RU2029965C1 - Capacitive sensor dielectric loss measuring device - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: capacitive sensor dielectric loss measuring device has voltage source 1, master frequency oscillator 2, reference voltage shaper 3, reference voltage modulator 4, phase detector 5 and 6, modulators 7 and 8, reference resistance box 9, second power amplifier 10, amplifier 11, integrators 12 and 13, display 14, first power amplifier 15, switch 16 reference capacitor C_o, and feedback capacitor C₁. EFFECT: improved measurement accuracy due to provision for AC measurements including loss caused by not only throughput conductivity current but also by dielectric loss of polarization and measurement of capacitive sensor parameters using three-pole circuit connection. 4 dwg

Description

 The invention relates to devices for measuring electrical quantities and can be used to measure dielectric losses in capacitor sensors and connecting lines, for example, electric capacitive fuel meters.

 Capacitor sensors designed to measure the dielectric constant are included in the measuring circuits of electric capacitance fuel meters with alternating current and provide information about the electric capacitance of the capacitor. Dielectric losses caused by partial electrical conductivity of the fuel, contamination of the fuel and the structural elements of the sensors, poor-quality insulation of the connecting line, worsen the reliability and accuracy of the readings of electric capacitive fuel meters. Therefore, during operation, it is required to check the dielectric loss of the capacitor sensors and the connecting line.

 Known devices for checking dielectric loss or insulation quality, for example, megohmmeters F4101 / 1 GOST 23706-79 or M4100 GOST 22261-76, in which the measurement is carried out according to a two-pole circuit for connecting the control object at constant current and at high voltages of 100 V or more.

 The well-known universal bridge E7-4, which measures the resistance value at direct and alternating current of 100 Hz from 0.1 Ohm to 10 MOhm with a supply voltage of the bridge 3.5 V with an error of ± 2%, but is not automatic, does not allow to separately measure the value resistances connected in a triangle, in the presence of a shunt capacitor.

 Instruments 4270A (manufactured in the USA) and MTsE-9A [1] measure C, q and t gδ and are not suitable for measuring dielectric losses directly in the form R.

 It is also known a device ("Radio", 1984, N 1), the basis of which is a DC amplifier, for measuring direct current.

 The direct current measurement has a significant drawback, since in this case the dielectric polarization losses in the sensors cannot be determined, which change with a change in the frequency of the alternating current. In addition, measurements are made according to the bipolar scheme of connecting the sensor without taking into account the shunt capacitance, while separately the components of the resistances connected in a triangle cannot be measured.

 The aim of the invention is to improve the accuracy of measuring the dielectric loss of capacitor sensors.

This goal is achieved by the fact that in the device for measuring the dielectric loss of capacitor sensors, containing a voltage source, an amplifier and an indicator, a driving frequency generator, a voltage driver, the first and second phase detectors, the first and second integrators, the first and second modulators, the reference modulator are introduced voltage, the first and second power amplifiers, a switch, a block of reference resistances, a reference capacitance and a feedback capacitance, the conclusions of which are connected respectively to the input and the output of the amplifier, the outputs of the reference capacitance are connected to the output of the second power amplifier and the input of the amplifier, the output of which is connected to the inputs of the first and second phase detectors, the outputs of which are connected respectively to the inputs of the first and second integrators, the outputs of which are connected respectively to the inputs of the first and second modulators, the outputs which are connected respectively to the inputs of the first and second power amplifiers, the output of the first power amplifier is connected to the first input of the switch, the second input of which is connected to the course of the amplifier and the output of the reference impedance block, the input of which is connected to the output of the reference voltage modulator, the input of which is connected to the control input of the second modulator and the fifth output of the reference voltage shaper, the input of which
connected to the output of the master frequency generator, the input of which is connected to the output of the voltage source, the first, second, third, fourth and sixth terminals of the voltage driver are connected respectively to the first and second control inputs of the second phase detector, with the first and second control inputs of the first phase detector and the control input of the first modulator, the third input of the switch is connected to the ground bus, and the first, second and third outputs of the switch are the first, second and third outputs of the device One indicator is connected to the output of the first integrator.

 In this case, the master frequency generator and the driver of the reference voltage are designed to generate the reference voltages necessary to control the modulators and phase detectors. Phase detectors and integrators for active and reactive components are designed to separate the amplified unbalance signal of the measuring bridge and integrate them into orthogonal components. Modulators are introduced to generate feedback voltages of the circuits along the active and reactive components. Power amplifiers are designed to amplify feedback signals of circuits for active and reactive components. A set of reference resistances is introduced to measure the limits of measurement of the triangle of the total conductivity of the sensor.

