WO2022208117A1

WO2022208117A1 - Method and measurement arrangement for on-site measurement of the moisture content of grains

Info

Publication number: WO2022208117A1
Application number: PCT/HU2022/050025
Authority: WO
Inventors: Ferenc VÖLGYI; Gábor DÉVAI
Original assignee: Dunakontroll Kft.
Priority date: 2021-03-30
Filing date: 2022-03-23
Publication date: 2022-10-06
Also published as: HUP2100133A2; EP4314785A1; HU231483B1

Abstract

Method and arrangement for on-site measurement of the moisture content of grain crops in an open or openable metal container (1), wherein the metal container (1) has planar side walls (2, 3) extending from a rectangular base. Pairs of transmitting and receiving antennas (4,5) is used for transmitting and receiving RF signals in the microwave range, facing each other in pairs with respect to their directional characteristics. One or more pair of transmitting and receiving antennas (4, 5) are placed on a vertically movable frame (6), and during measurement are moved from a position above the grain crop in the container (1) to a position immersing into the grain crop in the container (1).

Description

METHOD AND MEASUREMENT ARRANGEMENT FOR ON-SITE MEASUREMENT OF

THE MOISTURE CONTENT OF GRAINS

The present invention relates to a method for on-site measurement of the moisture content of grain crop in an open or openable metal container, wherein the metal container has planar side walls extending from a rectangular base, in the method at least one pair of transmitting and receiving antennas is used for transmitting and receiving RF signals in the microwave range, facing each other in pairs with respect to their directional characteristics, and arranged at a predetermined from each other in the axis direction, the transmitting antenna is fed with RF signals in the microwave range, and the received signals of the receiving antenna are transmitted to an evaluation unit. The invention further relates to a measuring arrangement for performing the method.

More specifically, the method is used for intermittent, real-time (on-line) microwave moisture measurement of agricultural grain crops in a metal container open from above wherein a device comprising at least a pair of opposed transmitting antennas on a common frame capable of transmitting radio frequency signals, and a receiving antenna for receiving the transmitted signals is immersed in the content of the container from above, by means of a power supply and a control unit in control connection with at least one of the antennas, the transmitting antenna transmits a radio frequency signal, which signal is input to the signal processing unit by means of the receiving antenna. The direction of radiation of the transmitting and receiving antennas is on one axis and they are immersed in a high attenuation medium during measurement. The immersion of the precision-oriented antennas makes the measurement of the materials inside the metal container possible, while the high attenuation prevents the antennas from being coupled to the metal wall. By positioning of the antennas, it is possible to influence how much of the total contents of the container is affected by the measurement, so that the representativeness of the measurement can be modified according to the given quality assurance requirements.

The measurement of moisture in grain crops is crucial at all stages of cultivation technology and post-harvest crop handling. Determining the exact water content is very important during drying and storage of crops. The present invention relates to a technology for measuring the moisture content of grain crops in a metal container. The measuring system, which implements the microwave transmission vector measurement, determines the moisture content of agricultural grain crops and seeds transported in a metal container open from above in a batch operation without sampling. In the case of a load, it is advisable to carry out the measurement in 1 to 3 places by temporarily stopping the vehicle carrying the container.

The closest solution known in the state of the art is our utility model application U1500107, registration number 4625, which is a structural arrangement for a radio frequency measuring system for determining the moisture content of various materials. The apparatus of this utility model has a transmitter for transmitting a radio frequency signal and a receiver for receiving the signal from the transmitter and a power supply, characterized in that it has an antenna for transmitting the signal to a receiver, a control unit in control communication with at least one of the transmitter or the receiver and a signal processing unit. The measuring principle and the basic arrangement of the present invention are the same as the arrangement described in claim 1 of the utility model, however, the utility model does not mention how it is possible to perform a transfer measurement in a metal container, since the metal container shields the microwave measurement. The solution according to the utility model and thus the present invention also performs a transmission (attenuation, phase-shift) measurement, however, the utility model does not describe a support frame for fixing at least one antenna pair and a measuring method, which makes measuring the moisture content of the material in the metal container possible.

