JP2026000745A - Insulation Resistance Tester - Google Patents

Abstract

An insulation resistance meter that suppresses the effects of induction noise while ensuring the accuracy of constant voltage control is provided.
[Solution] The insulation resistance meter (1) comprises a primary winding (121) to which voltage is supplied and cut off by a switching element (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), a limiting resistor element (18) connected between the other end of the secondary winding and the output terminal of the insulation resistance meter, a capacitor element (15) having one end connected to one end of the secondary winding and the other end connected to the other end of the secondary winding and constituting a low-pass filter (20) together with the limiting resistor element, a voltage detection unit (17) that detects the voltage between the other end of the capacitor element and one end of the limiting resistor element, and a current detection unit (16) that detects a current (Ir) flowing through an object to be measured (9), and a control unit (19) that controls the switching element by constant voltage control based on an output signal -Vb from the current detection unit and an output signal Vd from the voltage detection unit so that the voltage value of the DC voltage remains constant.
[Selected Figure] Figure 1

Description

The present invention relates to an insulation resistance meter that detects leakage current flowing through a measurement object when a DC voltage is applied to the measurement object.

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, part of the output of the voltage doubler rectifier circuit is applied to the oscillator as a detection signal via a voltage divider circuit, and the other part is applied via a protective resistor to a terminal to which one end of the resistor being measured is connected.

Japanese Patent Application Publication No. 4-274768

With the insulation resistance tester described above, induced noise can sometimes enter through the terminal to which one end of the resistor being measured 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 being measured.

The present invention was developed to address these issues, and aims to suppress the effects of induced noise while ensuring the accuracy of constant voltage control.

According to one aspect of the present invention, an insulation resistance meter measures current leaking from a measurement object while a DC voltage is applied to the measurement object. The insulation resistance meter includes a primary winding to which a voltage from a DC power source is supplied and cut off by a switching element, and 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. The insulation resistance meter also includes a limiting resistor element connected between the other end of the secondary winding and the output terminal of the insulation resistance meter to limit the current input to the output terminal of the insulation resistance meter when a voltage is applied to the output terminal of the insulation resistance meter from an external source, and a capacitive 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, forming a low-pass filter together with the limiting resistor element. The insulation resistance meter also includes a voltage detection unit that detects the magnitude of the voltage between the other end of the capacitive element and one end of the limiting resistor element, and a current detection unit that detects the magnitude of the current flowing through the measurement object. The insulation resistance meter also includes a control unit that controls the operation of the switching element using constant voltage control 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 remains constant.

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

However, by placing the voltage detection unit between the limiting resistor and the capacitor, a limiting resistor is placed between the voltage detection unit and the output terminal of the insulation resistance tester. Therefore, even if the operation of the switching element is controlled in accordance with the output signal of the voltage detection unit so that the DC voltage applied to the measurement target remains constant, a control error will occur due to the voltage drop across the limiting resistor.

To address this issue, according to this aspect, the insulation resistance tester uses a current detection unit to detect the magnitude of the current flowing through the limiting resistor element in order to estimate the magnitude of the voltage drop across the limiting resistor element, and incorporates this detection result into the output signal of the voltage detection unit. This reduces control errors caused by the voltage drop across the limiting resistor element.

In addition, even if the low-pass filter is unable to sufficiently remove 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 from the voltage detection unit. This means that the effects of induced noise that cannot be completely removed by the low-pass filter can also be suppressed.

As a result, this aspect makes it possible to suppress the effects of induced noise while ensuring the accuracy of constant voltage control.

FIG. 1 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to a first embodiment. FIG. 2 is an explanatory diagram showing the operation of the insulation resistance meter. FIG. 3 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the second embodiment. FIG. 4 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the third embodiment. FIG. 5 is a circuit diagram showing a modified example of the voltage detection section that constitutes the insulation resistance meter.

Each embodiment of the present invention will be described below with reference to the accompanying drawings. Throughout this specification, the same or equivalent elements will be designated by the same reference numerals.

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

The insulation resistance meter 1 is a measuring device used to measure the insulation resistance of a measurement object 9, such as a household distribution board, power receiving equipment in buildings and factories, 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.

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

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 to be measured 9 by the person performing the measurement.

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 below 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.

For example, when the output voltage Vout is less than 5000 V, the insulation resistance tester 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.

