Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/02—Food
  • G01N33/04—Dairy products
• • 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
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
  • G01N27/18—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by changes in the thermal conductivity of a surrounding material to be tested

Definitions

• the present invention relates to a method for detecting changes in the state of a liquid or gelled medium, for example the phenomena of gelling of a liquid fluid or of liquefaction of a gel.
• the invention also relates to a device for detecting changes in the state of a liquid fluid in the process of gelling or liquefaction. This invention is particularly applicable to the food industries.
• Berridge method may be used (standard method OG March 20, 1981) that are placed in three different tubes an identical mixture of milk and coagulant, these tubes being arranged in a water bath at 30 ° C and driven by a rotational movement of 3 rpm. We then observe, for each tube, the moment when flakes appear on the walls and we thus calculate an average time which is called visible flocculation time (Tfv).
• Tfv visible flocculation time
• This method is based on the visual acuity of the experimenter and manufacturers want an automatic device.
• the visible flocculation time (Tfv) is located before the instant (Ti &) associated with the inflection point of the temperature curve. It then appears necessary, in this case, to have other information making it possible to determine, in a more precise manner, the visible flocculation time, always by means of an automatic device.
• the method for detecting changes of state according to the invention uses the highlighting of exploitable information on the setting time from the measurement of the phase shift of the response of a probe supplied by a low frequency sinusoidal current. It appears in fact that the moment when the change of state of the medium takes place corresponds substantially to the instant (TiR) associated with the point of inflection of the phase shift or delay curve (R).
• the invention relates to a method for detecting changes in the state of a liquid or gelled medium according to which the phase difference between a rectified low frequency sinusoidal current supplying a resistance probe placed in the medium and the output signal of the medium is measured. said probe for delivering information indicative of the change in state of the medium.
• the invention also relates to a device for detecting changes in the state of a liquid or gelled medium comprising a probe supplied, by means of a generator, by a rectified low frequency sinusoidal current and a measurement unit of the voltage connected on the one hand, to the terminals of the probe and on the other hand, to an electronic data processing unit.
• a platinum wire probe is advantageously used.
• the invention therefore also relates to a method for detecting changes in the state of a liquid or gelled medium according to which energy is supplied in the form of heat to the medium by means of a first probe, powered by a current continuous and constant, and which delivers a signal indicative of the temperature of this first probe, this signal providing first information indicative of the change in state of the medium, characterized in that the phase difference between a rectified low-frequency sinusoidal current is measured, supplying a second probe and the output signal of said second probe to deliver a second piece of information indicative of the change of state of the medium, these two pieces of information being used to determine the moment when the change of state of the medium occurs.
• the invention also relates to a device for detecting changes in the state of a liquid or gelled medium
• a device for detecting changes in the state of a liquid or gelled medium comprising a first probe supplied, via a first generator, by a direct and constant current, and a first voltage measurement unit connected on the one hand, to the terminals of the first probe and on the other hand, to an electro-computer processing unit, characterized in that it further comprises a second probe supplied by intermediary of a second generator, by a rectified low frequency alternating current and a second voltage measurement unit connected on the one hand, to the terminals of said second probe and on the other hand, to said electro-computer processing unit .
• the invention also relates to a method of detecting changes in the state of a liquid or gelled medium according to which energy is supplied in the form of heat by means of a first probe which delivers a signal indicative of the temperature of this first probe, this signal providing first information indicative of the change in state of the medium, characterized in that said first probe is supplied by a high frequency alternating current and in that the phase difference between a sinusoidal current is measured rectified low frequency supplying a second probe and the output signal of said second probe to deliver a second piece of information indicative of the change of state of the medium, these two pieces of information being used to determine the moment when the change of state of the medium occurs.
• the invention also relates to a device for detecting changes in the state of a liquid or gelled medium comprising a first probe supplied with current via a first generator, and a first connected voltage measurement unit on the one hand, at the terminals of the first probe and on the other hand, at the terminals of an electronic data processing unit, characterized in that said first generator delivers a high frequency alternating current and in that said device comprises plus a second probe supplied, via a second generator, by a rectified low frequency alternating current and a second voltage measurement unit connected on the one hand, to the terminals of said second probe and on the other hand, to said electronic data processing unit.
• patent application FR-2626371 discloses a method of studying and controlling the phenomena of gelling of a liquid fluid or of liquefaction of a gel, the purpose of which is to take into account the variations in temperature of the medium susceptible to be coagulated or gelled and to use these characteristics to obtain information solely relating to coagulation phenomena in the strict sense.
