Insulation resistance meter

Abstract

To provide an insulation resistance meter capable of suppressing influence of induction noise while securing accuracy of constant voltage control.SOLUTION: An insulation-resistance meter 1 includes a primary winding 121 to which a voltage is supplied and interrupted by a switching device 13, a secondary winding 122 having one end connected to a reference potential and the other end connected to an output-terminal T1 of the insulation-resistance meter 1, and a limiting resistance device 18 connected between the other end of the secondary winding and the output-terminal of the insulation-resistance meter. A capacitive element (15) that constitutes a low-pass filter (20) together with a limiting resistance element, a voltage detection unit (17) that detects a voltage between the other end of the capacitive element and one end of the limiting resistance element, and a current detection unit (16) that detects a current (Ir) flowing through a measurement target (9) are provided, and a control unit (19) that controls a switching element such that a voltage value of a DC voltage becomes constant by constant voltage control is provided on the basis of an output signal (- Vb) of the current detection unit and an output signal (Vd) of the voltage detection unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulation resistance tester that detects leakage current flowing through an object to be measured when a DC voltage is applied to the object to be measured. [Background technology]

[0002] Patent Document 1 discloses an insulation resistance meter in which an oscillator is connected to the base of a transistor, the collector of the transistor is connected to the other end of the primary winding of a transformer, and a voltage doubler rectifier circuit is connected to the secondary winding. In this insulation resistance meter, a portion of the output of the voltage doubler rectifier circuit is applied to the oscillator as a detection signal via a voltage divider circuit, and another portion is applied via a protective resistor to a terminal to which one end of the resistor under test is connected. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-274768 Summary of the Invention [Problem to be solved by the invention]

[0004] In the insulation resistance meter described above, induced noise may enter through the terminal to which one end of the resistor under test is connected. In this case, the induced noise is superimposed on the detection signal input to the oscillator via the voltage divider circuit, making it difficult to apply a constant DC voltage to the resistor under test.

[0005] The present invention has been made in view of these problems, and has as its object to suppress the influence of induction noise while ensuring the accuracy of constant voltage control. [Means for solving the problem]

[0006] According to one aspect of the present invention, an insulation resistance tester measures a current leaking from an object to be measured while a DC voltage is applied to the object to be measured. The insulation resistance tester includes a primary winding that is supplied with and cut off voltage from a DC power supply by a switching element, and a secondary winding that has one end connected to a reference potential and the other end connected to the output terminal of the insulation resistance tester. The insulation resistance tester also includes a limiting resistor element that is connected between the other end of the secondary winding and the output terminal of the insulation resistance tester and that limits the current input to the output terminal of the insulation resistance tester when a voltage is applied to the output terminal of the insulation resistance tester from an external source. The insulation resistance tester also includes a capacitor element that has one end connected to one end of the secondary winding and the other end connected to the other end of the secondary winding and that, together with the limiting resistor element, forms a low-pass filter. The insulation resistance tester also includes a voltage detector that detects the magnitude of the voltage between the other end of the capacitor element and one end of the limiting resistor element, and a current detector that detects the magnitude of the current flowing through the object to be measured. The insulation resistance meter further includes a control unit that controls the operation of the switching element based on the output signal of the current detection unit and the output signal of the voltage detection unit so that the voltage value of the DC voltage is constant through constant voltage control. [Effects of the Invention]

[0007] According to this aspect, the low-pass filter consisting of a limiting resistor element and a capacitor element reduces the induced noise superimposed on the output signal of the voltage detection unit that detects the voltage between the limiting resistor element and the capacitor element, thereby suppressing the effects of the induced noise.

[0008] However, since the voltage detector is located between the limiting resistor and the capacitor, a limiting resistor is interposed between the voltage detector and the output terminal of the insulation resistance meter. Therefore, even if the operation of the switching element is controlled in accordance with the output signal of the voltage detector so that the DC voltage applied to the object to be measured remains constant, a control error will occur due to the voltage drop across the limiting resistor.

[0009] To address this issue, according to this aspect, the insulation resistance meter uses a current detector to detect the magnitude of the current flowing through the limiting resistor in order to estimate the magnitude of the voltage drop across the limiting resistor, and the detection result is added to the output signal of the voltage detector, thereby reducing control errors caused by the voltage drop across the limiting resistor.

[0010] In addition, even if the low-pass filter is unable to sufficiently remove the induced noise, the induced noise superimposed on the output signal is detected by the current detection unit, and the control unit can remove the induced noise using the output signal of the voltage detection unit, thereby suppressing the effects of the induced noise that cannot be completely removed by the low-pass filter.

[0011] Therefore, according to this aspect, it is possible to suppress the influence of induction noise while ensuring the accuracy of constant voltage control. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing the operation of the insulation resistance meter. [Figure 3] FIG. 3 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the second embodiment. [Figure 4] FIG. 4 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the third embodiment. [Figure 5] FIG. 5 is a circuit diagram showing a modified example of the voltage detection section that constitutes the insulation resistance meter. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification, the same or equivalent elements are designated by the same reference numerals throughout.

[0014] (First embodiment) FIG. 1 is a circuit diagram showing the circuit configuration of an insulation resistance tester 1 according to the first embodiment.

[0015] The insulation resistance meter 1 is a measuring device for measuring the insulation resistance of a measurement object 9, such as a household distribution board, power receiving equipment in a building or factory, a transformer, or a motor. The resistance value of the insulation resistance of the measurement object 9 is, for example, several MΩ to several TΩ.

[0016] Insulation resistance meter 1 detects the leakage current flowing from object to be measured 9 to detection terminal T2 while outputting output voltage Vout, which is a DC voltage, from output terminal T1 and applying it to object to be measured 9. Insulation resistance meter 1 then calculates the insulation resistance value of object to be measured 9 by dividing the voltage value of output voltage Vout by the detected value of the leakage current.

[0017] A pair of cables with probes at the tips are connected to the output terminal T1 and the detection terminal T2, respectively, and the pair of probes are brought into contact with both ends of the object 9 to be measured by the measurer.

