SU1195288A1 - Dielectric characteristics meter - Google Patents

Description

The invention relates to measuring non-electric values by electrical methods and can be applied when measuring the dielectric characteristics of materials. five

The purpose of the invention is to improve the accuracy of measurement of dielectric characteristics and the expansion of the measurement range.

Fig. 1 shows the block diagram of the dielectric characteristics meter; in fig. 2 is an equivalent circuit of a resonant measuring two-pole device with a primary p measuring transducer; in fig. 3 is a block diagram of a phase locked loop (PLL) unit; on fig 4 - generalized phase response of a short-circuit trigger.

Measuring dielectric characteristics contains a resonant measuring two-terminal 1, primary measuring transducer 2, made in the form of a two-electrode 25 surface-mounted capacitor, controlled capacitance 3 and the equivalent of controlled capacitance 4, which represent two groups of varicaps, common points of which are interconnected, controlled resistance 5 and equivalent controlled resistances 6, which are field-effect transistors, a linear amplifier 7, element

8 positive feedback, block $

9 amplitude stabilization unit 10 phase-locked loop frequency, reference frequency generator 11, capacitor-frequency converter 12, resistance-frequency converter 13, dielectric constant meter 14 and dielectric loss tangent meter 15.

Moreover, the positive feedback element 8 is connected between the input and output of the amplifier 7, the output of which is connected to the input of the stabilization unit 9, the output of which is connected to the controlled resistances 5, 6. The two inputs of the phase locked loop 10 (PLL) are connected to the outputs of the amplifier 7 and the reference frequency generator 11, and the inputs of the meter 15 are connected to the outputs of the converters 12 and 13. 55

Resonant measuring two-terminal 1 with primary measuring converter 2, linear amplifier 7 with element 8 positive

feedback, the amplitude stabilization unit 9 and the controlled resistance 5 form an oscillator, the oscillation amplitude of which is stabilized by shunting the resonant measuring two-terminal 1 controlled by the resistance 5.

The device works as follows.

The primary transducer 2 is placed on the sample under study, which leads to a change in the capacitance and conductivity of the transducer.

A change in the conductivity of the primary measuring transducer 2 causes a change in the conductivity of the controlled resistance 5 and, accordingly, the equivalent of the controlled resistance 6 by the same value. A change in the conductivity ‘of the equivalent of controlled resistance 6 leads to a corresponding change in the output signal of the resistance-frequency converter 13. The change in the oscillation period of the output signal of the resistance-frequency converter 13 is directly proportional to the change in the conductivity of the primary transducer 2.

When the capacitance of the primary measuring transducer 2 changes, the magnitude of the controlled capacitance 3 and the capacitance of the equivalent controlled capacitance 4 change by the same value. Changing the capacitance · equivalent to the controlled capacitance 4 leads to a corresponding change in the output signal of the converter 12 "capacitance-frequency".

The change in the oscillation period of the output signal of the converter 12 "capacitance-frequency" is directly proportional to the change in the capacitance of the primary measuring transducer 2.,

The signal from the output of the converter 12 "capacitance-frequency" is fed to the input of the gauge 14 of the dielectric constant ^ which records the change of the oscillation period of the converter 12 "capacitance-frequency" in units of dielectric constant.

Transmitter Outputs

12 "capacitance-frequency" and the converter 13 "resistance-frequency" are fed to the inputs of the meter 15 tan3

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of the dielectric loss angle, which records the ratio of the signals fed to it in terms of the dielectric loss tangent.

The autogenerator formed by a resonant measuring two-pole 1, primary measuring transducer 2, a linear amplifier 7 with a positive feedback element 8, an amplitude stabilization unit 9 Yu and a controlled resistance of 5, shunting resonant measuring dipole 1 controlled resistance 5 maintains a constant signal amplitude on the resonant measuring dipole 1 and on the primary measuring transducer 2.

The block-10 phase-locked loop frequency 20 and the reference frequency generator 11, tots maintain a constant frequency of the oscillator.

The total conductivity of a resonant measuring two-pole device with a primary measuring transducer ¹ Leu according to the equivalent circuit (see Fig. 2) is defined by the following expression: (1)

* 1 1 g γίΤ

X (ω) where - loss resistance of the primary measuring transducer; 35

K - resistance of parallel losses of the resonant measuring two-port;

С _х - capacity of the primary measuring converter; 40

C is the capacitance of the resonant measuring two-pole;

σ is the inductance of the resonant ’measuring dipole; 45

n is the resistance of consecutive losses of the resonant measuring two-pole in the inductive branch;

ω - working frequency.

Depending on the material, the resistance K _x and the capacitance ϋχ of the primary transducer change.

In the prototype, an amplitude-modulated signal is fed to the resonant measuring two-terminal and to the? ·! the construction of the resonant measuring two-pole is carried out so that

the amplitudes of the two side frequencies were the same. This means that the moduli of the full conductivity of the resonant measuring two-pole device will be the same at both side frequencies.