The insulation resistance meter 1 may also 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.

The insulation resistance tester 1 includes a battery 11, a transformer 12 having a primary winding 121 and a secondary winding 122, a switching element 13, a rectifying element 14, a capacitance element 15, a current detection unit 16, a voltage detection unit 17, a limiting resistance element 18, and a control unit 19. The insulation resistance tester 1 also includes a leakage current detection unit 21.

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 terminal of battery 11 is connected to one end of the primary winding 121 of transformer 12, and the negative terminal of battery 11 is connected to ground potential G. Ground potential G here is the reference potential that serves as the basis for operation of insulation resistance meter 1.

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

The primary winding 121 is connected to the input terminal of the switching element 13 to supply and cut off DC voltage from the battery 11. The other end of the primary winding 121 is connected to the input terminal of the switching element 13.

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

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 via the rectifier element 14 to the other end of the capacitance element 15, the voltage detection unit 17, and one end of the limiting resistor element 18.

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.

In the first embodiment, an N-channel metal-oxide semiconductor field-effect transistor (MOSFET) is used 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.

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

Specifically, when an on-voltage is applied to the gate terminal of the switching element 13, the source terminal and drain terminal of the switching element 13 become conductive, and 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 drain terminal of the switching element 13 become non-conductive, and the current supply to the primary winding 121 is cut off.

The rectifying element 14 is an element for converting the 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, with the anode of the rectifying element 14 connected to the other end of the secondary winding 122 and the cathode of the rectifying element 14 connected to the other end of the capacitive element 15.

Capacitance element 15 is an element that smooths the AC voltage generated in secondary winding 122 by the switching operation of switching element 13 and converts the AC voltage to DC voltage together with rectifier element 14; it 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.

The capacitance value of the capacitance element 15 is set so as 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 within the range of several tens of nF to several hundred nF.

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 resistor element 18.

In the first embodiment, the current detection unit 16 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 implemented by a resistive element 161.

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 ground potential G.

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

As a result, 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 resistive element 161. The current detection unit 16 outputs the voltage signal generated at one end of the resistive element 161 as the output signal (-Vb).

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

The voltage detection unit 17 in the first embodiment is a voltage divider circuit composed of voltage-dividing resistor elements 171 and 172 connected in series. 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.

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.

The voltage detection unit 17 outputs the voltage division signal generated at the connection point between the voltage division resistance elements 171 and 172 to the control unit 19 as a detection signal. 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.

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

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.

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.

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.

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

The adder circuit 191 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. The output signal (-Vb) generated at one end of the secondary winding 122 is proportional to the amount of voltage drop across the limiting resistor 18, and the voltage value becomes more negative as the secondary current flowing through the secondary winding 122 increases, and the negative voltage value becomes smaller as the secondary current decreases.

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 resistor element 18 is taken into account, 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.

Then, the adder circuit 191 outputs the output signal Ve, which is the sum of the output signal (-Vb) of the current detection unit 16 and the output signal Vd of the voltage detection unit 17, to the boost control circuit 192. In other words, the adder circuit 191 feeds back an estimated signal of the output voltage Vout to the boost control circuit 192.

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 remains constant. The boost control circuit 192 generates a PWM signal for PWM control of the switching element 13 and supplies it to the gate terminal of the switching element 13.

Specifically, the boost control circuit 192 applies an on voltage to the gate terminal of the switching element 13 so that current is supplied from the battery 11 to the primary winding 121, 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.

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

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

In a processing unit (not shown), the insulation resistance meter 1 calculates the insulation resistance value of the object to be measured 9 using the current value of the leakage current detected by the leakage current detection unit 21 and the voltage value of the output voltage Vout.

Next, the operation of the insulation resistance tester 1 will be explained with reference to Figure 2.

First, the 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.

If there are electrical 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 from 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.

In the insulation resistance tester 1 of the first embodiment, this induced noise is removed by a low-pass filter 20 composed of a capacitive element 15 and a limiting resistor element 18.

In particular, the connection line L1 between the other end of the capacitance element 15 and one end of the limiting resistance element 18 is less susceptible to inductive noise entering from the output terminal T1. Therefore, the output signal of the voltage detection unit 17, which detects the voltage of the connection line L1, is less susceptible to inductive noise than in a circuit configuration in which the voltage detection unit 17 is placed between the other end of the limiting resistance element 18 and the output terminal T1.

