BRIEF DESCRIPTION OF THE DRAWINGS
The method according to the invention is described in more detail hereinafter with reference to an embodiment, as well as with reference to two curves, in which:
FIG. 1 shows a block diagram of the method according to the invention,
FIG. 2 shows a measurement of the triacetin value in mg in comparison with reference values,
FIG. 3 shows the comparison of measured moisture values with predetermined reference values and,
FIG. 4 shows a schematic view of a microwave measuring device for determining a local softener concentration.
DESCRIPTION
The method according to the invention is described in more detail hereinafter with reference to FIG. 1. In a first step 10 filter rods are removed from the production process manually or automatically through a filter rod hopper. The filter rod hopper supplies the removed filter rods for measuring to a filter rod measuring station. In one method step 12 in the filter rod measuring station, the mass M of the filter rod is provided. In a subsequent step 14 the filter rod is supplied to a microwave sensor. The microwave measuring device has a microwave resonator into which the filter rod to be measured is introduced. In the microwave resonator a stationary wave is formed with the resonance frequency, with which a filter rod to be measured interacts. The filter rod with its spatial expansion and its electrical properties alters the resonator so that the resonance curve occurring in the resonator is altered. Two alterations in the resonance curve are important for the measurements. On the one hand, a shift of the resonance frequency occurs. This variable is denoted by A. The second characteristic variable is the shift B of the resonance curve. The alteration A may be primarily due to the real part of the dielectric constant of the inserted filter rod, whilst the alteration B is primarily based on the imaginary part of the dielectric constant. Generally, the parameter A is used for determining the mass of the product. The ratio of the variables B/A is independent of the mass and provides an indication of the moisture content.
In step 14 the microwave sensor detects, in a manner known per se, the measured variables A and B. In a subsequent step 16, the measurement of the draw resistance (PD) is carried out which is also denoted as “pressure drop”. The draw resistance specifies the pressure drop through the filter rod which is present with a defined air flow. It is important here that measurements are carried out with stationary air flow and transient effects are not considered, as occur when increasing or reducing the air flow.
In a final method step 18 the diameter of the filter rod is measured.
The data obtained in the filter measuring station are processed in an evaluation unit in the measuring station. Particularly advantageous for the measurement of the triacetin mass is the following formula:
Mtriacetin=a0+a1*A+a2*B+a3*M+a4*PD.
This formula is important in that the variables PD for determining the triacetin mass enter into the equation.
The moisture content is determined as:
Mmoisture=b0+b1A+b2*B+b3·M/A,
even a term b4?M/B being able to be considered additionally to or instead of the b3 term.
FIG. 2 shows for different titres (1.6 Y30, 2.5 Y36, 3.0 Y35 and 5.0 Y40) the comparison between measured moisture content values on the ordinate with predetermined reference values on the abscissa. It is clearly visible that a reliable detection of the moisture is carried out with the method according to the invention. It is a distinctive feature in the determination of the moisture content in the filter rod that this is able to be carried out independently of the titre. In other words, a set of parameters (b0, b1, b2, b3) which, independently of the titre of the material, discloses the moisture content.
Shown in FIG. 3 is the measurement of the triacetin content. In this connection, again the measured variables are applied to the ordinate, whilst predetermined reference values are applied to the abscissa. Also in this case the above formula is a reliable measurement for determining the triacetin mass in the filter rod. In contrast to the determination of moisture, with the determination of triacetin, the coefficient set (a0, a1, a2, a3, a4) is not independent of the titre of the material. This means that for evaluating the measured data, the titre of the material additionally has to be known in order to select the correct set of parameters.
In addition to the aforementioned formula in which the triacetin mass is detected directly dependent on the measured variables A, B, M and PD, there is also the possibility of determining the dry masses in an approximate manner via other combinations (tabular values). Thus it is known, for example, to determine the approximate dry mass from the value of the draw resistance and the diameter of the filter rod. From the dry mass, the triacetin amount may then again be determined in combination with the measured mass M and the characteristics of the microwave measuring device. Combining these tabular values for the dry mass with the microwave measured values has, therefore, the object of improving the insufficient accuracy of these tabular values and compensating for the variation in moisture effect. In contrast to the predetermined formula, consideration is additionally given in this case to the measured variables A, B, M and the draw resistance PD, as well as the diameter (D) of the filter rod. As, however, the approximate dry mass is only determined by two measured variables, this method is on the whole less accurate than that first described.
FIG. 4 shows a microwave measuring device which is suitable for measuring a triacetin profile in a filter rod. The microwave measuring device corresponds in its construction substantially to the microwave measuring device known from EP 0 889 321 A1. The microwave measuring device according to FIG. 4 has a resonator cavity 20 through which a filter rod 22 is transported in the direction 24. The filter rod 22 is supplied to the resonator cavity via a guide tube 26. Due to the selected geometry for the resonator cavity, the characteristic variables A and B are measured in a region 28. The guide tube 26 has a diameter 28 which is slightly larger than the diameter of the filter rod 22. In the region 30 the guide tube 26 is placed on the resonator body. The microwaves are fed into the resonator cavity 20 via a microwave transmitting aerial 32, where they are measured and/or again decoupled via a microwave receiving aerial 34. The resonator cavity is defined by an upper part 36 and a lower part 38. The geometry is selected in this case such that the height D is markedly smaller than the extension of the resonator cavity in its expansion transversely to the direction of transport 24. The measured values A and B provide information about the triacetin concentration in the portion 28 and thus allow by transport of the filter rod 22 a plurality of portions on a filter rod to be measured. Each individual portion may be evaluated according to the method disclosed above.
Tests have shown that when measuring, the time passed since the production of the filter rod also has an important effect. It has been shown that it is possible to operate within the first ten minutes, with a coefficient set which is time-independent. If the time duration of 10 minutes from the application of the triacetin is exceeded and thus hardening has started, it has been proved that the coefficient sets for determining the triacetin mass are altered. A determination of the triacetin mass is, however, also possible with the altered coefficient set.
In a particularly preferred embodiment, the detected measured data are processed by a control unit and compared with predetermined reference values. If the comparison shows that the triacetin value or the dry value of the processing material which is actually present deviates too sharply from the corresponding reference value, a warning signal may be triggered. The accuracy of the measurements has also shown that the measured values are, in principle, suitable for adjusting both the mass flow and the triacetin flow in the process of manufacturing the filter rod.
Patent Application
20080054912
