JPH046489A - Verifying and testing method for operation of search coil of metal detector - Google Patents

Abstract

PURPOSE:To enable execution of an operation test without stopping a production line for a while and also to facilitate collection of a test piece by providing a small passage in the vicinity of a transportation pipe of a detecting element and by passing the test piece therethrough. CONSTITUTION:A transmission coil 2 generating an alternating-current magnetic field and two reception coils 3 and 4 being symmetric with respect to the coil 2 are disposed on the outer periphery of a pipe transporting a nonmetallic object. Voltages induced in the coils 3 and 4 are combined differentially by differential connection of the coils 3 and 4, the induced voltages offset each other at output ends (a) and (b) and no output appears at a differential amplifier 5. When a metal body 6 passes through a space of a magnetic field formed by the coils 2, 3 and 4, a change is made to occur in the alternating-current magnetic field by the metal body 6 and the number of lines of magnetic force intersecting the coils 3 and 4 does not become equal. Therefore values of the voltages e1 and e2 induced in the coils 3 and 4 are different and the difference between them appears as an output signal e0. The output signal e0 is amplified by the differential amplifier 5 and becomes a detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a test method for confirming whether a search coil of a metal detector is in a normal operating state.

(2) Conventional technology and its problems Conventionally, when a saw-type metal detector is installed on a production line, a search coil is installed around the outer circumference of the pipe through which raw materials or products flow through the production line. It is customary. Therefore, when testing the operation of a conventional metal detection device, the production line must be temporarily stopped to prevent production raw materials or products from flowing through the search coil or the installed pipe, and then the small metal sphere is inserted into the acrylic Tests were carried out by pouring a test metal sphere called a test piece embedded in resin into the pipe. However, this method requires the test piece to be collected after the test, or the pipe is usually laid completely closed with a flange connection. Retrieving test pieces is troublesome. For this reason, there were problems in adjusting the detection sensitivity of the metal detector and in daily maintenance and inspection.

(3) Purpose of the Invention The purpose of the present invention is to confirm the operation of the search coil of a metal detector, which can easily collect test pieces without stopping the production line in which the search coil is installed. The objective is to provide a test method.

(4) Structure and operation of the invention In order to achieve this object, the operation confirmation test method of a search coil of a metal detector according to the present invention is a transmission method that generates an alternating magnetic field around the outer periphery of a transport pipe that transports non-metallic objects. A coil and two receiving coils that are symmetrical with respect to the transmitting coil are arranged, and a metal object within the non-metallic object is detected by a differential composite output of each alternating current magnetic field output from the two receiving coils. In the metal detector configured as shown in FIG. It has a configuration characterized by conducting tests to confirm operation.

The present invention will be explained in detail below with reference to the drawings.

First, a metal detector to which the present invention is applied will be explained. FIG. 1(a) shows the basic configuration of a metal detector, in which one transmitting coil 2 (LO) and two receiving coils 3 (Ll), 4 ( L
2) are arranged and the receiving coils 3.4 are differentially connected, each having the same shape and dimensions. Further, the two receiving coils 3 and 4 are arranged at symmetrical positions with the transmitting coil 2 at the center. FIG. 1(b) is an equivalent circuit of the metal detector of FIG. 1(a).

Here, a high frequency current is supplied from the oscillator 1 to the transmitting coil 2 to generate an alternating magnetic field. In the magnetic field generated by the transmitting coil 2, the number of magnetic fluxes where the lines of magnetic force intersect with the receiving coil 3 and 4 are equal. As a result, the voltages (e 1 and e 2) induced in the receiving coils 3 and 4 are equal in phase, and both voltages are differentially combined by the differential connection of the receiving coils 3 and 4, and the output terminals a of the receiving coils 3 and 4 are The induced voltages cancel each other out at -b,
It cannot be applied to the output of the differential amplifier 5. That is, the output voltage is in a zero equilibrium state.

In this state, as shown in FIG. 1(a), the metal body 6 or the coil 2. 3. 4, the metal body 6 causes a change in the alternating current magnetic field, and the receiving coil 3
, 4 are no longer equal. As a result, the voltages el and e2 induced in the coils 3 and 4 have different values, and the difference between el and e2 is obtained as the output signal eO. The output signal eO is amplified by the high frequency differential amplifier 5 and becomes a detection signal.

FIG. 2 shows an example of the basic configuration of the detection coil section used in the present invention, and 8 indicates a transmitting coil 2, a receiving coil 3,
This is a small passage through which a test piece is passed near the bobbin 7 provided with the test piece. Near the outside of the coil bobbin 7 is the coil 2.
3. 4, the magnetic field generated by the transmitting coil 2 is spreading, and the state of the magnetic field is balanced.

If a metal object passes through the magnetic flux of this magnetic field, a detection operation can be obtained. In the present invention, as shown in Fig. 2, a small passage is provided near the outside of the coil bobbin 7, for example in parallel with the coil bobbin 7, through which a test piece (metal sphere for testing) can pass, and this passage 8 is used for an operation test. This eliminates the drawbacks of the prior art.

Figure 3 shows a second line in the transport line pipe 9 that transports powder and granules.
It is a figure which shows the case where the detection coil part of the metal detection apparatus as shown by the dotted line in a figure is not incorporated. The object to be transported is the detection coil 2.
3. 4 is placed inside the pipe 9. The transport pipe 9 is directly flange-connected to the opening of the detection section (search coil). To determine whether an operation test is necessary for checking the detection sensitivity of the metal detection device or for daily maintenance, this test can be performed by passing a metal sphere 9 of a predetermined standard diameter through the small passageway 8 and observing the detection operation.

(5) Effects of the Invention As explained in detail above, according to the present invention, a passage large enough for a test piece to pass through is provided near the coil pipe of the detection section, and the test piece is passed through the second passage to perform an operation test. By using it, operation tests can be performed without temporarily stopping the production line, and test pieces can be easily collected.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are block diagrams and equivalent circuit diagrams showing the basic structure of the metal detector to which the present invention is applied, and FIG. 2 is a perspective view showing the basic structure of the detection coil section used in the present invention. 3 are perspective views of the detection coil section for explaining the present invention in detail. DESCRIPTION OF SYMBOLS 1... Oscillator, 2... Transmission coil, 3.4... Receiving coil, 5... Differential amplifier, 6... Test piece, 7... Coil bobbin, 8... Small passage, 9...Transportation pipe, 10...Detection coil section. Patent applicant Nissin Electronic Industries Co., Ltd.

Claims (1)

[Claims] A transmitting coil that generates an alternating current magnetic field and two receiving coils that are symmetrical to the transmitting coil are arranged around the outer periphery of a transport pipe that transports non-metallic objects, and each alternating magnetic field output from the two receiving coils is In a metal detector configured to detect a metal object in the non-metallic object using a differential combined output, an alternating magnetic field from either the transmitting coil or the two receiving coils is applied near the transport pipe. An operation confirmation test of a search coil for a metal detector, characterized in that the operation confirmation test is performed based on the detection output obtained when a small metal ball for testing is passed through a small passage provided to intersect the magnetic flux. Method.