chip AD630, and can extract a weak sinusoidal signal, so that voltage signals at two ends of the resistor Rx to be detected can be extracted by using a lock-in amplifier module. The lock-in amplifier module mainly comprises an alternating current amplifying circuit, a band-pass filter circuit, a trigger shaping circuit, a phase shifter circuit, a square wave driving circuit, a phase-sensitive detection circuit, a low-pass filter and a direct current amplifier. The alternating current amplifying circuit is mainly used for carrying out alternating current amplification on weak sinusoidal signals at two ends of the resistor to be detected, and the band-pass filtering circuit is mainly used for filtering noise and the like. The trigger shaping circuit is mainly used for triggering a sinusoidal signal into a square wave signal, and the phase shifter circuit is mainly used for completing phase adjustment and ensuring that the phase of the phase shifter circuit is in the same phase with another path of input signals of the phase-sensitive detection circuit. The phase-sensitive detection circuit is used for completing multiplication operation on two paths of input signals, and the sum of a direct current signal and a plurality of alternating current signals which are in direct proportion to the amplitude of sinusoidal signals at two ends of a resistor to be detected can be obtained by utilizing the correlation of two same-frequency and same-phase signals. After passing through a low-pass filter, the measured signal can be extracted. And then the direct current signal output by the low-pass filter is sent to an AD converter built in an STM32 single chip microcomputer to obtain digital quantity. And finally, the STM32 singlechip reversely calculates the amplitude of the sinusoidal voltage signals at the two ends of the resistor to be detected according to the formula of each module circuit, converts the amplitude into an effective value, and calculates the resistance value of the resistor to be detected.
Specifically, as shown in fig. 3, for the circuit topology of the ac amplifying circuit, a sinusoidal signal in the measurement circuit module generates a sinusoidal signal with a frequency of 1KHz and a peak-to-peak value of 700mV by the RC bridge oscillation circuit, the reference resistor is 2 kilo-ohms, and the resistance range of the resistor to be measured is 0-2000 ohms (0-2 ohms, 2-200 ohms, 200-2000 ohms), so the peak-to-peak value of the input signal of the ac amplifier divided by the reference resistor is 0-350mV, therefore, sinusoidal voltage signals with different amplitudes need to be amplified by different multiples to be used as a signal of the phase-sensitive detection chip AD630, and therefore, different amplification multiples need to be designed for resistors with different measurement ranges. Since three range gears need to design 3 different amplification factors (20 times, 100 times and 800 times), the amplification factors of the three range gears can be arbitrarily controlled by an STM32 singlechip through cascade connection by dividing the amplification factor into two stages. The first stage is amplified by 20 times, and the second stage is respectively amplified by 1 time, 5 times and 40 times to realize the purpose of amplifying by 20 times, 100 times and 800 times of three measuring ranges.
Specifically, as shown in fig. 4, the bandpass filter circuit is designed to have a circuit topology in which the center frequency of the bandpass filter is 1000HZ, only signals in a frequency band near the center frequency are allowed to pass through the bandpass filter, and signals of frequencies other than the frequency band are effectively attenuated. Because the small signal is mixed with too much noise signal and interference of other signals, the small signal is amplified, and the noise signal and other signals are also amplified. The band-pass filter of the embodiment selects the integrated filter chip UAF42, which can attenuate other noise signals and other signal interferences outside the frequency band range around the central frequency of 1000 Hz.
Calculation of center frequency since the frequency generated by the RC bridge oscillator circuit is 1000Hz, the resistance values of resistors RF1 and RF2 of the UAF42 chip peripheral circuit are calculated according to the formula and circuit diagram of the UAF42 chip handbook. The calculation formula is as follows:
because the UAF42 integrates R1, R2, C1, and C2 in a chip, where R1 ═ R2 ═ 50K, C1 ═ C2 ═ 1000pF, and W ═ 2 pi f, the following processes:
the formula shows that: RF1 ≈ RF2 ≈ 158K.