From expression (1) it can be seen that the real part of the total conductivity depends on the frequency, i.e. the real part of the total conductivity at both side frequencies will be different.

But since the modules of full conductivity are equal, it follows that the imaginary parts of the total conductivity on both side frequencies will be different in magnitude. Consequently, the resonant measuring bipolar will not be precisely tuned to resonance, which causes inaccuracy in determining the dielectric constant.

I The error in determining the dielectric constant depends on the loss resistance of the primary measuring transducer and on the resistance. successive losses of the resonant measuring two-pole and inductive branch, therefore

C _x + C const (2)

In the proposed dielectric characteristics meter using the input of the phase-locked loop and the reference frequency generator, the constant frequency of the oscillator is maintained. And also, based on the fact that the change in capacitance C _{x of the} primary transducer is compensated by changing the capacitance C of the resonant measuring bipolar by the same value, and the change in conductivity 1 / E _{x is} compensated by changing conductivity 1 / H by the same value, we get:

C _x + C = const

V δ ^{= const}

(3)

(four)

Therefore, the inventive meter does not have a methodological error associated with the dependence of the resonant frequency on the active resistance of the circuit and the dependence of the quality factor on the capacitance.

Block 10 phase-locked loop (PLL) consists of the following functional units (see. Fig. 3): controlled capacity (varicap) 16, the oscillator 17, the comparator 18,

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trigger 19, KZ-trigger (phase detector) 20, one-shot 21, one-shot 22, element OR 23, integrating link 24 with correction.

A comparison of the frequencies of the auto-oscillator signals and the reference frequency generator occurs in the phase detector, which is built on a short-circuit trigger 20.

The signal of the reference frequency generator through the one-shot 21 is fed to the input 3 of the trigger 20, and the signal of the oscillator through the comparator 18, the trigger (frequency divider) 19 and the one-shot 22 is fed to the input to the same trigger 20. The output of the phase detector produces a signal whose average value is proportional to integral of the difference of compared frequencies. From the phase detector, the signal pos-20 stumbles on the integrating link 24 with correction, consisting of two current sources 25 and 26, two switches 27 and 28, an integrating capacitor 29, and a correction chain from the capacitor 30 and resistor 31. At the output of this link, we obtain the control voltage, the average value of which is proportional to the double integral of the difference of compared frequencies. This voltage through a controlled capacitance (varicap) 16 affects the frequency of the oscillator 17, bringing it closer to the double frequency of the signal of the reference frequency generator. At = ± 2ΐη, (where 35 η is 0, 1, 2., ..) detector 20 has

indefinite state. To eliminate uncertainty when a phase detector passes the signal through zero, a coincidence block 23 (element OR) selects these points and changes the phase of the oscillator 17 of the generator 17 by 180 ° (trigger 19) in jumps, providing a transition to the middle of the next smooth section of the characteristic . The moment of the jump through the point of uncertainty is determined by the duration of the pulses of one-shot 21, 22. The process of entering the PLL into the hold mode is displayed on the phase response of the detector by arrows (see Fig. 4). It consists in the alternation of a smooth movement to the origin of coordinates along inclined sections and an abrupt transition through points of uncertainty. In the steady state, the inputs of phase detector 20 are fed 180 ° phase-shifted signals (and if the current sources 25 and 26 are identical and there are no leakage currents in capacitors 29 and 30 after the phase detector). The use of second-order PLLs necessitates the introduction of a correction for the characteristics of the integrator. It is made on the capacitor 30 and the resistor 31, which slow down the rotation of the phase of the IZK at higher frequencies in the unit gain band of the system, creating a margin of stability in phase.

-M2

I,

15

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FIG A

Claims (1)

DIELECTRIC CHARACTERISTICS MEASURER, containing a resonant measuring two-pole, primary measuring transducer, controlled capacitance, dielectric loss tangent meter, equivalent of controlled capacitance, capacitance-frequency transducer and measuring dielectric permittivity, characterized in that, in order to improve the accuracy of dielectric measurements and expansion, measurement range, a linear amplifier with a positive feedback element is introduced into it, the amplitude stabilization unit dy controlled resistance equivalent managed resistance unit phase-locked loop, the reference generator and transducer impedance - frequency, and inputs a linear amplifier with an element of positive feedback and controlled resistance connected to the terminals of the resonance measuring two-terminal network, the primary ^- the transmitter and controllable capacitance, yield linear amplifier is connected to the input of the amplitude stabilization unit and with one of the inputs of the phase locked loop, in Ora input coupled to an output of the reference generator block output PLL Cpd. Yen with common points of controlled capacity and equivalent managed capacity, the output of the amplitude stabilization unit is connected to a controlled resistance and equivalent controlled resistance, which is also connected to the converter resistance frequency, the output of which is connected to one of the inputs of the dielectric loss tangent meter, and its second input connected to the output of the converter capacitance - frequency and the input of the dielectric constant meter, the input of the converter capacitance - frequency connected to the equivalent of control Avaya capacity. 1 "1195288’ 2