LCR test circuit and test method
By designing simplified digital LCR testing circuits and testing methods, the existing LCR testing methods are solved, and the circuit is simple, small in size, low in cost and strong anti-interference ability is achieved, which is suitable for integration into automated production lines.
Patent Information
- Application Number
- CN202510077885.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-17
- Publication Date
- 2025-05-13
AI Technical Summary
The existing LCR testing methods have problems such as complex circuits, large size, high cost and weak anti-interference ability, and are difficult to integrate into automated production lines.
A test circuit including an LCR device to be tested and a program control module is designed. The program control module is connected with an analog front-end module and a acquisition module. Through a simplified digital LCR testing method, an AC signal is applied to the LCR device to be tested, the voltage difference and current are measured, and the component parameters are calculated.
It realizes simple circuit, small size, low cost, easy integration, and strong anti-interference ability. It is suitable for use in various instruments and equipment with strict volume requirements.
Smart Images
Figure CN119986143A_ABST
Abstract
Description
Technical Field
[0001] The present invention is applied to the technical field of electronic equipment testing, and particularly relates to an LCR testing circuit and a testing method. Background Art
[0002] LCR testing refers to a test method that evaluates the performance of three basic electronic components, inductance, capacitance and resistance, by measuring their characteristics. LCR testers are widely used in the fields of electronic manufacturing, electronic component inspection and research and development. They are very important in the quality control of high-frequency and precision electronic products. In the production and testing of high-quality components, reducing errors can improve product consistency and reliability.
[0003] The commonly used LCR test methods on the market are bridge measurement method and digital LCR meter method. The bridge measurement method is a traditional LCR measurement method that uses a bridge circuit consisting of four arms, at least one of which contains the L, C or R element to be measured, and the other arms are known standard elements or elements with adjustable parameters. When the bridge is balanced, that is, the current and voltage through each arm of the bridge meet specific balance conditions, the L, C, and R values can be calculated based on the parameters of the known components and the balance state of the bridge. The digital LCR meter applies an AC signal of a certain frequency to the component to be tested, and measures the voltage difference, current and other parameters generated by the signal at both ends of the component, and then calculates the impedance characteristics of the component.
[0004] The above LCR test methods have their own advantages and disadvantages in terms of test accuracy and convenience. The bridge LCR test method has a relatively simple circuit, but its test range is narrow, its anti-interference ability is weak, and its operation is more troublesome. The digital LCR meter test method has a wide test range and strong anti-interference ability, but the cost is very high, which can be tens of thousands. Moreover, the instruments of the above test methods are large in size and difficult to integrate into the automated production line.
[0005] The disadvantages of bridge testing LCR are mainly reflected in speed, frequency range, environmental impact, and operation complexity. It is necessary to adjust the balance of the bridge to achieve accurate measurement of the component to be tested. The appropriate frequency, precise adjustment, and good connection will affect the final measurement results. Therefore, when using the bridge, make sure to set it up correctly and operate it carefully. Although it is still applicable in some low-frequency and low-precision applications, the operation is more complicated and is gradually being replaced by digital LCR.
[0006] However, the digital LCR test method solves the shortcomings of the bridge test LCR. It has a high degree of automation. The user only needs to set the test frequency, test range and other parameters, connect the component to be tested to the measurement port, and the instrument can automatically complete the measurement process. It has an intuitive user interface and is easy to learn and use. Moreover, digital technology and advanced circuit design enable it to have a strong suppression ability against interference signals and can work stably in a more complex electromagnetic environment. However, the corresponding shortcomings are also exposed. Due to the use of advanced digital technology and high-performance electronic components, its price is relatively expensive, and the subsequent maintenance cost may also be high. Therefore, it is necessary to provide an LCR test circuit and test method, which has the advantages of simple circuit, small size, low cost, easy integration, and strong anti-interference ability. Summary of the invention
[0007] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an LCR test circuit and a test method, which have the advantages of simple circuit, small size, low cost, easy integration and strong anti-interference ability.