Several studies deal with measuring the moisture content of maize in a microwave apparatus, one of the first relevant articles being the Versatile microwave moisture sensor (F. Volgyi, Conference Proceeding SBMO'89, Sao Paulo, Brazil, 1989, Vol. II, pp. 457-462). Among other things, the article introduces a moisture content measuring device that measures the water content of wet corn with microwave using a batch sampler. The sampler is a container openable at the top and the bottom separately in a controllable manner, located on the wall of a tube for conveying the corn. When the upper trapdoor is opened, the maize fills the container with the transmitter and receiver antennas on its walls, closes its trapdoors for the duration of the measurement, empties the sample by opening the lower trapdoor and prepares for measuring another sample by closing the lower trapdoor. The solution differs from the present invention in that it is only suitable for measuring a small amount of sample and measures at a high frequency (8-10 GHz). The above solution is similar to the present invention in that it uses microstrip antennas. The antennas used in close solutions can be divided into three groups: horn antennas, focused beam antennas, and microstrip antennas. In the case of lens focused beam antennas, it is easy to implement and also allows the calculation if the test sample is located further away from the antennas, but such antennas require a lot of space (1 -5 m long equipment). Horn antennas also require more space than microstrip antennas, which can be completely flat and 3 to 8 mm thin. In the case of horn antennas and microstrip antennas, the sample is in direct contact with the antenna, so in these cases the near-field effect already occurs. Close solutions measure at a high frequency (8-10 GHz), where the near field effect becomes manageable above an antenna distance of 15 cm for horn antennas, while it requires only 3-4 cm for microstrip antennas (Figure 2). It is worth mentioning that the referenced solution was the first to use low-cost microwave building blocks instead of an expensive vector network analyzer, thus making a wide range of applications possible. A similar solution is disclosed in Patent Application U.S. 1 ,900,195,259, which describes a probe for measuring moisture content. The probe contains a support member, a transmitting antenna, a receiving antenna and a limiter, which prevents direct signal transmission between the two antennas. The device is based on the principle of near-field coupling, so it does not measure the transmission radiation, so it is only suitable for measuring the moisture content of a small amount of relatively low-moisture materials located in the immediate vicinity of the probe. Due to the attenuation, this arrangement allows the measurement of moisture content at most 2-9%.

Patent application GB 2359630 discloses a solution which is also suitable for real-time measurement of moisture content. During operation, the transmitting antenna emits low frequency microwaves through the sample to a receiving antenna. To determine the moisture content, the attenuation of the microwave radiation and a second parameter are measured. The second parameter can be the phase or in case of porous sample the resonant frequency. The technical solution is suitable for measuring pasta, baked goods, cereals, flour, coffee, soups, granules and nuts. As the materials to be measured must flow between the antennas, this solution is not suitable for measuring materials transported in a container.

The device described in US2020182906 comprises a sensor head and a measuring unit. The sensor head consists of a first probe and a second probe. The first probe contains the transmitting antenna and the second probe contains the receiving antenna. The first probe is arranged opposite the second probe, spaced a certain distance from it. The measuring unit comprises a signal generator which generates a measuring signal. The medium between the two antenna sections changes the output signal. The sensor head may further include an electrical conductivity sensor for determining the electrical conductivity of the medium. During the measurement, the moisture content is determined by measuring the delay time of the electromagnetic wave emitted from the first probe and then calculating the relative permittivity of the medium. The description thus includes a structure that holds the antenna pairs, but its size is much smaller, according to the measurements described in the description, the air gap above 1 mm impairs the measurement possibilities, so it is not possible to determine the moisture content of the grain product with this structure. The technical solution referred to does not measure attenuation.

In summary, there are technical solutions that use a pair of antennas mounted on a frame immersed in the tested medium, some that measure the moisture content of the tested medium by measuring transmission parameters, but none of the solutions mentions the positioning of the antenna pairs according to the present invention for implementing the measuring method in a high attenuation medium. The measurement in the metal container is not yet solved. There is no arrangement that determines the moisture content by measuring a transfer vector by using an antenna pair immersed in a medium transported in a metal container. In the known solutions the moisture content of the grain crops is measured in a sampling vessel, possibly in a streaming place, but these solutions are not suitable for comprehensive quality control during delivery to a plant.

