Measuring method and measuring device

Abstract

A measuring method according to one embodiment of the present disclosure is a method for measuring a voltage in order to obtain impedance of an object to be measured, the measuring method including applying an AC current having a predetermined frequency to the object to be measured, removing a frequency component other than the predetermined frequency from a voltage of the object to be measured to which the AC current has been applied, and measuring the voltage from which the frequency component has been removed.

Description

Measurement method and measuring device

[0001] The present disclosure relates to a method and a measuring device for measuring voltage.

[0002] Conductive patterns provided on a circuit board or the like, or elements such as coils, capacitors, and resistors arranged on the conductive patterns may be inspected for quality by applying current or voltage by contacting probes to both ends thereof. There is known a method of inspecting a printed wiring board by contacting a first probe to one end of a conductive pattern and contacting a second probe to the other end via an insulator to measure the amount of potential displacement of the first probe (Japanese Patent Application Laid-Open No. 2016-033511).

[0003] Japanese Patent Application Laid-Open No. 2016-033511

[0004] The inspection method of Patent Document 1 can surely detect a change in the amount of potential displacement when a voltage is applied to the first probe by contacting the second probe to the other end of the conductive pattern via the insulator, and accurate inspection is said to be possible. The conductive patterns on a circuit board or the like are miniaturized, and accordingly, the elements arranged on the conductive patterns are miniaturized, have lower resistance, and have lower capacitance. For this reason, it is required to perform low-impedance measurement for inspecting the circuit board. For example, when measuring the resistance value of a low-resistance element by applying a direct current, the voltage that can be detected from this low-resistance element is small, and it may be difficult to obtain an accurate resistance value while securing the S / N ratio against external noise such as hum. In this case, it is conceivable to measure the voltage by removing frequency components other than the direct current applied to the low-resistance element using an LPF (Low Pass Filter: low-frequency removal) circuit having a large time constant and obtain an accurate resistance value. When using an LPF having a large time constant, the settling time is long, and the time required for accurate measurement of the voltage may increase.

[0005] In view of the circumstances as described above, an object of the present disclosure is to provide a measurement method capable of accurately obtaining the impedance in a circuit board or the like in a short time.

[0006] (1) A measurement method according to one aspect of the present disclosure is a method for measuring voltage in order to determine the impedance of an object to be measured, comprising: applying an alternating current having a predetermined frequency to the object to be measured; removing frequency components other than the predetermined frequency from the voltage at the object to which the alternating current is applied; and measuring the voltage from which the frequency components have been removed.

[0007] (2) In (1) above, when removing the frequency component, it is preferable to amplify the differential voltage between the two terminals connected to the object to be measured.

[0008] (3) In (1) or (2) above, the voltage of the object to be measured, which is placed on the circuit board, may be measured.

[0009] (4) In any of (1) to (3) above, the predetermined frequency is a single frequency, and it is preferable to remove frequency components other than the single frequency from the voltage of the object to be measured to which the alternating current having the single frequency is applied, and measure the voltage from which the frequency components have been removed.

[0010] (5) In any of (1) to (4) above, the frequency component to be removed is preferably noise that propagates to at least one of the object being measured and the measurement environment of the object being measured.

[0011] (6) A measuring device according to one aspect of the present disclosure includes a current generation circuit that applies an alternating current having a predetermined frequency to an object to be measured; a filter circuit that includes a bandpass filter circuit that removes frequency components other than the predetermined frequency from the voltage at the object to be measured to which the alternating current is applied; and a voltage measuring circuit that measures the voltage output from the filter circuit.

[0012] A measurement method according to one aspect of this disclosure can accurately determine the impedance of a circuit board in a short amount of time.

