JPS6117084A - Metal passage detection circuit - Google Patents

Abstract

PURPOSE:To achieve an expanded metal detectable range and stabilized circuits, by detecting the time at which metal approaches most with an IC oscillation circuit so arranged that the intensity of oscillation varies as the metal approaces and a detection circuit which detects and smooths AC signal outputted from the oscillation circuit. CONSTITUTION:Peak wave detection circuits are added. A peak wave detection circuit 6 which detects peak voltage from the output of a detection circuit 5 is provided and a Schumitt circuit 7 applies hysteresis to a signal outputted from the detection circuit 6. The sensor voltage outputted from the detection circuit 5 decreases as metal approaches and reaches the lowest level when the metal approaches a coil most. As the metal separates away from the coil, the decreased voltage increases to return to the original condition. The time of causing the largest change in the voltage, when the metal approaches most is detected with the peak wave detection circuit 6 and a signal is sent to the Schumitt circuit 7 to indicate the metal passages. Thus, the passage of a metal piece is detected hourly while expanded metal detectable range and stabilized circuits can be promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a metal passage detection circuit that can detect the passage of a metal piece and output the time of passage as an electrical signal.

(Conventional configuration and its problems) A conventional metal detection circuit will be explained with reference to drawings.

Figure 2 (a) shows a coil that serves as a metal detection sensor, 1
(b) is a coil in which coil 1 is replaced with a circuit symbol.

Fig. 3 shows a conventional metal passage detection circuit using coil 1, 2 shows the coil with a circuit symbol, and 3
Reference numeral 4 indicates an LC oscillation circuit having the coil 1 as the L component, 4 an amplifier circuit for amplifying the alternating current signal of the oscillation circuit 3, and 5 a detection circuit for smoothing the alternating current signal of the amplifier circuit 4 into a DC voltage. Three oscillation circuits When the DC power supply voltage VCC is applied, the oscillation transistor T? Then, oscillation starts due to the feedback capacitor C2. The oscillation condition of this oscillation circuit 3 is set between the condition where oscillation starts by adjusting the feedback capacitor 02 and the like and the condition where oscillation is completely stabilized, and is in a gold-detection state. The metal piece is coil 1 (
When the metal piece approaches point 2) in Figure 3, the metal piece changes the Q of the coil 1 and destroys the oscillation conditions of the oscillation circuit 3.As the metal piece approaches, the oscillation amplitude decreases, and at the same time it is amplified by the amplifier circuit 4 and is amplified by the detection circuit 5. DC voltage smoothed by (hereinafter referred to as sensor voltage),
will also decrease. The reference voltage vrf, which is input to the comparator COM and divided by the resistors R3 and R4, is set lower than the sensor voltage when there is no metal in the vicinity. When the sensor voltage decreases due to the proximity of metal and becomes smaller than the reference voltage vrf, the signal is inverted by the comparator COM and outputs the proximity of metal as a signal. Further, when the metal moves away from the metal as opposed to approaching, the oscillation condition of the oscillation circuit 3 returns to the previous state, and the sensor voltage 2 also returns to the original voltage. At this time, the sensor voltage, which was below the reference voltage vrf, becomes above ■rf, so the output of the comparator COM is inverted again and outputs the separation of the metal as a signal. However, with this circuit, it is possible to detect the approach and separation of a metal piece when it passes over coil 1, but when a metal piece comes directly above coil 1 (when it comes closest to coil 1 when passing a metal piece) ) could not be detected. (Objective of the Invention) The present invention aims to eliminate the above-mentioned drawbacks.
The present invention provides a metal passage detection circuit capable of detecting passage of metal while stabilizing the circuit.

(Structure of the Invention) The metal passage detection circuit of the present invention includes an LC oscillation circuit whose oscillation intensity changes as metal approaches, a detection circuit that detects and smoothes an AC signal output from the oscillation circuit, and a detection circuit output voltage. It consists of a peak wave detection circuit that detects the maximum voltage change at the point when metal is closest, and can not only detect the approach of metal, but also detect the passage of metal, that is, the point at which metal is closest, and By negative feedback of the output voltage of the detection circuit to the LC-oscillator circuit, it is possible to widen the range through which metal can pass, and by performing delayed feedback when negative feedback of the output voltage of the detection circuit to the LC oscillation circuit. ,
It is insensitive to gradual changes in temperature characteristics, voltage characteristics, etc., and by passing through metal, feedback is less likely to be applied to sudden changes, making it possible to improve sensitivity.

(Description of Embodiment) Fig. 1 is a diagram showing an embodiment of the metal detection circuit according to the present invention, which is a conventional circuit with a peak wave detection circuit added.
7 is a peak wave detection circuit that detects the peak voltage from the output of the detection circuit 5, and 7 is a seamit circuit that applies hysteresis to the signal output from the peak wave detection circuit 6. The sensor voltage output from the detection circuit 5 decreases as the metal approaches the coil, and becomes the lowest voltage when the metal approaches the coil most. Also, as the metal moves away, the voltage that had decreased returns to its original state and increases. The peak wave detection circuit 6 detects the time when the metal approaches the maximum voltage change and sends a signal to the Schmitt circuit 7 as a metal passing signal (Sig).

