Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1990-05-29
1992-07-28
Wieder, Kenneth A.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324690, G01R 2726
Patent
active
051343797
DESCRIPTION:
BRIEF SUMMARY
This invention relates to detecting apparatus.
More particularly, the invention relates to detecting apparatus for detecting the amount or presence of material in a detection zone.
In many manufacturing systems, it is of importance to know very accurately the number of articles which have been placed in a package. In some circumstances it is not possible to obtain satisfactory checking information by visual inspection or by weighing. It is thus an object of the invention to provide detecting apparatus which can provide very accurate information as to the amount or presence of material in a detection zone. The packages are conveyed into the detection zone and the amount or quantity of material in the packages can be monitored by the apparatus of the invention.
According to the present invention there is provided apparatus for detecting the amount or presence of material in a detection zone, said apparatus comprising:
a first electrode;
input signal means for supplying an electric input signal to the first electrode;
a second electrode, said detection zone being located between said first and second electrodes;
a third electrode which substantially surrounds the second electrode and is larger than the second electrode; and
receiving means for detecting signals on the second electrode, the signal on the second electrode being responsive to material in the zone.
Preferably, the second and third electrodes are not electrically connected but are maintained at near the same electric potential whereby the electric field between the first and second electrodes is, in use, substantially linear and fringing fields, if any, occur only between the first and third electrodes at their outer edges.
Preferably the second electrode is narrow so that a narrow slice of material in the zone is detected. This enables very accurate monitoring so carried out compared to known techniques which, generally speaking, scan only relative wide areas and are affected by fringing fields.
Apparatus of the invention can be very conveniently arranged to operate on a conveyor line upon which packaged articles pass. The articles pass through the detection zone and hence the articles pass between the first electrode and the second and third electrodes. Preferably the first electrode comprises a plate over which the article pass and the second and third electrodes are located above the first electrode. The input signal means may comprise an oscillator for applying a sinusoidal voltage to the first electrode. The detecting means may comprise an operational amplifier having a known capacitive feedback loop. The arrangement is such that articles in the detecting zone, especially non-metallic articles, alter the effective dielectric properties within the zone thereby altering the effective capacitance between the first and second electrodes. This alteration is reflected at the output of the operational amplifier and with suitable detecting circuitry can be used to provide information as to the number of articles in a package or the quantity of material in a package.
In accordance with the present invention there is also provided a detection circuit for detecting the amount or presence of material in a detection zone, said circuit comprising:
a first electrode and a second electrode, said detection zone being located between said first electrode and said second electrode, and said first electrode being supplied, in use, with an electric input signal; and
an operational amplifier with an input connected to said second electrode and having a capacitor in a feedback loop between said input the output of the amplifier, the signal outputted by the amplifier being responsive to the material in the zone.
In accordance with the present invention there is also provided a detection device for use in detecting the amount or presence of material in a detection zone, said device comprising:
a first electrode;
a second electrode substantially parallel with respect to and opposite said first electrode; and
a third electrode which substantially surrounds, is substan
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patent: 4683418 (1987-07-01), Wagner et al.
patent: 4922181 (1990-05-01), Pullan
patent: 4958129 (1990-09-01), Poduje et al.
Junger Richard E.
Maher Anthon J.
Detection Systems Pty. Ltd.
Regan Maura K.
Wieder Kenneth A.
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