JP2000075049A - Detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a detection circuit by which an object is detected precisely. SOLUTION: In a detection circuit, a periodic-signal generation circuit 1 which generates a periodic signal is provided, and a comparison circuit 3 which outputs a comparison signal A on the basis of the comparison of a change value Va changed according to a change in the amplitude of the periodic signal based on an object to be detected with a threshold value Vth is provided. The detection circuit is constituted in such a way that a one-shot-pulse generation circuit 4 which outputs a pulse signal B in a prescribed width from the start of the output of the comparison signal A is installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection circuit for detecting a metal detection object.

[0002]

2. Description of the Related Art Conventionally, there is a detection circuit of this type shown in FIG. This device forms a detector together with the detector main body, and includes a periodic signal generation circuit 1, a detection circuit 2, and a comparison circuit 3.

As shown in FIG. 12, a detector body 10 is provided with a through hole 10a, and a detection area 10b for detecting an intruding object X is set in the through hole 10a.

The periodic signal generating circuit 1 includes a parallel circuit P including a coil L and a capacitor C, and generates a high-frequency signal having a predetermined amplitude as a periodic signal. The terminal voltage of the capacitor C of the periodic signal generation circuit 1
Fluctuates according to the change in the amplitude of the high-frequency signal based on the detection of the detection object X that has entered the camera.

[0005] detection circuit 2 includes detecting transistor Tr, a detection resistor r _1. The base of the detection transistor Tr is connected to one end of the capacitor C, and the terminal voltage of the capacitor C that fluctuates as described above is used as the base voltage. Therefore, in the detection transistor Tr, the base current fluctuates according to the terminal voltage of the capacitor C, and the collector current fluctuates accordingly. Detection resistor
In r1, _one end on the upstream side in the current direction is connected to the reference voltage circuit 20 that outputs the reference voltage Vcc, and the other end on the downstream side in the current direction is connected to the emitter of the detection transistor Tr. The other end voltage of the detection resistor r _1, when the collector current of the detecting transistor Tr is not flowing, is identical to the one end voltage is the reference voltage Vcc, a voltage drop occurs by the collector current flows Therefore, the absolute value is equal to the reference voltage Vcc.
Smaller than.

The comparison circuit 3 comprises a comparator CO, resistors for both voltage divisions.
r ₂ , r ₃ , and a transistor for hysteresis are provided. Comparator CO compares the other end voltage of the detection resistor r ₁ is the variation value Va which varies in conjunction with the variation of the terminal voltage of the threshold value Vth and the capacitor C, and outputs a comparison signal. Specifically, the threshold value Vth, the comparator high side threshold is selected in accordance with the output of the CO Vth ₁ or low voltage side threshold Vth ₂
Consists of The comparator CO, when the other end voltage of the detection resistor r ₁ is higher than the threshold Vth, and outputs a comparison signal A of "H", the other end voltage of the detection resistor r ₁ is the threshold When the voltage is lower than Vth, the comparison signal A of “L” is output.

Next, the operation of this device will be described.
When a metal sensing object X enters the sensing area 10b set in the through hole 10a of the detector body 10, the periodic signal generating circuit 1
The eddy current flows on the surface of the detection object X due to the high-frequency magnetic field generated by the high-frequency signal and consumes the energy of the high-frequency signal, so that the amplitude of the high-frequency signal becomes smaller than the predetermined amplitude and has The change in the high-frequency signal based on the phase becomes smaller than when the change has been made, and the fluctuation width of the terminal voltage of the capacitor C that fluctuates according to the change in the high-frequency signal also becomes smaller.

As described above, when the fluctuation range of the terminal voltage of the capacitor C is small, the maximum value of the terminal voltage value of the capacitor C is lower than in the state before the fluctuation width is small. The minimum value increases. Therefore, even if the base voltage of the detection transistor Tr at both ends of the capacitor C is a low voltage value that allows a sufficient base current to flow before the fluctuation width becomes small, if the minimum value is high in this way, only becomes higher voltage value is not flowed current having a small current value be flowed or not allowed to flow the base current, since only current flow smaller current value is also flowing or collector current is also not flow, at detection resistor r ₁ However even small voltage drops in the voltage drop occurs or does not occur not occur, the other end voltage threshold value Vth of the detection resistor r _1, details higher than the high voltage side Vth _1, the comparator CO is , And outputs a comparison signal of “H” indicating detection of the detection object X.