Specifically, as shown in fig. 5, the circuit topology of the phase-sensitive detector circuit is a circuit topology of the phase-sensitive detector circuit, and the phase-sensitive detector circuit is mainly used to perform multiplication of an input signal of a signal channel and a reference signal of a reference channel, and obtain a sum of a dc signal proportional to the amplitude of a signal to be detected and a plurality of ac signals by using the correlation between the two signals with the same frequency and the same phase, where the value of the dc signal is the maximum value after the two input signals with the same frequency and the same phase. Let the measured signal (sinusoidal signal) be as in equation (3):
X(t)＝VsCOS(ω0t+θ) (3)
the reference signal is a square wave signal, and the formula is shown as (4):
the output after passing through the phase sensitive detection circuit is as the formula (5):
the output after passing through the low-pass filter satisfies formula (6):
as can be seen from equation (6), in order to maximize the output value of the phase-sensitive detector circuit, two signals of the phase-sensitive detector chip AD630 are in the same phase, i.e., θ is 0, and since the magnitude of the output signal of the switching phase-sensitive detector is not affected by the magnitude of the amplitude of the reference signal (square wave signal), the output of the phase-sensitive detector after passing through the low-pass filter is as shown in equation (7):
specifically, as shown in fig. 6, in order to trigger the circuit topology of the shaping circuit, the circuit utilizes the characteristics that the open-loop voltage gain has a high value, the input resistance between the two input ends has a high value, the output resistance has a low value, and the linear region of the circuit is nearly a vertical line, so that the sinusoidal signal can be converted into the square wave signal. Because the two signals input into the AD630 have 180-degree phase reversal, the circuit adopts phase reversal input, so that the two signals input into the AD630 can ensure that the phases of the two signals are the same through the adjustment of a phase shifter in a signal channel, the output value reaches the maximum and is a positive value, otherwise, the output value also reaches the maximum but is a negative value, and a phase inverter module is required to be added in the later period, so that the principle of achieving the same function and simplifying as much as possible is violated.
Specifically, as shown in fig. 7, for the circuit topology of the phase shifter circuit, the RC phase shift is adopted in the circuit, and the phase difference between the reference signal of the reference channel and the measured signal of the signal channel can be adjusted by 0 to 180 degrees. The imaginary part of the transfer function of the circuit, such as formula (8), is a negative number, and the real part determines whether the real part is a positive value or a negative value according to the values of R18, R20 and W, R, C, so that the phase shift angle of the phase shift circuit appears in the third quadrant and the fourth quadrant, thereby realizing the phase shift of 0-180 degrees, and when the resistance values of R18 and R20 are equal, if the value of the angular frequency W is about 1/(RC) and is not equal to 1/(RC), the phase shift angle will shift the phase in the two ranges of 0-90 degrees and-90-180 degrees respectively. Wherein, the formula (8) is as follows:
specifically, as shown in fig. 8, the circuit topology of the square wave driving circuit is shown, and the circuit converts a sinusoidal signal into a square wave signal by using the characteristic that the open-loop voltage gain is large, so that the signal is relatively stable.
Specifically, as shown in fig. 9, the circuit topology of the low-pass filter is a low-pass filter with a cut-off frequency of 5Hz designed in the circuit, and the low-pass filter is used for filtering an ac signal and narrowing a bandwidth, so that a dc signal proportional to a signal to be measured can be extracted.
Is prepared from formula (9) and formula (10)
ωc＝2πf(9)
It can be seen that when the cutoff frequency is 5HZ, R × C is 0.031831, so when C is 1uf, R ≈ 32K. Because the phase difference of the two signals input into the AD630 is 0 degree, the output signals of the two input signals after passing through the AD630 are the sum of a direct current signal and a plurality of alternating current signals, so the cut-off frequency of the embodiment is 5Hz, and the core function of the embodiment is to filter the alternating current component and obtain the direct current signal which is in direct proportion to the measured signal.
Specifically, as shown in fig. 10, the circuit topology of the range conversion module is that the range conversion module is an STM32 single chip microcomputer, and determines whether to control the on or off of the triode to control the attraction or release of the relay coil and further control the amplification factor of the ac amplifier module by judging whether the resistance value of the current resistor to be measured is matched with the range, so as to automatically complete the switching of the range; the hardware circuit is mainly designed by 4 SRD-09VDC-SL-C type relays, 4 s9013NPN type triodes, 4 IN4001 diodes and 4 kilo-ohm, 500-ohm and 0-ohm resistors. The principle is that the STM32f407 single chip microcomputer is used for controlling the range conversion circuit to control the amplification factor in the alternating current amplifier module, so that the resistors under different range gears can have different amplification factors, and the automatic switching of the ranges is realized.