[0018] The insulation resistance meter 1 of the first embodiment performs constant current control to keep the leakage current flowing through the object to be measured 9 constant when the output voltage Vout is less than a predetermined voltage value, and performs constant voltage control to keep the output voltage Vout constant when the output voltage Vout reaches the predetermined voltage value. For example, the current value of the leakage current that is kept constant is several nA to several mA, and the voltage value of the output voltage Vout that is kept constant is several hundred V to several thousand V.

[0019] For example, when the output voltage Vout is less than 5000 [V], the insulation resistance meter 1 performs constant current control to maintain the leakage current at a constant 1 [mA], and when the output voltage Vout reaches 5,000 [V], it performs constant voltage control to maintain the output voltage Vout at a constant 5,000 [V].

[0020] The insulation resistance meter 1 may be configured to perform constant current control to keep the leakage current flowing through the object to be measured 9 constant when the insulation resistance of the object to be measured 9 is less than a predetermined resistance value, and to perform constant voltage control to keep the output voltage Vout constant when the insulation resistance of the object to be measured 9 is equal to or greater than the predetermined resistance value.

[0021] Insulation resistance meter 1 includes battery 11, transformer 12 having primary winding 121 and secondary winding 122, switching element 13, rectifying element 14, capacitive element 15, current detection unit 16, voltage detection unit 17, limiting resistance element 18, and control unit 19. Insulation resistance meter 1 also includes leakage current detection unit 21.

[0022] Battery 11 is a DC power supply that outputs a DC voltage. For example, the voltage value of battery 11 is designed to be several volts. The positive electrode of battery 11 is connected to one end of primary winding 121 of transformer 12, and the negative electrode of battery 11 is connected to ground potential G. Ground potential G here is the reference potential that serves as the reference when insulation resistance meter 1 operates.

[0023] The transformer 12 is a converter that converts a secondary voltage generated in the secondary winding 122 by utilizing electromagnetic induction and mutual induction between the primary winding 121 and the secondary winding 122 into a voltage value different from the primary voltage supplied to the primary winding 121. The transformer 12 of the first embodiment is used as a step-up transformer that converts the secondary voltage into a voltage value higher than the primary voltage.

[0024] The primary winding 121 is supplied with and cut off DC voltage from the battery 11 by the switching element 13. The other end of the primary winding 121 is connected to the input terminal of the switching element 13.

[0025] One end of the secondary winding 122 is electrically connected to the ground potential G, and the other end of the secondary winding 122 is electrically connected to the output terminal T1 of the insulation resistance meter 1.

[0026] In the first embodiment, one end of the secondary winding 122 is connected to one end of the capacitance element 15 and one end of the current detection unit 16, and the other end of the secondary winding 122 is connected to the other end of the capacitance element 15, the voltage detection unit 17, and one end of the limiting resistance element 18 via the rectifying element 14.

[0027] The switching element 13 supplies and cuts off the DC voltage from the battery 11 to the primary winding 121. The switching element 13 is realized by a semiconductor element such as a bipolar transistor (BJT), a field effect transistor (FET), an insulated gate bipolar transistor (IGBT), or a gallium nitride (GaN) transistor.

[0028] In the first embodiment, an N-channel metal oxide semiconductor field effect transistor (MOSFET) is employed as the switching element 13. The gate terminal, source terminal, and drain terminal of the N-channel MOSFET correspond to the control terminal, input terminal, and output terminal of the switching element 13, respectively.

[0029] The drain terminal of switching element 13 is connected to ground potential G, and the gate terminal of switching element 13 is connected to the output terminal of control unit 19. Current is supplied to and cut off from primary winding 121 by the switching operation of switching element 13, which is performed in accordance with a PWM signal from control unit 19.

[0030] Specifically, when an on-voltage is applied to the gate terminal of the switching element 13, the source terminal and the drain terminal of the switching element 13 are brought into a conductive state, and a current is supplied to the primary winding 121. On the other hand, when an off-voltage is applied to the gate terminal of the switching element 13, the source terminal and the drain terminal of the switching element 13 are brought into a non-conductive state, and the current supply to the primary winding 121 is cut off.

[0031] The rectifying element 14 is an element for converting an AC voltage generated in the secondary winding 122 into a DC voltage. In the first embodiment, a diode is used as the rectifying element 14, and the anode of the rectifying element 14 is connected to the other end of the secondary winding 122, and the cathode of the rectifying element 14 is connected to the other end of the capacitive element 15.

[0032] Capacitance element 15 is an element that smoothes the AC voltage generated in secondary winding 122 by the switching operation of switching element 13 and converts the AC voltage into a DC voltage together with rectifier element 14, and is a so-called smoothing capacitor. Capacitance element 15 is connected in parallel to secondary winding 122. Specifically, one end of capacitance element 15 is connected to one end of secondary winding 122, and the other end of capacitance element 15 is connected to the other end of secondary winding 122.

[0033] The capacitance value of the capacitance element 15 is set to smooth the AC voltage generated in the secondary winding 122 by the operation of the switching element 13. For example, the capacitance value of the capacitance element 15 is designed to be a value within a range from several tens [nF] to several hundreds [nF].

[0034] The current detection unit 16 detects the magnitude of the current flowing through the object to be measured 9. The current flowing through the object to be measured 9 flows from the ground potential G connected to one end of the secondary winding 122 through the secondary winding 122 and the limiting resistance element 18.

[0035] The current detection unit 16 in the first embodiment detects the magnitude of the secondary current flowing through the secondary winding 122 as the magnitude of the current flowing through the object to be measured 9. The current detection unit 16 is realized by a resistive element 161.

[0036] The resistance value of the resistive element 161 is designed to be, for example, several hundred Ω, and in the first embodiment, is designed to be, for example, approximately 300 Ω. One end of the resistive element 161 is connected to one end of the secondary winding 122, and the other end of the resistive element 161 is connected to the ground potential G.

[0037] The secondary current flowing through secondary winding 122 is output from ground potential G via secondary winding 122 to output terminal T1 of insulation resistance meter 1. As a result, a voltage drop occurs at one end of resistive element 161, which is disposed between ground potential G and secondary winding 122, due to the secondary current flowing therethrough, and a voltage corresponding to the magnitude of the secondary current is generated.