As a result, 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 effects of induced noise have been suppressed, allowing the output voltage Vout to be maintained constant with high precision.

However, by placing the voltage detection unit 17 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 connection line L1 to the voltage detection unit 17 and the output terminal T1.

The secondary current Ir flowing through the secondary winding 122 flows through the limiting resistor element 18, causing a voltage drop (Ir x Ro). 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 x Ro) that occurs across the limiting resistor element 18. This voltage drop (Ir x Ro) can reach a maximum of approximately 100 V.

The amount of drop in the output voltage Vout caused by the limiting resistor 18 varies depending on the magnitude of the secondary current Ir. Therefore, if the amount of drop in the output voltage Vout were set to a fixed value, the error between the output voltage Vout and the set value Vset would increase depending on the magnitude of the secondary current Ir.

To address this issue, in the first embodiment, a current detection unit 16 that detects the magnitude of the secondary current Ir is disposed between one end of the secondary winding 122 and ground potential G.

As a result, as the secondary current Ir increases, the voltage drop (Ir x Ro) across the limiting resistor 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.

Similarly, as the secondary current Ir decreases, the voltage drop (Ir x Ro) across the limiting resistor 18 reduces the amount of drop in the output voltage Vout, and the amount of drop in the output signal (-Vb) generated at one end of the secondary winding 122 also reduces.

In this way, the amount of drop in the output voltage Vout due to the voltage drop (Ir x Ro) of the limiting resistor 18 is proportional to the amount of drop from 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.

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 decrease in the output voltage Vout caused by the voltage drop (Ir x Ro) across the limiting resistor element 18 during constant voltage control. In other words, it is possible to maintain a constant output voltage Vout regardless of the magnitude of the secondary current Ir.

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, thereby maintaining the output voltage Vout at the set value Vset.

Furthermore, if the low-pass filter 20 is not able to sufficiently remove inductive noise, the inductive noise will cause the current Ir flowing through the limiting resistor element 18 to fluctuate, which will in turn 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 inductive noise can also be removed by the output signal (-Vb) of the current detection unit 16.

As described above, in the insulation resistance tester 1, the voltage detection unit 17 is placed between the capacitive element 15 and the limiting resistor 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) corrected for the output signal Vd of the voltage detection unit 17 based on the output signal (-Vb) of the current detection unit 16, which takes into account the voltage drop (Ir x Ro) across the limiting resistor element 18. This allows the output voltage Vout to be maintained at the set value Vset with high precision and stability.

Next, we will explain the effects of the first embodiment.

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

The insulation resistance tester 1 also includes a capacitance element 15, one end of which is connected to one end of the secondary winding 122 and the other end of which is connected to the other end of the secondary winding 122, which, together with the limiting resistance element 18, forms a low-pass filter 20; a voltage detection unit 17, which 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, which detects the magnitude of the current flowing through the secondary winding 122.

The insulation resistance tester 1 also 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 DC voltage (Vout) remains constant through constant voltage control.

With this configuration, the voltage detection unit 17 is placed between the limiting resistor element 18 and the capacitor element 15 that make up the low-pass filter 20, so the low-pass filter 20 reduces 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 effects of induced noise on constant voltage control.

However, by placing the voltage detection unit 17 between the limiting resistor 18 and the capacitor 15, the limiting resistor 18 is interposed between the voltage detection unit 17 and the output terminal T1 of the insulation resistance meter 1. For this reason, even if the operation of the switching element 13 is controlled in accordance with the output signal Vd of the voltage detection unit 17 so that the voltage value of the output voltage Vout, which is the DC voltage applied to the object to be measured 9, remains constant, a control error will occur equal to the voltage drop (Ir x Ro) that occurs across the limiting resistor 18.

To address this issue, the insulation resistance tester 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 x Ro) across the limiting resistance element 18. By incorporating the detected result into the output signal Vd of the voltage detection unit 17, the insulation resistance tester 1 can reduce control errors caused by the voltage drop (Ir x Ro) across the limiting resistance element 18.

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

Therefore, according to the first embodiment, it is possible to suppress the effects of induced noise while ensuring the accuracy of constant voltage control.

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

With this configuration, the low-pass filter 20 can accurately remove induced noise superimposed on the output terminal T1 of the insulation resistance meter 1.

