Application of Micro Capacitor Remote Measurement Technology in Informatization Reconstruction of Cement Industry
A senior cement expert said thirty years ago that the management scheduling of cement plant production is, in a sense, the management and scheduling of the material level in the material warehouse. However, for a long time, the monitoring of the material level of cement plants has always been a technical problem that cannot be solved. The vast majority of cement plants are currently using the most primitive method to obtain production level information such as production scheduling team accounting.
Over the years, the cement plant has invested a lot of funds and manpower in order to address the automatic monitoring of material levels in large warehouses. It has purchased and installed various hammer-type, steel-belt, and ultrasonic level gauges, all of which cannot adapt to the harsh environment of cement production. Can not be reliable and practical long-term. The capacitive level gauge I developed in the 1970s, with its simple structure and low cost of installation, has promoted thousands of units in hundreds of cement factories throughout the country. However, it failed to escape the long-term reliable use of the demolition. After repeated studies, we found that traditional capacitive level gauges have a dielectric constant greater than air and have a principle of detecting a change in the capacitance formed between the probe and the reservoir wall in response to changes in the material. Capacity direct simulation of material level method design. The premise of this design principle is that the dielectric constant of the material is a constant that is greater than that of air, and that the change in capacitance is proportional to the change in material level. In practice, the dielectric constant of a material in any material warehouse changes with the particle size, composition, density, moisture and other factors of the material. Not only is it not a constant, but the change in the dielectric constant caused by the different moisture content is The material dielectric constant of several times or even several times. It is for this reason that this level gauge cannot work reliably for a long time. Finding the cause, we found the direction to solve the problem, not the capacitive sensor itself has a problem, but the method used to detect the dielectric constant related to the size of the capacity to directly indicate the height of the material level. This overly simple simulation makes the uncertainty of the dielectric constant manifest directly at the level of the material level, resulting in inaccuracy of the material level detection result and fundamentally losing the long-term reliability of use. Segmented self-calibrating material level meter solves the long-term reliability of material level detection by eliminating the influence of dielectric constant on the test results and avoiding two major shortcomings of manual correction.
Stage self-correction level gauge working principle diagram shown in Figure 1
The national invention patent "a method of segmented capacitance level detection" (ZL940013.4) breaks through the traditional method of directly simulating material level with a probe capacitor, adopts digital and single chip and technology, and will be a continuous one. The capacitive electrode is a segmented electrode with several equal-length independent capacitive electrodes connected to each other. From the top to the bottom, the height in the reservoir is divided into several segments of capacitance formed between each segment and the tank wall. The size of each segment is related to the amount of material in the segment relative to the space. The same micro-capacitance remote transmission measuring circuit is controlled by the single-chip microcomputer and the capacitances of each segment are respectively detected. From the relative size of the capacitance, it can be determined that the air and the material interface are located. The capacitance is cj and the following segments are full. Material section, the electric capacity is cm. With the gravity of the material, the higher the density, the greater the cm, but regardless of the value of the full material, the height of the material in the material is the geometric length of the segment, which is independent of cm. The total material height is the sum of the total height of all full sections below and the high reading level of the interface section. which is:
LW=N.L0+LJ (1)
Where N is the number of full blocks
L0 is the length of the segment geometry
LJ is interface level height
We believe that the material density and dielectric constant at the interface are the same as those of the material below the adjacent full material, and the two-stage capacitor structure is also the same. Therefore, the ratio of the interface section material level to full-scale material level is equal to the ratio of the two sections of capacity, that is:
LJ=CJ/CM.L (2)
So LW=(N+CJ/CM ).L0 (3)
From the above three formulas of the detection process, it can be seen that the material level detection result of this method has nothing to do with the absolute value of the segment capacitance, and is only related to the above two adjacent capacitance ratios. Therefore, all the factors that affect the size of the capacitance are in operation. eliminate. Therefore, changes in the material particle size, composition, moisture, and temperature will not affect the material level detection results. Compared with the traditional capacitive level gauge, the level gauge made by this method does not need to adjust the zero point when emptying the material in the use, and it does not need the manual calibration for parameter calibration. As long as there is more than one piece of empty material in the grain store, you can zero the point. It can be seen from formula (3) that the measurement reference is L0, that is, the geometric length of the segment electrode. As long as it is stored in the microcontroller, real-time self-calibration is realized without any manual maintenance. Fundamentally guarantee the long-term reliability of use. This level meter product has been run in the 36M high wheat warehouse of Qingdao Flour Mill and has been verified and praised.
The level transmitter used for oil detection developed by this principle has an accuracy of 5/10000, but there are many differences between the material level detection and the liquid level detection. The liquid level is horizontal and the material level is uneven. The interface height is as much as tens of centimeters. In the interface part, the size of the segment capacitance is substantially proportional to the amount of material in the segment of the space electric field, ie volume, so the calculated height is the average value of the volume of material. Large-scale silos, especially powder warehouses such as the cement factory's raw material storehouse, often cause empty material columns due to material arching. At this time, the principle material is a continuous premise and is destroyed, which will result in a certain calculation error. But on the other hand, since the capacitance detection value of each segment directly reflects the volume concentration of the space material in the segment, the detection value of each segment of capacitance can be checked at any time by pressing a key. Objectively, the material level meter has the ability to detect the internal arching of the reservoir in time. Situation and location. It is convenient for users to deal with the unique function of avoiding affecting production in time.
The material level meter consists of three parts: 9-segment capacitor electrode, transmitter and material level controller. The single-chip microcomputer completes all detection, display and control functions. It has LED digital and light column percentage two kinds of display and upper and lower limit control report and alarm functions. In addition to the material level display, each segment detection value can be checked by pressing the key button to understand the distribution of each material in the library. Each level gauge is equipped with RS485 computer communication interface, which can send real-time material level height and 9-segment level to the upper machine. Detection of digital information, communication distance up to 1.2KM, users can easily form a DCS library cluster management system, in the cement plant information transformation has a wide range of application prospects.
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