JPH0564782U - Insulation resistance / voltage converter - Google Patents

Abstract

(57) [Abstract] [Purpose] When converting the insulation resistance of a dielectric to a voltage, the charge and discharge of the dielectric is accelerated and noise is reduced. [Configuration] A charging / discharging power supply, a non-linear resistance, a non-measurement dielectric, and a current / voltage converter were connected in series. The non-linear resistance shows a low value at the beginning of charge and discharge, and is selected as a value at which the measurement error reaches an allowable value at the end. The current / voltage converter is a capacitance feedback / integrator, and the product of the capacitance value of this capacitance and the resistance value of the nonlinear resistance when a low voltage is applied is selected to be a certain value or more.

Description

[Detailed description of the device]

[0001]

[Technical field of invention]

 The present invention relates to measurement of a dielectric material, and more particularly to conversion of insulation resistance value into voltage value.

[0002]

[Prior art and problems]

 In electronic parts such as capacitors and printed circuit boards, and mechanical parts such as plastics, their electrical insulation resistance is an important factor in trade as one of the parameters showing quality. Therefore, various measures have been taken for the measurement. Of these, the part that converts the insulation resistance into voltage is particularly important, and the converters shown in FIGS. 2 and 3 have been used conventionally. It should be noted that in FIG. 1, FIG. 2 and FIG. 3, the components having the same reference numbers have the same function. In FIG. 2, the output voltage of the charging / discharging power source 1 which is also the power source for measurement is the discharge voltage (usually zero) or the charging voltage (usually the measured voltage V of the device under test 3)._m), Power supply resistance 2 (resistance value R_s), The device to be measured 3 having an insulation resistance and the resistor 4 for detecting current (resistance value R_m) Is applied to the series circuit. The device under test 3 is described as a capacitive device for convenience of explanation of the present invention, but in general, it can be replaced by any dielectric material. When the charging of the device under test 3 is substantially completed, the insulation resistance R of the device under test 3 _x And output voltage V appearing between the terminals of resistor 4_oThe relationship is as follows. V_O= V_mR_m/ (R_s+ R_m+ R_x) V_m, R_m, R_sIs known, R_xIs calculated by the following equation. R_x= V_mR_m/ V_O-R_s-R_m Voltage V_OHigh precision can be easily obtained by measuring R_xTo V_OInsulation resistance / current converter to convert to R_xIt can be said that the measurement accuracy of is substantially determined. In the circuit of FIG. 2, R_xBecomes larger V_OR to reduce the decrease in_mAnd V_mIn order to increase the_mC_x; However, C_xIs the value of the parallel capacitance component of the device under test 3) becomes large, and V_OThe noise contained in becomes large. The main reasons are that the impedance of the entire circuit is increased and it becomes easier to receive external noise, and that the noise generated by the resistor 4 is increased. In order to eliminate the above-mentioned drawback of FIG. 2, in the integrating converter of FIG. 3, a feedback capacitor 6 (capacitance value C is provided between the inverting input terminal and the output terminal 7 of the high input impedance amplifier 5)._f2) and a switch 8 connected in parallel, and the resistor 4 in FIG. 2 is replaced by an integrator having a non-inverting input terminal grounded. The switch 8 is closed to charge the device under test 3, the switch 8 is opened after the charging is completed, and appears at the output terminal 7 after T seconds. Voltage V_oTo measure. V_oIs given by C_fV_o= V_mT / (R_s+ R_x) Therefore R_xIs given by R_x= V_mT / (C_fV_o) -R_s However, external noise v_nWhen is present and is equivalently added to the output of the charging / discharging power supply 1, the result is as follows. v_nIs a line spectrum derived from a commercial power source, and has an absolute value V_n, Angular frequency ω _n , Then V_oV added to_nIngredient is R_sω_nC_xWhen is much smaller than 1, V_nC_x/ C_fAnd R_sω_nC_xWhen is much larger than 1, V_n/ (Ω_nC_fR_s). C_x/ C_fCan easily exceed 100 (eg C_x= 1 μF, C_f= 0.01 μF), generally R_sChoose a large enough. However_,This way C_xCharging and discharging time constant (C_xR_s) Becomes large and it becomes difficult to convert quickly. Also, the required R_sValue of ω_nAnd C_xIt is desirable to change with_,In prior art devices R_sIs the value of R_xIt is set by the expected value of.

[Problems to be solved by the device]

 The purpose of the present invention is to connect a non-linear resistance in series to the device under test to speed up the charging / discharging of the non-measurement device, and to easily improve the signal-to-noise ratio when converting the insulation resistance to voltage. Is.

[Means for Solving the Problems]

 In the present invention, in the circuit of FIG. 2, a non-linear resistance in which a high resistance is connected in parallel to an anti-parallel connection of low leakage current diodes and a series connection of low resistance is connected in series to the device under test 3. Therefore, when a high voltage is applied to the non-linear resistance, the resistance value is low and it is high when a low voltage is applied. Therefore, the charge / discharge speed at the beginning of charge / discharge is increased, and the output noise at the end of charge / discharge is reduced.