• the temperature of the medium is measured by means of a first probe delivering a first signal, while providing said medium with energy in the form of heat by means of a second probe sufficiently distant from the first probe so as not to disturb the latter by variations in temperature, this second probe delivering a signal corresponding to its temperature, after which the signals emitted by the probes are processed after amplification and correction in an electronic data processing unit using the signal for measuring the temperature of the medium to correct the signal supplied by the second thermal quantity probe, so that the information contained in the signal relates to coagulation phenomena strictly speaking.
• the device more particularly intended for the implementation of the above method is characterized by the association of a first probe ensuring the measurement of the temperature of the liquid fluid and a second probe intended to supply energy in the form of heat between.
• These two probes are supplied by DC and constant currents of low value and deliver signals which are transferred, after amplification and correction, to an electronic data processing unit.
• the invention therefore also relates to a method for detecting changes in the state of a liquid or gelled medium according to which:
• the temperature of the medium is measured by means of a first probe, supplied with constant direct current, and delivering a first signal indicative of the temperature of this medium,
• energy is supplied in the form of heat to the medium by means of a second probe, supplied by a direct and constant current and which delivers a second signal indicative of the temperature of this second probe,
• a corrector stage which corrects the signal delivered by the second probe by taking into account the signal delivered by the first probe to deliver a first piece of information, strictly indicative of the change in state of the medium, characterized in that :
• the invention therefore also relates to a device for detecting changes in the state of a liquid or gelled medium comprising:
• a second probe supplied, via a second generator, by a direct and constant current and a second voltage measurement unit connected on the one hand, to the terminals of the second probe and on the other hand, to said electronic data processing unit, characterized in that it further comprises a third probe supplied, by means of a third generator, by a rectified low frequency alternating current and a third unit for measuring the connected voltage d on the one hand, at the terminals of said third probe and on the other hand, at said electronic data processing unit, said processing unit respectively combining the signals coming from the second and third probes with that delivered by the first probe in a correcting stage , to determine the moment of change of state of the medium.
• the second probe which delivers a signal indicative of its temperature, not by a constant direct current, but by a high frequency alternating current.
• the invention also relates to a method for detecting changes in the state of a liquid or gelled medium according to which: - the temperature of the medium is measured by means of a first probe, supplied with constant direct current, and delivering a first signal indicative of the temperature of this medium,
• energy is supplied in the form of heat to the medium by means of a second probe, which delivers a second signal indicative of the temperature of this second probe,
• a corrector stage which corrects the signal delivered by the second probe, taking into account the signal delivered by the first probe to deliver first information, strictly indicative of the change of state of the medium, characterized in that said second probe is supplied by a high frequency alternating current and in that:
• phase shift between a rectified low frequency sinusoidal current, supplying a third probe and the output signal of said third probe, is measured to deliver a third signal
• the invention also relates to a device for detecting changes in the state of a liquid or gelled medium comprising:
• Figure 1 is a schematic view of a first detection device according to the present invention.
• FIG. 2 represents, for a half-period, the curve (I) of an example of sinusoidal current supplying the probe according to the invention as well as the temperature curve ( ⁇ ), corresponding to the response signal of the probe.
• FIG. 3 represents the curve (R) of the delay of the response signal of the probe supplied by a sinusoidal current of frequency 25 Hz as a function of time as well as the curve (& max ) of maximum temperature as a function of time, corresponding to this response signal.
• Figure 4 represents the curve (R) of the delay of the response signal of a probe fed by a sinusoidal current of frequency of 50 mHz as a function of time as well as the maximum temperature curve ( - ⁇ ' max ) and n function of the time, corresponding to this response signal.
• FIG. 5 represents the curve (R) of delay of the response signal of a probe supplied by a sinusoidal current of frequency of 100 mHz as a function of time as well as the maximum temperature curve ( ⁇ " max ) as a function of time, corresponding to this response signal.
• Figure 6 shows a schematic view of a second detection device according to the invention.
• Figure 7 shows a schematic view of a third detection device according to the invention.
• FIG. 8 represents a curve of evolution of the maximum temperature as a function of the dry extract for a frequency of 100 mHz.
• Figure 9 represents the evolution curve as a function of time of the decimal logarithm of the reduced temperature of a probe fed by a step current.
• FIG. 10 represents a curve of evolution of the dry extract as a function of the temperature of a probe supplied with a direct and constant current.