[0038] Therefore, an output signal (-Vb) whose voltage value changes depending on the magnitude of the secondary current flowing through the secondary winding 122 is generated at one end of the resistance element 161. The current detection unit 16 outputs the voltage signal generated at one end of the resistance element 161 as the output signal (-Vb).

[0039] The voltage detection unit 17 detects the magnitude of the voltage of the connection line L1 extending between the other end of the capacitance element 15 and one end of the limiting resistance element 18. The voltage detection unit 17 of the first embodiment is connected between the connection line L1 and the ground potential G.

[0040] The voltage detection unit 17 of the first embodiment is a voltage dividing circuit configured by voltage dividing resistor elements 171 and 172 connected in series to each other. The resistance values ​​of the voltage dividing resistor elements 171 and 172 are designed to be, for example, several hundred MΩ, and in the first embodiment, are designed to be approximately 300 MΩ.

[0041] Specifically, one end of the voltage-dividing resistor element 171 is connected to the connection line L1, the other end of the voltage-dividing resistor element 171 is connected to one end of the voltage-dividing resistor element 172, and the other end of the voltage-dividing resistor element 172 is connected to the ground potential G.

[0042] The voltage detection unit 17 outputs a voltage division signal generated at the connection point between the voltage division resistance element 171 and the voltage division resistance element 172 as a detection signal to the control unit 19. The output signal of the voltage detection unit 17 is a voltage signal proportional to the magnitude of the voltage generated in the connection line L1.

[0043] Limiting resistor 18 is a resistor that limits the current input to output terminal T1 of insulation resistance meter 1 when an external voltage is applied to output terminal T1 of insulation resistance meter 1. Limiting resistor 18 is connected between the other end of secondary winding 122 and output terminal T1 of insulation resistance meter 1.

[0044] The resistance value Ro of the limiting resistor 18 is designed to be, for example, within a range from several kΩ to several hundred kΩ. In the first embodiment, the resistance value of the limiting resistor 18 is designed to be 100 kΩ.

[0045] Furthermore, the limiting resistor 18, together with the capacitor 15, constitutes a low-pass filter 20 that reduces induced noise. At least one of the resistance value of the limiting resistor 18 and the capacitance value of the capacitor 15 is designed so that the cutoff frequency of the low-pass filter 20 is lower than the frequency of the induced noise.

[0046] The control unit 19 performs constant voltage control based on the output signal (-Vd) generated at one end of the secondary winding 122 and the output signal Vd of the voltage detection unit 17, and controls the operation of the switching element 13 so that the voltage value of the output voltage Vout remains constant.

[0047] In the first embodiment, the control unit 19 includes an adder circuit 191 and a boost control circuit 192 .

[0048] Adder circuit 191 adds the output signal (-Vb) generated at one end of secondary winding 122 and the output signal Vd of voltage detection unit 17. The output signal (-Vb) generated at one end of secondary winding 122 is proportional to the amount of voltage drop across limiting resistance element 18, and the voltage value increases toward the negative side as the secondary current flowing through secondary winding 122 increases, and the negative voltage value decreases as the secondary current decreases.

[0049] Therefore, by adding the output signal (-Vd) indicating a negative voltage value to the output signal Vd of the voltage detection unit 17, the voltage drop of the limiting resistance element 18 is taken into consideration, and the output signal Ve of the addition circuit 191 can be used as a detection signal indicating the voltage value of the output voltage Vout.

[0050] The adder circuit 191 then outputs an output signal Ve obtained by adding the output signal (-Vb) of the current detector 16 and the output signal Vd of the voltage detector 17 to the boost control circuit 192. That is, the adder circuit 191 feeds back an estimated signal of the output voltage Vout to the boost control circuit 192.

[0051] The boost control circuit 192 constitutes a control circuit that controls the operation of the switching element 13 so that the output signal Ve of the adder circuit 191 is constant. The boost control circuit 192 generates a PWM signal for PWM-controlling the switching element 13 and supplies the PWM signal to the gate terminal of the switching element 13.

[0052] Specifically, the boost control circuit 192 applies an on voltage to the gate terminal of the switching element 13 so that current is supplied to the primary winding 121 by the battery 11, or applies an off voltage to the gate terminal of the switching element 13 so that the current supply to the primary winding 121 is cut off.

[0053] As described above, the boost control circuit 192 performs PWM control to alternately switch the conductive state and non-conductive state of the switching element 13, thereby causing the switching element 13 to perform a switching operation. This keeps the voltage value of the output voltage Vout constant at a predetermined set value.

[0054] Leakage current detection unit 21 detects the magnitude of leakage current flowing through measurement object 9. Specifically, leakage current detection unit 21 detects the magnitude of leakage current flowing in from detection terminal T2 of insulation resistance meter 1. Leakage current detection unit 21 is configured with, for example, an IV conversion circuit and an AD conversion circuit.

[0055] Insulation resistance meter 1 calculates the insulation resistance value of measurement object 9 in a processing section (not shown) using the current value of the leakage current detected by leakage current detection section 21 and the voltage value of output voltage Vout.

[0056] Next, the operation of the insulation resistance tester 1 will be described with reference to FIG.

[0057] First, a set value Vset of the output voltage Vout is input to the boost control circuit 192, and the boost control circuit 192 performs constant voltage control so that the output voltage Vout is maintained at the set value Vset.

[0058] In this case, if there are electric wires carrying AC signals near the insulation resistance meter 1 or the object to be measured 9, induced noise of, for example, 50 Hz or 60 Hz may enter through the output terminal T1 of the insulation resistance meter 1. The voltage value of this induced noise may reach several hundred volts, for example, near high-voltage electrical power lines.

[0059] In the insulation resistance meter 1 of the first embodiment, the low-pass filter 20, which is configured from the capacitance element 15 and the limiting resistance element 18, removes this induced noise.