Furthermore, according to the first embodiment, the capacitance value of the capacitance element 15 is a predetermined value that smooths the AC voltage generated in the secondary winding 122 by the operation of the switching element 13 and suppresses induced noise.

With 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, together with the limiting resistance element 18, induced noise can be suppressed.

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.

This configuration allows the current detection unit 16 to be realized with a simple circuit configuration.

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 remains constant.

With 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, so 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 remains constant, thereby maintaining the voltage value of the output voltage Vout at a constant value.

In addition, 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 remains constant.

With this configuration, constant current control is performed before constant voltage control is performed, thereby preventing excessive current from being supplied to the object to be measured 9.

Second Embodiment
In the first embodiment, the current detection unit 16 is disposed 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 this is not limitative. Therefore, a second embodiment in which the arrangement of the current detection unit 16 is changed will be described with reference to FIG.

Figure 3 is a circuit diagram showing the circuit configuration of the insulation resistance tester 2 according to the second embodiment.

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

The current detection unit 16A 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 via the secondary winding 122 and the limiting resistor element 18 to the object to be measured 9, and then flows into the leakage current detection unit 21 from the detection terminal T2 of the insulation resistance meter 2.

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 implemented by a resistive element 162. The resistance value of the resistive element 162 is, for example, several hundred Ω, and in the second embodiment, it is designed to be, for example, 500 Ω.

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

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

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 negatively proportional to the voltage drop across the limiting resistor element 18, with the voltage value increasing toward the positive side as the current flowing through the object to be measured 9 increases, and the positive voltage value decreasing as the secondary current decreases.

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 across 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.

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, which is then output to the boost control circuit 192. In other words, the subtraction circuit 191A feeds back an estimated signal of the output voltage Vout to the boost control circuit 192.

The boost control circuit 192 controls the operation of the switching element 13 so that the output signal of the subtraction circuit 191A remains constant. This maintains the output voltage Vout applied to the object to be measured 9 at a set value.

Next, we will explain 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.

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.

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 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.

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

Next, we will explain the effects of the second embodiment.

In the second embodiment, the insulation resistance meter 2 further includes 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 2. The current detection unit 16A is a resistive element 162 connected between the detection terminal T2 of the insulation resistance meter 2 and the leakage current detection unit 21, and the output signal of the current detection unit 16A is an output signal Vc generated at the detection terminal T2, which is connected to one end of the resistive element 162.

With this configuration, the resistor element 162 is placed between the detection terminal T2 of the insulation resistance meter 2 and the leakage current detection unit 21, so the output signal Vc generated at the detection terminal T2 of the insulation resistance meter 2 is negatively proportional to the amount of voltage drop across the limiting resistor element 18.

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

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 remains constant.

With this configuration, the output signal Vc, which indicates a positive voltage value, is negatively proportional to the voltage drop (Ir x Ro) across the limiting resistor element 18. 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, which indicates the estimated value of the output voltage Vout, remains constant, thereby maintaining the voltage value of the output voltage Vout constant.

(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 for the boost control circuit 192, but constant voltage control may not 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.

Figure 4 is a circuit diagram showing the circuit configuration of the insulation resistance tester 3 according to the third embodiment.

Insulation resistance meter 3 includes the circuit configuration of insulation resistance meter 2 shown in Figure 3, as well as an output voltage detection unit 31, a processing unit 32, and a display unit 33.

The output voltage detection unit 31 is a voltage detection unit different from the voltage detection unit 17, and detects the magnitude of the output voltage Vout generated at the output terminal T1 of the insulation resistance meter 3. The output voltage detection unit 31 in the third embodiment is a voltage divider circuit composed of voltage-dividing resistor elements 311 and 312 connected in series with each other.

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 ground potential G.

The output voltage detection unit 31 outputs the divided voltage signal generated at the connection point between the voltage-dividing resistor elements 311 and 312 to the processing unit 32 as the output signal Vd1.

The processing unit 32 acquires the output signal Vd1 from the output voltage detection unit 31, the output signal Vd from the voltage detection unit 17, the output signal Vc from the current detection unit 16A, and the output signal Vc1 from the leakage current detection unit 21.

In constant voltage control, the processing unit 32 determines whether the output signal Vd1 from 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 the 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.