[0008] The technical solution adopted by the present invention is: the present invention comprises an LCR device to be tested and a program control module, wherein the program control module is connected to an analog front-end module and an acquisition module, wherein the analog front-end module is connected to the acquisition module, and the analog front-end module comprises a front-end amplification buffer unit, an impedance voltage acquisition unit, and a reflux acquisition unit connected in sequence; The front-end amplification buffer unit includes a common-direction proportional amplifier, a unit gain buffer and a first multiplexer connected in sequence, the impedance voltage acquisition unit includes a first voltage follower, a first instrument operational amplifier and a second multiplexer, and the reflux acquisition unit includes a reverse proportional amplifier, a second instrument operational amplifier and a third multiplexer. The first multiplexer is connected to the first voltage follower and the third multiplexer via the LCR device to be tested, the LCR device to be tested is connected to the third multiplexer via an acquisition resistor, the first voltage follower and the second multiplexer are both connected to the first instrument amplifier, the reverse proportional amplifier and the third multiplexer are both connected to the second instrument amplifier, and the first instrument amplifier and the second instrument amplifier are both connected to the acquisition module.
[0009] It can be seen from the above scheme that the present application uses a digital LCR test method to apply an AC signal of a certain frequency to the LCR device to be tested, and measures the voltage difference, current and other signals generated by the signal at both ends of the components of the LCR device to be tested. The component parameters are calculated through the impedance characteristics of L, C, and R, which simplifies the digital LCR circuit, retains the advantages of the digital LCR test method, and also solves the problem of high cost, taking into account the advantages of the bridge LCR test.
[0010] In summary, this application has the following advantages: 1. Low cost. No high-speed ADC is required to restore the sinusoidal AC signal. Then a high-computing processor is used to calculate and obtain the test value. The RMS detector is used directly to complete the acquisition of the AC signal. Then the MCU only needs to convert and calculate the effective value information output by the RMS detector.
[0011] 2. Small size, easy to integrate, and can be used in various instruments and equipment with strict volume requirements.
[0012] 3. Strong anti-interference ability, using the four-wire method to collect the data at both ends of the components to be tested, eliminating the influence of parasitic parameters of some paths; 4. According to the actual measurement accuracy requirements, we can adjust and replace the operational amplifier and multiplexer and other components, use domestically produced MCUs and operational amplifiers of similar models, or use the DAC peripherals of the MCU to output AC sine wave signals for testing, which can reduce costs to a certain extent. These alternative solutions can be used in other application systems and will be more targeted and functional.
[0013] A preferred solution is that the program control module includes an MCU unit and a signal generator, the DDS_VOUT pin of the signal generator is connected to the pin corresponding to the non-inverting proportional amplifier, and the MCU unit communicates with the signal generator via SPI; the signal generator is used to generate a sinusoidal AC signal for testing.
[0014] A preferred solution is that the acquisition module includes a relay, an RMS detector, and a second voltage follower, the AC_SIGNAL_TO_RMS pin of the relay is connected to the output end of the first instrument amplifier, the AC_SIGNAL_CURR pin of the relay is connected to the output end of the second instrument amplifier, the relay is connected to the RFIN end of the RMS detector, the VRMS end of the RMS detector is connected to the positive input end of the second voltage follower, and the output end of the second voltage follower is connected to the VRMS_OUT port of the MCU unit.