The Hungarian patent P9601630, published by Ferenc Volgyi et al. , utilizes the modern microwave technologies of that time. The above-mentioned patent titled "Method and equipment for measuring the parameters of material systems" utilizes modulated scattering technique (MST) and the principles of wireless local area networks (WLANs). It is suitable for the continuous testing of large chipboards during production. Due to the significant microwave attenuation of grain crops, MST technology cannot be used to achieve the current objective.

For automatically operated grain dryers, moisture sensors are required that provide continuous, on-line (real-time) information on the condition of the grain. This system for measuring the moisture content of maize is described by F. Volgyi in the document: Integrated microwave moisture sensors for automatic process control (Ch.15 in book Microwave Aquametry, IEEE Press, New York, pp.223-238, ISBN 0-7803-1146-9.) that uses flat-panel microstrip antennas and low-cost microwave circuit elements. The method is not suitable for testing large quantities of grain in a metal container.

U.S. Patent No. 8,629,681 to Trabelsi and Nelson uses a single frequency attenuation and phase measurement to determine the moisture content and density of granular and piece materials. Their method essentially utilizes the principles laid down previously, which were previously presented at ISEMA (International Society for Electro Magnetic Aquametry) conferences. The novelty of their method is that they also calculate the density and provide an algorithm suitable for dropping the uncertainty of the phase measurement. As their system is for measurement in a sample holder, it cannot be used for measurement in a metal container.

The printed (microstrip) antennas already quoted above and methods for producing circular polarization can be found in the book titled Antenna Theory, Analysis and Design (by Balanis, C. A., 1997., published by John Wiley & Sons, Inc. New York, ISBN 0-471 -59268- 4, p. 941.).

An interesting method that can be used in reflective technology is described by Ferenc Volgyi in his article published in England (Volgyi, F. 2007. Application of microwave aquametry in civil engineering and in power generation, Meas. Sci. Technol., 18 (2007), 1094-1104, IOP Publ., Ltd., UK.). Transmitting and receiving antennas placed on one side are cross-polarized. The reflector on the other side amplifies the received signal and also rotates the polarization. With this method, significant attenuations can be bridged, but the homogeneity and “polarization keeping” properties of the medium are important, so it cannot be used in grain crops.

For storing and using agricultural grain crops it is very important to know the moisture content of a consignment. Although the moisture content of corn, wheat, soybeans and rice in the rainy autumn season is between 23-28%, the crops are still harvested to maintain the still high grain content at that time. However, in order to avoid mold and rot, this moisture content must be reduced to less than 13%. It would therefore be important, both economically and technologically, to know the moisture content at the time of delivery. The problem is that currently there is no moisture measurement device and procedure which can provide representative data of the total quantity delivered during container delivery. Containers used to deliver crops are typically made of metal and they are open from above. The samples taken to determine the moisture content are of small quantity, the results of their drying test are not representative relating to the entire consignment, and the principles of measurement by radiating the entire load do not work due to the metal wall of the container.

The inventor's recognition has been influenced by the prior art telecommunications solutions used by military organizations: interception of antenna pairs operating at 60 GHz is difficult because waves of this frequency are effectively attenuated by air, so perceptible communication takes place between only precisely directed transmitting and receiving antennas. In the present case, too, this phenomenon is exploited when the high-attenuation medium prevents the antennas from being coupled to the wall of the metal container, while at the same time measuring the material between the two antennas can be performed. The moisture content of fodder and crops is currently measured by manual sampling and by means of devices capable of examining small samples. Such measurements are not representative of the total load, they show a large variance in values, and do not allow large quantities of material to be measured in a short time.

It has been realized that our microwave system based on measuring transmission vectors, which has already been used successfully to measure the moisture content of paper bales, could also be used to measure grain crops if the transmitting and receiving antennas were immersed in the grain crops from the open top of the containers. Thus, the moisture content of the grain in the space between two antennas arranged in a known distance attenuates the emitted radiation, the modified values of which are detected at the receiving antenna. With this solution, it is possible to measure the moisture content of a large amount of material transported in open metal containers in a short time.

