SU822082A1 - Moisture-content meter - Google Patents

Description

The invention relates to a measurement technique, in particular to automatic moisture meters of various media with high and variable electrical conductivity. A resonant capacitance meter is known, which contains a high-frequency voltage generator, a resonance, an alternating LC circuit, a high-frequency oscillator loading, a voltmeter measuring a high-frequency voltage on the circuit; and a tuning indicator at resonance. A working capacitance cell, a graduated lossless capacitor replacing the sensor capacitance measurements, and non-reactive resistance are connected to the LC circuit. This device stabilizes active losses by maintaining a constant high frequency voltage level on the circuit when the cell is empty and filled with the test substance by changing non-reactive resistance. A disadvantage of this device is the need to shunt the primary converter (LC circuit with capacitive cell) non-reactive resistance. In this case, the total conductivity of the LC circuit is always greater than the maximum conductivity of the sensor with the test substance, which leads to a decrease in the accuracy of capacitance measurement in the study of substances with a wide range of electrical conductivity measurement. Closest to the proposed device for measuring humidity, which contains a parallel measuring circuit consisting of an inductor, a capacitive sensor, a semiconductor modulating capacitance and a capacitor that compensates for the measurement of the capacitance of the sensor; high frequency generator; modulator, demodule tor. phase-sensitive amplifier 2J. A disadvantage of this device is a decrease in sensitivity due to a decrease in the steepness of the static characteristic of the oscillating circuit when the loop is shunted by the resistance of the active loss of the test substance, which leads to a decrease in the accuracy of humidity measurement. The reduction in the sensitivity of this device is due to the fact that the overall gain in the feedback loop, installed with an empty capacitance sensor, based on the requirements of stability, when the sensor is filled with a lossy substance, decreases due to a decrease in the slope of the static characteristic (transfer coefficient) measuring circuit.

The purpose of the invention is to improve the accuracy of moisture measurement in a wide range of active losses of the test substance.

To achieve this goal, a moisture sensor containing a capacitive sensor included in a measuring LC circuit with a modulating capacitor, a generator, a coupling element of a generator with a measuring LC circuit, a modulator, a demodulator, a phase-sensitive amplifier and a compensating capacitor are additionally introduced included amplitude detector, functional transducer and multiplier, with the amplitude detector hof connected to the LC measuring circuit, the second multiplier input connected to the demodulator, and the multiplier output is connected to the input of the phase-sensitive amplifier.

The drawing shows a functional diagram of the proposed device.

The device consists of a measuring circuit 1 consisting of an inductance coil 2, a capacitive sensor 3, a modulating capacitance 4 and a compensating capacitor 5, one input through a coupling element 6 connected to an RF voltage generator 7, another input - to a modulator 8, and output - with a demodulator 9 and an amplitude detector 10, the output of which is connected to the input of the functional converter 11. The multiplier 12 is connected to the output of the functional converter 11 by the first input, the second input to the output of the demodulator 9, and the output to the phase input Sensitivity of the amplifier 13, whose output is connected through mehancheskoy communication with compensating emkostk) 5.

The device works as follows.

The measuring-circuit 1 receives a high-frequency voltage of a fixed frequency from the generator 7 through the communication element. The modulation is carried out by periodically changing the capacitance of the modulating varicaps block 4. The modulating varicaps control the modulating varicaps. 1 RF voltage is amplitude-modeled. Low Frequency Envelope

 n is allocated by demodulator 9 and

arrives at the second input of the multiplier 12. The average high-frequency voltage and „present on the measuring circuit 1, is detected by the amplitude detector 10 and is fed to the input of the functional converter 11.

The output voltage from the multiplier is 12,

DM U equal .. l, is fed to the input faIJ

; A sensitive amplifier 13. The voltage from the output is phase-sensitive. amplifier 13 is equal to

5 K ,. where Kg is the amplification factor of the phase-sensitive amplifier, controls the change in the e L of the compensating capacitor To.k, so that the voltage of the low-frequency envelope Yz tends to zero, i.e. the system is brought to equilibrium and measuring LC circuit 1 is tuned to the frequency of RF generator 7.

The total gain of the automatic loop tuning system in resonance along the feedback loop is equal to

42ii; -,

where is the speaker

sensor capacity increment;

t, and

the change in the output voltage of the phase-sensitive amplifier according to the increment of the capacitance HC;

To the transfer coefficient of the measuring LC circuit;

to"

demodulator transmission coefficient;

1 / and multiplier transfer coefficient 5; transmission factor soothing amplifier.

It follows that the overall gain of the system for automatically adjusting the loop to resonance does not depend on the voltage on the measuring loop, and consequently, on the active loss of the test substance.

Claims (2)

Invention Formula A device for measuring the humidity of substances with high and variable electrical conductivity, containing a capacitive sensor included in a measuring LC circuit with a modulating capacitor, a generator, a communication element of a generator with a measuring LC-circuit, modulator, demodulator, phase-sensitive amplifier and compensating capacitor, differing in that, in order to improve the accuracy of humidity measurement in a wide range of active losses, a series-connected amplitude detector, a functional converter and a multiplier are added, and the input the amplitude detector is connected to the measuring LC circuit, the second input of the multiplier is connected to the demodulator, and the output of the multiplier is connected to the input of the phases of the sensing amplifier. Sources of information taken into account in the examination 1, Aime F. Dielectric measurements. M., Himi, 1967, p. 34 2. Measuring equipment, 1976, No. 7, p. 75-78 (prototype).