[0015] A preferred embodiment is that the test method comprises the following steps: Step 1, set the signal generator to output a sinusoidal AC signal of known frequency, which is applied to the LCR device to be tested with unknown parameters after amplification and buffering by the front-end amplification and buffering unit. Since the impedance characteristics of L, C, and R will generate a potential difference on both sides of the position component, the effective value V (Rf_CURR_RMS) of the potential difference applied to both ends of the LCR device to be tested is collected through the impedance voltage collection unit and the collection module. Assuming that the current passing through the LCR device to be tested is Ix, the impedance of the LCR device to be tested is Zx: Step 2: The AC signal passes through the LCR device to be tested with unknown parameters and the collection resistor to return to the ground. The effective value V (Zx_CURR_RMS) of the potential difference across the collection resistor is obtained through the return collection unit and the collection module. Since the components of the LCR device to be tested are connected in series with the collection resistor, the current I passing through the collection resistor is equal to the current Ix passing through the LCR device to be tested, that is, ; Step 3: The current I passing through the acquisition resistor is: Step 4: If the unknown parameter component of the LCR device to be tested is the inductor L, the inductance value is calculated as follows: Step 5: If the unknown parameter component of the LCR device to be tested is a capacitor C, the capacitance value is calculated as follows: Step 6: If the unknown parameter component of the LCR device to be tested is a resistor R, the resistance value is calculated as follows: . BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 is a system block diagram of the present invention; Figure 2 is a circuit schematic diagram of the analog front-end module; Figure 3 is a circuit schematic diagram of the program-controlled module; Figure 4 It is a circuit schematic diagram of the acquisition module. DETAILED DESCRIPTION
[0017] like Figure 1 and Figure 2 As shown, in this embodiment, the present invention includes an LCR device to be tested 1, a program control module 2, the program control module 2 is connected to an analog front-end module 3 and an acquisition module 4, the analog front-end module 3 is connected to the acquisition module 4, and the analog front-end module 3 includes a front-end amplification buffer unit 5, an impedance voltage acquisition unit 6, and a reflux acquisition unit 7 connected in sequence; The front-end amplification buffer unit 5 includes a non-inverting proportional amplifier U7, a unit gain buffer U5 and a first multiplexer U6 connected in sequence, the impedance voltage acquisition unit 6 includes a first voltage follower U8, a first instrument amplifier U9 and a second multiplexer U10, and the reflux acquisition unit 7 includes a reverse proportional amplifier U14, a second instrument amplifier U11 and a third multiplexer U12; The first multiplexer U6 is connected to the first voltage follower U8 and the third multiplexer U12 via the LCR device 1 to be tested, the LCR device 1 to be tested is connected to the third multiplexer U12 via the acquisition resistor Rf, the first voltage follower U8 and the second multiplexer U10 are both connected to the first instrument amplifier U9, the reverse proportional amplifier U14 and the third multiplexer U12 are both connected to the second instrument amplifier U11, and the first instrument amplifier U9 and the second instrument amplifier U11 are both connected to the acquisition module 4.
[0018] The model of the non-inverting proportional amplifier U7 is OPA192, the model of the unit gain buffer U5 is BUF634, and the model of the first multiplexer U6 is ADG1404. The non-inverting proportional amplifier U7 follows and amplifies the AC signal output from the signal generator U2, and then inputs it to the unit gain buffer U5 to enhance the output current capability of the non-inverting proportional amplifier U7, and then inputs it to the first multiplexer U6 to adjust the current limiting and phase margin by selecting different resistors.
[0019] The model of the first voltage follower U8 is OPA2192, the model of the first instrument amplifier U9 is INA8421), and the model of the second multiplexer U10 is ADG1401. The AC signal through the front-end amplification buffer unit 5 is connected to the L, C, and R components of the unknown parameters of the LCR device 1 to be tested, and then fed back to the first voltage follower U8 through a four-wire method. After passing through the first voltage follower U8, it is connected to the first instrument amplifier U9 to collect and amplify the potential difference generated after the AC signal enters the components of the position parameters.
[0020] The model of the reverse proportional amplifier U14 is OPA192, the model of the second instrument amplifier U11 is INA8421, the model of the third multiplexer U12 is ADG1401, and the model of the third multiplexer U12 is ADG1404. The current of the AC signal passing through the front-end amplifier buffer unit 5 passes through the L, C, and R components of unknown parameters, enters the reverse proportional amplifier U14, and then flows back through the virtual ground formed by the reverse proportional amplifier U14. Due to the virtual short and virtual open analysis of the operational amplifier, the current will flow through the known acquisition resistor Rf and the third multiplexer U12 and then flow back to the virtual ground, so the voltage passing through the known acquisition resistor Rf is collected by the second instrument amplifier U11, and the current passing through the unknown components can be obtained by calculation.