[0013] Figure 1 is a schematic diagram showing a measuring device according to one embodiment of the present disclosure. Figure 2 is a schematic diagram showing the waveform of the voltage supplied by the voltage generation circuit of the measuring device in Figure 1 to the current generation circuit. Figure 3 is a schematic diagram showing the waveform of the current supplied by the current generation circuit of the measuring device in Figure 1 to the object to be measured. Figure 4 is a schematic diagram showing the waveform of the voltage output by the object to be measured by the measuring device in Figure 1. Figure 5 is a schematic diagram showing the waveform of the voltage output by the filter circuit of the measuring device in Figure 1. Figure 6 is a schematic diagram showing the waveform of the voltage output by the detection circuit of the measuring device in Figure 1. Figure 7 is a flowchart showing a measuring method according to one embodiment of the present disclosure.

[0014] The embodiments of this disclosure will be described in detail below, with reference to the drawings as appropriate.

[0015] [Measurement Method] A measurement method according to one aspect of the present disclosure is a method for measuring voltage in order to determine the impedance of an object to be measured, comprising: applying an alternating current having a predetermined frequency to the object to be measured; removing frequency components other than the predetermined frequency from the voltage at the object to which the alternating current is applied; and measuring the voltage from which the frequency components have been removed.

[0016] The measurement method may, for example, measure the voltage obtained by removing the frequency components from the voltage generated at the object T to be measured using a measuring device 1 as shown in Figure 1. The measuring device 1 comprises a current generation circuit 20 that applies an alternating current having a predetermined frequency to the object T to be measured, a filter circuit 30 including a bandpass filter circuit that removes frequency components other than the predetermined frequency from the voltage at the object T to which the alternating current is applied, and a voltage measurement circuit (not shown) that measures the voltage output from the filter circuit 30. The voltage measurement circuit is not particularly limited and may be a known voltage measuring instrument. The voltage measurement circuit and the filter circuit 30 may be configured as an integral part.

[0017] The object to be measured T is not particularly limited and may be a part or all of a conductor pattern on a circuit board, or it may be an element placed on a circuit board such as a resistor, coil, or capacitor. That is, the measuring device 1 may be used to determine the impedance of a circuit board between a pair of terminals P1 and P2 (e.g., a probe) connected to the object to be measured T, or it may be used to determine the impedance of an element placed on a circuit board. The element may be a single element or a group of elements connected together. The group of elements may be of the same type or of multiple (different) types. The element may be alone (independent and not placed on a circuit board) or it may be placed on a circuit board.

[0018] The current generation circuit 20 receives a voltage from the voltage generation circuit 10, which generates an AC voltage (see Figure 2) having a predetermined frequency, and passes it to the object T to be measured as an AC current (see Figure 3) having the predetermined frequency. The predetermined frequency of the AC current is not particularly limited and may be arbitrarily set based on the characteristics of the object T to be measured, the expected noise frequency, etc. The predetermined frequency may be a single frequency.

[0019] The alternating current having the predetermined frequency generated by the current generation circuit 20 is applied to the object T to be measured via one terminal P1. The other terminal P2 is preferably grounded. The pair of terminals P1 and P2 are electrically connected to the filter circuit 30. In other words, the measuring device 1 measures the voltage of the object T to be measured using the four-terminal method.

[0020] The filter circuit 30 includes a band-pass filter (BPF) circuit section that removes frequency components other than the predetermined frequency from the frequency of the voltage between a pair of terminals P1 and P2. That is, the filter circuit 30 includes a BPF, and this BPF extracts the waveform (the predetermined frequency) that the alternating current had from the voltage waveform (see Figure 4) generated on the object T to be measured when the alternating current having the predetermined frequency is applied. The BPF circuit section may consist of a low-pass filter (LPF) circuit section that removes frequency components higher than the predetermined frequency and a high-pass filter (HPF) circuit section that removes frequency components lower than the predetermined frequency.