[0009]

In the above-described conventional detection sensor, when the detection object X passes through the through-hole 10a at a low speed, the time for which the detection object X is located in the detection area 10b becomes longer, and the detection resistance r is increased. _{The time when} the other end voltage of ₁ becomes higher than the high voltage side threshold value Vth ₁ becomes longer like Tl, and as shown in FIG. 13, the time when the comparison signal is "H" becomes longer, and conversely, detecting when an object X is passed through the through hole 10a at a high speed, the detection time situated within the region 10b is shortened as Ts, the other end voltage of the detection resistor r ₁ is the high-voltage side threshold Vth
_The time during which the comparison signal is higher than ₁ becomes shorter, and as shown in FIG. 13, the time during which the comparison signal is “L” becomes shorter. For example, in order to clarify the distinction between the comparison signal and noise,
When a process of generating noise is performed when the time “H” is shorter than a predetermined time, the detected object is actually
Even though X penetrates through hole 10a, it is determined that sensing object X has not entered sensing area 10b, and sensing object X cannot be accurately detected. I will.

The time T1 to the time T5 shown in FIG.
When the detection object X enters the detection area 10b and then collides with the periphery of the through hole 10a of the detector body 10 and rebounds, as shown in FIG. detected object X from entering again the detection area 10b, will be called chattering occurs, accordingly, as shown in FIG. 15, the other end voltage twice of the detection resistor r _1, the high voltage side sill and has become higher than the value Vth _1, for detecting the object X is only once that has passed through the through-hole, will be detected as if passed twice, is possible to accurately detect a detection object X I can no longer do it.

The present invention has been made in view of the above points, and an object of the present invention is to provide a detection circuit capable of accurately detecting a detection object.

[0012]

According to a first aspect of the present invention, there is provided a periodic signal generating circuit for generating a periodic signal, and wherein the periodic signal generating circuit changes the amplitude of the periodic signal based on a detected object. A comparison circuit that outputs a comparison signal based on a comparison between the fluctuation value and the threshold value, and a one-shot pulse generation circuit that outputs a pulse signal of a predetermined width from the start of the output of the comparison signal. The configuration is provided.

According to a second aspect of the present invention, in the first aspect, a logic circuit for outputting an output signal while at least one of the comparison signal and the pulse signal is being output is provided. I have.

According to a third aspect of the present invention, there is provided a periodic signal generating circuit for generating a periodic signal, and a comparison signal based on a comparison between a threshold value and a fluctuation value which fluctuates in accordance with an amplitude change of the periodic signal based on the detected object. A comparison circuit that outputs a second comparison signal based on a comparison between the integration value of the comparison signal and a second threshold value by the integration circuit. And a second comparison circuit that outputs the same.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. This detection circuit forms a detector together with the detector body 10, and includes a periodic signal generation circuit 1, a detection circuit 2, a one-shot pulse circuit 4,
An output circuit 5 is provided.

As shown in FIG. 3, the detector main body 10 is provided with a through hole 10a, in which a detection area 10b for detecting an intruding detection object X is provided inside the detector main body 10. It is set by the provided coil 10c.

The periodic signal generating circuit 1 generates a high-frequency signal having a predetermined amplitude as a periodic signal.
A first mirror circuit transistor Tr ₁ , a second mirror circuit transistor Tr ₂ , a first mirror circuit resistor R ₁ , a second mirror circuit resistor R ₂ , a constant current circuit CC ₁ , a coil L,
First oscillation capacitor C ₁ , second oscillation capacitor
C ₂ and a feedback resistor R ₃ are provided.

First transistor Tr for mirror circuit₁Is
Second mirror circuit transistor Tr _TwoAnd the first and second
Mirror resistor R of 2₁, R_TwoTogether form a mirror circuit M
The emitter of which is for the first mirror circuit
Resistance R₁Reference voltage circuit that outputs a reference voltage Vcc via
20 and the collector is connected to the base and
And the first constant current circuit CC₁Through collector and base
Is grounded. Second mirror circuit transistor Tr
_TwoMeans that the emitter is a second mirror circuit resistor R_TwoThrough
Connected to the reference voltage circuit 20 and the base is connected to the first mirror circuit.
Transistor Tr₁It is connected to the.

