JPS5841507Y2 - metal detector - Google Patents

Description

[Detailed description of the invention] This invention is a metal detector that detects disturbances in the magnetic field caused by the object when the object enters the magnetic field created by the excitation coil, and detects whether the object is metal. It is related to.

This type of metal detector is used, for example, in the corridors of nuclear power plants to detect attempts to remove radioactive materials.

Then, an alternating current is supplied to an excitation coil placed in the passage, and when a metal body passes through the magnetic field generated by this current, an electric current flows through the metal body, and a magnetic field is generated secondary by this electric current. It is used to detect the presence of metal objects.

When the metal body passing through is a magnetic body, the excitation magnetic field itself changes in addition to the secondary magnetic field, so
This is also detected.

Although metal detection is performed in this manner, it is often necessary to adjust and check detection sensitivity, alarm level, etc. before starting detection or during detection.

The usual method for this adjustment and inspection is to actually bring the test piece close to the detection section, but instead to inspect only the detection system by adding a pseudo signal to the input of the electronic circuit.

The former method has poor reproducibility and workability regarding the posture and position of the test piece, while the latter method has problems in that the entire device cannot be inspected.

This idea realizes a metal detector that can perform inspection and adjustment of the entire system with excellent reproducibility and accuracy using an extremely simple configuration. A test coil that can be switched between a closed-loop state and a closed-loop state is installed in the magnetic field, and the test coil is in an open-loop state during actual measurements and in a closed-loop state during inspection.

The above switch is installed outside the magnetic field. The operation will be explained below based on FIG. 1, which outlines the main parts of this invention.

In Fig. 1, 1 is an excitation coil, 2 is a power source for supplying alternating current to the excitation coil 1, 1a is a magnetic field formed by the excitation coil 1, 2a and 2b are detection coils, and 3 is a magnetic field induced in the detection coil. 4 is a test coil, 5 is a resistor, and 6 is an on/off switch.

A magnetic field 1a is formed by an alternating current supplied from a power source 2 to an exciting coil 1.

This alternating magnetic field generates an induced voltage in the detection coils 2 a and 2 b.

This induced voltage is 90° out of phase with the excitation current.

In other words, if no metal object enters the excitation magnetic field, a 90° phase-shifted voltage approximately proportional to the excitation current will be generated in each of the detection coils 2a and 2b, and normally the voltage induced in both coils will be Both coils are coupled in such a way that they cancel each other out.

In the present invention, the test coil 4 is placed in a magnetic field in advance with the switch 6 open.

Since this coil is also made of metal, some eddy current naturally flows therethrough, and the magnetic field accompanying this eddy current is generated as a constant voltage at the output ends of the detection coils 2a, 2b.

Since this voltage may cause measurement errors, it is electrically balanced (cancelled) within the signal processing section 3.

When a metal object enters the excitation magnetic field in the above state, the signal processing section 3 amplifies the output of the detection coil and the alarm 3a issues an alarm.

Next, we will explain the inspection operation of the present invention to check whether the device itself is operating normally.

As mentioned above, the switch 6 is open and the test coil 4
When the test coil 4 is in an open loop state, a voltage is generated between the terminals of the coil due to the excitation magnetic field, but since no loop current flows, the above-mentioned eddy current flowing through the test coil 4 is only a small amount.

However, when the switch 6 is closed, a closed loop is formed between the test coil 4, the resistor 5, the switch 6, and the test coil 4, and a loop current flows.

Since this is sufficiently larger than the above-mentioned eddy current, the magnetic field due to this loop current is detected by the detection coils 2a and 2b, and the same state as when the metal object has entered is output to the signal processing section 3.

Of course, the loop current is determined by the resistance value of the resistor 5, but if the resistor 5 is a variable resistor and the magnitude of the loop current corresponds to the size of the metal object that can be detected, the variable resistor 5 can be By making appropriate adjustments, a detailed inspection operation of the metal detector is possible.

Further, depending on whether the metal of the incoming object is a magnetic material or not, a phase difference may or may not occur between the detection voltage detected by the detection coils 2a and 2b and the excitation voltage.

For example, if the incoming metal has no magnetism at all, this phase difference will be 180°.

Therefore, when performing an inspection operation assuming such a phase shift, a capacitor (not shown) is inserted in parallel or in series with the resistor 5 to adjust the phase of the closed loop current flowing through the test coil 4. Just adjust it.

It goes without saying that an inductance may be used instead of a capacitor, and that both may be used in combination to adjust the phase.

Furthermore, a plurality of resistors 5 may be used and changed over by a switch, and inspections at multiple levels may be performed step by step by changing over the switches.

As detailed above, this device has a very simple configuration in which, in addition to the excitation coil and detection coil, there is also a test coil that can be closed looped by a switch located outside the excitation magnetic field, resulting in improved reproducibility compared to conventional methods. Since it not only allows good inspection operations but also enables inspection operations from a remote location, its effects are extremely significant when put to practical use.

[Brief explanation of the drawing]

FIG. 1 is a diagram for schematically explaining a metal detector according to an embodiment of this invention. 1... Excitation coil, 1a... Magnetic field, 2
...Power supply, 2a, 2b...Detection coil, 3...Signal processing unit, 4...Test coil, 5...Resistor , 6... Open/close switch.

Claims (1)

[Scope of utility model registration request] When an object enters the magnetic field created by the excitation coil, the detector detects disturbances in the magnetic field caused by the object and determines whether the object is metal.The detector can be switched between open-loop and closed-loop states by operating a switch. A metal detector characterized in that a test coil that can be switched between the two is installed in the magnetic field, and the test coil is in an open-loop state during actual measurement and in a closed-loop state during inspection.