[0021] like Figure 3 As shown, in this embodiment, the program control module 2 includes an MCU unit U1 and a signal generator U2, the DDS_VOUT pin of the signal generator U2 is connected to the corresponding pin of the non-inverting proportional amplifier U7, and the MCU unit U1 communicates with the signal generator U2 via SPI; the signal generator U2 is used to generate a sinusoidal AC signal for testing.
[0022] The model of the MCU unit U1 is STM32F103, the model of the signal generator U2 is AD9833, and the program control module 2 also includes other peripheral circuits that meet the minimum system of the single-chip microcomputer. The MCU unit U1 completes the communication with the signal generator U2 through SPI, and controls the MUX switching through its own GPIO pin; the signal generator U2 is used to generate a sinusoidal AC signal for testing.
[0023] like Figure 4 As shown, in this embodiment, the acquisition module 4 includes a relay K1, an RMS detector U4, and a second voltage follower U3. The AC_SIGNAL_TO_RMS pin of the relay K1 is connected to the output end of the first instrument amplifier U9, the AC_SIGNAL_CURR pin of the relay K1 is connected to the output end of the second instrument amplifier U11, the relay K1 is connected to the RFIN end of the RMS detector U4, the VRMS end of the RMS detector U4 is connected to the positive input end of the second voltage follower U3, and the output end of the second voltage follower U3 is connected to the VRMS_OUT port of the MCU unit U1.
[0024] The model of the relay K1 is G6K-2F-Y-DC5V, the model of the RMS detector U4 is AD8361, and the model of the second voltage follower U3 is OPA188. The signal collected from the voltage module and the current module of the analog front-end module 3 enters the RMS detector U4 through the DC blocking capacitor after switching through the relay K1. The signal follows the ADC of the MCU unit U1 through the RMS detector U4 to obtain the RMS value of the voltage parameters of the L, C, and R components added to the unknown parameters.
[0025] like Figures 1 to 4 As shown, in this embodiment, the testing method includes the following steps: Step 1, set the signal generator U2 to output a sinusoidal AC signal of known frequency, which is applied to the LCR device 1 to be tested with unknown parameters after amplification and buffering by the front-end amplification buffer unit 5. Since the impedance characteristics of L, C, and R will generate a potential difference on both sides of the position component, the effective value V (Rf_CURR_RMS) of the potential difference applied to both ends of the LCR device 1 to be tested is collected through the impedance voltage acquisition unit 6 and the acquisition module 4. Assuming that the current passing through the LCR device 1 to be tested is Ix, it is concluded that the impedance of the LCR device 1 to be tested is Zx: Step 2: The AC signal passes through the LCR device 1 to be tested with unknown parameters and flows back to the ground through the collection resistor Rf. The effective value V (Zx_CURR_RMS) of the potential difference across the collection resistor Rf is obtained through the return collection unit 7 and the collection module 4. Since the components of the LCR device 1 to be tested are connected in series with the collection resistor Rf, the current I passing through the collection resistor Rf is equal to the current Ix passing through the LCR device 1 to be tested, that is, ; Step 3: The current I passing through the acquisition resistor Rf is: Step 4: If the unknown parameter component of the LCR device 1 to be tested is an inductor L, the inductance value is calculated as follows: Step 5: If the unknown parameter component of the LCR device 1 to be tested is a capacitor C, the capacitance value is calculated as follows: Step 6: If the unknown parameter component of the LCR device 1 to be tested is a resistor R, the resistance value is calculated as follows: .
[0026] Although the embodiments of the present invention are described with practical solutions, they do not constitute limitations on the meaning of the present invention. For those skilled in the art, it is obvious to modify the implementation scheme and combine it with other solutions based on this description.
