SU682810A1 - Capacitance surface sensor - Google Patents

Description

one

The invention relates to a measurement technique, namely, devices for measuring and studying the dynamics of turbulent motion of interacting phases on their interface formed by a film of liquid moving along a contact element and a turbulent gas flow in a mass transfer apparatus, in particular, in a mobile irrigated nozzle.

Known designs of sensors based on measuring the dielectric constant of the medium. Known designs are not suitable for measuring the amplitude and frequency of change of the contact surface of the interacting phases.

Closest to the invention is a surface capacitive sensor containing two isolated parallel-mounted electrodes. However, the known sensor has a low limit of measured film thicknesses and has a low sensitivity. This is due to the design of the sensor, since its capacitance between the electrodes is much larger than the capacitance at the ends of the electrodes, due to which the useful signal has a small value. The use of additional amplifying equipment leads to a distortion of the useful

information, and this reduces the measurement accuracy.

The aim of the invention is to expand the measurement range and improve accuracy.

For this, the electrodes are made in the form of parallel rings with a width of 1.5-2 mm, isolated from each other by a dielectric layer not exceeding 0.1 mm, and the ratio of the electrode width to its thickness is no more than 20.

The specified ratio of the width of the electrode to its thickness corresponds to the highest sensitivity of the sensor, since

the ratio of LSK (change in the annular capacitance) to Cn (the constant capacitance between the electrodes) increases due to a decrease in the latter. The optimum width of the electrode is in the range of 1.5-2 mm, which is caused by the condition of fixing the waves of the smallest length at their maximum frequency (high-frequency component) superimposed on the low-frequency carrier wave with a maximum amplitude.

Claims (1)

The choice of the size of the dielectric layer in the interelectrode space of no more than 0.1 mm is determined by the spectral characteristic of the change in the thickness of the liquid films, i.e. the amplitude and frequency of the wave motion of the liquid films on the surface of the nozzle. In the general case, for any liquid, HAAI is the width of the electrode; 5 - dielectric thickness; e is the base of the natural logarithm; K is the wavelength of the high-frequency component superimposed on the carrier; A - maximum carrier amplitude. In FIG. Figure 1 shows the design of a surface sensor embedded flush (on the measuring surface side) into an electrically insulating material with a low tangent of dielectric loss angle at high frequencies (for example, polystyrene); in fig. 2 shows section A-A in FIG. one; in fig. Figure 3 shows the individual elements of the sensor, forming the whole landing element with a built-in flush sensor, for example, a ball nozzle to clarify the method of manufacturing and assembling the surface capacitive sensor; in fig. 4 is a block diagram of a measurement circuit. The sensor contains insulating material 1, electrodes 2 in the form of rings, an interelectrode layer of dielectric 3, slots 4 for wires connecting the sensor to the measuring bridge, a thin, flexible, shielded actuator 5. Electrodes 2 are put on one of the constituent parts of the ring 1, between which there is a dielectric layer 3, while the soldered ends of the flexible shielded wire 5 to the electrodes 2 are inserted into the slots 4 of the ring 1. Then the electrodes are pressed against the second part of the composite ring 1, planted on the glue of the dissolved starting material. Parts of the nozzle element 6 are rigidly attached to the ends of the sensor, thereby forming the whole nozzle element itself without changing the size and shape of the latter. In the center of one part of the sphere of the element 6, the shielded wire 5 is rigidly fixed in this place. This is necessary so as not to break the contact at the points where the electrodes are soldered to the ends of the shielded wire during operation of the sensor. FIG. 4 shows the measuring block diagram, which shows a stabilized power supply unit 7, a high frequency generator 8, a high frequency resonant amplifier 9, a measuring high frequency bridge 10, a detecting unit 11, a recording device 12. The sensor works as follows. The nozzle element with an integrated capacitive sensor and a portion of the shielded flexible wire connecting the sensor electrodes to the measuring bridge 10 is placed in a layer of the moving nozzle. The length of the placed part of the wire is chosen so that the sensor can move freely throughout the volume of the device. In the advanced fluidization mode, the nozzle element with a built-in sensor, like the entire layer of the moving nozzle, performs pulsation and circulation movements, but the sensitive surface of the sensor is almost always perpendicular to the flow of the interacting phases. As it moves, the nozzle element with an integrated sensor falls into zones with higher or lower irrigation density, which causes a constant change in the thickness of the moving liquid film on its surface. In addition, the motive liquid film is turbulized by a gas flow. This also leads to its constant change, and consequently, to the renewal of the contact surface of the phases. If there is a liquid film on the sensitive surface of the electrodes 2 and the alternating high-frequency voltage applied to the measuring bridge, where the sensor is included in one of its arms (Fig. 4), some distribution of the density of the electric field lines is formed between the liquid and gas phases, with a higher density in a medium with a large dielectric constant (in the liquid film). As the thickness of the liquid film increases, the electric field lines pass through it, thereby causing an increase in the terminal capacity of the measuring electrodes. This increase will be until the liquid film goes beyond the propagation of the electric field. The latter is due to the distance between the electrodes, their shape and size. A change in the end capacitance causes an imbalance of the measuring bridge, which was previously balanced in the absence of a liquid film on the sensor surface with the help of a variable capacitor Cr (Fig. 4). The bridge is powered by alternating voltage, stabilized in amplitude and frequency, outputted by blocks 8, 9. The imbalance signal is detected by the detecting unit 11 and fed to a recorder or oscilloscope 12. To eliminate the instability of the measuring circuit signal from the direct contact of the fluid with the surface of the sensing element, the surface it is covered with a thin layer of lacquer resistant to the circulating medium and impacts. Thus, the proposed surface capacitive sensor makes it possible to measure with high accuracy the dynamic characteristics of the interface surface formed by a liquid film on the surface of a mobile irrigated nozzle, predominantly rotation bodies, in a wide range of loads (for liquid 25-100 and gas 1-7 m / s) for mass transfer apparatus. Claims of the invention Surface capacitive sensor containing two isolated from each other parallel mounted electrodes, characterized in that, in order to expand the range of measurements and improve accuracy, the electrodes are made in the form of parallel rings 1.5-2 mm wide, isolated from each other by a dielectric layer not exceeding 0.1 mm, and the ratio of the width of the electrode to its thickness is no more than 20. Cpuz.3