The present invention in its most general form, is the method and measuring arrangement of the preamble, wherein one or more pair of transmitting and receiving antennas are placed on a vertically movable frame, and during measurement are moved from a position above the grain crops in the container to a position immersing into the grain crops in the container. In the following, the invention will be described by means of the Figures, wherein:

Figure 1 shows the measuring device according to the invention immersed into a full container, in a partially broken-up representation;

Figure 2 is the general view of the measuring device according to the invention immersed into an empty container;

Figure 3 is a plan-view of an arrangement comprising a pair of measuring pair arranged at an angle to the walls;

Figure 4 is plan-view of an arrangement comprising a pair of measuring pair arranged perpendicular to the walls; and

Figure 5 is a plan-view of an arrangement comprising two measuring pairs arranged at an angle to the walls.

In the different Figures the identical component parts have the same reference numbers.

In the general arrangement according to the invention, a container 1 is shown in Figure 1 in a partially broken-up representation which is open or openable from above, having flat metal side walls 2, 3 extending upwards from a rectangle base. The container 1 contains grain crop filled up to the surface F. The object of the present invention is to measure the moisture content of the grain crop on the spot. For this purpose, RF signals in the microwave range are used. An antenna pair comprising a transmitting antenna 4 and a receiving antenna 5 facing each other in terms of their directional characteristics. These are mounted on a stable frame 6. The distance between the transmitting antenna 4 and the receiving antenna 5 is known and constant due to the frame 6. The frame 6 is fixed to a moving device so that during the measurement the antennas can be immersed in the medium to be examined in a depth m below the surface F with the frame 6. The transmitting antenna 4 and the receiving antenna 5 and the frame 6 can preferably move relative to a stand higher than the height of the container 1 to be measured. Advantageously, a vertical rod provides a vertical connection between the transmitting antenna 4, the receiving antenna 5 and the frame 6. The received signals of the receiving antenna 5 are sent to an evaluation unit (not shown) where they are processed. This processing is not part of the present invention.

Fig. 2 shows the measuring device of Fig. 1 , in a general view, placed in an empty container, to illustrate the positioning of the meter.

The device according to the invention is guided and driven during the measurement from a position above the grain crop to a depth m immersing into the grain crop in the container 1 . Before the measurement, the vehicle carrying the container 1 stops at the measuring point. The moving device on the stand immerses the transmitting antenna 4 and the receiving antenna 5 mounted on the frame 6 into the content of the container 1 , below the surface F. To this end, the transmitting antenna 4 and the receiving antenna 5 are streamlined, for example in the form of a shield or a lance, and, if appropriate, the frame 6 is streamlined in such a way that immersion in the crop is hindered as little as possible.

After immersion, the measurement process takes a few seconds, during which the transmitter antenna 4 generates a signal by means of a driver and a signal generator, which is modified as it passes through the medium (attenuation, phase shift) depending on the specific amount of water in the medium. The receiving antenna 5 receives the modified signal, from which the system can deduce the specific amount of water.

According to a preferred embodiment, circularly polarized printed (microstrip) antennas with a ceramic coating are used for the measurements. The printed transmitter antenna 4 and receiving antenna 5 are flat, which allows easy immersion in the grain crop, and with this type the near-field coupling also interferes less with the evaluation of the measurement results.

Another advantage of using circularly polarized transmitter antenna 4 and receiver antenna 5 is that due to their internal structure the grain products absorb microwave radiation to varying degrees depending on their orientation. Although in most cases (especially for spherical crops such as soybeans, peas, etc.) the arrangement of the grains in a container is random, so the seeds in different orientations are evenly distributed during each measurement, and by using the circularly polarized transmitter antenna 4 and receiver antenna 5 attenuation anomalies (especially in case of elongated crops) resulting from the random arrangement can also be eliminated. The standard moisture content of the grain crops during delivery also allows measurement in any antenna direction, but when measuring a medium with a lower moisture content, i.e. a medium with less attenuation, the radiation may reach the metal wall of the container 1. Fig. 3 shows an arrangement in which in such cases the axis direction 7 of radiation must deviate from the longitudinal or transverse axis of the container 1 so that the radiation reflected from the metal wall of the container 1 does not affect the measurement. In the event of a deviation from the length L in the longitudinal direction and from the width W of the container 1 in the transverse direction, the reflected radiation travels a longer distance, thereby suffering significant attenuation before reaching the receiving antenna (again). However, according to the embodiment shown in Figure 4, the axis direction 7 of the radiation can be parallel to the longitudinal direction of the container 1 of length L or the transverse direction of the container 1 of width W.

