Method and apparatus for the determination of at least one property of a product

The invention relates to a method for detecting at least one property of a substance by evaluating the detuning caused by the presence of the substance of an RF resonator to which microwaves are fed and from which a high-frequency signal influenced by the substance is taken, the resonance frequency shift thereof and attenuation against a signal unaffected by the substance is detected, wherein microwaves with at least two different frequencies are fed to the resonator, the resonance frequency shifts are detected by comparing the resonance curves of the resonator that are not influenced and influenced by the material, and the attenuation is detected by comparing the amplitudes of the resonance curves at the frequencies of the supplied microwaves.

The invention also relates to an arrangement for detecting at least one property of a substance, with a resonator to which microwaves can be supplied by a generator and from which a high-frequency signal influenced by the substance for detecting its resonance frequency shift and attenuation compared to that unaffected by the substance Signal can be removed and fed to an evaluation circuit, with a supply of microwaves with at least two different frequencies from the generator to the resonator and with a resonance frequency shift by comparing the resonance curve influenced by the substance with respect to the resonance curve unaffected by the substance and the attenuation by comparing the amplitudes of the substance and Circuit arrangement detecting unaffected resonance curves.

The object on which the invention is based consists in a further development of the method described at the beginning and the arrangement specified above.

According to the method according to the invention, the solution is that microwaves of two frequencies are fed to the resonator, both of which are associated with a falling edge of the resonance curve.

Further refinements of the method according to the invention can be found in the subordinate method claims.

The arrangement mentioned at the outset is characterized by the supply of microwaves of two frequencies, both of which are associated with a falling edge of the resonance curve, to the resonator.

Further refinements of the arrangement according to the invention can be found in the subordinate arrangement claims.

The advantage associated with the invention is that the two values ​​of the rectangular modulation oscillation are easier to keep stable than, for example, a sinusoidal modulation oscillation. There are also advantages in the formation of the evaluation signals generated by the modulation.

In the drawing, the invention is explained in more detail using an exemplary embodiment.

Show it:<dl id="dl0001" compact="compact"><dt>Figure 1</dt><dd>1 a circuit arrangement for detecting quantities of a substance with a resonator arrangement, to which a microwave signal frequency-modulated by a rectangular oscillation is fed,</dd><dt>Figure 2</dt><dd>the course of the resonator curves and the evaluation signals with an empty and filled resonator arrangement corresponding to the circuit arrangement according to FIG. 1,</dd><dt>Figure 3</dt><dd>a circuit arrangement for detecting the dry mass and / or the wet mass of increments of a tobacco mass flow (cigarette rod) wrapped with a cigarette paper strip,</dd></dl>

In FIGS. 1 and 2, the frequency of a microwave output signal of a microwave generator 3 lying in the GHz range (for example at approximately 6 GHz) is periodically switched between two values ​​by a frequency control arrangement 24. For this purpose, a rectangular AC voltage of z. B. 100 Khz can be used. This is shown in FIG. 2a, in which the changes over time in the frequencies f are shown. The average frequency fm is changed periodically between two values ​​f2 and f1 in accordance with the rectangular curve s in the frequency range Δf. The output signal from the microwave generator 3 is fed via a circulator 18 to prevent feedback from a high-frequency resonator arrangement 1 (HF resonator) which is penetrated by a wrapped tobacco rod, that is to say a cigarette rod. The density / mass or moisture content of the tobacco moving through the resonator is to be determined using the circuit arrangement described below. In principle, a strand with a different filling, e.g. B. a so-called filter strand can be measured. Details of an RF resonator 1 which is very advantageous for the aforementioned purpose can be found in DE application 197 05 260 from 02/12/97 / US application 08-799129 from 02/13/97 / EP application 97102166 from 02/12/97.