[0021] The frequency components to be removed are preferably noise propagating to at least one of the object to be measured T and the measurement environment of the object to be measured T. That is, the frequency components removed by the BPF circuit section preferably include at least one of noise propagating to the object to be measured T and noise propagating to the measurement environment of the object to be measured T. The measurement environment includes, for example, a current source (voltage generation circuit 10, current generation circuit 20), and wiring connecting the current source and the object to be measured T. The frequency components may be all or part of the frequency components other than the predetermined frequency.

[0022] The filter circuit 30 may further include a common-mode rejection circuit and a balanced single-ended conversion amplifier circuit. The balanced single-ended conversion amplifier circuit and the LPF circuit may be configured integrally (as a single circuit). The filter circuit 30 has a pair of output terminals Op1 and Op2 that output a voltage from which the frequency components have been removed. The voltage measurement circuit measures the voltage between the pair of output terminals Op1 and Op2 (detection voltage), and the impedance of the object to be measured can be determined from the measured value. Specifically, the impedance of the object to be measured can be determined by dividing the detection voltage by the alternating current having the predetermined frequency generated by the current generation circuit 20.

[0023] The common-mode rejection circuit removes the common mode from the signals (voltages) input from the pair of terminals P1 and P2 and extracts the difference voltage. The common-mode rejection circuit is preferably configured to amplify the extracted difference voltage. By amplifying the difference voltage, the ease of measuring the detected voltage by the voltage measurement circuit can be improved.

[0024] The balanced single-ended conversion amplifier circuit amplifies the difference voltage after the common-mode rejection circuit, or further amplifies the difference voltage amplified by the common-mode rejection circuit. The balanced single-ended conversion amplifier circuit is preferably configured to amplify the difference voltage between a pair of terminals P1 and P2 to any desired level.

[0025] The BPF circuit section removes the frequency component from the differential voltage amplified by the balanced single-ended conversion amplifier circuit section. The filter circuit 30 outputs the signal from which the frequency component has been removed to output terminals Op1 and Op2. The voltage output from the filter circuit 30 has a waveform as shown in Figure 5, for example.

[0026] In measuring the detection voltage generated by passing an alternating current through an object to be measured, an integration circuit is sometimes used to improve measurement accuracy by integrating a voltage (signal) having a waveform proportional to the waveform of the alternating current. The measuring device 1 can measure the detection voltage with high accuracy by using, for example, synchronous detection, and therefore does not need to have the integration circuit, and the measurement time can be shortened by not having the integration circuit.

[0027] The measurement method using the measuring device 1 will be described below in accordance with the flowchart in Figure 7.

[0028] [S1: Preparation] Prepare the measuring device 1 and bring the ends of the pair of terminals P1 and P2 connected to the filter circuit 30 into contact with or connect to the object to be measured T. One terminal P1 may be further connected to the current generation circuit 20 at any point, and the other terminal P2 may be grounded at any point. Also, connect the voltage measuring circuit to the output terminals Op1 and Op2 of the filter circuit 30.

[0029] [S2: Voltage Generation] The voltage generation circuit 10 generates an AC voltage having a predetermined frequency. The frequency of the generated AC voltage is not particularly limited, but it is preferable to set it to a frequency higher than the frequency of the hum noise, for example, it may be 1 kHz, 5 kHz, or 10 kHz. The voltage generation circuit 10 is preferably configured so that the frequency of the generated AC voltage can be set arbitrarily.

[0030] [S3: Current generation] The current generation circuit 20 generates an alternating current having the predetermined frequency from a voltage having the predetermined frequency supplied from the voltage generation circuit 10.

[0031] [S4: Application] The alternating current having the predetermined frequency generated by the current generation circuit 20 is applied to the object T to be measured via terminal P1.