 In FIG. 1 shows a structural diagram of the proposed device for measuring the dielectric loss of capacitor sensors; in FIG. 2 is an equivalent sensor circuit; in FIG. 3 - equivalent circuit of the bridge; in FIG. 4 - time diagrams of the operation of the device.

The proposed device for measuring the dielectric loss of capacitor sensors contains a voltage source 1, a driving frequency generator 2, a driver 3 of the reference voltage, a modulator 4 of the reference voltage, the first and second phase detectors 5, 6, modulators 7, 8, block 9 of the reference impedances, the second power amplifier 10, amplifier 11, first and second integrators 12, 13, LED 14, the first power amplifier 15, switch 16, reference capacitance C _0, and a feedback capacitor C _1, the conclusions of which are connected respectively to the input and output y ilitelya 11, the conclusions of the reference capacitance C ₀ connected to the output of the second power amplifier 10 and the input of an amplifier 11 whose output is connected to inputs of the first and second phase detectors 5, 6, whose outputs are connected to inputs of the first and second integrators 12, 13, the outputs of which connected respectively to the inputs of the first and second modulators 7, 8, the outputs of which are connected respectively to the inputs of the first and second power amplifiers 15, 10, the output of the first power amplifier 15 is connected to the first input of the switch 16, the second input of which ohm is connected to the input of the amplifier 11 and the output of the reference impedance block 9, the input of which is connected to the output of the reference voltage modulator 4, the input of which is connected to the control input of the second modulator 8 and the fifth output of the reference voltage shaper 3, the input of which is connected to the output of the frequency generator 2, input
which is connected to the output of voltage source 1, the first, second, third, fourth and sixth outputs of the reference voltage driver 3 are connected respectively to the first and second control inputs of the second phase detector 6, with the first and second control inputs of the first phase detector 5 and the control input of the first modulator 7, the third input of the switch 16 is connected to the ground bus, and the first, second and third outputs of the switch 16 are the first, second and third outputs of the device, the input of the indicator 14 is connected to the output of the first egratora 12.

The master frequency generator 2 is made according to the multivibrator scheme, the driver 3 of the reference voltage is composed of a multivibrator with an emitter follower, two counters on IK triggers, a decoder on two-circuit matching circuits and a power amplifier. In this case, the device generates six consecutive pulses, the time and phase relationships of which are presented in the diagram (Fig. 4). Changing the duty cycle of pulses f ₁ , f ₂ and introducing slots at f ₃ , f _{4 is} necessary to exclude the influence of transients at the fronts E, U _R ^oc , U _c ^oc when they are added at the input of amplifier 11.

 The reference voltage modulator 4 is configured as an amplitude modulator on a 140 series op amp. The voltage of the reference frequency controls the state of the electronic switch connected to the amplifier input. Modulators 7, 8 are amplitude modulators on the op amp. Phase detectors 5, 6 can be performed by a half-wave detection scheme.

 The indicator 14 is a DC voltmeter MCH200, the scale of which is calibrated taking into account the multiplier indicated on the switch of measurement limits.

The switch 16 is a galette switch, with which the resistance R ₁ , R ₂ , R ₃ (figure 2) are alternately connected between the input of the amplifier 11 and the output of the power amplifier 15. Switching the reference resistances, and therefore the measurement limits, is carried out by electronic keys controlled by from the dial switch (switch 16).

In general, the proposed device is a bridge circuit with balancing the active and reactive components. The equivalent circuit of the bridge (Fig. 3) includes a reference resistance R ₀ and a capacitance C ₀ (device 9 and C ₀ , in Fig. 1); measured resistance R _x and capacitance C _x ; wherein U is the voltage at the outputs of the device 10 and 15; With _I - the input capacity of the device 11; E _about - the reference voltage specified by the device 4; shoulder U _R ^OS - corresponds to blocks 5, 12, 7, 15 in FIG. 1, the shoulder U _with ^os - corresponds to blocks 6, 13, 8, 10 in figure 1.

Отсюда U $\genfrac{}{}{0ex}{}{\text{o}}{\text{R}}$ ^c=

R_x напряжение, которое формируется детектором 5 и интегратором 12 и индицируется индикатором 14. Напряжение U_с ^ос компенсирует емкостной ток С_х. Из приведенной формулы видно, что величина напряжения U_R ^oc обратно пропорциональна величине эталонного сопротивления R_о. Таким образом, изменение пределов измерения достигается изменением величины R_о.The equilibrium of the two-coordinate bridge is determined from the circuit shown in figure 3, the following relationships:

From here u $\genfrac{}{}{0ex}{}{\text{o}}{\text{R}}$ ^c =

R _x voltage, which is generated by the detector 5 and the integrator 12 and is indicated by the indicator 14. The voltage U _with ^OS compensates for the capacitive current C _x . From the above formula it is seen that the voltage U _R ^{oc is} inversely proportional to the value of the reference resistance R _about . Thus, a change in the measurement limits is achieved by changing the value of R _about .