【Example】

 FIG. 1 is a schematic circuit diagram of an insulation resistance / voltage converter according to an embodiment of the present invention. The charging / discharging power supply generates an arbitrary voltage from 1V to 1000V and generates a power supply resistance 20 (resistance value R _S ), Through the smoothing capacitor 13, and further through the non-linear resistance 15, it is applied to the device under test 3. The value of the power supply resistor 20 is 1 kΩ, and the value of the smoothing capacitor 13 is 0.01 μF. The connection of the high input impedance amplifier 5 is the same as in FIG._fIs 1 pF to 0.1 μF, R_xIt is selected according to (the insulation resistance of the device under test 3) and the input current that changes due to charging and discharging. Immediately, a low capacitance value is selected at a low input current, and the required integration time T is set to a desired value (for example, 0.1 to 10 seconds). The nonlinear resistor 15 is configured by connecting a resistor 10 (several hundred kΩ to 100 MΩ) in parallel to a series connection of an antiparallel diode pair 11 and a resistor 12 (10 kΩ). The resistor 12 is for limiting the current flowing through the anti-parallel diode pair 11 during charging and discharging. A resistor for limiting the current flowing through the diode pair 11 may be provided outside the nonlinear resistor 15 in series with the device under test, for example. _n And angular frequency ω_n, The capacitance value C of the device under test 3_xIn the case of replacement with another device, it is troublesome to consider the resistance for limiting the current. Now, the noise that is not smoothed by the resistor 20 and the smoothing capacitor 13 is the magnitude V_nIs the angular frequency ω_nAnd the resistance values of the resistor 20, the resistor 10, the resistor 12, and the device under test 3 are R respectively._s, R_Ten, R₁₂, R_xAnd the capacitance values of the device under test 3 and the feedback capacitance 6 are C_xAnd C_fAnd The switch 8 is closed to set the output voltage of the charging / discharging power source 1 to a predetermined value V._mThen, the device under test is started. Initial charging time constant is R₁₂C_xThen, just before charging is completed, R_TenC_xBecomes The same applies to the case of discharging. If accurate conversion is desired, the waiting time from the start of charging to the start of conversion is V_mWhen is small, it becomes quite long. V_mIf the voltage exceeds 100V, R₁₂And R_TenSince the charging is accelerated at the ratio of, the waiting time can be 10 to 1/100. When the charging is completed, the switch 8 is opened and after T seconds, the output voltage of the amplifier 5 is read as the voltage corresponding to the insulation resistance. The output voltage at that time is V_OThen V_O Is the following formula. C_fV_O= TV_m/ (R_s+ R_Ten+ R_x) Generally R_s+ R_TenIs R_xSince it is sufficiently smaller than, the above equation is further approximated by the following equation. CV_O= TV_m/ R_x Next, noise V_nIs included in the output, but its magnitude V_onIs the following equation. V_on= V_n/ (R_TenC_fω_n) However, R_TenC_xω_nIs sufficiently larger than 1. V_OThe full scale value of V_ofAnd above V_onTo V_ofIf α times, then the following equation holds. V_n/ (R_TenC_fω_n) <ΑV_of Therefore, R_TenC_f> V_n/ (Ω_nV_ofα) Generally, α = 0.01 or less, so R_TenC_f> 100V_n/ (Ω_nV_of) Becomes. R_TenShould be as small as possible, so the above formula often gives the lower limit. V_n= 2_mV, V_of= 10V, ω_n= 2π × 50, R_TenC_fThe lower limit of is 6.64 × 10^-FiveΩF. C_f= 100pF, R_TenThe lower limit of is 664 kΩ.

[Effect of the device]

 As described in detail above, by implementing the present invention, the insulation resistance of the dielectric can be converted at high speed and with high accuracy. Moreover, it is easy to select an additional resistor for noise reduction.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of an insulation resistance / voltage converter according to an embodiment of the present invention.

FIG. 2 is a schematic circuit diagram of a conventional insulation resistance / voltage converter.

FIG. 3 is a schematic circuit diagram of another example of a conventional insulation resistance / voltage converter.

[Explanation of symbols]

 1: Charge / discharge power supply 2: Power supply resistance 3: Element to be measured (having converted insulation resistance) 4: Resistance for current detection (provides conversion output) 5: High input impedance amplifier 6: Feedback capacitance 7: Conversion output terminal 8: Switch 10: Noise reduction resistor 11: Low leakage current anti-parallel diode pair 12: Current limiting resistor 13: Smoothing capacitor

Claims (2)

[Scope of utility model registration request] 1. An insulation resistance / voltage conversion having the following characteristics (a) to (b), which is formed by connecting a charge / discharge power supply, a non-linear resistance, a device under test, and a current / voltage converter in series to form a loop. vessel. (A) The current / voltage converter connects a feedback capacitance to a high input impedance amplifier, integrates the input current, and gives a voltage output. (B) The non-linear resistance is formed by connecting the first resistance in parallel to the series connection of the anti-parallel connection diode pair and the second resistance. 2. The insulation resistance / voltage converter according to claim 1, wherein the product of the resistance value of the first resistor and the capacitance value of the feedback capacitance is selected to be larger than the value of the following equation. 100 V _n / (ω _n V _of ) where V _n and ω _n are the amplitude and angular frequency of the noise superimposed on the output of the charging / discharging power supply, and V _of is the full-scale value of the terminal voltage of the feedback capacitance. ..