[0060] In particular, induced noise entering from the output terminal T1 is less likely to be superimposed on the connection line L1 between the other end of the capacitance element 15 and one end of the limiting resistance element 18. Therefore, the output signal of the voltage detection unit 17 that detects the voltage of the connection line L1 is less susceptible to the influence of induced noise compared to a circuit configuration in which the voltage detection unit 17 is disposed between the other end of the limiting resistance element 18 and the output terminal T1.

[0061] Therefore, constant voltage control is performed by the boost control circuit 192 based on the output signal of the voltage detection unit 17 in which the influence of induction noise has been suppressed, so that the output voltage Vout can be maintained constant with high precision.

[0062] However, since the voltage detection unit 17 is placed between the other end of the capacitance element 15 and one end of the limiting resistance element 18, the limiting resistance element 18 is placed between the connection point of the voltage detection unit 17 on the connection line L1 and the output terminal T1.

[0063] A voltage drop (Ir×Ro) occurs in the limiting resistor element 18 because the secondary current Ir flowing through the secondary winding 122 flows through the limiting resistor element 18. As a result, the output voltage Vout drops below the detection voltage Va generated at the connection point of the voltage detection unit 17 by the voltage drop (Ir×Ro) generated in the limiting resistor element 18. This voltage drop (Ir×Ro) can reach a maximum of approximately 100 V.

[0064] Since the amount of drop in the output voltage Vout due to the limiting resistor element 18 varies depending on the magnitude of the secondary current Ir, if the amount of drop in the output voltage Vout were set to a fixed value, the error of the output voltage Vout from the set value Vset would become large depending on the magnitude of the secondary current Ir.

[0065] To address this issue, in the first embodiment, a current detector 16 is disposed between one end of the secondary winding 122 and the ground potential G to detect the magnitude of the secondary current Ir.

[0066] As a result, as the secondary current Ir increases, the voltage drop (Ir×Ro) of the limiting resistor element 18 increases the amount of decrease in the output voltage Vout, and the amount of decrease in the output signal (−Vb) generated at one end of the secondary winding 122 also increases.

[0067] Similarly, as the secondary current Ir decreases, the amount of drop in the output voltage Vout due to the voltage drop (Ir×Ro) of the limiting resistor element 18 decreases, and the amount of drop in the output signal (−Vb) generated at one end of the secondary winding 122 also decreases.

[0068] In this way, the amount of drop in the output voltage Vout due to the voltage drop (Ir×Ro) of the limiting resistor 18 is proportional to the amount of drop from the ground potential G at one end of the secondary winding 122 that appears in the output signal (-Vb) of the current detection unit 16. Therefore, by detecting the magnitude of the output signal (-Vb) of the current detection unit 16, it is possible to compensate for the amount of drop in the output voltage Vout that accompanies an increase or decrease in the secondary current Ir.

[0069] Therefore, in the first embodiment, the adder circuit 191 adds the output signal (-Vb) generated at one end of the resistor element 161 to the output signal Vd of the voltage detection unit 17. This compensates for the drop in the output voltage Vout caused by the voltage drop (Ir×Ro) of the limiting resistor element 18 during constant voltage control. That is, it becomes possible to keep the output voltage Vout constant regardless of the magnitude of the secondary current Ir.

[0070] Therefore, the boost control circuit 192 controls the operation of the switching element 13 based on the output signal Ve of the adder circuit 191, which estimates the output voltage Vout from the output signal Vd of the voltage detection unit 17, so that the output voltage Vout is maintained at the set value Vset.

[0071] Furthermore, if the inductive noise is not sufficiently removed by the low-pass filter 20, the inductive noise will cause the current Ir flowing through the limiting resistor element 18 to fluctuate, which will similarly cause the output signal (-Vb) of the current detection unit 16 to fluctuate. Therefore, in the adder circuit 191, the fluctuation in the output voltage Vout caused by the inductive noise can also be removed by the output signal (-Vb) of the current detection unit 16.

[0072] As described above, in the insulation resistance tester 1, the voltage detection unit 17 is disposed between the capacitive element 15 and the limiting resistive element 18 of the low-pass filter 20, which removes induced noise. The insulation resistance tester 1 then performs constant voltage control using a feedback signal (Ve) that is corrected for the output signal Vd of the voltage detection unit 17 based on the output signal (-Vb) of the current detection unit 16 to take into account the voltage drop (Ir × Ro) across the limiting resistive element 18. This allows the output voltage Vout to be maintained at the set value Vset with high accuracy and stability.

[0073] Next, the effects of the first embodiment will be described.

[0074] In the first embodiment, insulation resistance tester 1 detects leakage current flowing through object to be measured 9 while a DC voltage (Vout) is applied to object to be measured 9. Insulation resistance tester 1 includes primary winding 121, to which voltage from a DC power supply is supplied and cut off by switching element 13, secondary winding 122, one end of which is connected to reference potential (G) and the other end of which is connected to output terminal T1 of insulation resistance tester 1, and limiting resistor 18, which is connected between the other end of secondary winding 122 and output terminal T1 of insulation resistance tester 1 and which limits the current input to output terminal T1 of insulation resistance tester 1 when a voltage is applied to output terminal T1 of insulation resistance tester 1 from outside.

[0075] The insulation resistance meter 1 also includes a capacitance element 15 having one end connected to one end of the secondary winding 122 and the other end connected to the other end of the secondary winding 122, and constituting a low-pass filter 20 together with the limiting resistance element 18, a voltage detection unit 17 that detects the magnitude of the voltage between the other end of the capacitance element 15 and one end of the limiting resistance element 18, and a current detection unit 16 that detects the magnitude of the current flowing through the secondary winding 122.

[0076] Furthermore, the insulation resistance meter 1 includes a control unit 19 that controls the operation of the switching element 13 based on the output signal (-Vb) of the current detection unit 16 and the output signal Vd of the voltage detection unit 17 so that the voltage value of the DC voltage (Vout) is constant through constant voltage control.

[0077] According to this configuration, the voltage detection unit 17 is disposed between the limiting resistance element 18 and the capacitance element 15 that constitute the low-pass filter 20, and therefore the low-pass filter 20 reduces the induced noise that gets mixed into the output signal Vd of the voltage detection unit 17 used for constant voltage control. This makes it possible to suppress the influence of induced noise on constant voltage control.

