FI65497C - MAETAPPARATUR FOER BESTAEMNING AV TAETHET OCH FUKTHALT I KORNIGA ICH FIBROESA AEMNEN SAMT VAETSKOR - Google Patents

Description

65497

MEASURING INSTRUMENT FOR DETERMINING THE DENSITY AND MOISTURE OF GRANULAR, FIBROUS AND LIQUID SUBSTANCES

This invention relates to a radio frequency measuring sensor and system by which the density and moisture of snow, sand, grain, peat and similar poorly electrically conductive granular, fibrous or liquid substances or certain other properties can be determined by pushing the sensor. to the substance and by measuring the resonant frequency and quality factor of the resonator in the sensor.

Today, snow moisture is most commonly measured by calorimetric methods. The measurement is based on the fact that due to its melting temperature, snow placed in the hot water of a calorimeter requires more heat than heating the water in the snow 10 to the same temperature. The measurement is time consuming and its accuracy is very poor when the snow is relatively dry (humidity a few percent or less). Slightly more accurate is the so-called. a cold calorimetric method in which the water contained in the snow is frozen. It uses a liquid with an initial temperature of about -50 ° C. Ko. liquids are often toxic and highly explosive. In practice, the accuracy it achieves is about one percentage point. In calorimeter measurements, snow must be sampled, which can change the structure and moisture of the snow.

Capacitance sensors are also currently used to measure the moisture content of snow, sand, grain and similar granular materials. They are based on measuring the change in capacitance caused by humidity. The mit background frequency is relatively small, usually in the frequency range 50 Hz ... a few MHz, where e.g. the ionic conductivity present in some substances degrades accuracy. A calibration curve is required for each substance, assuming that the density of the substance is always the same. If the density changes, the capacitance differs from the assumed value and an incorrect value is obtained for the humidity. The moisture content of peat and similar wet substances is measured by weighing the sample wet and after drying. Measurement takes a lot of time and energy. It is difficult to sample so that some of the water 30 does not run off.

2,6497 31 The measurement sensor and method of the present invention seeks to eliminate the weaknesses and sources of error of the above measurement methods. The measuring method presented here is characterized in that the measuring sensor is inserted into the substance to be measured and that it is a resonator operating in the radio frequency band 35, the resonant frequency and the goodness number of which are measured. The resonator is constructed in such a way that it does not substantially change the structure of the substance to be measured when it is pushed into the substance, but the electric and magnetic fields of the resonator penetrate it. In this case, the resonant frequency is primarily determined by the density of the substance to be measured, pe-40, and the quality factor depends primarily on the amount of water, i.e. moisture. For each substance to be measured, a graph showing the dependence of the resonant frequency and the goodness of number on the density and humidity can be determined either experimentally or in some cases also theoretically. In this case, both the density and the moisture of the substance to be measured can be determined from the diagram on the basis of the unambiguously measured resonant frequency and the goodness number. The measurement of the resonant frequency and the goodness number can be done very quickly, so the measurement method is suitable for fast field measurements.

In the following detailed description, reference is made to the following 50 figures.

Figure 1 Measuring sensor made of needles and strip at the front.

Figure 2 Side sensor made of needles and strip.

Figure 3 Diagram showing the dependence of snow dlelectric constant and loss angle on density and humidity.

55 Figure 4 Measuring sensor made of needles and two strips.

Figure 5 Measuring sensor for a printed circuit.

Figure 6 Measuring sensor for a printed circuit with a circular resonator.

Figure 7 Resonator made of needles and a printed circuit.

60 Figure 8 Measuring sensor made in a metal tube.

Fig. 9 is a block diagram of an electron silk apparatus with which the resonant frequency and the quality factor of the measuring sensor 62 are measured automatically.

65497 63 The measuring sensors according to the invention, which are suitable for measuring the density and humidity 65 of snow, sand, grain and other granular or fibrous substances, are shown in Figures 1 and 2 and 4 ... 7. The measuring sensor in Figure 1 consists of two thinner metal A and a resonator made of a metal strip B connecting them, to which two coaxial wires D and E are connected by switch loops C for measuring the resonant frequency and the goodness number. The resonator and the coupling loops 70 are attached to each other and to the measuring lines by means of a thin insulating material plate F. There can also be only one test lead and switch loop. Figure 2 shows the measuring sensor from the side. The pins A, the strip B and the plate F must be sufficiently thin that they do not significantly affect the density of the substance, but are so strong that the resonator can be pushed into the substance to be measured, if necessary. Experiments have shown that, for example, 3 mm thick rods with a distance of 25 mm and a length of 80 mm form a suitable resonator for measuring snow, grain and loose sand, but other dimensions are naturally possible depending on the situation. The rods and the strip connecting them form an open transmission line resonator at one end 80, the resonant frequency of which is known to be 11, the frequency at which the line is a quarter wavelength in the substance to be measured. On the basis of the resonant frequency, the real part of the dielectric constant of the substance can thus be calculated, and on the basis of the goodness number, the angle of loss of the substance is obtained, which naturally takes into account the resonator's own losses. The dimensioning according to the above example leads to the substances to a resonant frequency in the UHF range. Figure 3 shows a graph for snow, from which the density and moisture of the snow are determined when the dielectric constant and the loss angle are measured. In general, it is preferable to select the resonator size 90 so that the resonant frequency is at VHF, UHF, or SHF. In this case, several substances are avoided, e.g. in snow and sand, ions at lower frequencies caused by large variations in dielectric constant, which make the measurement method inaccurate.