If Uo is a Vpp sine signal of 700mV, the reference resistance Ro is 2k, and the resistance to be measured is 1 ohm, the voltage value at the two ends of the resistance to be measured is approximately a sine signal of 0.350mV peak-to-peak value. The lock-in amplifier needs to extract the sinusoidal signal of the peak-to-peak value of 0.350mV, because the resistance value of the resistor to be tested is different from 0-2 kilo-ohm, the voltage at the two ends of the resistor to be tested is also different from 0-350mV peak-to-peak value, if the lock-in amplifier needs to extract the sinusoidal signals, different amplification factors need to be designed for different range gears in the alternating current amplifier part, so the alternating current amplification part of the lock-in amplifier needs to be graded, different amplification factors need to be designed for the resistance value range of different range gears, two extreme values of the range gear need to be considered, if the selected range gear is 0-2 ohm, the STM32 single chip microcomputer can control the corresponding I/O port to enable the base of the corresponding triode (NPN type) to be in a conducting state, and further control the corresponding relay attracting contact, thereby different amplification factors are realized, and the STM32 single chip microcomputer can also control the I/O ports, the other triodes are in a cut-off state, so that the corresponding relay coil releases the contact, thereby realizing different amplification factors in the range of different range gears.
Specifically, the working principle of the measurement of the resistance to be measured is as follows:
this is accomplished by measuring the resistance of 1000 ohms, 100 ohms, 1 ohm in sequence. The ranges of the digital quantity corresponding to the three measuring range steps can be obtained through theoretical analysis and calculation respectively as follows: 0-2 ohms (digital values 0-221), 2-200 ohms (digital values 27-2517), 200-.
The first step is as follows: after the system is powered on and initialized, the range is firstly switched to the third gear of 200-2000 ohms by controlling the range conversion circuit.
The second step is that: measuring a resistor of 1000 ohms (at this time, we do not know that the resistance value is 1000 ohms), converting a voltage signal at two ends of the resistor to be measured by an ADC (analog to digital converter) which is arranged in a lock-in amplifier and an STM32 into a digital value 1843, judging that the digital value is in a digital value range of 200-.
The third step: if the resistance value of the resistance is measured again to be 100 ohms, the range is in the third range at the moment, the amplification factor is 20, (although 100 ohms is the range of 2-200 ohms, the amplification factor is 100), the digital quantity obtained after the voltage signals at the two ends of the resistance to be measured are subjected to the locking amplifier and the AD conversion is 263, and the STM32 judges that the digital quantity 263 obtained through the AD conversion is not in the range of 200-2000 ohms range, so that the range conversion circuit is controlled to switch the range of 200-2000 ohms to the range of 2-200 ohms. At the moment, the resistance value of the resistor to be measured is in a range of 2-200 ohms, the amplification factor is 100, then the digital quantity of voltage signals at two ends of the resistor to be measured after passing through a lock-in amplifier and AD conversion is changed from original 263 to 1316, STM32 carries out corresponding operation according to various formulas by judging that the digital quantity is in the range of the digital quantity of the range of 2-200 ohms (27-2517), and the STM32 carries out corresponding operation according to various formulas to display the calculated resistance value of the resistor to be measured on an LCD.
The fourth step: if the measured resistance value is 1 ohm, the measuring range is in the second range at the moment, the amplification factor is 100, (although 1 is the measuring range of 0-2 ohm, the amplification factor is 800), the digital quantity obtained after voltage signals at two ends of the resistor to be measured are subjected to locking amplifier and AD conversion is 11, STM32 controls the measuring range conversion circuit to switch the measuring range of 2-200 ohm to the measuring range of 0-2 ohm by judging that the digital quantity 11 obtained by the STM32 is not in the range of 2-200 ohm measuring range. At the moment, the resistance value of the resistor to be measured is in a range of 0-2 ohms, the amplification factor is 800, the voltage signals at two ends of the resistor to be measured are converted from the original 11 to 89 after passing through the lock-in amplifier and the AD again, STM32 judges that the digital quantity is in the range of 0-2 ohms range digital quantity (0-221), operation is carried out according to various formulas, and the calculated resistance value of the resistor to be measured is displayed on an LCD.
Specifically, the ADC uses a 12-bit AD converter built in the STM32f407 to take an average value every 60 times of conversion, and then returns the average value to a called function in the main function.
