RU2130606C1 - Gear measuring moisture content of loose substances - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: gear incorporates container of examined substance-capacitive humidity converter, compactor and measurement electric circuit. Capacitive humidity converter has three electrodes, one common and two external, and is manufactured in the form of rectangular vessel made from dielectric material that is divided into three sections, first and second ones are meant to take in examined substance and third one is filled with material having dielectric permittivity equal to dielectric permittivity of dry substance at moment of measurement. Capacitive humidity converter presents differential capacitor. Three electrodes of capacitor are connected to bridge circuit. Electric circuit incorporates generator, bridge circuit, differential amplifier with rectification, amplifier with changeable bias to which output unit processing output signal by level is linked and recorder connected in series. All components of gear are housed in one case, electronic components are assembled on one board, electrodes of capacitive humidity converter are made from flat metal plates. Window of container of examined substance protrudes above upper base of case. Compactor is mounted above window of container. EFFECT: enhanced productivity of measurements with increased accuracy, simplified design f gear. 3 dwg

Description

 The invention relates to measuring technique and can be used to measure the moisture content of bulk solids.

 A device for operational measurements of grain moisture is known - US patent N 3,794,911. Publ. in "Inventions abroad. N 4, 1974. The device is a capacitive moisture meter and contains a housing, a receiver - a capacitive humidity transducer, a measuring circuit with a processor and registration of reference data and moisture content of a grain sample, an electrical mechanism for fixing the weight poured into a grain receiver, an electric a circuit for measuring weight and controlling the operation of the device, an electrical circuit for introducing amendments for the difference between the actual temperature and the reference one.

 The main disadvantages of the device are the design complexity and the dependence of the measurement accuracy on the weight of the grain sample, dielectric loss, temperature, and the fact that the device is focused only on measuring grain moisture.

 For measuring the moisture content of bulk materials, a device is known - copyright certificate N 815600, publ. in the "Bulletin of inventions and discoveries", N 11, 1981 (prototype).

 The device comprises a horizontal cylindrical body, a press device with a piston (seal), a weighing device, a capacitive moisture transducer — a receiver of the test substance, a capacitive weight transducer, instrumentation (measuring electric circuit), and the body is mounted on a weighing device made of two plate electrodes forming a capacitor, the signal of which corrects the linearity of the measurement results.

 Humidity measurement is performed as follows. The device is oriented in a horizontal plane, the test substance is placed in a receiver, pressed with a certain pressure. The output characteristic of a capacitive humidity transducer is a measure of the moisture content of a sample of a substance, and it is recorded.

 The main disadvantages of this device are: the need for a fixed installation of the device, its strict orientation, because there is a weighing device; a significant dependence of the measurement results on the degree of compression, the quality of the weight mechanism, temperature; dependence of measurement results on dielectric loss.

 These disadvantages lead to a decrease in the measurement performance and a limitation of their accuracy, in addition, the design of the device is complicated.

 The aim of the present invention is to increase the measurement performance with increasing accuracy and simplifying the design of the device.

 This goal is achieved by the fact that in a device for measuring the moisture content of bulk substances containing a housing, a receiver-capacitive moisture converter, a sealant, a measuring electrical circuit, a power supply, a capacitive humidity converter is made in the form of a rectangular container of dielectric material, limited on two sides by two flat electrodes, is divided by a common electrode in parallel with two others into two equal sections, one of which is divided into two sections, the second and third, while the third section is filled with a material with a dielectric constant equal to the maximum dielectric constant of the substances studied for moisture, and made with the possibility of changing the dielectric constant, in addition, the common electrode is installed below the top of the tank, and external electrodes smaller than the walls are installed at its level and are remote from the bottom and lateral surfaces, a sealant is installed above the receiver with the possibility of releasing the receiver window, the measuring electrical circuit includes series-connected g generator, a bridge circuit to which the electrodes of a capacitive humidity transducer are connected, a differential amplifier with rectification, an amplifier with a variable bias, the output of which is connected to the output signal processing unit in terms of level, a recorder.

 A capacitive transducer, also known as a receiver of an analyte, represents a differential capacitor. When the receiver is filled with dry matter, the differential electric capacity is 0, because in the first and second sections, one substance, and in the third section, the dielectric constant is selected equal to the same dry matter characteristic. If there is moisture in the substance, a difference appears in the electrical capacitance due to the different sizes of the first and second sections, i.e. different amounts of moisture in the first section and in the other two. Capacitive difference characterizes the degree of moisture of the test substance.

