Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
  • G01N27/221—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance by investigating the dielectric properties
• • A—HUMAN NECESSITIES
  • A24—TOBACCO; CIGARS; CIGARETTES; SIMULATED SMOKING DEVICES; SMOKERS' REQUISITES
  • A24C—MACHINES FOR MAKING CIGARS OR CIGARETTES
  • A24C5/00—Making cigarettes; Making tipping materials for, or attaching filters or mouthpieces to, cigars or cigarettes
  • A24C5/32—Separating, ordering, counting or examining cigarettes; Regulating the feeding of tobacco according to rod or cigarette condition
  • A24C5/34—Examining cigarettes or the rod, e.g. for regulating the feeding of tobacco; Removing defective cigarettes
  • A24C5/3412—Examining cigarettes or the rod, e.g. for regulating the feeding of tobacco; Removing defective cigarettes by means of light, radiation or electrostatic fields

Definitions

• the invention relates to a Meßvomchtung for determining a dielectric property, in particular the humidity and / or density of a product, in particular of tobacco, cotton or other fiber product, according to the preamble of arrival 1.
• the invention further relates to a corresponding measurement method.
• capacitive measuring devices for determining the moisture or the mass of tobacco are known in which a measuring capacitor and a coil are connected as frequency-determining parts in a high-frequency resonant circuit (US 3,979,581, DE 25 00 299, DE 24 41 832, DE 37 43 216 C2, DE 38 25 111 Al).
• a high-frequency resonant circuit US 3,979,581, DE 25 00 299, DE 24 41 832, DE 37 43 216 C2, DE 38 25 111 Al.
• the affected by the product resonant frequency and resonant amplitude of the high frequency field are determined.
• the temperature dependence of the capacitor and the coil affects the accuracy of measurement.
• Special, particularly temperature-stable capacitors and coils, as known for example from DE 37 43 216 C2 are complicated and expensive.
• the use of a large capacitance and a large inductance may be required to produce the measuring resonance frequency used, which leads to an increase in the production costs and the size of measuring capacitor and coil.
• the object of the present invention is to provide a structurally simple and compact high-frequency measuring device with high accuracy and improved stability to temperature influences.
• the invention solves this problem with the features of the claims 1 and 29.
• a running high-frequency wave and a substantially non-resonant circuit means in which therefore the measuring capacitor is not frequency-determining part of a measuring resonant circuit, can on the use of a temperature effects sensitive resonant circuit coil can be dispensed with.
• the term "high-frequency" means, in contrast to the microwave range, fields with a frequency below 100 MHz, as a rule the frequency is more than 10 kHz, preferably more than 100 kHz, more preferably the frequency is at least 1 MHz, in particular for tobacco more preferably at least 5 MHz, since at lower frequencies towards a sufficiently accurate measurement is possible only in an increasingly limited range.
• the part of the circuit device serving to determine the measured variables is usually connected downstream of the actual measuring circuit which comprises the measuring capacitor. While the measuring circuit usually has an output for the affected by the product high-frequency wave, the Meßierenbestungsscnies usually has two outputs for the specific measured variables. It is also possible that the measuring circuit and the Meß istnbeéessscnies form a unit.
• the measured variable determining circuit is connected upstream of the actual evaluation device for determining the dielectric property of the product. It is also possible that the Meß istnbeticiansscnies and the evaluation form a unit.
• the portion of the circuit device serving to determine the measured variables is designed to be digital-electronic.
• a particularly simple and therefore preferred method is based on the orthogonality of the sine and cosine components and comprises the measurement of a discrete number of n measured values, for example voltage values, over each oscillation period of the high-frequency field, separate multiplication of the n measured values with corresponding sine and cosine values and separate summation of these sine and cosine products. The sums obtained represent the measured variables or can be further processed to determine the measured variables.
• the measuring capacitor comprising part of the circuit device is an RC element, preferably with an operational amplifier. This is preferably an RC differentiating element, but it can also be used, for example, an RC integrator.
• parts of the sensor are made of a material having a low coefficient of thermal expansion in order to minimize the effects of temperature fluctuations on the measuring accuracy.
• the sensor may have an additional means for keeping constant the temperature of the measuring capacitor.
• An additional device for measuring the temperature of the measuring capacitor for example a temperature sensor, is conceivable, - A - to correct the measurement signal accordingly.
• the capacitor is arranged substantially perpendicular to the transport direction of the product.
• the capacitor plates are arranged perpendicular to the transport direction. This makes it possible to arrange the electrodes at a short distance from each other, for example below the strand thickness of the product. As a result, an improved resolution can be achieved when measuring the product profile in the longitudinal direction.
