Water level alarm

FIELD: measuring engineering.

SUBSTANCE: water level alarm comprises the section of coaxial long line provided with inner conductor projecting beyond its end. The section is connected with the high-frequency generator and recorder. The generator is made of a self-excited oscillator. The section is connected to the frequency generating circuit of the self-excited oscillator. The recorder is made of a frequency meter. The projecting part of the inner conductor is made of two members of the same length, but different diameters. The diameter of the end part exceeds that of the other part of the projecting part of the inner conductor by a factor of ten. The projecting part of the conductor can be covered with a dielectric shell.

EFFECT: enhanced sensitivity.

1 cl, 5 dwg

 

The invention relates to measuring technique and can be used for highly accurate level detection and the position of the boundary section of various substances in containers, in particular, to interface the air - liquid-air - granular material (such as cement, ground coal), liquid - liquid (e.g., oil - water).

Known microwave devices (ed. mon. The USSR N756215, 1136024, 1210069, CL G 01 F 23/28) to determine (alarm) level (the boundary between two substances), and an RF device for determining the position of the boundary, the level of various substances containing sensitive element in the form of two pieces of a heterogeneous long lines (ed. mon. N281848, MCL G 01 F 23/28). Their disadvantage is a rather complicated structure and a low accuracy of the alarm.

Also known level switch (position of the boundary between substances)that is closest to the technical nature of the proposed device and adopted as a prototype (U.S. Pat. USA N4503383, CL G 01 R 27/26, NAT. CL 324/61, 1985). This detector prototype contains a segment of a long coaxial line sensor as a termination. This sensitive element is made in the form of the inner conductor specified coaxial line, which protrudes its length; it is subject to contact with controlled substances is, forming the boundary of the section, or one substance in the case definition (alarm) level. Information on the availability at the point of alarm boundaries substances is variation in the degree of attenuation of electromagnetic waves, which are recorded in the detector output. This detector is designed to detect the position of the boundary between oil and water in the tank.

The disadvantage of this detector is its low sensitivity, characterized by a small change in the value of informative parameter (voltage amplitude) at the point of control when passing the boundary of substances. This low sensitivity is due to the major influence on the informative parameter of the detector is equivalent to the capacity of a segment of a long line, far exceeding the capacity of the sensing element.

The aim of the invention is to increase the sensitivity.

The goal of the proposed detector substance in the vessel, containing a segment of a long coaxial line with an inner conductor projecting beyond its end connected with the cut of a long line of high-frequency generator and the Registrar, is achieved by the fact that the generator is made in the form of oscillator, cut long lines included in his customizados chain, the Registrar is the frequency, and the ledge is the one part of the specified inner conductor is made of two sections of equal length, but different diameter, the diameter of the terminal portion is not less than 10 times the diameter of the other protruding part of the inner conductor. The protruding portion of the inner conductor may be covered with a dielectric shell.

The goal is achieved by the combination of features set forth in the claims.

A distinctive signs, according to the authors, is, first, the execution of the generator in the form of oscillator, secondly, the inclusion of a segment of a long line in his customizados chain, thirdly, the implementation of this protruding part of the two sections of equal length but of different diameters, the diameter of the terminal portion is not less than 10 times the diameter of the other protruding part of the inner conductor; fourth, covering the protruding part protruding part of the inner conductor.

The set of distinctive features of the proposed device makes it new properties: an increase in the area of the end portion of the sensing element and, as a consequence, the corresponding increase in its electrical capacitance; use as an informative parameter measuring the frequency of the oscillator and, as a consequence, improving the accuracy of measurement.

These properties provide a positive effect, formulated in a whole the proposal. Not known to the authors of the technical solution, containing the same set of distinctive features and exhibiting the same properties as the proposed device, i.e., it is, according to the authors, meets the criterion of "substantial differences".

The proposed device is illustrated by drawings. Figure 1. shows a diagram of the device. Figure 2 - scheme of the sensing element. Figure 3 shows the use of the device when the control level of the substance in the tank top. Figure 4 shows graphs of the variation of the frequency of the oscillator from the h level to the controlled substances with different moisture content. Figure 5 shows the coordinate values corresponding to the frequencies in figure 4, relative to the sensing element. Here we have introduced the notation: 1 - cut the long line, 2 - protruding portion of the inner conductor, 3 - oscillator, 4 - Registrar, 5 and 6, respectively, the thicker and the thinner part of the conductor 2, 7 - dielectric shell, 8 - grounded conductor, 9 - dielectric sleeve, 10 - metal casing, 11 is a controlled substance.

The device operates as follows. Cut a long line 1 is a high-frequency resonator electromagnetic waves. Being included in customizados the oscillator circuit 3 (Fig 1), which in this oscillator, it determines the frequency f of its generation. This cha is Thoth f is an informative parameter alarm: when the surface of a controlled substance in the point of control is an abrupt change in the frequency f. The values of this frequency and its changes are recorded by the Registrar 4, which in this case is the frequency. The operating frequency range is determined mainly by the length of the longest line 1. In practice, this frequency range is usually not more than 150 MHz.