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

Furthermore, if the output signal Vd1 of the output voltage detection unit 31 is outside a predetermined voltage tolerance range, the processing unit 32 outputs measurement failure information indicating an insulation resistance measurement failure to the display unit 33. Possible measurement failures include component failures in the insulation resistance meter 3 or abnormalities in the measurement target 9.

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, for example, based on the set value Vset of the output voltage Vout in constant voltage control, the resistance value Ro of the limiting resistor element 18, and an inherent control error.

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.

In constant current control, the processing unit 32 determines whether the output signal Vc1 from 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 the inherent control error in 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.

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

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, for example, based on the output current setting value and the inherent control error in constant current control.

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.

The display unit 33 displays measurement failure information if the output signal Vd from the voltage detection unit 17 falls outside a specific voltage tolerance range, or if the output signal Vd1 from the output voltage detection unit 31 falls outside a predetermined voltage tolerance range.

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

The insulation resistance meter 3 may be equipped with the current detection unit 16 shown in Figure 1 instead of or in addition to the current detection unit 16A. In this case, the display unit 33 may display measurement failure information when the output signal (-Vb) of the current detection unit 16 is outside a specific voltage tolerance range.

Next, we will explain the effects of the third embodiment.

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 falls outside a predetermined voltage tolerance range.

This configuration allows the operator to be notified of measurement errors, such as component failures in the insulation resistance meter 3 or abnormalities in the object to be measured 9, during constant voltage control.

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.

This configuration allows the voltage detection unit 17 to detect a measurement failure even in situations where the output signal Vd1 of the output voltage detection unit 31 does not change due to a malfunction. Therefore, the measurement status of the insulation resistance meter 3 can be displayed more accurately than if measurement failure information were displayed only when the output signal Vd1 of the output voltage detection unit 31 falls outside a predetermined voltage tolerance range.

In addition, 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.

This configuration allows the operator to be notified of measurement errors, such as component failures in the insulation resistance meter 3 or abnormalities in the object to be measured 9, during constant current control.

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.

This configuration allows the current detection unit 16A to detect a measurement failure even in situations where the output signal Vc1 of the leakage current detection unit 21 does not change due to a malfunction. Therefore, the measurement status of the insulation resistance meter 3 can be displayed more accurately than if measurement failure information were displayed only when the output signal Vc1 of the leakage current detection unit 21 falls outside the specified current tolerance range.

In the above embodiment, the voltage detection unit 17 is composed only of voltage-dividing resistor elements 171 and 172, but other passive elements may also be connected. Therefore, a modified example of the voltage detection unit 17 will be briefly described with reference to Figure 5.

Figure 5 is a circuit diagram showing a modified configuration of the voltage detection unit 17. This modification includes a capacitive element 173 in addition to the circuit configuration of the voltage detection unit 17 shown in Figure 1.

Capacitor element 173 is an element that compensates for the phase delay that occurs in voltage detection unit 17 due to capacitor element 15 and other factors, and is a so-called phase compensation capacitor. Capacitor element 173 is connected in parallel to voltage-dividing resistor element 171. The capacitance value of capacitor element 173 is determined in advance, taking into account the capacitance value of capacitor element 15 and other factors.

In this way, by placing a phase compensation capacitance element 173 in the voltage detection unit 17, the phase delay that occurs in the voltage detection unit 17 is compensated for, thereby reducing the phase delay of the output signal of the voltage detection unit 17.

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

The above describes embodiments of the present invention, but these embodiments merely illustrate some of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

In the above embodiment, the other end of the limiting resistor 18 is directly connected to the output terminal T1 of the insulation resistance meters 1 to 3. However, a protective resistor may be connected between the other end of the limiting resistor 18 and the output terminal T1 of the insulation resistance meters 1 to 3. Even in this case, the output signal of the current detection unit 16 or 16A compensates for the voltage drop that occurs in the limiting resistor 18 and the protective resistor, so the same effects as in the above embodiment can be achieved.

1 to 3 Insulation resistance meter 121 Primary winding 122 Secondary winding 13 Switching element 15 Capacitive element 16, 16A Current detection unit 17 Voltage detection unit 18 Limiting resistor element 19 Control unit 191 Addition circuit 191A Subtraction circuit 192 Boost control circuit 20 Low-pass filter 21 Leakage current detection unit 31 Output voltage detection unit 33 Display unit

Claims (11)

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.