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Abstract

Содержание

1.Introduction

To provide the population with high-quality food, it is necessary to ensure proper conditions for the storage of agricultural products. These conditions can be achieved by improving process control systems related to improving product quality, increasing shelf life and reducing losses. In modern conditions, universal devices are needed to control the moisture content of various agricultural materials without additional adjustment with high measurement accuracy.

Measurement of grain moisture should be carried out at different stages of its processing, since moisture is the most important indicator of grain quality. Water affects the livelihoods of all living organisms, especially the grain itself and microorganisms that may be on its surface. The humidity value characterizes and reflects the amount of nutrients in the grain, as well as its readiness for storage and further processing. Wet grain contains fewer nutrients, and during long-term storage may change and deteriorate. The presence of moisture activates physical and physiological processes, negatively affects storage and processing.

2. Actuality of the topic.

The number of methods of Moore FSM's hardware optimization is known: minimization of the amount of states (state reduction) and their specific encoding (state assignment), using features of target basis and algorithm of functioning, multilevel logic circuit's implementation. Mentioned methods are quite effective, but for getting the most economic FSM's implementation they have to be used jointly.

3. Overview and selection of methods for creating the instrument.

Methods of measuring humidity can be divided into two groups:
- mass transfer methods based on preliminary transfer of moisture to the auxiliary medium;
- methods based on the measurement of one or several properties of a wet material without prior separation of water and the sample under study (non-mass transfer).

In the methods of the second group, the value functionally related to the humidity of the material is measured. These methods require preliminary calibration in order to establish the relationship between the moisture content of the material and the measured value[1].

Mass transfer methods

The most common method is the drying method (thermo-hydraulic), which consists in air-heat drying of a sample of a material until it reaches equilibrium with the environment; this equilibrium is conditionally considered equivalent to the complete removal of moisture. In practice, drying to constant weight is used; most often used so-called accelerated methods of drying. In the first method, drying is completed if two consecutive weighings of the test sample give the same or very close results. Since the drying rate gradually decreases, it is assumed that this removes almost all the moisture contained in the sample. The duration of determination by this method is usually from several hours to a day or more. In accelerated methods, drying is carried out for a certain, much shorter period of time at elevated temperatures (for example, the standard method for determining the moisture content of grain by drying the ground sample at +130 degrees for 40 minutes).

The following methodological errors are inherent in determining the moisture content of solid materials by drying:
- during the drying of organic materials, along with the loss of hygroscopic moisture, there is a loss of volatile; at the same time, when drying in air, oxygen absorption takes place due to oxidation of the substance, and sometimes thermal decomposition of the sample;
- the cessation of drying corresponds not to the complete removal of moisture, but to an equilibrium between the pressure of water vapor in the material and the pressure of water vapor in the air; - removal of bound moisture in colloidal materials is impossible without destruction of the colloidal particle and is not achieved during drying;
- in some substances during drying, a waterproof crust is formed, which prevents further removal of moisture.The following methodological errors are inherent in determining the moisture content of solid materials by drying:
- during the drying of organic materials, along with the loss of hygroscopic moisture, there is a loss of volatile; at the same time, when drying in air, oxygen absorption takes place due to oxidation of the substance, and sometimes thermal decomposition of the sample;
- the cessation of drying corresponds not to the complete removal of moisture, but to an equilibrium between the pressure of water vapor in the material and the pressure of water vapor in the air;
- removal of bound moisture in colloidal materials is impossible without destruction of the colloidal particle and is not achieved during drying;
- in some substances during drying, a waterproof crust is formed, which prevents further removal of moisture.

Some of these errors can be reduced by drying in vacuum at a low temperature or in an inert gas flow. However, vacuum drying requires a more cumbersome and complex apparatus than for air-heat.

In the most common method of drying (in drying cabinets) there are errors depending on the equipment and drying technique used. For example, the results of determining the humidity depend on the duration of drying, on the temperature and atmospheric pressure at which the drying took place. Temperature is especially important when using accelerated methods, when lowering the temperature greatly affects the amount of moisture removed. The results of drying are also influenced by the shape and size of the cupboard and the drying cabinet, the temperature distribution in the drying cabinet, the speed of air movement in it, the possibility of entrainment of dust or small particles of the sample, etc. For materials subjected to grinding before determining the humidity, decrease moisture in the sample during grinding. This decrease is especially great if the sample is heated during grinding.

As a result, drying is a purely empirical method, which is not determined by the true value of humidity, but by a certain conventional value, more or less close to it. Moisture determinations made under unequal conditions give poorly comparable results. Significantly more accurate results are obtained by vacuum drying, usually performed in a chamber at a pressure of 25 mm Hg. Art. and lower to constant weight.