• the sensor is designed to pass the product through the space formed between the electrodes of the measuring capacitor in order to allow a complete and uniform detection of the product. It is therefore preferably not a stray field sensor.
• the senor comprises a plurality of measuring capacitors arranged across the width of the product.
• This arrangement allows a simple measurement of a product profile across the width of the product.
• the electrodes fed with the high frequency wave are kept at the same potential, for example simply shorted, in order to minimize crosstalk between the measuring capacitors.
• the other electrodes are also preferably kept virtually at the same potential by means of inverting operational amplifiers.
• Fig. 1 a schematic circuit of a substantially analog measuring device
• 2 shows a differential measuring circuit for a measuring device
• 3 shows an integrating measuring circuit for a measuring device
• FIG. 5 shows a cross-sectional view of a capacitive sensor in a further embodiment
• FIG. 6 shows a schematic circuit of a substantially digital measuring device
• FIG. 8 shows an operational amplifier for a differential measuring circuit for the measuring device from FIG. 7.
• Measurement signals corresponding to the measured variables are passed to the evaluation device 21, for example a correspondingly programmed computer, by means of which the desired dielectric property, for example the moisture and / or the density, of the product 12 is determined from the determined measured variables. Due to the evaluation of two independent measured variables, it is possible, for example, to determine a product density independent of the product density and / or a product density independent of the product moisture. For the evaluation can be used in the evaluation 21 stored and previously in a calibration procedure certain calibration curves.
• the embodiment of FIG. 1 relates to a substantially analog measuring device.
• the high frequency generator 13 comprises a harmonic oscillator 22 for generating a high frequency wave.
• the voltage amplitude U e of the generated high-frequency wave is preferably kept constant by means of a control device 23-26 in order to allow a measurement uninfluenced by fluctuations in the input amplitude.
• the high frequency wave generated by the harmonic oscillator 22 is fed to a controllable amplifier 23.
• the output signal of the amplifier 23 is fed to a rectifier 24, whose output signal is passed through the low-pass filter 25 to a controller 26.
• a signal dependent on the generated high-frequency wave is expediently conducted to the circuit device 28 via a line 34, 234 provided in addition to the measuring line via the measuring capacitor 11 in order to be able to use the phase information of the input signal for determining the phase shift of the output signal.
• the signal thus obtained is proportional to the output amplitude U a times the sine (or cosine) of the phase shift ⁇ .
• FIG. 1 A preferred embodiment of a high frequency sensor 38 is shown in FIG.
• the sensor 38 is constructed substantially rotationally symmetrical about the longitudinal axis L.
• the product strand 12 for example a tobacco rod
• the sensor comprises two rotationally symmetrical, disc-shaped, oriented perpendicular to the longitudinal direction L base body 40, 41, which are spaced apart by means of an outer, annular, non-conductive limiting body 44 and each having a central through hole 39 for the product strand.
• the measuring capacitor 11 is therefore designed as a plate capacitor with plate-shaped electrodes 15, 16, which are oriented in a circular disk and perpendicular to the longitudinal direction L and have a central passage opening for the product strand 12.
• the field lines are substantially parallel to the transport direction.
• Between the base bodies 40, 41 a field-filled space 45 is formed, which is closed by the limiting body 44 radially outward.
• the high frequency field extends into the central product space 46 and is there with the product 12 in interaction.
• the plates 15, 16 have a smaller radius than the base body 40, 41 in order to prevent leakage of the high-frequency field in the vicinity of the sensor.
• the plates 15, 16 of the plate capacitor 11 can be arranged at a small distance d from each other in order to improve the measuring resolution in the longitudinal direction L and to allow an accurate measurement of the product profile in the longitudinal direction.
• the distance d may in particular be less than the diameter of the product strand 12 and, for example, less than 8 mm, preferably less than 4 mm.
• the main body 40, 41 each have a rschreib enförmi conditions, axially outwardly extending, comprising the product strand extension 47, 48.
• the extensions 47, 48 have an inner-walled metallic surface or coating 49, which is expediently connected to the electrodes 15, 16.
• the metallic coating 49 forms a metallic chimney to prevent leakage of the field from the product feedthrough openings of the condenser 11.
• the field-filled space 45 formed between the electrodes 15, 16 may be partially or completely filled, apart from the product space, with a dielectric material for positively influencing the field profile.
• the bodies 40, 41, 44 of the sensor 38 are preferably made of a non-conductive material with a very low coefficient of thermal expansion, for example Zero dur, in order to achieve increased dimensional stability of the sensor 3S against temperature influences. Due to the reduced dependence of the capacitance characteristics of the measuring capacitor 11 on the ambient temperature, an improved measuring accuracy can be achieved.