The coil L has one end connected to the collector of the _second mirror circuit transistor Tr ₂ ,
The other end is grounded. The first and second oscillation capacitors C ₁ and C ₂ are connected in series to form a series circuit S 2 connected in parallel with the coil L. The connection point voltage of these first and second oscillation capacitors C ₁ and C ₂ changes according to the phase of the high-frequency signal, and even if they have the same phase, the high-frequency signal based on the detection of the detection object X Fluctuates according to the change in the amplitude of. The voltage fluctuation based on the detection of the detection object X will be described later in detail. Feedback resistor R ₃
Is connected to the connection point of the first and second oscillation capacitors C ₁ and C ₂ and the emitter of the second transistor Tr ₂ .
The feedback resistor R _3, the first and second oscillation capacitor
The phase at the connection point between C ₁ and C ₂ is fed back to the mirror circuit M.

The detection circuit 2 includes a detection resistor R ₄ , a detection transistor Tr ₃ , and a smoothing capacitor C ₃ . One end of the detection resistor R ₄ on the upstream side in the current direction is connected to the reference voltage circuit 20, and the other end on the downstream side in the current direction is a detection transistor.
It is connected to the emitter of the Tr _3. When the collector current of the detection transistor Tr ₃ is not flowing, the other end voltage of the detection resistor R ₄ is the same as the one end voltage which is the reference voltage Vcc, but a voltage drop occurs due to the flow of the collector current. the absolute value is smaller than the reference voltage Vcc, the will be described in detail later, by which the amplitude of the high-frequency signal is varied based on detection of the detected object X, the collector current of the sensing transistor Tr ₃ also varies, It fluctuates in conjunction with those fluctuations.

The base of the detection transistor Tr ₃ has a first oscillation capacitor C ₁ and a second oscillation capacitor C _2.
And the collector is grounded. Smoothing capacitor C ₃ has its one end connected to the emitter of the detecting transistor Tr _3, the other end is grounded. The smoothing capacitor C ₃ smoothes the other end voltage of the detection resistor R ₄ which is a pulsating current voltage when the current flows.

The comparator circuit 3 includes a comparator CO _1, the first voltage dividing resistor R _5, the second voltage dividing resistors R _6, third voltage dividing resistors R _6, hysteresis transistor Tr _4. Comparator CO
Reference numeral ₁ denotes a detection resistor R ₄ which is a fluctuation value Va that fluctuates in accordance with fluctuations in the threshold voltage Vth and the terminal voltage of the smoothing capacitor C _3.
And outputs a comparison signal A.

[0023] Specifically, the threshold Vth is made of a high-voltage side threshold Vth ₁ or low voltage side threshold Vth _2. The high voltage side threshold value Vth ₁ is obtained by dividing the reference voltage Vcc by the first to third voltage dividing resistors R ₅ , R ₆ , R _{7 and} the first voltage dividing resistor R ₅ and the second voltage dividing resistor R ₅ . it is a connection point voltage between the pressure resistance R _6. The low voltage side threshold Vth _2, the reference voltage Vcc is first and second voltage dividing resistors R _5, a first voltage dividing resistor R ₅ will be divided by R ₆ second dividing it is a connection point voltage between the resistor R _6. Then, the threshold Vth is described in detail later, in accordance with the output of the comparator CO _1, the high voltage side threshold Vth
Either ₁ or the low-side threshold Vth ₂ is selected. This comparator CO ₁ outputs a comparison signal A of “H” when the other end voltage of the detection resistor R ₄ is higher than the threshold value Vth, and the other end voltage of the detection resistor R ₄ is a threshold. When the value is lower than the value Vth, the comparison signal A of “L” is output.