Figure 4 shows a circuit with a feedback circuit added to the peak wave detection method shown in Figure 1, where 8 is an LC oscillation circuit with a variable capacitance element VC for the feedback capacitance of the conventional LC oscillation circuit, and 9 is a detection circuit. This is a feedback circuit that applies feedback to the variable capacitance element VC of the LC oscillation circuit 8 using the output sensor voltage of 5. This feedback loop consists of negative feedback. The sensor voltage decreases due to the proximity of metal. If this proximity of the metal continues, there is a distance from the coil 1 to the metal at which the sensor voltage becomes Ovl and the oscillation circuit stops oscillating. When the sensor voltage reaches QV, multiple voltages cannot be detected accurately. In order to prevent this, when the output sensor voltage of the detection circuit 5 decreases too much, feedback is activated, and negative feedback is activated through the feedback circuit 9 to the variable capacitance element VC of the oscillation circuit 8 so that the oscillation does not stop.

By reducing the distance from the coil 1, where the oscillation is stopped, to the metal, the range in which metal can be detected can be widened.

FIG. 5 shows a circuit in which a feedback circuit with a delay is added to the peak wave detection method and feedback method circuit shown in FIG. This is a feedback circuit that feeds back to the variable capacitance element of circuit 8. To distinguish it from the feedback circuit 9 in Fig. 4, 9 is C DC)
The feedback circuit 11 is an (AC) feedback circuit. Since this (AC) feedback circuit 11 has the sensor voltage delayed by the delay circuit 10, no feedback is applied to the temporary passage of metal, and the time is long (more than the time constant of the delay circuit 10). ) Feedback is applied to the oscillation circuit 8 in response to fluctuations, thereby stabilizing the oscillation. In this way, this circuit has both the stabilizing feedback circuit 11 and the feedback circuit 9 for preventing oscillation stoppage, and uses the peak wave detection circuit 6 to detect when metal passes.

(Effects of the Invention) As described above, according to the present invention, by adding the peak wave detection circuit to the metal detection circuit, (1) it is possible not only to detect metal but also to grasp the passing point of the metal; It is possible to determine the speed and direction of movement of a piece of metal by combining these.

By adding a trench feedback circuit to the above peak wave detection method circuit.

(2) It is possible to prevent oscillation from stopping due to the proximity of metal, and to widen the detectable range in which the peak wave detection method can work accurately.

Furthermore, by adding a feedback circuit with a delay to the peak wave detection method circuit described above, (3) stable oscillation can be achieved against relatively long changes in time, such as voltage and temperature changes, and metal Sensitivity is not impaired because feedback is not applied to transient events such as transit.

(4) It is easy to adjust the oscillation amplitude, and there is less risk of oscillation stopping or oscillation saturation due to adjustment errors.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the metal detection circuit of the present invention,
Figure 2 shows a coil serving as a metal detection sensor; (a) is a perspective view of the coil, (b) is a circuit diagram of the coil, Figure 3 is a conventional metal detection circuit, and Figure 4 is an embodiment of the present invention. FIG. 5 shows a metal passing detection circuit using a peak wave detection method and a feedback method according to an embodiment of the present invention. 3.8...Oscillation circuit, 4...Amplification circuit, 5...Detection circuit, 6...Peak wave detection circuit, 7...Semit circuit 9.11...Feedback circuit, 10...・Delay circuit. Figure 1 Figure 2 1'°ゝ(b) Figure 3, 3 Figure 4, 8

Claims (4)

[Claims] (1) An LC oscillation circuit whose oscillation intensity changes as metal approaches, a detection circuit that detects and smoothes the AC signal output from the oscillation circuit, and a detection circuit output voltage that detects the maximum voltage change at the time when the metal comes closest. A metal passing detection circuit consisting of a peak wave detection circuit for detection. (2) An LC oscillation circuit whose oscillation intensity changes as metal approaches, a detection circuit that detects and smoothes the alternating current signal output from the oscillation circuit, and a detection circuit output voltage that measures the maximum voltage change at the time when the metal comes closest. A metal passage detection circuit comprising a peak wave detection circuit for detecting a peak wave, and a feedback circuit for negative feedback of the output of the detection circuit to the LC oscillation circuit. (3) The metal passage detection circuit according to claim (2), wherein the LC oscillation circuit has a variable capacitance element, and the output of the detection circuit is fed back to the variable capacitance element. (4) Claim (2) characterized in that the feedback circuit includes a delayed feedback circuit having a delay circuit.
Metal passage detection circuit described in Section 1.