To ensure the required alarm about finding a surface in a controlled point cut long lines 1 alarm contains the target sensor element in the form of a protruding part of the inner conductor 2. A long line can be, in particular, high frequency 50 Ohm cable RC-50. This lengthening of the internal conductor line 1 consists of two parts 5 and 6 of equal length but of different diameters (figure 2). The diameter of the outer thickened portion 5 of the conductor 2 is not less than 10 times (in practice 10-20 times) greater than the diameter of the other 6 protruding part of the conductor 2. This increase in the diameter of the outer part provides a substantial increase in the sensitivity of the device, because this increases the surface area of the face part and then the corresponding electric capacity. Choosing the geometrical parameters of this terminal part of the line segment 1, you can set the threshold detector by forming near the conductor 2 of the corresponding distribution of high-frequency electromagnet the field. The threshold may correspond to a direct contact of the end of the conductor 2 with a controlled substance 11 or a certain distance of the end surface of the substance. The accuracy of response (alarm) high and is determined by the accuracy of finding the values of the detected frequency f, which is provided in the circuit of this device.

Figure 2 shows the connection of an end section of the line 1 to its protruding part: inner conductor lines 1 connected (continued) to the nearby end of the conductor 2; their diameters may be the same or may have a different meaning. Outer conductor of the line 1 is connected to the grounded conductor 8 (case), closed by metal casing 10 (for sealing). When selecting the diameter of the part (rod) 6 conductor 2 connected to the line 1, it is advisable to ensure equality of impedances specified portion of the conductor 2 and the long line 1 (for example, 50 Ohms, if the long line cable RK-50). The dielectric sleeve 8 on the metal rod 6 serves to ensure the rigidity of the sensing element.

If the controlled substance is imperfect dielectric (e.g., water or wetted material), characterized by a large value of tangent of dielectric loss angle, to increase dobrot the STI resonator - cut a long line 1 - the surface of the conductor 2 should be covered with a dielectric casing 7, for example, PTFE. This informative signal (frequency f) is large enough to register the value.

In the manufactured and tested in practice, the level switch in the settings section of the line 1 and the protruding part 2 were selected as follows: long line 1 - cable RK-50 (an impedance of 50 Ohms); the length of each side of the Explorer 2-25 mm; the diameter of its thickened part 5 aluminium 30 mm; the diameter of its thin part 6 stainless steel 2 mm; the thickness of the PTFE membrane 7-2,5 mm, This device provides high-precision detection (alarm) level of various bulk materials and liquids contained in containers.

The application of the proposed device can be used by the control-side side wall and the upper end of the capacity. The second option is preferable as it is not associated with the violation of the integrity of the design capacity. In many cases, in practice this option is only valid. He is seen here as an example of the application of the proposed device. In tanks containing the controlled substance 11 (bulk material, liquid), have a vertically long period of line 1 of the device (figure 3). While it made the surrounding part 2 is in the area of control of the level of the substance.

Figure 4 shows a graph of frequency f depending on the level h of dry and wet granular material, such as powdered coal mass, after crushing in a ball mill for coarse grinding or moisture-containing fluid with a variable moisture content. Frequency f0corresponds to the value of the level h0substances while being sensitive element protruding part 2 - in the air. Frequency f2and f3correspond to the level h2in the interaction of the sensing element with a controlled substance 11 having respectively a zero W0and the maximum Wmaxthe moisture content. Actuation of the detector can be installed in direct contact conductor 2 with a substance, and when it contacts the surface of a substance in its electromagnetic field in the area of contactless operation. The threshold f1when the control of such substances with a variable or unknown moisture content can be installed at some point, which correspond to the frequency f1=(f0+f2)/2. Its value lies between the values of frequency f0and f2accordingly, for air and dry matter. This choice of frequency f1actuation provides reliable alarm if the storage capacity of a substance with an arbitrary moisture content: when this choice is E. the frequency coordinate of the alarm level is between the values of h w(the maximum value of W) and h1and changing the coordinates when changing the moisture content is within a small tolerance.

If the measured frequency f>f1the Registrar issues a signal corresponding to the absence of substance in a controlled area. If f≤f1the surface of the controlled substance is in this field.

Really the moisture content W is in the range of 0-25%. As a consequence, variable moisture content leads to some error alarm level. The higher the moisture content, the lower the value of the level is the operation of the device. Figure 4 shows that when the maximum value of the moisture content of the operation of the device occurs when the value of the level hwthat is less than the actual value of h1. When an unknown moisture content coordinate activation (alarm) is located on a plot within the range between h1(when W=0) and hw(when W=Wmax). Error δ=h1-hwthe Desk level, but really small and does not exceed the allowable value. So for ground coal with a maximum moisture content of 25% error does not exceed 5 mm figure 5 shows the relative position relative to the sensing element 2 level values of h0h2and coordinate h h1measured from the bottom of the tank with the coordinate h=0. The coordinate of h0corresponds to the frequency f0; the coordinate of h2correspond to the frequency f2(when W=0) and f3(W=Wmax); the real coordinate of the h2may correspond to any frequency in the frequency range from f2to f3depending on the moisture content between the values of W=0 and Wmax. At the chosen frequency f1trigger (alarm) device occurs at the point with coordinate values in the range of hw(W=Wmax) to h1(W=0).

Thus, the proposed device allows a high precision level detection of various solids, liquids in containers. In particular, it can be used in CHP plants based on coal, in the automated control systems of technological process of coal for high-level control of ground coal in the bunkers.

1. The level switch of the substance in the vessel, containing a segment of a long coaxial line with an inner conductor projecting beyond its end connected with the cut of a long line of high-frequency generator and the Registrar, characterized in that the generator is made in the form of oscillator, cut long lines included in his customizados chain, the Registrar is the frequency, and are the first part of the said inner conductor is made of two sections of equal length, but different diameter, the diameter of the terminal portion is not less than 10 times the diameter of the other protruding part of the inner conductor.

2. The detector according to claim 1, characterized in that the protruding part of the said inner conductor covered by a dielectric sheath.



 

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