The hysteresis transistor Tr ₄ has a base connected to the output terminal of the comparator CO ₁ , an emitter grounded, and a collector connected to the second voltage dividing resistor R ₆ and the third voltage dividing resistor R ₇ . Connected to a connection point. When “H” is output from the output terminal of the comparator CO ₁ , the hysteresis transistor Tr ₄ conducts between the collector and the emitter, and the second voltage dividing resistor R ₆ and the third voltage dividing resistor R ₇ so a current flows from the connection point between the current does not flow to the third voltage dividing resistors R _7. Then, the threshold value Vth
From the high voltage side threshold Vth ₁ to the low voltage side threshold Vth
Switch to ₂ . Conversely, the hysteresis transistor Tr _4, when "L" is output from the output terminal of the comparator CO _1, the collector emitter becomes disconnected state, a second voltage dividing resistors R ₆ third dividing no longer current flows from the connection point between the resistor R _7, so that current flows through the third voltage dividing resistors R _7. Sonaruto, the threshold voltage Vth is switched from the low voltage side threshold Vth ₂ to the high voltage side threshold Vth _1.

As shown in FIG. 2, the one-shot pulse circuit 4 includes a one-shot pulse first comparator CO ₂ , a one-shot pulse second comparator CO ₃ , and a one-shot pulse first transistor Tr. _5, the second transistor Tr ₆ for the one-shot pulse, the first resistor R ₈ for the one-shot pulse, the second resistor R ₉ for the one-shot pulse, the third resistor R ₁₀ for the one-shot pulse, when a one-shot pulse 4th
Resistor R _11, a fifth resistor R ₁₂ one-shot pulse capacitor C ₄ for one-shot pulse, consisting of the flip-flop F.

The capacitor C ₄ for one-shot pulse, while being connected in parallel with the collector-emitter of the first transistor Tr ₅ for one-shot pulse is serially connected to the first resistor R ₈ for the one-shot pulse.

First comparator CO for one-shot pulse
₃ is the comparator CO _{1 of the} comparison circuit 3 at its non-inverting input terminal.
Is input from the input terminal IN, and the reference voltage Vcc is divided into the inverting input terminal by the one-shot pulse second resistor to the one-shot pulse fourth resistor R ₉ , R ₁₀ , and R _11. It becomes Te second for one-shot pulse 3 of the resistor R ₁₀ and the connection point voltage V of the fourth resistor R ₁₁ for the one-shot pulse
th ₃ is input.

Second comparator for one-shot pulse CO
_FourIndicates that the reference voltage Vcc is one-shot
Pulse capacitor C_FourAnd one shot pulse
1 resistance R₈For one-shot pulse
Capacitor C_FourAnd first resistor R for one-shot pulse₈With
The connection point voltage is input, and the reference voltage Vcc is
Are the second resistor for one-shot pulse or one-shot pulse
4th resistor R₉, R_Ten, R ₁₁Is divided by
Second resistor R for shot pulse₉And one-shot pulse
Third resistor R_TenConnection point voltage Vth_FourIs entered.

The output value from the one-shot pulse first comparator CO ₂ is input to the S terminal of the flip-flop F, and the one-shot pulse second comparator CO ₃ is input to the R terminal.
From the Q terminal, and when "H" is input to the S terminal from the Q terminal, the first value for the one-shot pulse
Together towards the transistor Tr ₅ and second respective bases of the transistors Tr ₆ for the one-shot pulse "L" is output, when the "L" is input to the R terminal, first for one-shot pulse towards the respective transistors Tr ₅ and the second transistor Tr ₆ for the one-shot pulse of the base is output "H".

Second transistor for one-shot pulse
Tr ₆ through the fifth one-shot pulse resistor R _12, the reference voltage Vcc is applied to the collector. The connection point between the collector and the fifth resistor R ₁₂ for the one-shot pulse of the one-shot pulse for the second transistor Tr _6, the output terminal OUT which outputs towards the output circuit 5 is connected, for one-shot pulse When the second transistor Tr ₆ is in a non-conductive state, the one-shot pulse fifth resistor R ₁₂
Since no current flows, a voltage drop does not occur according to the fifth resistor R ₁₂ for the one-shot pulse is "H" is output from the output terminal OUT, and conversely, the second transistor Tr ₆ is a one-shot pulse during a conductive state, a current flows through the fifth resistor R ₁₂ for the one-shot pulse, the voltage drop occurs due to the fifth resistor R ₁₂ for the one-shot pulse "L" is output from the output terminal OUT .