• the sensor device shown in Figure 1 comprises a platinum resistance probe 1 of 100 ohms at 0 ° C and 138.5 ohms at 100 ° C, packaged in a glass bulb, for example having a length of 20 mm, and a 2 mm diameter, this probe having a heating length of 14 mm.
• the platinum lead of the probe is supplied with sinusoidal current rectified from a current source 2.
• with I ma ⁇ 50 mA (1)
• This value of l max corresponds to an effective intensity I 0 of 35 mA.
• the probe supply current therefore comprises a succession of positive half-waves.
• the model milk is reconstituted from a milk powder at the rate of 100 g / kg, supplemented with 10 ml of calcium chloride (stock solution of 0.1 mol / 1) and 1 ml of thiomersal (stock solution of 100 g / 1) and using a temperature of
• the model rennet is in the form of a solution prepared from powdered rennet, the composition of which is as follows: 4438 mg of active chy osine and 63 mg of bovine pepsin per kg. A 50 mg concentration of rennet powder for 1 kg of milk, i.e. 0.22 mg of active chymosin.
• the solution comprises 0.05 mol / l sodium acetate buffer (pH approximately 5.5-5.6) to which 0.1% bovine serum albumin is added. The final concentration is 5% (m / v) of rennet.
• this signal is illustrated by curve I of FIG. 2.
• the voltage across the terminals of the wire is measured by a measurement unit 3, at the output of which is connected an electro-computer processing unit 4.
• This delivers the response signal from the probe, illustrated by the curve of this same Figure 2. It can be seen that this response curve, temperature curve, has a maximum value ( ⁇ ma ⁇ ) and a delay (R) with respect to to the sinusoidal supply current.
• Figure 3 shows that, for a frequency of 25 mHz, the delay signal increases suddenly before reaching a plateau. It is then possible to associate the moment when the medium changes state at the moment (TiR) of the inflection point of the delay curve of the response (R). With regard to the maximum temperature curves shown in Figures 3 to 5, the analysis of descriptive parameters of the evolution of & ma ⁇ over time shows that these curves are identical regardless of the frequency.
• T ⁇ being the time associated with the inflection point of the maximum temperature curve (Q- max )
• Pi ⁇ being the slope at the point of inflection of the curve (6> - max ).
• the maximum temperature curve corresponds to the temperature curve which would be obtained with a probe supplied by a constant direct current.
• Supplying a probe with a low frequency sinusoidal current provides information on the coagulation moment, which is associated with the moment (TiR) corresponding to the inflection point of the delay curve (R).
• Figure 3 shows that the instant (TiR) linked to the inflection point of the delay curve (R) is before that (Ti ⁇ ) of the inflection point of the maximum temperature curve ( max ) •
• the determination of the optimal frequency is subject to two constraints: having a relatively short input time and therefore a relatively high frequency as well as a relatively large phase shift to easily determine the inflection point of the delay curve (R) and therefore a relatively low frequency.
• the various measurements carried out show that this optimal frequency is between 10 and 50 mHz. It then appears interesting to associate the detection method which has just been described with that of document EP-01444443 which has just been recalled. This second method according to the invention will be described with reference to Figure 6.
• FIG. 6 represents a second device for detecting changes of state according to the invention comprising a first probe 5, with platinum resistance, supplied by a direct and constant current, for example of 35 mA, via a first generator 6.
• the voltage at the terminals of this first probe 5 is measured by a measurement unit 7 the output of which is connected to a unit 4 of electronic data processing. This establishes the response curve of the probe supplied with direct current, temperature curve as a function of time and can determine the moment (Ti &) when the inflection point of the temperature curve occurs.
• the voltage at the terminals of this second probe 1 is measured, as in the first device according to the invention, by a measurement unit 3, the output of which is connected to the computer processing unit 4.
• unit 4 establishes the curve (R) of the delay of the response signal from the second probe supplied with alternating current, as well as the curve ( ⁇ max- 1 ° th maximum temperature, corresponding to this response signal.
• L unit 4 can then determine the instant (TiR) corresponding to the point of inflection of the delay curve. It can finally, according to the values of Ti ⁇ * st TiR, give an improved value of the visible flocculation time (Tfv ) and thus precise information on the moment when the change of state of the environment occurs.