[0078] Meanwhile, since voltage detection unit 17 is disposed between limiting resistance element 18 and capacitance element 15, limiting resistance element 18 is interposed between voltage detection unit 17 and output terminal T1 of insulation resistance meter 1. For this reason, even if the operation of switching element 13 is controlled in accordance with output signal Vd from voltage detection unit 17 so that the voltage value of output voltage Vout, which is a DC voltage applied to object to be measured 9, is constant, a control error will occur corresponding to the voltage drop (Ir × Ro) that occurs across limiting resistance element 18.

[0079] To address this issue, the insulation resistance meter 1 is equipped with a current detection unit 16 that detects the magnitude of the current Ir flowing through the limiting resistance element 18 in order to estimate the magnitude of the voltage drop (Ir × Ro) across the limiting resistance element 18. By incorporating the detection result into the output signal Vd of the voltage detection unit 17, the insulation resistance meter 1 can reduce control errors caused by the voltage drop (Ir × Ro) across the limiting resistance element 18.

[0080] In addition, even if the low-pass filter 20 is not able to sufficiently remove the induced noise, the induced noise superimposed on the output voltage Vout is detected by the current detection unit 16, and therefore the induced noise contained in the output signal Vd of the voltage detection unit 17 can be removed by the control unit 19. Therefore, according to the configuration of the first embodiment, the influence of the induced noise that cannot be completely removed by the low-pass filter 20 can also be suppressed.

[0081] Therefore, according to the first embodiment, it is possible to suppress the influence of induction noise while ensuring the accuracy of constant voltage control.

[0082] Furthermore, according to the first embodiment, the cutoff frequency of low-pass filter 20 is lower than the frequency of the induced noise superimposed on output terminal T1 of insulation resistance meter 1.

[0083] According to this configuration, low-pass filter 20 can accurately remove induced noise superimposed on output terminal T1 of insulation resistance meter 1.

[0084] Furthermore, according to the first embodiment, the capacitance value of the capacitance element 15 is a value that is predetermined so that the AC voltage generated in the secondary winding 122 by the operation of the switching element 13 is smoothed and induced noise is suppressed.

[0085] According to this configuration, by connecting the capacitance element 15 in parallel with the secondary winding 122, the AC voltage caused by the operation of the switching element 13 can be smoothed, and in cooperation with the limiting resistance element 18, induction noise can be suppressed.

[0086] In addition, in the first embodiment, the current detection unit 16 is a resistive element 161 connected between one end of the secondary winding 122 and a reference potential (G), and the output signal of the current detection unit 16 is an output signal (-Vd) generated at one end of the secondary winding.

[0087] According to this configuration, the current detection unit 16 can be realized with a simple circuit configuration.

[0088] Furthermore, according to the first embodiment, the control unit 19 includes an adder circuit 191 that adds the output signal (-Vb) generated at one end of the secondary winding 122 and the output signal Vd of the voltage detection unit 17, and a boost control circuit 192 that controls the operation of the switching element 13 so that the output signal of the adder circuit 191 is constant.

[0089] According to this configuration, the output signal (-Vb) indicating a negative voltage value is proportional to the voltage drop (Ir x Ro) of the limiting resistor element 18, and therefore the voltage value of the output voltage Vout can be estimated by adding the output signal (-Vd) to the output signal Vd of the voltage detection unit 17 using a simple adder circuit 191. Therefore, the boost control circuit 192 controls the operation of the switching element 13 so that the output signal Ve of the adder circuit 191 is constant, and therefore the voltage value of the output voltage Vout can be maintained constant.

[0090] Furthermore, in the first embodiment, before performing constant voltage control, the control unit 19 performs constant current control, which controls the operation of the switching element 13 based on the output signal (-Vd) of the current detection unit 16 so that the current Ir output from the output terminal T1 of the insulation resistance meter 1 is constant.

[0091] According to this configuration, by executing constant current control before executing constant voltage control, it is possible to avoid supplying excessive current to the object to be measured 9.

[0092] Second Embodiment In the first embodiment, the current detection unit 16 is arranged between one end of the secondary winding 122 and the ground potential G to detect the magnitude of the current flowing through the object to be measured 9, but the present invention is not limited to this. Therefore, a second embodiment in which the arrangement of the current detection unit 16 is changed will be described with reference to FIG.

[0093] FIG. 3 is a circuit diagram showing the circuit configuration of an insulation resistance meter 2 according to the second embodiment.

[0094] Insulation resistance meter 2 has current detection unit 16A and subtraction circuit 191A instead of current detection unit 16 and adder circuit 191 of control unit 19 of insulation resistance meter 1. Other components of insulation resistance meter 2 are the same as or equivalent to those of insulation resistance meter 1, so a description thereof will be omitted here.

[0095] Current detection unit 16A detects the magnitude of the current flowing through object to be measured 9. The current flowing through object to be measured 9 flows from ground potential G connected to one end of secondary winding 122 through secondary winding 122 and limiting resistor element 18 to object to be measured 9, and then flows from detection terminal T2 of insulation resistance meter 2 to leakage current detection unit 21.

[0096] In the second embodiment, the current detection unit 16A detects the magnitude of the current flowing into the leakage current detection unit 21 as the magnitude of the current flowing through the measurement object 9. The current detection unit 16A is realized by a resistive element 162. The resistance value of the resistive element 162 is, for example, several hundred Ω, and in the second embodiment, is designed to be 500 Ω, for example.

[0097] One end of resistor element 162 is connected to detection terminal T2 of insulation resistance meter 2, and the other end of resistor element 162 is connected to the input terminal of leakage current detection unit 21. In other words, resistor element 162 is connected between detection terminal T2 of insulation resistance meter 2 and the input terminal of leakage current detection unit 21.

[0098] The current detection unit 16A outputs an output signal Vc generated at one end of the resistance element 162 to the subtraction circuit 191A as a detection signal of the leakage current.