[0032] [S5: Removal of frequency components] The filter circuit 30 takes in the differential voltage between a pair of terminals P1 and P2, and removes unwanted frequency components other than the predetermined frequency using the BPF circuit section before outputting it. The voltage generated when an AC current having the predetermined frequency is applied to the object T to be measured is assumed to be an AC voltage with the same frequency as the AC current generated by the current generation circuit 20. Therefore, if a voltage with a frequency other than the predetermined frequency is generated, these are unwanted frequency components, i.e., noise components (error components). If the frequency of the AC current generated by the current generation circuit 20 is a single frequency, then the frequency components in the voltage other than the single frequency become noise components. The signal (voltage) output from the filter circuit 30 has a high S / N ratio because unwanted frequency components have been removed. The filter circuit 30 may amplify the differential voltage to an arbitrary level.

[0033] [S6: Measurement] The voltage measurement circuit measures the detection voltage output by the filter circuit 30. Since the noise component has been removed from this detection voltage, the impedance of the object T to be measured can be accurately measured.

[0034] In the measurement [S6], it is preferable to detect (including synchronous detection) the frequency of the AC voltage generated by the current generation circuit 20 and the frequency of the detected voltage output by the filter circuit 30. In other words, the measuring device 1 may further include a detection circuit (not shown). The detection circuit may be included in the voltage measurement circuit. The voltage output from the detection circuit has a waveform such as that shown in Figure 6. By including the detection circuit in the measuring device 1, it can be confirmed that the noise component has been removed, and the accuracy and ease of the measurement can be improved.

[0035] This measurement method eliminates unwanted frequency components during measurement, thus eliminating the need for noise countermeasures such as shielding the measuring device, the object being measured, and the wiring connecting them. Furthermore, when measuring a resistive element with a resistance of less than 1 ohm (on the order of mohm) using a DC current, it may take time to adjust the measuring equipment, such as adjusting the offset voltage and ensuring the settling time. This measurement method applies an AC current to the object being measured T, thus reducing the time required for preparation (adjustment) for measurement, and allowing for quick and easy measurement. Moreover, this measurement method eliminates unwanted frequency components from the voltage generated at the object being measured T to which the AC current is applied, enabling highly accurate measurements. Therefore, the impedance of the object being measured T can be easily and accurately determined.

[0036] [Other Embodiments] The embodiments described above do not limit the configuration of the present invention. Accordingly, the embodiments may omit, substitute, or add components to each part of the embodiments based on the description herein and common technical knowledge, and all such additions should be interpreted as falling within the scope of the present invention.

[0037] The measurement method disclosed herein can accurately determine the impedance of circuit boards and the like in a short amount of time, and is therefore suitable for use in the manufacturing and quality control of circuit boards and the like.

[0038] 1. Measuring device 10. Voltage generation circuit 20. Current generation circuit 30. Filter circuit Op1, Op2 output terminals P1, P2 terminals T. Object to be measured

Claims

1. A method for measuring voltage to determine the impedance of an object to be measured, comprising: applying an alternating current having a predetermined frequency to the object to be measured; removing frequency components other than the predetermined frequency from the voltage at the object to which the alternating current is applied; and measuring the voltage from which the frequency components have been removed.

2. The measurement method according to claim 1, wherein, when removing the frequency component, the differential voltage between two terminals connected to the object to be measured is amplified.

3. The measurement method according to claim 1 or 2, which measures the voltage of the object to be measured that is placed on a circuit board.

4. The measurement method according to claim 1 or 2, wherein the predetermined frequency is a single frequency, and the method involves removing frequency components other than the single frequency from the voltage of an object to be measured to which an alternating current having the single frequency is applied, and measuring the voltage from which the frequency components have been removed.

5. The measurement method according to claim 1 or 2, wherein the frequency component to be removed is noise propagating to at least one of the object to be measured and the measurement environment of the object to be measured.

6. A measuring device comprising: a current generation circuit that applies an alternating current having a predetermined frequency to an object to be measured; a filter circuit including a bandpass filter circuit that removes frequency components other than the predetermined frequency from the voltage at the object to which the alternating current is applied; and a voltage measuring circuit that measures the voltage output from the filter circuit.

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