Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Reexamination Certificate
1997-09-24
2001-12-04
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
C073S061790, C073S064530, C073S598000, C073S600000, C073S627000, C073S628000
Reexamination Certificate
active
06324901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention refers to a method for detecting foreign bodies in liquid or solid material masses, especially in foods, as wall as to a device for implementing this method.
2. Description of the Prior Art
Numerous foods, especially milk products, e.g. yoghourts as well as baby food, are often produced on large scale in industrial manufacturing processes. Before filling the finished foods, a thorough examination for any foreign bodies possibly existing is required among other tasks. These foreign bodies can get into the foods during the production process on the one hand, or, on the other hand, they can exist in individual ingredients, e.g. fruit.
Within fish processing, light tables are used, e.g. for examining fish fillets. For obvious reasons, however, these tables are not suitable for examining the foods mentioned above and, in addition, they have the disadvantage that the actual testing is made by visual inspection and it cannot therefore be automated.
Moreover, there are known X-ray apparatuses using X-rays according to the same principle in which the visual inspection is made via a display screen. This method has one additional disadvantage, viz. the corresponding working places are subjected to increased intensity of radiation.
From DE-OS 40 13 402, a process for the detection of gas bubbles in liquid-filled pipes is known, as well as the device needed for this process, in which a transmitter and a receiver are positioned on either side of the pipe and transmit single impulses fixed in length and level to determine the presence of gas bubbles within the pipe through the change in the impulses after traversing the liquid. This well-known process is not suitable for the examination mentioned above since it can only detect a gas phase within a liquid phase. The difference in density between gas and liquid is much higher than that between foreign bodies and food (viscose mass and liquid mass).
From the magazine “Elektronik”, Nr. 25/1991, a “particle detective” is known that works with high frequency ultrasound according to the (Doppler) principle. The disadvantage of this method is that it again is very work-intensive and cannot be automated.
Finally, in U.S. Pat. No. 4,607,520, a process and a device for the detection of bubbles in a flow of liquid is described. For this process, ultrasound impulses are sent through a designated segment of the liquid to be examined. During a time frame that is opened after the impulse running time, it is checked whether the impulses reached the receiver. If this is not the case, it is assumed that there is a lack of homogency (a gas bubble) within the designated segment. Again, this process is not suitable for the testing of food for any foreign body contents.
The invention was therefore based on the requirement to specify a method for detecting foreign bodies in viscous or liquid material masses, especially in foods, as well as a device for implementing this method and also enabling automated testing.
SUMMARY OF THE INVENTION
As to the method, this requirement is met by continuous conveying of the material mass at predetermined speed through a measurement line section, by the transmission of ultrasonic signals through the material mass transported in the measurement line section, by the reception of the transmitted ultrasonic signals after passing through the material mass, by a comparison of at least one received ultrasonic signal with at least one transmitted ultrasonic signal for detecting variations of at least one predefined signal parameter, as well as by generating an alarm and/or activation signal when the variation of at least one signal parameter exceeds or falls short of a predetermined limit value, in order to interrupt the material transport and/or to divert the material mass from the transport flow.
Foreign bodies can be recognized quite easily even if the foods screened are not homogenous, but contains solid pieces, as long as the length and frequency of the ultrasound impulses transmitted are predetermined. In that case, a weakening in amplitude without a change in duration of the impulse signals the presence of a foreign body, whereas the presence of e.g. a piece of fruit or another form of concentration as well as a lowering in the concentration of sugar would cause a change in duration of the signal as well as a weakening in amplitude.
One especially advantageous development of this process is to warm up the mass to be tested before running the examination. This method leads to improved results, especially in goods containing pectine, where the foreign bodies (i.e. seeds) are much better discernable from solid pieces of food (i.e. pieces of fruit).
The process preferably also contains an adaptive reinforcement of the ultrasound signal/s and/or an adaptation of the border value/s. This allows for an optimum adaptation to the permeability and consistency of the good to be examined.
Finally, it is also possible to control the amplitudes of the sent ultrasound signals in such a way that the amplitudes of the received ultrasound signals are constant, where the change in manipulated variable is compacted to the predetermined border value. The ultrasound signals are preferably pulsed, so that the running time between transmitter and receiver provides an additional controlling value.
The device according to invention comprises at least one ultrasonic transmitter and at least one ultrasonic receiver, with the measurement line section being led through between the transmitter and the receiver. As an alternative to this, the device can also have a reflector from which the ultrasonic signals are reflected after passing through the measurement line section, pass through the measurement line again, and are finally picked up by the receiver(s). A wall of the measurement line section, e.g. a tube wall, can likewise be used for sound reflection.
One advantage of these solutions lies in the fact that the application of ultrasonic signals leads to no radiation exposure of the environment and that they can be implemented at very low cost because the transmitter and receiver elements, as well as the evaluation unit, require no costly safety provisions, and because generally available standard products can be used. Apart from this, it is quite easy to make a fail-safe test setup for ultrasonic testing due to the fact that high-frequency acoustic signals generally do not exist in the environment at all—or they only exist with very low intensity—and they can be easily screened.
In addition, the power consumption of a corresponding device according to invention is very low in comparison with the known devices or methods mentioned.
One of the predetermined signal parameters is preferably the amplitude of the ultrasonic signals.
Besides, the speed of the variation of amplitude of several ultrasonic signals received successively can also be used as an additional or alternative signal parameter.
Furthermore, a signal parameter—preferably the amplitude of the transmitted ultrasonic signal—can be controlled in such a way that the amplitude of the received signal remains constant, with the variation of the manipulated variable being compared with a predetermined limit value.
It is also possible to modulate the transmitted ultrasonic signals and to evaluate a phase displacement between the transmitted and the received signal as signal parameter.
The preferred method for detecting foreign bodies, which influence ultrasonic signals in quite different ways, is either to use several ultrasonic transmitters operating at different frequencies, or to trigger an ultrasonic transmitter so that its frequency always covers a predefined frequency band.
Several single transmitters and, if applicable, the receiver allocated to each transmitter are preferably Clocked individually in order to avoid mutual interferences.
If the material mass to be tested is filled in receptacles, with the receptacles being formed in a second material mass within the measurement line section, foods that are already packed can also be
Flüh Gerd
Katten Wolfgang
Krieger Josef
Rost Manfred
John Lezdey & Assoc
Larkin Daniel S.
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