[0099] The subtraction circuit 191A subtracts the output signal Vc generated at one end of the resistor element 162 from the output signal of the voltage detection unit 17. The output signal Vc generated at one end of the resistor element 162 is in a negative proportional relationship with the amount of voltage drop across the limiting resistor element 18, and the voltage value increases toward the positive side as the current flowing through the object to be measured 9 increases, and the positive voltage value decreases as the secondary current decreases.

[0100] Therefore, by subtracting the output signal Vc indicating a positive voltage value from the output signal Vd of the voltage detection unit 17, the voltage drop of the limiting resistor element 18 is taken into account, and the output signal Ve of the subtraction circuit 191A can be used as a detection signal indicating the voltage value of the output voltage Vout.

[0101] The subtraction circuit 191A then subtracts the output signal Vc of the current detection unit 16A from the output signal Vd of the voltage detection unit 17 to obtain an output signal Ve, and outputs the result to the boost control circuit 192. That is, the subtraction circuit 191A feeds back an estimated signal of the output voltage Vout to the boost control circuit 192.

[0102] The boost control circuit 192 controls the operation of the switching element 13 so that the output signal of the subtraction circuit 191A is constant, thereby maintaining the output voltage Vout applied to the object under test 9 at a set value.

[0103] Next, a description will be given of an example of the circuit configuration of the leakage current detection unit 21. The leakage current detection unit 21 includes an IV conversion circuit 211 and an AD conversion circuit 212.

[0104] The IV conversion circuit 211 converts the leakage current flowing into the detection terminal T2 into a voltage corresponding to the magnitude of the leakage current. The IV conversion circuit 211 outputs a voltage signal indicating the magnitude of the converted voltage to the AD conversion circuit 212.

[0105] The IV conversion circuit 211 of the second embodiment includes an operational amplifier 211A and a resistive element 211B. The inverting input terminal (−) of the operational amplifier 211A is connected to the other end of the resistive element 162 and one end of the resistive element 211B, and the non-inverting input terminal (+) is connected to the ground potential G. The output terminal of the operational amplifier 211A is connected to the other end of the resistive element 211B and the input terminal of the AD conversion circuit 212.

[0106] The AD conversion circuit 212 converts the analog output signal of the IV conversion circuit 211 into a digital signal, and outputs the converted digital signal indicating the magnitude of the leakage current to a processing unit (not shown).

[0107] Next, the effects of the second embodiment will be described.

[0108] In the second embodiment, insulation resistance tester 2 further includes leakage current detection unit 21 that detects the magnitude of leakage current flowing in from detection terminal T2 of insulation resistance tester 2. Current detection unit 16A is a resistive element 162 connected between detection terminal T2 of insulation resistance tester 2 and leakage current detection unit 21, and the output signal of current detection unit 16A is output signal Vc that appears at detection terminal T2, which is connected to one end of resistive element 162.

[0109] With this configuration, the resistor element 162 is disposed between the detection terminal T2 of the insulation resistance meter 2 and the leakage current detection unit 21, so that the output signal Vc generated at the detection terminal T2 of the insulation resistance meter 2 has a negative proportional relationship with the amount of voltage drop across the limiting resistor element 18.

[0110] Therefore, by using the output signal Vc generated at the detection terminal T2, it is possible to take into account the voltage drop amount of the limiting resistance element 18 in the output signal Vd of the voltage detection unit 17, thereby enabling constant voltage control to be performed easily and accurately.

[0111] In addition, the control unit 19 of the second embodiment has a subtraction circuit 191A that subtracts the output signal Vc generated at the detection terminal T2 from the output signal Vd of the voltage detection unit 17, and a boost control circuit 192 that controls the operation of the switching element 13 so that the output signal of the subtraction circuit 191A is constant.

[0112] According to this configuration, the output signal Vc indicating a positive voltage value is in a negative proportional relationship with the voltage drop (Ir×Ro) of the limiting resistor element 18, and therefore the voltage value of the output voltage Vout can be estimated by using a simple subtraction circuit 191A to subtract the output signal Vc from the output signal Vd of the voltage detection unit 17. The boost control circuit 192 controls the operation of the switching element 13 so that the output signal Ve of the subtraction circuit 191A indicating the estimated value of the output voltage Vout becomes constant, and therefore the voltage value of the output voltage Vout can be maintained constant.

[0113] (Third embodiment) In the second embodiment, the output signals of the current detection unit 16A and the voltage detection unit 17 are used to generate the feedback signal of the boost control circuit 192, but there are cases where constant voltage control cannot be performed correctly due to a defect in the current detection unit 16A or the voltage detection unit 17. As a countermeasure to this, a third embodiment in which defects in the current detection unit 16A and the voltage detection unit 17 are detected will be described with reference to FIG.

[0114] FIG. 4 is a circuit diagram showing the circuit configuration of an insulation resistance tester 3 according to the third embodiment.

[0115] Insulation resistance meter 3 includes an output voltage detection unit 31, a processing unit 32, and a display unit 33 in addition to the circuit configuration of insulation resistance meter 2 shown in FIG.

[0116] Output voltage detection unit 31 is a voltage detection unit different from voltage detection unit 17, and detects the magnitude of output voltage Vout generated at output terminal T1 of insulation resistance meter 3. Output voltage detection unit 31 of the third embodiment is a voltage dividing circuit configured by voltage dividing resistor elements 311 and 312 connected in series to each other.

[0117] Specifically, one end of the voltage-dividing resistor element 311 is connected to a connection line L2 extending between the other end of the limiting resistor element 18 and the output terminal T1, the other end of the voltage-dividing resistor element 311 is connected to one end of the voltage-dividing resistor element 312, and the other end of the voltage-dividing resistor element 312 is connected to the ground potential G.

[0118] The output voltage detector 31 outputs a divided voltage signal generated at the connection point between the voltage dividing resistor elements 311 and 312 to the processor 32 as an output signal Vd1.

[0119] The processing unit 32 acquires the output signal Vd1 of the output voltage detection unit 31, the output signal Vd of the voltage detection unit 17, the output signal Vc of the current detection unit 16A, and the output signal Vc1 of the leakage current detection unit .