• a control device not shown, is preferably provided for keeping the sensor temperature constant. It is also conceivable that the base body 40, 41 of the sensor 38 completely or partially made of metal.
• the measuring device 10 has a means 222 for generating a scanning signal having a sampling frequency which is higher by a factor n than the frequency of the high-frequency wave.
• the sampling signal is passed via line 70 to the A / D converter 66.
• the measured values sampled by means of the A / D converter 66 are passed to the digital processing device 67, which is programmed to determine suitable, independent measured quantities.
• each sampled measured value is multiplied on the one hand with the corresponding value of the sine function and on the other hand with the corresponding value of the cosine function.
• the scanning signal is passed via the line 70 to the processing device 67.
• the sine and cosine values can, for example, be taken from corresponding tabular memories 68, 69.
• the n sine values and n cosine values thus obtained are then summed separately over a period of the high frequency field so that two sums are obtained.
• the high-frequency input signal is passed via the line 234 to the processing device 67, so that it operates in phase with the high-frequency generator 13.
• the two desired measured quantities dependent on the amplitude and the phase of the measurement signal influenced by the product 12 can be unambiguously determined on the basis of specific orthogonality relationships.
• the determined measuring signals are conducted via the output lines 19, 20 to the evaluation device 21, in which the evaluation is carried out, for example, by means of a computer program stored therein.
• the signal generated by the radio frequency source 222 may also be used to generate the radio frequency wave used for the measurement.
• the signal generated by the high-frequency source 222 is divided by the factor 60 into a phase-synchronous rectangular oscillation with the measuring frequency of 5 MHz in the present case and then into a phase-synchronous sinusoidal signal by means of the PLL circuit 61 same frequency converted.
• the control device 223, 62-64, 226 for keeping constant the voltage amplitude U e of the high-frequency wave output by the amplifier 223 can also be designed in digital electronic form.
• the output of the amplifier 223 is fed to an A / D converter 62 which is driven via a line 65 with the sampling signal of 50 MHz, whereby per sample n samples of the amplifier 223 output signal are generated.
• the measured values sampled by the A / D converter 62 are sent to the digital processing device 63.
• each sampled voltage value is multiplied by the corresponding value of the cosine function.
• the scanning signal is passed via the line 65 to the processing device 63.
• the cosine values can, for example, be taken from a corresponding tabular memory 64. The n cosine values obtained in this way are then summed over a period of the high-frequency field.
• the high-frequency input signal is conducted via a line 71 to the processing device 63, so that it operates in phase with the high-frequency generator 13.
• the output signal of the processing device 63 is forwarded to the controller 226, which controls the amplifier 223 in such a way that the output signal of the processing device 63 and thus the amplitude U e of the oscillation at the output of the amplifier 223 has a constant value.
• the embodiment according to FIG. 7 is used in particular for measurement on a wide, web-shaped product 312, for example a tobacco web, a tow web or a cotton fleece whose width B is substantially greater, for example at least by a factor of 3, than its height H.
• a Another application relates to the measurement of a plurality of adjacent product strands, such as tobacco strands.
• the transport direction is perpendicular to the paper plane.
• Corresponding parts are designated by corresponding 300 reference numerals.
• a plurality of measuring capacitors 31 IA, 31 IB, ... are used, here for example six, which are arranged across the width of the product. This arrangement makes it possible to measure a profile, for example the density profile, across the width of the product.
• each measuring capacitor 31 IA, 31 IB, ... downstream inverting operational amplifier 330 is particularly advantageous in this embodiment, since this the output electrodes 316A, 316B, ... all Meßkondensatoren 31 IA, 31 IB, ... virtually on the same potential, in particular mass are laid. As a result, the crosstalk between the measuring capacitors 31 IA, 31 IB, ... is minimized.

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• 2004
  • 2004-12-22 DE DE102004063228A patent/DE102004063228B4/de not_active Expired - Fee Related
• 2005
  • 2005-12-17 WO PCT/EP2005/013831 patent/WO2006069721A2/de active Application Filing
  • 2005-12-17 US US11/793,947 patent/US7679377B2/en not_active Expired - Fee Related
  • 2005-12-17 CN CNA2005800442487A patent/CN101088008A/zh active Pending
  • 2005-12-17 JP JP2007547352A patent/JP4526043B2/ja not_active Expired - Fee Related
  • 2005-12-17 EP EP05821925A patent/EP1836482A2/de not_active Withdrawn

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