As shown in FIG. 2b, the average frequency fm is preferably at the turning point of the resonance curve u0, which was determined in the resonator 1 without tobacco for different frequencies of the microwaves supplied. The course of the resonance curve in resonator 1 containing the material to be measured is shown in FIG. 2b. f0 and f are the resonance frequencies when the resonator 1 is empty or filled. The lower frequency value f1 on the resonance curve u0 of the empty resonator 1 corresponds to the value Uof1, on the resonance curve u of the sample containing resonator the value Uf1; the upper frequency value f2 corresponds to the value UOf2 (resonance curve uO of the empty resonator 1) or Uf2 (resonance curve u of the resonator 1 filled with material to be measured). The output signals of the resonator 1, that is to say the resonance signals at the lower (f1) and the higher (f2) modulation value, are sent via a further circulator 19 to suppress unwanted feedback of a microwave diode 22 (e.g. of the HP 8472 B type from Hewlett -Packard) supplied, which converts the microwave signal into a DC voltage signal. This signal is fed to a scanning arrangement 51, which is controlled by a synchronizing arrangement 52 as a function of the rectangular AC voltage of the frequency control arrangement 24. The control takes place in such a way that the voltage values ​​of the resonator 1 are queried just when the microwave generator 3 feeds microwaves with the higher or lower frequency values ​​f2 or f1 of the modulation oscillation s to the resonator 1. In this way, the values ​​Uf2 and Uf1 can be obtained, which are transferred to short-term memories 53 and 54, respectively. Their output signals are a summing element 56, which has the value ½<maths id="math0001"><math display="inline"><mrow><mtext>(Uf2 + Uf1) = Ug</mtext></mrow></math><img file="EP0902277A1_D0001.tif" /></maths> forms, as well as a subtraction element 57 which supplies the difference <maths id="math0002"><math display="inline"><mrow><mtext>Uf2-Uf1 = Ua</mtext></mrow></math><img file="EP0902277A1_D0002.tif" /></maths> forms both output signals. These signals are fed to an evaluation arrangement 11 described in FIG. 3, in which the density / mass values ​​or the moisture values, in particular of the tobacco in the cigarette rod, are determined.

A special circuit arrangement can ensure that the microwave generator 3 receives a correction signal via line 31 as soon as the average frequency fm migrates from the turning point of the resonance curve u0. The correction signal brings the frequency fm of the output signal of the generator back to the value that corresponds to the turning point of the resonance curve.

FIG. 3 schematically shows the processing of the signals Ua, Ug from FIGS. 1 and 2 in the evaluation arrangement 11 for determining the mass / density values. The signals are first stored in digitized form in memories SUg, SUa. These signals are queried by a scanning arrangement in a sequence, the specific increments of the cigarette rod passing through the resonator 1, for. B. 1 mm correspond. This means that with a production speed of the cigarette rod of 10,000, 60 mm long cigarettes / min. the sampling rate is 100 microseconds, i.e. the values ​​(signals) are sampled in the memories SUg and SUa every 100 microseconds. With even shorter transmission pulses Ig and Ia, the values ​​are transmitted in computing stages Rg and Ra, in which they are offset against constants for initial values ​​Ag and Aa. In a simple case, the calculation can be carried out using polynomials of the type <maths id="math0003"><math display="inline"><mrow><mtext>a + b Ug = Ag</mtext></mrow></math><img file="EP0902277A1_D0003.tif" /></maths> or. <maths id="math0004"><math display="inline"><mrow><mtext>c + d Ua = Aa</mtext></mrow></math><img file="EP0902277A1_D0004.tif" /></maths> respectively. The constants a, b, c and d are determined by parameterization, in which cigarettes are measured with masses / densities precisely determined by weighing with regard to the assigned Ug and Ua values. The constants can be determined from the relationships between different densities / masses and the associated values ​​of Ug and Ua. In principle, higher order polynomials or other functions can also be used. The output signals Ag and Aa are fed to an adder Ad, whose output signal Ae corresponds to the density / mass. If the signal Ae emitted by Ad deviates from the exact value of the mass / density, a correction element Kg can emit an empirically determined correction signal Ak to a further addition element Add, the output signal Aed of which corresponds even more precisely to the density / mass value of the tobacco rod.

In principle, the measurement signals can be evaluated in the same way according to the tobacco moisture of the tobacco rod. Instead of certain known weights (density / mass), cigarettes with certain known wet masses, that is to say with different values ​​of the relative humidity, are then used for the parameterization.