[0120] In constant voltage control, the processing unit 32 determines whether the output signal Vd1 of the output voltage detection unit 31 is outside a predetermined voltage tolerance range. The predetermined voltage tolerance range is determined, for example, based on the set value Vset of the output voltage Vout and an inherent control error in constant voltage control. In the third embodiment, the upper limit of the predetermined voltage tolerance range is set to a positive number [%] relative to the set value Vset, and the lower limit is set to a negative number [%] relative to the set value Vset.

[0121] If the output signal Vd1 of the output voltage detector 31 is outside the predetermined voltage tolerance range, the processor 32 determines that there is a component failure, such as the switching element 13, the voltage detector 17, or the controller 19 of the insulation resistance meter 3, or that there is an abnormality in the object to be measured 9, and stops the measurement process of the insulation resistance meter 3.

[0122] Furthermore, if the output signal Vd1 of the output voltage detector 31 is outside a predetermined voltage tolerance range, the processor 32 outputs measurement failure information indicating a measurement failure of the insulation resistance to the display 33. Possible measurement failures include a component failure in the insulation resistance meter 3 or an abnormality in the object to be measured 9.

[0123] In addition, the processing unit 32 may determine whether the output signal Vd of the voltage detection unit 17 is outside a specific voltage tolerance range. The specific voltage tolerance range is determined based on, for example, the set value Vset of the output voltage Vout, the resistance value Ro of the limiting resistor element 18, and an inherent control error in constant voltage control.

[0124] If the output signal Vd1 of the output voltage detection unit 31 is outside a predetermined voltage tolerance range, or if the output signal Vd of the voltage detection unit 17 is outside a specific voltage tolerance range, the processing unit 32 stops the measurement process and outputs measurement failure information to the display unit 33.

[0125] In the constant current control, the processing unit 32 determines whether the output signal Vc1 of the leakage current detection unit 21 is outside a predetermined allowable current range. The predetermined allowable current range is determined, for example, based on the set value of the output current and an inherent control error in the constant current control. In the third embodiment, the upper limit of the predetermined allowable current range is set to several [mA], and the lower limit is set to 0 [mA].

[0126] If output signal Vc1 of leakage current detection unit 21 is outside the predetermined voltage tolerance range, processing unit 32 determines that there is a component failure in insulation resistance meter 3 or an abnormality in measurement object 9, and stops the measurement process of insulation resistance meter 3. Furthermore, if output signal Vc1 of leakage current detection unit 21 is outside the predetermined voltage tolerance range, processing unit 32 outputs measurement failure information to display unit 33.

[0127] In addition, the processing unit 32 may determine whether the output signal Vc of the current detection unit 16A is outside a specific voltage tolerance range. The specific voltage tolerance range is determined based on, for example, the set value of the output current in constant current control and an inherent control error.

[0128] If the output signal Vc1 of the leakage current detection unit 21 is outside a predetermined voltage tolerance range, or if the output signal Vc of the current detection unit 16A is outside a specific voltage tolerance range, the processing unit 32 stops the measurement process and outputs measurement failure information to the display unit 33.

[0129] The display unit 33 displays measurement failure information when the output signal Vd of the voltage detection unit 17 falls outside a specific voltage tolerance range, or when the output signal Vd1 of the output voltage detection unit 31 falls outside a predetermined voltage tolerance range.

[0130] In addition, the display unit 33 displays measurement failure information when the output signal Vc of the current detection unit 16A is outside a specific voltage tolerance range, or when the output signal Vc1 of the leakage current detection unit 21 is outside a predetermined voltage tolerance range.

[0131] 1 in place of or in addition to current detection unit 16A. In this case, display unit 33 may display measurement failure information when the output signal (-Vb) of current detection unit 16 is outside a specific voltage tolerance range.

[0132] Next, the effects of the third embodiment will be described.

[0133] In the third embodiment, the insulation resistance meter 3 includes an output voltage detector 31 that detects the output voltage Vout generated at the output terminal T1 of the insulation resistance meter 3 as another voltage detector, and a display 33 that displays measurement failure information indicating a measurement failure of the insulation resistance if the output signal of the output voltage detector 31 is outside a predetermined voltage tolerance range.

[0134] According to this configuration, under constant voltage control, it is possible to notify the person making the measurement of measurement defects such as component failures in the insulation resistance meter 3 or abnormalities in the object to be measured 9.

[0135] In addition, the display unit 33 of the third embodiment displays measurement failure information when the output signal Vd of the voltage detection unit 17 falls outside a specific voltage tolerance range, or when the output signal Vd1 of the output voltage detection unit 31 falls outside a predetermined voltage tolerance range.

[0136] This configuration allows voltage detection unit 17 to detect a measurement failure even in situations where output signal Vd1 does not change due to a malfunction of output voltage detection unit 31. This makes it possible to display the measurement status of insulation resistance meter 3 more accurately than if measurement failure information were displayed only when output signal Vd1 of output voltage detection unit 31 was outside a predetermined voltage tolerance range.

[0137] Furthermore, in the third embodiment, the insulation resistance meter 3 is equipped with a leakage current detection unit 21 that detects the magnitude of the leakage current flowing in from the detection terminal T2 of the insulation resistance meter 3, and the display unit 33 displays measurement failure information if the output signal Vc1 of the leakage current detection unit 21 is outside a predetermined current tolerance range.

[0138] According to this configuration, under constant current control, it is possible to notify the person making the measurement of measurement defects such as component failures in insulation resistance meter 3 or abnormalities in object to be measured 9.

[0139] In addition, the display unit 33 of the third embodiment displays measurement failure information when the output signal Vc of the current detection unit 16A falls outside a specific current tolerance range, or when the output signal Vc1 of the leakage current detection unit 21 falls outside a predetermined current tolerance range.

[0140] This configuration allows current detection unit 16A to detect a measurement failure even in situations where output signal Vc1 does not change due to a malfunction of leakage current detection unit 21. This makes it possible to display the measurement status of insulation resistance meter 3 more accurately than if measurement failure information were displayed only when output signal Vc1 of leakage current detection unit 21 falls outside a predetermined allowable current range.