In distillation methods, the sample is heated in a vessel with a certain amount of liquid that is not miscible with water. The evolved water vapors, together with the vapors of the liquid, are subjected to distillation and, passing through a refrigerator, are condensed in a measuring vessel in which the volume or mass of water is measured. However, distillation methods are also characterized by many shortcomings and sources of error, including systematic ones.

Extraction methods are based on extracting moisture from the sample under study with a water-absorbing fluid and determining the characteristics of the liquid extract depending on its moisture content — density, refractive index, boiling point or freezing temperature, etc.

The basis of chemical methods is the treatment of a sample with a reagent that chemically reacts only with the moisture contained in the sample. The amount of water in the sample is determined by the amount of liquid or gaseous reaction product. So for the grain, you can use the K. Fisher titration. The method is based on the reaction known in analytical chemistry:

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The method is characterized by versatility, high sensitivity and accuracy, applicable in a wide range of moisture content (can be used as a model). Usually the end of the titration is determined visually or by electrometric method.

Determination of moisture by mass transfer methods lasts from many hours (drying to constant weight) to 1 hour (accelerated drying methods) or at best to tens of minutes, which prevents their use as rapid methods.

Non-mass transfer methods

In these methods, the assessment of humidity is made by changing its various properties.

Mechanical methods are based on the measurement of moisture-changing mechanical characteristics of solid materials (crush resistance). These methods, characterized by their simplicity, are characterized by low accuracy. Of the non-mass transfer methods, the most important and most widely used are those physical methods that are presented in Figure 1.

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Figure 1 - Classification scheme of physical methods for measuring humidity

Methods based on measuring the non-electrical properties of materials.

Radiometric methods developed in recent decades are based mainly on modern methods of studying the composition, structure and properties of a substance, using the interaction of various types of electromagnetic oscillations and nuclear radiation with the substance under study. The general advantages of the considered group of methods are the non-contact method of measurement and the absence of violation of various fields (temperature, humidity, mechanical deformations, and so on) in the object of measurement. At the same time, their application requires complex equipment.

The method of nuclear magnetic resonance (NMR) is based on resonant absorption of radio frequency energy by the nuclei of hydrogen atoms (protons) of water when a wet material is placed in a constant magnetic field. The main disadvantages of the NMR method compared with other methods of measuring humidity remain the complexity and cumbersomeness of the equipment used and its higher cost.

Optical methods are based on the dependence of the optical properties of materials on their moisture content. For solid materials, infrared and visible spectral regions are used. The advantage of these methods is the simplicity of the design. At the same time, they are not applicable at high moisture contents, and a change in the particle size distribution and the presence of impurities that differ in their optical characteristics can cause large errors.

Thermophysical methods are based on the dependence of the material's moisture content on its thermophysical properties — thermal conductivity coefficient λ, specific heat capacity c, and thermal diffusivity coefficient а = λ/сρ (ρ is the material density). This dependence is observed in all capillary-porous materials. The disadvantages of the thermophysical method include the strong influence of the density of the material, its granulometric contact; the presence of surface moisture in the contact zone can cause large errors. Therefore, one cannot expect high accuracy from this method.

Ultrasonic methods are based on the dependence of the characteristics of ultrasonic vibrations on the properties and composition of the medium in which ultrasound propagates. They usually use the dependence of the velocity of propagation of ultrasonic vibrations on the moisture content of the material under study. The disadvantage of these methods is low accuracy [2].

Electrical moisture measurement methods.

The basis of electrical methods for measuring humidity is the dependence of parameters characterizing the behavior of wet materials in electric fields on moisture.

Conductometric methods are based on measuring the electrical conductivity of the material at a constant current and alternating current of industrial or sound frequency.

Moisture-containing materials, being dielectrics in dry form with a specific volume resistance of ρv=1010–1015 оhм*сm and higher, as a result of humidification, become semiconductors; the value of ρv decreases to 10–2–10–3 оhм*сm. The resistivity varies, therefore, depending on the humidity in an extremely wide range, covering 12-18 orders of magnitude.

When measuring in the field of decimeter, centimeter and millimeter waves, it is necessary to consider systems with distributed parameters. Consider methods for measuring humidity at ultrahigh frequencies. These methods are classified into:
- methods based on measuring the characteristics of the field of standing waves;
- methods based on measuring the characteristics of the field of waves passing through a wet material (optical methods)[3]

.

