Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1993-06-16
2001-09-04
Snow, Walter (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
Reexamination Certificate
active
06285185
ABSTRACT:
The invention relates to an apparatus for determining the type of a battery or accumulator, the apparatus comprising at least one excitation coil coupled to energising means for generating an alternating magnetic field, means for placing the battery or accumulator in said alternating magnetic field and detection means for measuring the induction during the presence of the battery or accumulator in the alternating magnetic field. An application of such a device is the separation of used primary and secondary batteries according to their chemical contents. Separation is desirable for recycling certain types of batteries without contamination by other types or for disposal of spent batteries in special dumps for hazardous waste without filing up the special dump with large amounts of batteries with non-hazardous contents.
The invention also relates to a method for determining the type of a battery or accumulator, comprising the steps of
placing a battery or accumulator in an alternating magnetic field having at least one frequency;
measuring an induction caused by the presence of the battery or accumulator in the alternating magnetic field; and
classifying the battery in accordance with the measured induction.
Such an apparatus and method are known from WO 91/15036. In that document a method and an apparatus is described in which a battery or accumulator (primary or secondary battery) is placed in an excitation coil which, when energised, induces a magnetic flux in the battery. The flux is detected by means of a sense coil. The induced current in the sense coil is analyzed in analyzing means and provides information about the material of the battery or accumulator, enabling to identify the battery as being of a certain type. A drawback of the known method and apparatus is that the selectivity between some of the types of batteries is insufficient, causing a significant overlap in the identification.
Alternative ways of selection, for example by weight, by measuring the force acting upon the battery in a static magnetic field, by measuring the magnetic permeability or any combination of those, also provide insufficient selection due to the large spread of these parameters within a class of batteries and the overlap between different classes. In addition, the different kinds of measurements to be performed reduce the speed of measurement considerably.
It is, inter alia, an object of the invention to provide an apparatus and method for the identification of batteries that is more selective than the known method and apparatus.
To this end, the apparatus in accordance with invention is characterised in that the apparatus further comprises means for establishing a quasi-static magnetic field in the battery or accumulator during the measurement of the induction, said quasi-static magnetic field being applied for causing a substantial saturation in at least a portion of ferromagnetic parts of the battery or accumulator. The invention is based upon the insight that a major reason for the lack of selectivity of the known method is that, presently, many batteries and accumulators are provided with protective and ornamental jackets made of steel (iron). Due to these jackets many batteries have a large iron content which dominates the electromagnetic properties. When the steel jacket is saturated by the quasi-static magnetic field, the magnetic induction for the alternating magnetic field is largely determined by the interior of the battery.
The quasi-static magnetic field is a magnetic field that is substantially constant on the time scale of a measurement, for example, ten to twenty periods of the alternating magnetic field. In view of this time scale, the quasi-static magnetic field may cycle with a frequency about two orders of magnitude below the frequency of the alternating magnetic field. The quasi-static field can be applied both by means of electromagnets or permanent magnets. Permanent magnets provide a constant magnetic field and do not consume energy, while electromagnets allow adjustment of the field strength and simple on and off switching for measurements with and without the saturating magnetic field. The quasi-static magnetic field can be arranged in any direction, but preferably it is oriented perpendicular to the longitudinal axis of the battery. The strength of the quasi-static magnetic field is subjected to an upper limit. Accumulators such as Ni—Cd and Ni(M)H, comprise a ferromagnetic metal (Ni) in the interior which metal should not become completely saturated.
A preferred embodiment of the apparatus according to the invention is characterised in that said detection means comprise at least a sense coil placed near the excitation coil and in that said excitation and sense coils are arranged for surrounding the battery or accumulator during measurement of the induction. In this embodiment the excitation and sense coils form a transformer in which the battery or accumulator under test acts as the transformer core. In this arrangement an inductive coupling almost completely formed by the battery between the coils is achieved, resulting in a measurement with large sensitivity.
An embodiment of the apparatus according to the invention may be further characterised in that the energising means are arranged for energising the excitation coil with an alternating current of constant amplitude. Excitation by an alternating current with a constant (top—top) amplitude generates an alternating magnetic field with a constant amplitude as well, irrespective of the self-induction of the excitation coil. The latter will change due to the presence of the battery or accumulator near the coil. In contradistinction to the apparatus known from WO 91/15036, which uses excitation by an alternating voltage, in the present embodiment the source of excitation as detected by the sense coil is constant.
The apparatus according to the invention can be further characterised in that the energising means is arranged for energising the excitation coil with a low frequency in the range between about 1 kHz and about 5 kHz, preferably around 3 kHz, and/or with a high frequency above about 10 kHz, preferably around 40 kHz. At low frequency alternating magnetic fields have a large penetration depth. Consequently, the induction measured at low frequency reflects the composition of the battery as a whole. As it takes a number of periods, for example ten, of the alternating magnetic field to perform a measurement, higher frequencies are favoured to reduce measurement time. A frequency of about 3 kHz provides a value for which the whole battery contributes to the measured induction and for which the duration of a measurement is short enough for sorting large amounts of batteries and accumulators economically. At higher frequencies eddy currents at the surface become important and the penetration depth is reduced. Above about 10 kHz, the composition of the outer layers of the battery gradually dominates the measured induction. At about 40 kHz only a relative thin layer, in as far not saturated by the quasi-static magnetic field, contributes while the technical requirements for the energising means and the excitation coil are still economically feasible. Generating an alternating magnetic field at significantly higher frequencies becomes more complicated and more expensive.
An embodiment of the apparatus according to the invention may be further characterised in that the energising means is arranged for energising the excitation coil with an intermediate frequency in the range between about 5 kHz and about 10 kHz. An additional measurement in this frequency range, in particular in the range between 6 and 8 kHz, provides a distinction between batteries and accumulators with a large ferromagnetic content in the outer layer and with a large ferromagnetic content in the interior. An example of the first type is the alkaline battery and of the second type the Ni—Cd and Ni(M)H accumulator.
An embodiment of the apparatus according to the invention is characterised in that the energising means is arranged for simultaneousl
Bartlett Ernestine C.
Snow Walter
Spain Norman N.
U.S. Philips Corporation
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