According to another preferred embodiment, shown in Figure 5, another pair of transmitting antenna 4 and receiving antenna 5 are arranged on the frame 6 holding the transmitting antenna 4 and receiving antenna 5. The axis direction 7 of radiation of them is preferably perpendicular to the first pair of antennas and they are used for performing a control measurement.

In the technical solution according to the invention, the measurement of the transmission values is performed, which is more advantageous than the resonator and the reflection measurement. During the resonator measurement, the container 1 itself causes disturbing resonances at lower frequencies. Reflection measurement allows less sensitivity and less accurate measurement.

According to a preferred embodiment, the direction of the axis direction 7 of radiation between the transmitting antenna 4 and receiving antenna 5 of the frame 6 according to Figure 3 or 5 may deviate optionally, preferably 10-80 degrees from the longitudinal axis or the transverse axis perpendicular to it. This placement ensures that the reflection from the metal side walls of the container 1 is kept to a minimum. There is no reflection from the bottom of the container 1 due to the high microwave attenuation of the medium and the suitably designed vertical directional characteristics of the transmitting antenna 4 and receiving antenna 5. This characteristic and the absorption of the medium also help to ensure that the radiation of the transmitting antenna 4 and receiving antenna 5 pressed into a depth m (preferably m = 0.4-0.8 m) does not enter the free space from the inside. According to the invention, the preferred axis direction 7 distance is 0.5-2.0 m, preferably approx. 0.8 m, the measurement frequency is preferably around 0.4-1 .0 GHz, advantageously around 900 MHz. In addition to these values and the dynamic range of the measuring device, grain crops with a high moisture content can also be measured. The exact dimensions are preferably determined according to the desired representativeness, the size of the container 1 , the static parameters determining the stand and the movement of the stand.

The result of the measurement may be influenced by the temperature; therefore, a thermometer probe is mounted on the support frame 6 and the measured value can be used for calculation.

The following examples illustrate the use of the invention in specific cases.

Examples

Example 1/a

Corn has a moisture content of 23-28% at harvest. It then contains the most nutrients, but it must be kept below 13% for storage. Accordingly, the test range is the moisture content of 10-30%. The moisture content, set at around 10%, 20% and 30%, was determined accurately by drying. At 900 MHz, the wavelength is -33.3 cm, so the signal cannot resonate in principle, even in a case of a large corn kern (about 15 mm in length). At 4.5 GHz, resonance is already possible at high humidity contents, just as 100 MHz is not suitable, because in that case the conduction currents already affect the measurement, which in turn depends on the salt content.

Maize measurement results for an immersion depth of 0.8 m and a distance of 1 .0 m in the axis direction 7:

Average dimensions of corn kernels: L= 10.7 mm, W= 7.6 mm, H= 4.2 mm.

The “longish” form factor is: FT= [L/(W.H)^A1/2]-1 =0.89 spherical shape embossed on two sides (Oblate). Average dry density ro = 0.69-0.83 g/cm3. The measurement data show that for q> 20% the phase shift can be used to determine the humidity.

Example 1/b Maize measurement results for an immersion depth of 0.4 m and a distance of 1.0 m in the axis direction 7:

The measurement results show that at the 0.4 m immersion, part of the transmitter energy is radiated into the environment, so less transmission attenuation is measured, especially for drier material, and the reflections caused by the metal wall can also be detected. It can be stated that in the case of 0.8 m immersion the measurement does not involve such disturbing reflections or losses, deeper immersion is not necessary, it is not economical due to the higher drag, in extreme cases the antennas may attach to the bottom wall of the container, which again reduces the reliability of the measurement result.

Example 1/c

Maize measurement results for an immersion depth of 0.8 m and a distance of 0.6 m in the axis direction 7:

Although the measured attenuation and phase values are comparable and suitable for calculation, the measured volume is cubically smaller than at greater antenna distances, thus the representativeness of the measurement is reduced.