The first group of methods includes:

a) a method based on measuring the standing wave field in a sample of a dielectric under study. Based on the calculation of the dielectric constant of a wet material, which is a function of moisture content, as measured by the value of the phase portion of the propagation constant. In practice, measurements are reduced to the determination of wavelengths in a system without a dielectric and with a dielectric, from which it is determined:

where λ0 and λд - respectively, the wavelength in free space and wet material

The elements in which the field distribution is recorded (or sensors in the case of moisture measurement) can be: one- and two-wire lines, a coaxial line, or waveguides. The disadvantages are the need to use samples of large volume and a decrease in the accuracy of measurements in the case of samples with large losses (high humidity);

b) a method based on the study of the field of standing waves arising from the reflection of electromagnetic energy from a sample of the material under study. The essence of the method consists in determining the propagation constant in the sample of the material to be measured by studying the pattern of standing wave distribution on a portion of the line that is not filled with a dielectric (with known loads connected behind the sample at the end of the line). There are various options for the location of the sample in the measuring element and the terminal load: complete filling of the cross section, the use of samples of different thickness, the creation of a short circuit mode and idling, variation of the sample thickness (thin and "infinite" layer), etc. In all cases, the process of measuring the dielectric constant the material is reduced to measuring the standing wave ratio and the displacement of the first minimum [4].

The calculation formulas are quite complex, the ambiguity in determining the dielectric constant is obtained, and, as a rule, one has to solve a system of transcendental equations;

c) a method based on the use of waves reflected from the surface of the sample being measured. In this case, to determine the dielectric constant, the parameters of the wave resulting from the interaction of the incident and reflected waves are used;

d) the resonance method is based on measuring the parameters of the resonator when the test material is introduced into it. Measuring the frequency of the resonator, determine the dielectric constant, and measuring its quality factor, determine the loss factor.

In the dielectric (capacitive) method, the wavelength and shortwave frequency ranges or ultrahigh frequencies are most often used. In the first case, the geometrical dimensions of the sensor and other elements of the measuring circuits are much smaller than the wavelength and can be considered as systems with lumped parameters

This method uses the mid-wave and short-wave frequency range (f = 0.1 - 30 MHz).

Under these conditions, the geometrical dimensions of the sensors are much smaller than the wavelength and can be considered as systems with lumped parameters.

The use of this method is associated with abnormally high dielectric constant of water; in the frequency range from 100 kHz to 100 MHz at room temperature, it can be considered close to 81, with a dielectric constant value of capillary-porous materials no more than 5-10.

Therefore, the electrical parameters of capillary-porous materials strongly depend on their humidity, that is, the capacity of the EPP is a function of humidity. However, the capacitive method of measuring humidity can be applied only if the majority of the water molecules in the substance are in the free state and the substance has a more or less constant physicochemical composition.

As EPP, sensors based on flat-parallel and coaxial capacitors are most often used.

When a controlled substance is introduced into the EPP, its electrical capacitance will increase by the value of the average dielectric constant of the material between the electrodes of the sensor. A change in capacitance will entail a change in the reactance of the sensor, and as a result of an increase in the current flowing through the URP of the moisture meter recorded by the measuring circuit. The dependence of the capacity of the EPP on the moisture content of the material is found experimentally [5].

The dielectric constant of materials ε in alternating electromagnetic fields used in process control is a complex value:

in which the real component ε' determines the material's ability to polarize in an electric field, and the imaginary component ε" (loss coefficient) characterizes the absorption of energy by the substance during polarization. The components of the complex dielectric constant (CDP) ε', ε" are related to the dielectric loss tangent tg δ and the electrical conductivity &sigma of the material by the relations:

where ω is the circular frequency of the electromagnetic field,
        ε0 = 8,854 10– F / m - electric constant

To measure the components of ε', ε", two-pole capacitive sensors with an internal electromagnetic field (measuring cells) or with an external field (probes) are usually used. The values of ε', ε" are determined by the components of the input impedance of the sensor, associated functional dependencies with ε', ε" [6].

The following factors influence the measurement accuracy: a change in the density of the material under study, a change in the temperature and conductivity of a substance, a change in the chemical composition. All of these factors introduce an error in the measurement process. In order to minimize these errors, special measures are taken. For example, it is entered automatically or a correction for changes in temperature and conductivity is taken into account. Measures are taken to ensure the constancy of the density of the measured substance in the sensor.

The advantages of the method are simplicity and not the high cost of the measuring circuit and the primary transducer, which allows to determine the moisture content of the material without disturbing its structure and without sampling; the method can be used in line mode; high measurement speed.

Disadvantages: low measurement accuracy, the influence of various factors (temperature, density, etc.) on the measurement result.

In the device under development, a capacitive method will be applied - measurement of humidity based on a change in capacitor capacitance.

This method of measuring humidity is chosen because its characteristic feature is the sensitivity of measurements, the possibility of continuous assessment of humidity in large volumes (large information capacity of the method). The latter is an important advantage, since in real production conditions there is always an uneven distribution of moisture in the volume.