Dividing the digital quantity which is subjected to ADC and is subjected to average value once per 60 times by the number of digits of the ADC, multiplying the quotient by 3.37 to obtain the analog quantity corresponding to the digital quantity, because the analog quantity which is output when the phase-sensitive detector module meets the requirement of 2 Vr/pi, the voltage signal which is input to the input end of the phase-sensitive detector can be reversely deduced, because the alternating current amplifier part amplifies a certain multiple, the voltage signal value at two ends of the resistor to be measured can be obtained by dividing the reversely deduced signal voltage by the amplification multiple of the corresponding range, and finally, the resistance value of the resistor to be measured can be obtained according to the function of the measuring circuit and can meet the following formula (11):
an RC bridge type oscillation circuit is used for generating a sinusoidal signal with the frequency of 1000Hz and the peak value of 700mV to a measuring circuit, a three-in-one and a half-out digital multimeter is used for measuring the resistance value of a resistor to be measured to serve as an ideal resistance value, the resistance value of the resistor to be measured by the device manufactured by the design serves as an actual resistance value, and the measuring result is shown in a table 4.1;
TABLE 4.1 resistance measurement data
In summary, assuming that the resistance of the resistor to be tested is 100 milliohms (the RC bridge oscillation circuit generates a sinusoidal signal with a peak-to-peak value of 700mv +2K reference resistor), according to the voltage division principle, the peak-to-peak value of the sinusoidal signal at the two ends of the resistor is 0.035mv, the device can extract the sinusoidal signal at the two ends of the resistor (extraction method: the sinusoidal signal is converted by a lock-in amplifier and an AD built in STM32 to obtain a digital quantity, and according to the formula of each module circuit, the peak-to-peak value of the sinusoidal signal can be calculated by back-stepping), thereby calculating the resistance of the resistor; the STM32 single chip determines whether to control the connection or the disconnection of the triode under the corresponding range (0-2 ohm, 2-200 ohm, 200 plus 2000 ohm) to control the attraction or the release of the relay coil and further control the amplification factor of the AC amplifier module by judging whether the resistance value of the current measured resistor is matched with the range, thereby completing the automatic switching of the range.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the application is not intended to be limited to the embodiments shown herein,
but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A weak signal-based small resistance measurement device, comprising:
the signal generating module is used for generating a sinusoidal signal with known frequency and known peak value by the RC bridge type oscillating circuit;
the measuring circuit module is used for obtaining sinusoidal signals at two ends of the resistor to be measured according to the sinusoidal signals;
the lock-in amplifier module is used for completing multiplication operation of the sinusoidal signals at the two ends of the resistor to be tested and the reference signal to obtain a direct current signal;
the processing module is used for carrying out ADC (analog to digital converter) conversion on the direct current signal to obtain a digital quantity, matching the digital quantity with the digital quantity corresponding to the current range, and calculating the resistance value of the resistor to be measured if matching is successful;
and the range conversion module is used for automatically switching the range gear when the digital quantity is not matched with the digital quantity corresponding to the current range gear.
2. The apparatus of claim 1, wherein the signal generation module comprises an RC bridge oscillator circuit.
3. The apparatus of claim 2, wherein the measurement circuit module comprises: a reference resistance and the resistance to be measured, wherein:
one end of the reference resistor is connected with the output end of the RC bridge type oscillation circuit, and the other end of the reference resistor is connected with the input end of the lock-in amplifier module and one end of the resistor to be tested;
one end of the resistor to be tested is connected with one end of the reference resistor, and the other end of the resistor to be tested is grounded.
4. The apparatus of claim 3, wherein the lock-in amplifier module comprises a phase-sensitive detector chip (AD 630).
5. The apparatus of claim 4, wherein the phase-sensitive detection chip AD630 comprises: the device comprises an alternating current amplifying circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a trigger shaping circuit, a phase shifter circuit, a square wave driving circuit, a low-pass filter and a direct current amplifier.
6. The apparatus of claim 5, wherein the processing module comprises an STM32 single chip microcomputer.
7. The apparatus of claim 6, wherein the span conversion module comprises: relay, triode and diode.
8. The apparatus of claim 7, further comprising: and the display circuit is used for displaying the resistance to be tested.
9. The apparatus of claim 8, wherein the display circuitry comprises: an LCD display.
10. The apparatus of claim 9, wherein the band pass filter circuit comprises: filtering chip UFA 42.
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