JPS63109387A - Metal detector - Google Patents

Abstract

PURPOSE:To clearly discriminate a signal level even when the difference in the signal level is small, by applying square operation to the signal detected by a magnetic detector, rectified by a synchronous rectifying circuit and differentiated and amplified by a differential amplifier before outputting said signal. CONSTITUTION:A magnetic detector 1 for magnetically detecting a magnetic metal body when said metal body arrives at the vicinity, an oscillator 2 exciting the exciting coil of the detector 1, a frequency doubling circuit 4 converting the signal of frequency (f) of the oscillator 2 to two times to output the same, a synchronous rectifier 3 for synchronously rectifying the output of the detector 1 by the signal of frequency 2f and a differential amplifier 5 for obtaining the change portion of detection output synchronously rectified are mounted. Then, the output of the amplifier 5 is inputted to a multiplier-divider 10. The multiplier-divider 10 has a function of x.y/z and the output of the amplifier 5 is inputted to the input terminals (x), (y) thereof and the signal of the square of said output is obtained as output to be applied to a comparator 9. Further, a sensitivity controller 11 is connected to the z-terminal of the multiplier-divider 10 and the voltage thereof is adjusted to change a dividing ratio and sensitivity is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a metal detector for detecting metals, particularly magnetic metals.

(B) Prior art As shown in FIG. 2, a conventional magnetic metal detector includes a magnetic detector 1, which includes an excitation coil, a detection coil, etc. is driven by an AC signal of frequency f generated by an oscillator 3. When a magnetic body is present in the vicinity of the magnetic detector 1, an induced magnetic field is generated in the magnetic body by the magnetic field generated by the excitation coil, and this is detected by the detection coil at a frequency of 2f.

On the other hand, the signal at the frequency of the oscillator 2 is input to the frequency doubler circuit 4, converted into a signal at the frequency 2f, and applied to the synchronous rectifier circuit 3. Thereby, the output of the magnetic detection section 1 is synchronously rectified and output. Then, this output is differentiated by a differential amplifier 5, and only the change in the DC component is derived. This DC variation is amplified by a DC amplifier 6, and then further amplified by an absolute value circuit 8.
The output value is compared with a predetermined reference level by a comparator 9, and the presence or absence of magnetic metal is determined. Note that 7 is a sensitivity adjuster.

(c) Problems to be solved by the invention When searching for magnetic metal using the above conventional metal detector,
When the signal difference between the target magnetic metal and iron sand or the like underground is small, there is a problem in that it is difficult to distinguish whether it is iron sand or magnetic metal.

In addition, when the power source of this type of metal detector is a battery, the offset voltage of the differential amplifier changes depending on the power supply voltage, the zero point of the DC amplifier output changes, and the detection level of the comparator changes, which can cause errors. There was a problem that there was a risk of detection.

In view of the above, the present invention is a metal detection system that is capable of distinguishing between the signal level of magnetic metal and the signal level of underground iron sand, etc., even if the difference is small, and that reduces the influence of zero point changes. The purpose is to provide equipment.

(d) Means and operation for solving the problems The metal detector of the present invention has a magnetic detection section including an AC signal source, an excitation coil excited by the AC signal source, and a detection coil that detects nearby magnetism. , a synchronous rectifier circuit that rectifies the output of this magnetic detection section, and a differential amplifier that differentiates the rectified output.
It consists of a squaring circuit that squares the output of the differential amplifier, and a comparator that compares the output of the squaring circuit with a predetermined value to determine the presence or absence of metal.

In this metal detector, if magnetic metal is present near the magnetic detection part, the magnetic change can be derived as in the conventional case, but in this case, the signal level between the magnetic metal and iron sand etc. underground Even if the difference is small, it is squared by the square calculation circuit and outputted, so that the level difference can be more clearly determined.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a block diagram of a metal detector showing an embodiment of the present invention.

In this embodiment metal detector, when a magnetic metal body comes nearby, there is a magnetic detector 1 that magnetically detects it, an oscillator 2 that excites the excitation coil of this magnetic detector 1, and a signal of the frequency f of this oscillator. A frequency doubler circuit 4 doubles and outputs the output, a synchronous rectifier circuit 3 synchronously rectifies the output of the magnetic detector 1 using a 2f signal from the frequency doubler circuit 4, and obtains a change in the synchronously rectified detection output. Differential amplifier 5 for
It is similar to the conventional one shown in FIG. 2 in that it is provided with. The feature of the metal detector of this embodiment is that the output of the differential amplifier 5 is further input to the multiplier/divider 10, and the multiplier/divider 10 has an input of x-y/z, and multiplies exactly xxy.
Furthermore, it has a division function that divides it by 2, and inputs the output of the differential amplifier 5 into both x and y input signals, obtains the square of the input signal as an output, and adds it to the comparator 9. ing. Note that a sensitivity adjuster 11 is connected to two terminals of the multiplier/divider 10, and by adjusting this voltage, the division ratio can be changed and the sensitivity can be easily adjusted.

In such an embodiment metal detection device, the magnetic detector 1
Even if the magnetic signal level detected by the magnetic metal body is very small and there is not much difference in signal level between the magnetic metal body and the underground iron sand, etc., these magnetic detection outputs are synchronously rectified by the synchronous rectifier circuit 3, and the differential amplifier If the input derived through step 5 is input to the multiplier/divider 1o and squared, the difference between both levels will become more noticeable, and at the predetermined level of the comparator 9, it can be clearly determined whether it is a magnetic metal object or just iron sand. can do.

Furthermore, regardless of whether the output of the differential amplifier 5 is of positive polarity or negative polarity, the comparator 9
This makes comparison easier.

(f) Effects of the Invention According to this invention, a signal detected by a magnetic detector, rectified by a synchronous rectifier circuit, and differentially amplified by a differential amplifier is squared by a square calculator using a multiplier/divider or the like. This is because the squared output signal is compared with a predetermined reference level to determine the presence or absence of magnetic metal.
Even when the signal levels are relatively close to each other,
This has the advantage of being able to more clearly distinguish differences and improving detection ability.

Furthermore, conventionally, a DC amplifier and an absolute value circuit have a DC amplification function, and the polarity is unified, but according to the present invention, it is possible to configure a squaring unit only with a multiplier/divider, etc. This has the advantage of allowing a simpler circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a metal detector showing an embodiment of the present invention, and FIG. 2 is a circuit block diagram showing a conventional metal detector. 1: Magnetic detector, 2: Oscillator, 3: Synchronous rectifier, 5: Differential amplifier, 9: Comparator, lO square divider.

Claims (1)

[Claims] (1) An AC signal source, a magnetic detection unit including an excitation coil excited by the AC signal source and a detection coil that detects nearby magnetism, a synchronous rectification circuit that rectifies the output of the magnetic detection unit, and a rectification output. A metal detector consisting of a differential amplifier that differentiates, a squaring circuit that squares the output of the differential amplifier, and a comparator that compares the output of the squaring circuit with a predetermined value to determine the presence or absence of metal.