 The retreat of the external electrodes from the bottom and side surfaces of the receiver reduces the dependence of the measurement results on uneven compaction. With this design, uneven compaction can take place only in the corner sections. The installation of electrodes below the top of the receiver allows evenly compacting substances with a low density, like flour, with a lightweight sealant with a piston shape identical to the joint shape of the first and second sections. Compaction of other substances, such as grain, soil, is not required.

 To change the dielectric constant in the third section using, for example, this technique. This section is filled with plates parallel to the electrodes of a substance with a dielectric constant maximum for the studied dry substances. By some mechanism, the plates can be separately removed from the core between the electrodes. Since the studied solids have a small dielectric constant from 5 to 2 (A. A. Lapshin. Electric moisture meters. Gosenergoizdat, Moscow, 1960, 114 pp.), The selection of the required dielectric constant is not difficult.

 The design with a differential capacitor allows you to take advantage of a two-channel electrical circuit with a generator, a measuring bridge, a differential amplifier with rectification, a variable bias amplifier, an output signal processing unit by level and a recorder (R. Til. "Electrical measurements of non-electric quantities. Energoizdat, M., 1987, 192 p.).

 The differential capacitor electrodes are connected to the two shoulders of the measuring bridge, powered by the signal of a medium-frequency generator, for example 400 - 500 kHz. The differential amplifier produces a difference signal proportional to the difference capacitance of the receiver, the amplifier with a variable bias allows you to set the countdown to 0 on the recorder scale.

 The level signal processing unit is made of series-connected variable resistances and switches, which allow you to close the resistance chain to a common point at the desired point. This unit, together with a mechanism for changing the dielectric constant in the third section of the receiver, allows you to smoothly configure the device to measure the moisture content of any bulk substance without any assumptions about its physical qualities and the use of a processor with memory.

 The mechanical design of the device and the operation of the differential measuring electrical circuit ensure the stability of the device, reduce the temperature effect, the influence of dielectric loss, nonlinearity in the formation of the output signal from the degree of moisture. This is because the harmful signals (interference) in both channels have the same nature and one sign and in the differential amplifier weaken each other. Ultimately, the measurement performance is increased by increasing the accuracy of the measurement results and simplifying the design of the device.

 In FIG. 1, 2 and 3 show a general diagram of the device, a top view of the receiver and the processing unit of the output signal by level. 1 - receiver - capacitive humidity transducer. 2, 3 and 4 - the first, second and third sections of the receiver. 5. Common electrode. 6. External electrodes. 7. Measuring circuitry. 8. The bridge circuit. 9. Differential amplifier with rectification. 10. Variable bias amplifier. 11. The node processing the output signal by level. 12. The registrar. 13. The generator. 14. The power supply. 15. Sealant. 16. Variable resistance. 17. Switches.

 The whole device is made in one case. Electronic elements of the measuring electrical circuit are assembled on one board. The receiver window protrudes above the upper base of the housing. The seal 15 is mounted above the receiver window.

 Calibration of the recorder scale is performed according to samples of known humidity. To remove the test substance from the receiver, the receiver window is freed from the seal and the device is tipped over, the small size and weight of the device allow this.

 Humidity measurement is as follows. The offset of the amplifier 10 sets the countdown 0. The test substance is poured into the receiver 1 above the level of the electrode 5. The moisture content in percent is removed from the scale of the recorder 12. If a substance of low density, like flour, it is poured to the top of the receiver, compacted and then humidity is fixed.

Claims (1)

 A device for measuring the moisture content of bulk solids, comprising a housing, a receiver - a capacitive humidity transducer, a sealant, a measuring electric circuit, a power supply unit, characterized in that the capacitive humidity transducer is made in the form of a rectangular capacitance of dielectric material, bounded on two sides by external flat electrodes, divided the common electrode is parallel to two others in two equal sections, one of which is divided into two sections - the second and third, while the third section is filled with mater Scrap with a dielectric constant equal to the maximum dielectric constant of the substances tested for humidity, and made with the possibility of changing the dielectric constant, in addition, the common electrode is installed below the top of the tank, and the external electrodes are smaller than the dimensions of the walls of the tank, installed at its level and removed from the bottom and side surfaces of the container, the seal is installed above the receiver with the possibility of releasing the receiver window, while the measuring electrical circuit includes no connected generator bridge circuit to which are connected a capacitive humidity transducer electrodes, a differential amplifier with a rectifying amplifier with variable displacement, which is connected to the output of the output node of the signal processing level, the registrar.

Images