Next, the operation of the one-shot pulse circuit 4 will be described. First comparator CO ₂ for one-shot pulse
The third resistor for one-shot pulse is connected to the non-inverting input terminal of
When the comparison signal A is higher than the connection point voltage Vth ₃ of the fourth resistor R ₁₁ for R ₁₀ and one-shot pulse "H" signal at a pulse signal is input, the first comparison for the one-shot pulse S of the flip-flop F from the output terminal of the heater CO ₂
"H" is input to the terminal, and "L" is the second transistor for the one-shot pulse from the Q terminal of the flip-flop F.
Since the input to the base of Tr _6, the collector emitter of the second transistor Tr ₆ is a disconnected state when a one-shot pulse, the pulse signal B starts to output a "H" from the output terminal OUT.

[0032] In this case, also the base of the first transistor Tr ₅ for a one-shot pulse, Q of the flip-flop F
Since "L" is input from the terminal, the collector emitter of the first transistor Tr ₅ becomes disconnected state when a one-shot pulse, the first through the resistor R ₈ reference voltage Vcc is the one-shot pulse for a one-shot pulse since applied to use the capacitor C _4, Yuki one-shot pulse capacitor C ₄ is charged, gradually terminal voltage increases.

[0033] Sonaruto connection point voltage between the first resistor R ₈ and the one-shot pulse capacitor C ₄ for one-shot pulse, the third resistor R for the second resistor R ₉ and a one-shot pulse for a one-shot pulse ₁₀ becomes higher than the connection point voltage Vth ₄ , so that the one-shot pulse second comparator CO
"H" from the output terminal of ₃ to the R terminal of flip-flop F
There is input, since "H" is input to the base of the second transistor Tr ₆ for the one-shot pulse from the Q terminal of the flip-flop F, the conductive state between the collector emitter of the second transistor Tr ₆ for the one-shot pulse Become
“L” is output from the output terminal OUT, in other words, the pulse signal B that is “H” is not output.

[0034] In this case, also the base of the first transistor Tr ₅ for a one-shot pulse, Q of the flip-flop F
Since "H" is input from the terminal, between the collector emitter first transistor Tr ₅ becomes conductive for the one-shot pulse, the charge stored in the one-shot pulse capacitor C ₄ is discharged, the original state Return to.

The output circuit 5 is a one-shot pulse circuit 4
When a pulse signal B is input from the controller, a signal is output to an external device (not shown) based on the pulse signal B.

Next, the operation of the entire detection circuit will be described. When the metal sensing object X approaches the present detection circuit, an eddy current flows on the surface of the sensing object X due to a high-frequency magnetic field generated by the high-frequency signal generated by the periodic signal generation circuit 1 and consumes the energy of the high-frequency signal. ,
The amplitude of the high-frequency signal becomes smaller than the predetermined amplitude, and the change in the high-frequency signal based on the phase becomes smaller than when the high-frequency signal has the predetermined amplitude, and the first and second signals change according to the change in the high-frequency signal. The fluctuation width of the connection point voltage of the oscillation capacitors C ₁ and C ₂ of the _second capacitor is also reduced.

As described above, in a state where the fluctuation range of the connection point voltage between the first and second oscillation capacitors C ₁ and C ₂ is small, the first and second oscillation capacitors C ₁ and C ₂ are not changed. The maximum value and the minimum value of the connection point voltage value become lower and higher than the state before the fluctuation width becomes smaller. Accordingly, the base voltage of the detection transistor Tr ₃ are first and second connecting point voltage of the oscillation capacitors C _1, C _2, a low voltage which can sufficiently flow the base current in a state before variation width is reduced Even if it is the value, if the minimum value is high in this way, a high voltage value is attained in which a base current cannot be passed or a current having a very small current value can be passed even if the base current can be passed. Thus, detecting transistor Tr _3, since only current flow smaller current value is also flowing or collector current is also not flow, the detection resistor R ₄
However even small voltage drop voltage drop generated or not generated not occur at the other end voltage threshold value Vth of the detection resistor R _4, details higher than the high voltage side threshold Vth ₁ , Comparator CO ₁ outputs comparison signal A of “H” to one-shot pulse circuit 4.

