SU457023A1 - Automatic concentration meter - Google Patents

Description

one

The invention relates to the field of material research using electrical detection means and can be used for continuous automatic measurement, for example, asbestos content in waste.

The known automatic meter comprises a high-frequency generator associated with three resonant circuits, a capacitive differential sensor included in two respectively disturbed oscillating circuits, a phase detector and a recording instrument.

In order to improve the measurement accuracy by automatically compensating for the thickness of the material under investigation on the measurement results in the appropriately detuned contours of the measuring device, in addition to the differential capacitive sensor, a differential inductive sensor is included, which stabilizes the operating points of the contours when the sensor capacitance changes. Structurally, the sensor ECAs are combined into one inductive-capacitive differential sensor.

FIG. 1 is a schematic diagram of the device; in fig. 2-: the principle of compensation for changes in the thickness of the material under study.

An automatic component concentration meter consists of a high frequency generator 1; resonant circuits 2-4, communication coils 5-7; high-frequency transformers 8, 9, detectors 10, 11 and indicating device. Loops 2, 3 have a completely similar circuit and leads for connecting an inductive-capacitive differential sensor with an inductive coil of 12 IK electrodes 13-15. The electrodes 13, 14 and the differential inductive coil 12 are mounted on a dielectric plate 16 that is movable relative to the electrode 15. The sensor is designed as a single unit and is closed by a common sKpaiHOM to eliminate mutual induction from the coils 17 and 18.

Contour 4 has a higher Q value than contours 2 and 3 and is designed to eliminate zero point drift when the circuit parameters change under the effect of temperature, humidity and frequency fluctuations.

The electrode is made in the form of a fixed metal grounded plate. The electrodes 13, 14 and the inductive differential sensor with an inductive coil 12 are placed above the electrode 15 in such a way that under the action of its own weight they lie on the surface of the material under study.

In the absence of material between the sensor electrodes, the working points of circuits 2, 3 are respectively at points A and B, and co; Ntur 4 has a constant signal on the resonant frequency of the measuring generator

(Fig. 2). In this case, the currents of circuit 2, i.e. li, and circuit 3, i.e. Iz, coming into the primary winding of the transformer 8, are equal in magnitude and opposite in direction. In these conditions, the instrument arrow is in the zero position. If the tested sample 19 is placed between the electrodes of the sensor, then points A кон B of circuits 2, 3 move to points A and B, respectively, the current in circuit 4 will increase by A / i, the current in circuit 3 will decrease by A / 2. As a result, the arrow of the ammeter will show the deviation corresponding to D / 1 + -f A / 2. Therefore, the change in capacitance can be determined from this signal. However, it is known that the capacity of a two-plate parallel capacitor is defined by the expression:

0.88E5

Q

t.

where C is the capacitance of the capacitor, pf;

E is the dielectric constant of the material between the capacitor plates;

S is the area of the plates, is the distance between the capacitor plates, mm.

It can be seen from the formula that, at a constant area of the plates, the capacitance of the capacitor depends on the dielectric constant of the material under study and on the distance between the plates, which depends on the thickness of the sample under study. The inductance of the sensor with the inductive coil 12 depends on the distance from its grounded metal plate 15. The inductance decreases with decreasing distance tji and the capacitance of the sensor increases. But since the working point of the contour (or frequency) is determined from the expression:

/ slave -

2t. ALpC

Where

L Lk (.L.)

 Lk + (Lg ± D1)

Cp-C, + (C, ± DS),

then, in the proposed device, a decrease in the thickness of the sample under study (suppose that the sample did not change) causes a decrease in the interelectrode distance / x. which causes an increase in sensor capacity and

reduction of its inductance. Increasing the distances causes an increase in inductance and a decrease in capacitance. Selecting the parameters of inductance and capacitance of the sensor so that the working points A and B

they returned (due to the change in inductance) to points A and B, ensuring that a change in the thickness of the spa of the sample under study does not cause a measurement error.

Subject invention

An automatic concentration meter containing a high frequency generator associated with three resonant circuits, a capacitive differential sensor,

an inductance coil, a phase detector and a recording device, characterized in that, in order to increase accuracy by automatically compensating for the influence of the thickness of the test substance on the measurement results, the inductor, whose core is rigidly fixed, is located on one of the plates of the capacitive sensor and is mechanically connected with it, and the capacitive differential sensor is connected to the circuit in parallel with the inductor, which is an additional sensor.

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with.

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