Claims
1. An LCR test circuit, comprising an LCR device to be tested (1), characterized in that: The LCR test circuit comprises a program control module (2), the program control module (2) is connected to an analog front-end module (3) and a collection module (4), the analog front-end module (3) is connected to the collection module (4), and the analog front-end module (3) comprises a front-end amplification buffer unit (5), an impedance voltage collection unit (6), and a reflux collection unit (7) which are connected in sequence; The front-end amplification buffer unit (5) comprises a non-inverting proportional amplifier (U7), a unit gain buffer (U5) and a first multiplexer (U6) connected in sequence, the impedance voltage acquisition unit (6) comprises a first voltage follower (U8), a first instrumentation operational amplifier (U9) and a second multiplexer (U10), and the return current acquisition unit (7) comprises an inverting proportional amplifier (U14), a second instrumentation operational amplifier (U11) and a third multiplexer (U12); The first multiplexer (U6) is connected to the first voltage follower (U8) and the third multiplexer (U12) via the LCR device to be tested (1); the LCR device to be tested (1) is connected to the third multiplexer (U12) via an acquisition resistor (Rf); the first voltage follower (U8) and the second multiplexer (U10) are both connected to the first instrument amplifier (U9); the inverse proportional amplifier (U14) and the third multiplexer (U12) are both connected to the second instrument amplifier (U11); and the first instrument amplifier (U9) and the second instrument amplifier (U11) are both connected to the acquisition module (4).
2. The LCR test circuit according to claim 1, characterized in that: The program control module (2) comprises an MCU unit (U1) and a signal generator (U2); a DDS_VOUT pin of the signal generator (U2) is connected to a corresponding pin of the non-inverting proportional amplifier (U7); the MCU unit (U1) communicates with the signal generator (U2) via SPI; and the signal generator (U2) is used to generate a sinusoidal AC signal for testing.
3. The LCR test circuit according to claim 2, characterized in that: The acquisition module (4) comprises a relay (K1), an RMS detector (U4), and a second voltage follower (U3); the AC_SIGNAL_TO_RMS pin of the relay (K1) is connected to the output end of the first instrument amplifier (U9); the AC_SIGNAL_CURR pin of the relay (K1) is connected to the output end of the second instrument amplifier (U11); the relay (K1) is connected to the RFIN end of the RMS detector (U4); the VRMS end of the RMS detector (U4) is connected to the positive input end of the second voltage follower (U3); and the output end of the second voltage follower (U3) is connected to the VRMS_OUT port of the MCU unit (U1).
4. A method for testing an LCR test circuit as claimed in claim 3, characterized in that: The test method comprises the following steps: Step 1: Set the signal generator (U2) to output a sinusoidal AC signal of known frequency, which is applied to the LCR device (1) to be tested with unknown parameters after being amplified and buffered by the front-end amplification buffer unit (5). Since the impedance characteristics of L, C, and R will generate a potential difference on both sides of the position component, the effective value V (Rf_CURR_RMS) of the potential difference applied to both ends of the LCR device (1) to be tested is collected through the impedance voltage collection unit (6) and the collection module (4). Assuming that the current passing through the LCR device (1) to be tested is Ix, it is obtained that the impedance of the LCR device (1) to be tested is Zx: Step 2: The AC signal passes through the LCR device (1) to be tested with unknown parameters and flows back through the collection resistor (Rf) to the ground. The effective value V(Zx_CURR_RMS) of the potential difference across the collection resistor (Rf) is obtained through the return collection unit (7) and the collection module (4). Since the components of the LCR device (1) to be tested are connected in series with the collection resistor (Rf), the current I passing through the collection resistor (Rf) is equal to the current Ix passing through the LCR device (1) to be tested, that is, ； Step 3: The current I passing through the acquisition resistor (Rf) is: Step 4: If the unknown parameter component of the LCR device (1) to be tested is an inductor L, the inductance value is calculated in the following manner: Step 5: If the unknown parameter component of the LCR device (1) to be tested is a capacitor C, the capacitance value is calculated in the following manner: Step 6: If the unknown parameter component of the LCR device (1) to be tested is a resistor R, the resistance value is calculated in the following manner: 。