[0141] Although the voltage detection unit 17 in the above embodiment is configured only with voltage dividing resistors 171 and 172, other passive elements may also be connected. Therefore, a modified example of the voltage detection unit 17 will be briefly described with reference to FIG.

[0142] 5 is a circuit diagram showing a modified configuration of voltage detection unit 17. This modified configuration includes a capacitive element 173 in addition to the circuit configuration of voltage detection unit 17 shown in FIG.

[0143] The capacitance element 173 is an element that compensates for a phase delay that occurs in the voltage detection unit 17 due to the capacitance element 15 and the like, and is a so-called phase compensation capacitor. The capacitance element 173 is connected in parallel to the voltage dividing resistance element 171. The capacitance value of the capacitance element 173 is determined in advance in consideration of the capacitance value of the capacitance element 15 and the like.

[0144] In this way, by arranging the phase compensation capacitance element 173 in the voltage detection unit 17, the phase delay occurring in the voltage detection unit 17 is compensated for, and therefore the phase delay of the output signal of the voltage detection unit 17 can be reduced.

[0145] Therefore, the control unit 19 can maintain the output voltage Vout constant with higher precision than when performing constant voltage control using the output signal of a voltage detection unit that does not have the capacitance element 173 installed.

[0146] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0147] In the above embodiment, the other end of limiting resistor 18 is directly connected to output terminal T1 of insulation resistance meters 1 to 3, but a protective resistor may be connected between the other end of limiting resistor 18 and output terminal T1 of insulation resistance meters 1 to 3. Even in this case, the output signal of current detector 16 or 16A compensates for the voltage drop occurring in limiting resistor 18 and the protective resistor, so that the same effects as those of the above embodiment can be achieved. [Explanation of symbols]

[0148] 1~3 Insulation resistance tester 121 Primary Winding 122 Secondary Winding 13 Switching element 15 Capacitor element 16, 16A current detection section 17 Voltage detection section 18 Limiting Resistor 19 Control Unit 191 Addition Circuit 191A Subtraction Circuit 192 Boost control circuit 20 Low-pass filter 21 Leakage current detection section 31 Output voltage detection section 33 Display section

Claims

1. 1. An insulation resistance meter that detects leakage current flowing through an object to be measured while a DC voltage is applied to the object to be measured, a primary winding to which a voltage from a DC power supply is supplied and cut off by a switching element; a secondary winding having one end connected to a reference potential and the other end connected to the output terminal of the insulation resistance meter; a limiting resistor element connected between the other end of the secondary winding and an output terminal of the insulation resistance meter, for limiting a current input to the output terminal of the insulation resistance meter when a voltage is applied from outside to the output terminal of the insulation resistance meter; a capacitance element having one end connected to one end of the secondary winding and the other end connected to the other end of the secondary winding, the capacitance element constituting a low-pass filter together with the limiting resistance element; a voltage detection unit that detects the magnitude of a voltage between the other end of the capacitance element and one end of the limiting resistance element; a current detection unit that detects the magnitude of a current flowing through the object to be measured; a control unit that controls the operation of the switching element by constant voltage control based on an output signal of the current detection unit and an output signal of the voltage detection unit so that a voltage value of the DC voltage is constant; An insulation resistance tester comprising:

2. 2. The insulation resistance meter according to claim 1, a cutoff frequency of the low-pass filter is lower than the frequency of induced noise superimposed on the output terminal of the insulation resistance meter; Insulation resistance tester.

3. 3. The insulation resistance meter according to claim 2, a capacitance value of the capacitance element is a value determined in advance so that an AC voltage generated in the secondary winding by operation of the switching element is smoothed and the induction noise is suppressed; Insulation resistance tester.

4. 2. The insulation resistance meter according to claim 1, the current detection unit is a resistive element connected between one end of the secondary winding and the reference potential, The output signal of the current detection unit is a voltage signal generated at one end of the secondary winding. Insulation resistance tester.

5. 5. The insulation resistance meter according to claim 4, The control unit an adder circuit that adds a voltage signal generated at one end of the secondary winding and an output signal of the voltage detection unit; a control circuit that controls the operation of the switching element so that the output signal of the adder circuit is constant; Insulation resistance tester.

6. 2. The insulation resistance meter according to claim 1, a leakage current detection unit that detects the magnitude of the leakage current flowing in from a detection terminal of the insulation resistance meter; the current detection unit is a resistive element connected between a detection terminal of the insulation resistance meter and the leakage current detection unit, The output signal of the current detection unit is a voltage signal generated at the detection terminal. Insulation resistance tester.

7. 7. The insulation resistance meter according to claim 6, The control unit a subtraction circuit that subtracts a voltage signal generated at the detection terminal from an output signal of the voltage detection unit; a control circuit that controls the operation of the switching element so that the output signal of the subtraction circuit is constant; Insulation resistance tester.

8. 2. The insulation resistance meter according to claim 1, Another voltage detection unit detects a voltage generated at an output terminal of the insulation resistance meter; a display unit that displays measurement failure information indicating a measurement failure of the insulation resistance when the output signal of the other voltage detection unit is outside a predetermined voltage tolerance range; An insulation resistance tester comprising:

9. 9. The insulation resistance meter according to claim 8, the display unit displays the measurement failure information when the output signal of the voltage detection unit is outside a specific voltage tolerance range or when the output signal of the other voltage detection unit is outside the predetermined voltage tolerance range. Insulation resistance tester.

10. 2. The insulation resistance meter according to claim 1, a leakage current detection unit that detects the magnitude of the leakage current flowing in from a detection terminal of the insulation resistance meter; a display unit that displays measurement failure information indicating a measurement failure of the insulation resistance when the output signal of the leakage current detection unit is outside a predetermined current tolerance range; An insulation resistance tester comprising:

11. 11. The insulation resistance meter according to claim 10, the display unit displays the measurement failure information when the output signal of the current detection unit is outside a specific current tolerance range or when the output signal of the leakage current detection unit is outside the predetermined current tolerance range. Insulation resistance tester.

Images