The proposed device for measuring the dielectric loss of capacitor sensors works as follows. From the master frequency generator 2, pulses of frequency f _about and duty cycle 2 are supplied to a voltage driver 3, which generates six consecutive pulses f ₁ . . . f ₆ , designed to control phase detectors 5, 6 and modulators 7 and 8. The reference voltage E is generated by the reference voltage modulator 4 and is supplied to a set of reference resistances 9, switched depending on the selected limits using electronic keys (not shown in Fig.) . The input signal (bridge mismatch voltage) is supplied to an amplifier 11 with a low capacitive input impedance, covered by deep negative feedback C ₁ to reduce the influence of the unmeasured component of the resistance triangle (Fig. 2). From amplifier 11 the signal is fed to phase detectors 5 and 6. The first phase detector control feedback loop 5 of the active component carried voltages f ₃ and f _4, which are phase shifted by ¹⁸⁰ ° relative to each other.

Management second feedback loop of the phase detector 6 to the reactive component is performed voltage pulses f ₁ f ₂ and whose phases are shifted from each other by ¹⁸⁰ ° with respect to the voltage pulses and f _3, f ₄ to ^about 90. At the output of the phase detectors 5, 6, signals are generated that carry information about the degree and sign of the imbalance of the bridge, which are supplied to the integrators 12, 13, respectively. From the output of the first integrator 12 of the feedback loop for the active component, the DC signal is supplied to the indicator 14. DC voltages from integrators 12 and 13 are supplied to the modulators 7, 8 in antiphase, respectively, and are amplified by power to match the load. The voltage U _R ^oc supplied to the sensor-controlled capacitor, the voltage U _R ^oc - by reference capacitance C _o.

To fulfill the equilibrium condition of the measuring bridge, it is necessary that the voltages U _C ^oc and E are out of phase with the voltage U _R ^oc . The switch selects the type of work: measuring the insulation resistance of the sensor, measuring the insulation resistance between the sensor plates and the ground. A control object is connected to the switch 16, for example, a sensor, the equivalent circuit of which is shown in FIG.

 Improving the measurement accuracy is achieved as follows.

 Measurement with alternating current provides an objective control of dielectric losses, since it allows you to take into account losses caused not only by through-current conductivity, but also by dielectric polarization losses; in addition, a capacitor sensor is measured according to a three-pole switching circuit with the possibility of separate measurement of resistances connected in a triangle, regardless of the capacitance of the capacitor sensor.

The connection of the measured sensor is as follows (see Fig. 1 and 2). The measured resistance is connected to the input of the amplifier 11 and the output of the power amplifier 15 while simultaneously grounding unmeasured resistances:
when measuring R ₁ grounded R ₂ , R ₃ ,
when measuring R ₂ grounded R ₃ , R ₁ ,
when measuring R ₃ grounded R ₁ , R ₂ .

 Thus, when compared with the prototype, the proposed device for measuring the dielectric loss of capacitor sensors significantly increases the accuracy of the measurements.

Claims (1)

 DEVICE FOR MEASURING DIELECTRIC LOSSES OF CAPACITOR SENSORS, containing a voltage source, an amplifier and an indicator, characterized in that, in order to improve the measurement accuracy, a driving frequency generator, a voltage driver, the first and second phase detectors, the first and second integrators, the first and second modulators, a reference voltage modulator, first and second power amplifiers, a switch, a block of reference resistances, a reference capacitance and a feedback capacitance, the terminals of which are connected respectively, to the input and output of the amplifier, the outputs of the reference capacitance are connected to the output of the second power amplifier and to the input of the amplifier, the output of which is connected to the inputs of the first and second phase detectors, the outputs of which are connected respectively to the inputs of the first and second integrators, the outputs of which are connected respectively to the inputs of the first and the second modulators, the outputs of which are connected respectively to the inputs of the first and second power amplifiers, the output of the first power amplifier is connected to the first input of the switch, second the input of which is connected to the input of the amplifier and the output of the reference impedance unit, the input of which is connected to the output of the reference voltage modulator, the input of which is connected to the control input of the second modulator and the fifth output of the reference voltage driver, the input of which is connected to the output of the master frequency generator, the input of which is connected to the output of the voltage source, the first, second, third, fourth and sixth outputs of the driver of the reference voltage are connected respectively to the first and second control inputs of the second phase detector, with the first and second control inputs of the first phase detector and the control input of the first modulator, the third input of the switch is connected to the ground bus, and the first, second and third outputs of the switch are the first, second and third outputs of the device, the indicator input is connected to the output of the first integrator .

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