SU767522A1 - Capacitance flow rate transducer - Google Patents

Description

(54) CAPACITIVE FLOW CONVERTER

The invention relates to a measurement technique, in particular to the measurement of the consumption of dielectric materials and substances transported 5 inside pipelines, and can be used in the metallurgical, energy, construction and food industries. FOR the control of technology. gypsy processes associated with pneumat-10 matic transportation of bulk materials.

Devices are known that contain semi-annular, flat washer-shaped electrodes attached to the surface of a dielectric base included in the capacitance measuring circuit Sch.

Due to the significant difference in the linear expansion coefficients of the abrasion-resistant dielectric tube, which provides non-contact measurement, and the metal of the electrodes, these designs have a low temperature stability and cannot be used to measure the flow of high-temperature two-phase flows.

The closest technical solution to the proposed is a flow meter containing flat electrodes

fixed in horizontal planes on the surface of a dielectric tube providing non-contact flow measurement J.

The main drawback of the device is the low accuracy of the measurement of the flow of the high temperature flow. This is because a change in the temperature of the flow or the environment leads to a change in the linear dimensions of the dielectric tube, on both sides of which flat electrodes are fixed. This, in turn, increases the initial capacity during heating and increases with decreasing temperature. The change in distance is significant, since the linear expansion coefficients of the fluoroplastic pipeline and the metals used to make the electrodes differ by an order of magnitude.

The purpose of the invention is to improve the accuracy of measuring the high-temperature flow.

Claims (2)

The goal is achieved by the fact that one of the electrodes is made in the form of a closed shell with parallel sides, the dielectric section of the pipeline is hardened on one of its sides, with the second electrode being symmetrically relative to the parallel sides of the first electrode and in the free gap between electrodes placed dielectric strip. FIG. 1 shows a converter with a capacitance measurement circuit, general view; in fig. 2 is the same, section A-A in FIG. one; in fig. 3 is a graph of the relative change in the initial capacitance of the converter when the average electrode is displaced. The converter contains an electrode 1, made in the form of a shell, on one of the parallel planes of which the dielectric электри tube 2 is fixed. On its opposite side, an equal distance from the parallel surfaces of electrode 1, a flat electrode is fixed. On its surface, a dielectric strip 4 is placed to align the capacitance between electrode 3 and each of the planes of electrode 1 parallel. Instead of dielectric pad 4, a dielectric tube section is allowed 2. It is necessary to have a gap above the dielectric tube and parallel to the plane of the electrode 1. Electrodes 1 and 3 are enclosed in an electrostatic screen (not shown) and connected to the input of the measuring capacitance, which contains a bridge measuring circuit 5 fed from the generator b. The output of the bridge circuit 5 through the selective amplifier 7, the amplitude detector 8 and the normalizing amplifier 9 is connected to the input of the registering device 10. Before the measurement, the initial capacitance between electrodes 1 and 3 is compensated for by the tuning elements (not shown in the figure). The device works in the following way. Since electrode 3 is symmetrically located relative to parallel planes of electrode 1, the initial capacitance of the transducer is composed of two equal in size working and compensation capacitances. The working capacitance Sc is created in the area between the inspectors 1 and 3 in the zone of placement of the dielectric pipe 2 due to the penetration of the floor through the dielectric tube 2, and the compensation Scr of the electrode 3 in the area of the placement of the dielectric pad 4. Taking into account that the active surfaces of the electrodes 1 and 3 are equal to S, the initial capacitance of the converter is C + C k, k where k E, S; ta - dielectric constant of dielectric; J ЕО - dielectric constant of air; d is the distance between the electrodes. Then Co 2-5 With an increase in the temperature of the two-phase flow, which represents a mixture of particles with air, soy, heating of the dielectric tube 2 proceeds, leading to displacement of electrode 3 relative to parallel surfaces of electrode 1. At the same time, the initial capacitance of the converter changes by y - y ft 4J J o -dTId dfe 5 V, from where d ikd IX.Гк c & d) LNDS) from a-GDO1) (5) The relative change in the initial capacitance of the converter due to the inequality of the gaps of the measuring and compensation capacitance is AC .Cud).) GO VM 1- (Adi / c) Ha FIG. 3 shows the dependence of the function ud / d. When ud d, which has a merid during thermal deformation of the dielectric tube 2, the second term of the denominator can be neglected, then lc (Hd) (7) Analysis of formula (5) and its graph (Fig. 3) shows that in the region of small displacements of the electrode 3, caused by a change in the temperature of the two-phase flow, the initial capacitance of the converter Cd is almost unchanged. This is because the increase in the gap between the electrodes 1 and 3 when the dielectric tube 2 is heated and the associated decrease in the working capacity of the converter continuously and automaticallyIt is compensated by a corresponding increase in the compensation capacitance, due to a decrease in the gap between electrodes 3 and 1. Thus, when the two-phase flow temperature changes, the compensation capacitance of the converter performs automatic automatic compensation of changes in the working capacitance, as a result of which the initial capacitance of the converter remains constant when measuring the high-temperature flow. flow. The invention of the capacitive flow rate converter containing dielectric