Example 2

Wheat measurement results at an immersion depth of 0.8 m and a distance of 1.0 m in the axis direction 7:

Average dimensions of wheat grains: L= 7.2 mm, W= 2.7 mm, H= 2.2 mm, FT= 1 .95 Ellipsoidal average dry density: ro= 0.69-0.88 g/cm3.

Example 3 Soybean measurement results at an immersion depth of 0.8 m and a distance of 1.0 m in the axis direction 7:

Average soy sizes: L= 8.1 mm, W= 6.7 mm, H= 5.6 mm, FT= 0.32. Spherical seeds, average dry density: ro= 0.67-0.71 g/cm3. It is true for all the examples that the results of control measurements in the perpendicular direction do not differ significantly from the basic measurement.

Claims

1 . Method for on-site measurement of the moisture content of grain crops in an open or openable metal container (1 ), wherein the metal container (1) has planar side walls (2, 3) extending from a rectangular base, in the method at least one pair of transmitting antenna (4) and receiving antenna (5) is used for transmitting and receiving RF signals in the microwave range, facing each other in pairs with respect to their directional characteristics, and arranged at a predetermined distance from each other in the axis direction (7), the transmitting antenna (4) is fed with RF signals in the microwave range, and the received signals of the receiving antenna (5) are transmitted to an evaluation unit, characterized in that the one or more pair of transmitting and receiving antennas (4, 5) are placed on a vertically movable frame (6), and during measurement are moved from a position above the grain crop in the container (1) to a position immersing into the grain crop in the container (1)·

2. Method according to claim 1 characterized in that in the immersed position the axis direction (7) between the one or more pairs of transmitting antenna (4) and receiving antenna (5) are different from the direction perpendicular to the side walls (2, 3).

3. Method according to any of claims 1 -2 characterized in that the transmitting and receiving antennas (4, 5) are identically circularly polarized.

4. Method according to any of claims 1 -2 characterized in that the transmitting and receiving antennas (4, 5) are opposite polarized in pairs.

5. Method according to any of claims 1 -4 characterized in that the transmitting and receiving antennas (4, 5) are flat, printed (microstrip) antennas.

6. Method according to any of claims 1 -5 characterized in that the transmitting and receiving antennas (4, 5) have the form of a shield or a lance.

7. Method according to any of claims 1 -6 characterized in that two pairs of transmitting antennas (4) and receiving antennas (5) are used.

8. Method according to claim 7 characterized in that the axis direction (7) between the two pairs of transmitting antennas (4) and receiving antennas (5) is perpendicular to each other.

9. Measuring arrangement for implementing the method according to claim 1 for on-site measurement of the moisture content of grain crops in an open or openable metal container (1), wherein said metal container (1) has planar side walls (2, 3) extending from a rectangular base, containing at least on pair of transmitting antenna (4) and receiving antenna (5) applicable to transmit and receive RF signals in the microwave range, facing each other in pairs with respect to their directional characteristics, and arranged at a predetermined distance from each other in the axis direction (7), the one or more transmitting antennas (4) are fed with RF signals in the microwave range, and the received signals of said receiving antenna (5) are transmitted to an evaluation unit, characterized in that said one or more pairs of transmitting and receiving antennas (4, 5) are placed on a vertically movable frame (6), which is guided and driven during the measurement from a position above the grain crop in said container (1) to a position immersing into the grain crop in said container 1.

10. Measuring arrangement according to claim 9 characterized in that said frame (6) is fixed to a vertically movable structure.

11. Measuring arrangement according to any of claims 9-10 characterized in that in the immersed position said axis direction (7) between the one or more pairs of transmitting antenna (4) and receiving antenna (5) are different from the direction perpendicular to said side walls (2, 3).

12. Measuring arrangement according to claim 11 characterized in that said axis direction (7) between the one or more pairs of transmitting antenna (4) and receiving antenna (5) deviates 10-80 degrees from the direction perpendicular to said side walls (2, 3).

13. Measuring arrangement according to any of claims 9-12 characterized in that it contains two pairs of transmitting antennas (4) and receiving antennas (5).

14. Method according to claim 13 characterized in that said axis direction (7) between the two pairs of transmitting antennas (4) and receiving antennas (5) is perpendicular to each other.