• the unit 4 can also determine, from the curve (& max- 1 * th maximum temperature, a value of the instant corresponding to the inflection point of the curve ⁇ - max "As we saw previously, this information is not directly usable but can be used concurrently with that obtained by analyzing the temperature curve ( ⁇ ⁇ ) of the first probe 5 supplied with direct current.
• the first probe 5 can for example be chosen so that the effective intensity is 35 A. This is very advantageous since a discriminatory filtering is thus obtained ensuring greater precision in the measurement of the temperature of the wire. This also makes it possible to simplify the processing of the signal delivered by this first probe 5, processing carried out by the unit 4.
• the device according to the corresponding invention is similar to the second device described with reference to Figure 6, the main difference concerns the first generator 6 which must be able to deliver high frequency alternating current.
• a frequency higher than 200 mHz is preferably chosen.
• the invention relates to a third method for detecting changes in state which will be described with reference to FIG. 7.
• the third detection device represented in FIG. 7 comprises, in addition to the second detection device according to the invention, another probe 10 supplied, by means of another generator, by a constant direct current, for example of 1 my.
• This probe consists of a platinum resistance probe. The voltage across this probe is measured by a measurement unit 9, the output of which is connected to the computer processing unit 4.
• unit 4 determines:
• the unit combines these three signals in a correction stage, which corrects the response signals of the second and third probes 5 and 1, taking into account the signal delivered by the first probe to deliver an improved value of Tfv which is strictly indicative of the change of state of the environment.
• the probe supplied with direct current and which delivers a signal indicative of the temperature of this probe that is to say here the second probe 5, by a high frequency alternating current.
• the device according to the invention is again in this case, similar to the third device described with reference to Figure 7, the difference between these two devices concerns the generator 6 which must be able to deliver a high frequency alternating current. This frequency is preferably greater than 200 mHz.
• the third device which has just been described with reference to FIG. 7, is of particular interest for the determination of the dry extract of a milk.
• the device described with reference to FIG. 7 makes it possible to obtain four information on the dry extract of the milk tested by carrying out four different calibrations from skimmed milk by proceeding as follows.
• the probe 10 is supplied by a constant current of 1 mA and delivers a signal giving the temperature U M of the medium.
• the probe 1 is supplied with a low frequency alternating current.
• Unit 4 determines the delay curve (R) and the maximum temperature curve ( ⁇ " max ) and takes account of the signal - M delivered by the probe 10 to deliver information strictly indicative of the composition of the medium.
• a calibration is performed between the dry extract and the maximum temperature Max 'corrected by the temperature of the medium ⁇ * M , for a determined frequency
• An example of calibration is shown in Figure 8 for a frequency of
• the probe 5 is supplied with a direct current of a value of 1 mA during a given time interval, the current then suddenly passing to a value of 35 mA.
• the temperature of the probe is designated by & " F when it is supplied with a current of 35 mA.
• the first portion of the curve corresponds to the first part of the test where the probe is supplied with a current of 1 mA.
• Q- is worth on average CT M / (y- R is very close to 1, and has a zero decimal logarithm.
• the heat flow supplied by the Joule effect (Rtl 2 ) dissipates first in the probe (platinum wire and cylindrical body glass) causing it to heat up. This dissipation is due to the fact that the probe has a certain specific heat, it does not yet exchange with the surrounding medium. This phenomenon, which corresponds to the second portion of the curve, is less than 13 s.
• a milk-probe gradient then appears which has the effect of stimulating a conductive exchange between the latter two.
• the total flow is divided between the probe and the milk.
• the proportion of flow supplied to the milk increases, which has the effect of slowing down the temperature rise of the probe.
• This results in a sudden change in slope which corresponds to the start of the third portion of the curve.
• the film of milk near the probe undergoes an increase in its temperature therefore a decrease in its density and it is subjected to an upward force.
• a free convection regime then appears. This is the end of the third portion of the curve.
• the temperature of the probe stabilizes around F and R oscillates around a low value.
• the slope of the third portion of the curve can be related to the conductivity of the surrounding medium.
• thermal conductivity and dry extract.

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• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

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• 1990
  • 1990-09-28 FR FR9012038A patent/FR2667400B1/fr not_active Expired - Lifetime
• 1991
  • 1991-09-24 AU AU86470/91A patent/AU8647091A/en not_active Abandoned
  • 1991-09-24 WO PCT/FR1991/000744 patent/WO1992006369A1/fr not_active Application Discontinuation
  • 1991-09-24 EP EP19910917570 patent/EP0550607A1/de not_active Withdrawn

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