4. Prototype

In-line moisture meter "Fauna-P" is designed to measure moisture in the flow of grain and oilseeds and their products during the drying process in the shaft, carousel and other types of dryers, on the equipment of food industry enterprises.

The moisture meter is available in modifications: Fauna-P - for operation with one sensor (see Fig. 2), Fauna-PMD2 - with two sensors, Fauna-PMD3 - with three sensors, Fauna-PMD4 - with four gauges. The moisture meter has a unified output of 0 - 1.0 V, which allows its use in systems of regulation and control of technological processes [7].

Figure 2 - In-line Moisture Fauna –P

In-line moisture meter operates in continuous mode with automatic correction of measurements depending on temperature and other influencing factors.

The technical characteristics of the Fauna-P device are presented in Table 1.

Table 1 - Instrument Technical Specifications Fauna –P

The structure and principle of operation.

 The moisture meter implements a dielectric (capacitive) moisture measurement method and is a microprocessor device that provides display of humidity values, temperatures and names of controlled grains or oilseeds, an analog signal output proportional to the humidity value, for building automatic control systems for the drying process, the introduction of manual correction moisture measurement results to compensate for the influence of external influencing factors, the choice of controlled crops. Structurally, the moisture meter is made of two parts - the sensor and the indicator unit, connected by cable.

The sensor consists of two parallel metal strips and forming a capacitor. The change in capacitor capacitance is functionally related to changes in the value of the humidity of the controlled culture. A measuring unit, installed between parallel metal strips, converts the capacitor capacitance values into a measurement information signal, which is transmitted to the indicator unit via a connecting cable.

The indicator unit contains a microprocessor and elements of the measuring transducer. On the front panel there is a display, a button for the selection of monitored crops Select and two buttons Correction + and - for entering the correction of humidity readings. On the right wall of the unit is the power switch. On the bottom wall - connectors of the connecting cable and the signal cable, the input of the power cord and fuse holder. Structurally, the moisture meter "Fauna-P" consists of a sensor and an indicator unit, connected by a cable with a length of 10 m, but at the request of the customer the cable length can be increased to 50 m.

The sensor of the flow moisture meter Fauna-P is installed in places where the constant flow density is best ensured and there are no stagnant zones of grain, for example, in unloading points. The temperature in these places can reach 80 ° С. The temperature of the grain in the area of ??the sensor is constantly measured and displayed on the display unit. Changes in moisture readings associated with temperature changes are automatically compensated (corrected) for individual dependencies for each culture. A significant reserve for improving the measurement accuracy with the Fauna-P moisture meter is a reduction in the methodological graduation errors that occur when a sensor is installed in a working area of ??a technological unit (dryer) of a particular type. These are the so-called docking errors, which are caused by the own initial (electrical) capacity of the unit.

The sensor of the moisture meter Fauna-P is equipped with a compensator for the initial capacity, with the help of which the readings of the moisture meter are brought to factory calibration. The procedure of "docking" the sensor with this unit is carried out once after the installation is completed. The indicator block, as a rule, is installed on the control panel of the unit in an easily accessible place for the operator and is operated at a temperature from 5 to 40 ° C. After installation, the indicator block does not require adjustment.

5.Conclusion.

Master's thesis is devoted to the development of a device for measuring the moisture content of grain at a milling enterprise. In the course of the work, the optimum values of the error and moisture content of the grain were determined.

The above review of the methods shows us that the best method for solving the set task is the capacitive method for measuring the moisture content of the grain.

The prototype is the Fauna-P in-line moisture meter, which shows us all the qualities of the method. Which shows itself from the best party for use at the flour-grinding enterprise.

На момент создания сайта магистерская работа не завершена. Если есть вопросы просьба обращаться к автору.

References

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  2. Бензарь В.К., Техника СВЧ–влагометрии / Бензарь В. К.. – Минск: Высшая школа, 1974. – 349 с.
  3. Бесекерский В.А., Теория систем автоматического регулирования / Бесекерский В.А., Попов Е.П. – М: Наука, 1972. – 768 с.
  4. Брандт А.А., Исследование диэлектриков на сверхвысоких частотах – М.: Физматгиз, 1963. – 403 с.
  5. Бугров А.В., Высокочастотные емкостные преобразователи и приборы контроля качества / Бугров А. В. – М.: Машиностроение, 1982. – 94 с.
  6. Будницкая Е.А., Точные измерения комплексных сопротивлений емкостного характера / Будницкая Е. А., Карпенко В. П. // Измерительная техника. – 1967. – №8. – С. 44–47
  7. Интернет ресурс,Официальный сайт компании ОООЛепта по разработке, производству и поставки влагомеров для зерна, семян и других сыпучих материалов Режим доступа: http://www.agrolepta.ru/Fauna–P.htm. http://www.agrolepta.ru....