Figure 4 shows a measuring sensor, which is otherwise similar in structure to that of the sensor 95 of Figure 1, but with the fingers A is short-circuited ylapäässäkin B. Resonanssltaajuus sealing strip 96 is now the frequency at which the resonator is 65 497 April 97 1ikimäärin a half-wave length of the measurement medium. If the resonator is inserted into the substance to be measured, both strips B must be sufficiently thin that they do not significantly alter the structure of the substance.

Figure 5 shows a measuring resonator made by the printed circuit method. The metal li pattern is marked with dots in the figure. It has a resonator A made for the printed circuit G and coupling loops C. The measuring lines D and E are attached to the plate. The printed circuit insulator-105 plate is so thin that the resonator can be easily inserted into the material to be measured, if necessary. Of course, the resonator can also be, for example, circular in shape as in Fig. 6 or elliptical or rectangular without changing the measuring principle.

Fig. 7 shows a measuring sensor made of pins A attached 110 to a printed circuit G having a short-circuit strip B and switch loops C. The measuring wires D and E are attached to the printed circuit. They can be a rigid coaxial line and form a rigid arm from which the resonator can be inserted into the substance to be measured.

Figure 8 shows a measuring sensor suitable, for example, for measuring the moisture and density (fiber content) of leached peat and similar substances having a high water content. The resonator of the sensor is formed by two elongate slots J made at the end of the metal tube H, to which the measuring line K is connected by means of a coupling loop L. The measuring line is attached to a metal strip M. The end of the tube is provided with a tip N made of a durable material (metal 120 or insulating material), which facilitates the insertion of the sensor into the material to be measured. The resonator part of the tube from part N to part M can be filled with a suitable insulating material P, e.g. an araldii account, so that the surface of the tube is smooth and the substance to be measured does not enter the tube. There can, of course, also be 125 test leads and coupling loops. The metal tube can be inserted into the substance to be measured, e.g.

the bog, whereby by measuring the resonant frequency and the goodness number, the moisture content of the peat at the resonator is determined as previously described. According to experience, a resonator suitable for Finnish measurement is, for example, a pair of slits made in a 25 mm thick steel pipe, where the length of the slits-130 is 25 cm. The resonant frequency is then in the VHF range.

5 65497 131 Figures 1 and 2 and 4 ... 7 show only some possible measuring sensor structures. Other similar resonant structures, which are flat or rod-like, are naturally possible.

The measuring device according to the invention is, of course, also suitable, in addition to or instead of the density or moisture of granular, fibrous and liquid substances, for determining other properties which affect the dielectric constant or goodness number of the substance. Thus, the device can be used, for example, to determine the mixing ratio of two electrically different liquids and to determine the salt content of water.

140 The resonant frequency and the quality factor of the measuring sensor can be measured in ways known from microwave technology using either one or two measuring lines.

Fig. 9 shows a block diagram in an electron silk assembly assembled from known electronic components, with which the measurement of the resonant frequency 145 and the goodness number can be performed automatically. The signal source a becomes a signal via the direction switch b to the measuring sensor c. The signal source is a voltage-controlled oscillator, the frequency of which is swept with a triangular voltage over the entire required frequency range. A power proportional to the power flowing to the measuring sensor is obtained from the direction switch, which is already detected and the resulting voltage is confirmed. Similarly, the power coming out of the measuring sensor is detected and the voltage obtained is confirmed. A ratio of voltages is formed in the ratio element d, whereby the transmission curve of the measuring sensor is obtained. The peak value of the transmission curve% is determined by the peak value indicator e. At the same time, a voltage U3dB is calculated which is 3 dB lower 155 than the sampling circuit f determines the values Uki and U | <2 of the sweeping voltage at times Based on 2, the frequencies corresponding to the 3 dB bandwidth of the resonator are measured, and based on the average of U ^ itn and U | <2 ', the resonant frequency is obtained. The quality factor, in turn, is obtained on the basis of a resonant frequency of 160 and a bandwidth of 3 dB. If the frequency-voltage characteristic of the voltage-controlled oscillator is not sufficiently linear, the electronic part can be provided with a linearization circuit g.

Claims (7)

6 65497 1. A measuring device for determining the properties of granular, fibrous and liquid substances, comprising a high-power power supply, a measuring sensor and electronic circuits for recording measurement results, characterized in that the measuring sensor is a shaped resonator which can push electrical properties and properties of the substance and the magnetic field penetrates the material such that by determining the resonant frequency and losses of the resonator, two different properties of the material are detected simultaneously. Measuring device according to Claim 1, characterized in that a measuring sensor which is inserted into the moist substance is used for simultaneous determination of the density and moisture of the substance. Measuring sensor according to Claim 1, characterized in that the resonator is assembled from metal 11 trees A and a strip or strips B connecting them. Measuring sensor according to Claim 1, characterized in that the resonator is made, in whole or in part, on a sturdy thin printed circuit. t A measuring sensor according to claim 1, characterized in that the measuring wire or wires are rigid, forming a hand-line for inserting the sensor into the substance to be measured. Measuring sensor according to Claim 1, characterized in that the resonator is formed by a gap or slits made in the side of the metal tube to be inserted into the substance to be measured.