Then, the one-shot pulse circuit 4 to which the comparison signal A of "H" is input is applied to the detection object X at a low speed for a long time Tl in order to pass through the through hole at a high speed in a short time Ts.
In an attempt to pass the output circuit a pulse signal B of a predetermined width T corresponding to the charging time of the one-shot pulse capacitor C ₄
5, and the same output as the pulse signal B is output from the output circuit 5, indicating that the detection object X has been detected.

In such a detection circuit, the pulse signal output from the one-shot pulse generation circuit 4 has a predetermined width T from the start of the output regardless of the time when the comparison signal A is "H". Therefore, for the purpose of discrimination from noise, for example, even if a process in which the time during which the comparison signal A is “H” is shorter than a predetermined time is regarded as noise is performed,
As shown in FIG. 4, by detecting the detected object X based on the pulse signal B having the predetermined width T so as not to be regarded as noise, the detected object X can be reliably detected.

Next, a second embodiment of the present invention will be described below with reference to FIGS. Note that the same elements as those in the first embodiment are denoted by the same reference numerals, and only the differences from the first embodiment will be described. This embodiment is basically the first
Similar to the embodiment, except that the comparison signal A from the comparator CO ₁
Alternatively, a logic circuit 6 for outputting an output signal C is provided while at least one of the pulse signals B from the one-shot pulse circuit 4 is being output, and the same output as the output signal C is output. Circuit 5
Is detected.

In such a detection circuit, although the detection object X should be detected only once, for example, as shown in the state from time T1 to time T5 shown in FIG. Even if so-called chattering, which is detected twice away or so, occurs, when the comparison signal A is output based on the detected object X, the pulse signal B also starts to be output, and the pulse signal B or the comparison signal is output. When at least one of the signals A is output, the logic circuit 6 outputs the output signal C once. Therefore, by detecting the detection object X based on the output signal C, it is possible to perform an erroneous detection due to chattering. Thus, the effect that the detection object X can be reliably detected can be further achieved.

As shown in FIG. 8, after the detection object X passes through the through-hole at high speed for a short period of time Ts, after a time longer than a predetermined width T, it passes at low speed for a long time Tl. At this time, since the chattering is not apparent, the pulse width is set to T for a long time following the output signal C having the predetermined width T.
An output signal C of l is output.

Next, a third embodiment of the present invention will be described with reference to FIGS.
This will be described below based on No. 10. This embodiment is basically the same as the first embodiment, except that the one-shot pulse circuit 4 is replaced by an integration circuit 7 and a second comparison circuit 8.

[0044] Specifically, the integrating circuit 7 is for integrating the comparison signal A outputted from the comparator CO _1, consisting of the integrating resistor R ₁₃ and the integrating capacitor C _5. Integrating resistor
R ₁₃ has one end connected to the comparator CO ₁ of the comparator circuit 3. Integrating capacitor C ₅ has one end resistance for integration
Is connected to the other end of R _13, the other end is grounded.

The second comparison circuit 8 includes a second comparator CO ₅ ,
Fourth dividing resistor R _14, and a fifth voltage dividing resistors R _15. The second comparator CO ₄ compares the second threshold value Vth ₅ with an integrated value D obtained by integrating the comparison signal A,
And outputs a comparison signal E to the base of the output circuit 5 and a hysteresis transistor Tr _4. Specifically, the second threshold value Vth ₅ is dividing resistor of the reference voltage Vcc is the fourth and fifth
It is pressed by R _11, R ₁₂ minutes a divided voltage becomes. The second comparator CO ₅ is the integrated value D is at higher than the second threshold value Vth _5, and outputs a second comparison signal E of "H",
The same output as the second comparison signal E is output from the output circuit 5 to indicate that the detection object X has been detected. Further, the second comparator CO ₅ is configured such that the integrated value D is equal to the second threshold value Vth.
When it is lower than ₅ , the second comparison signal E of “L” is output.

In such a detection circuit, even if the fluctuation value fluctuates rapidly based on the detected object X, a comparison signal output based on a comparison between the fluctuation value and the threshold value is output by the integration circuit 7. integrated integrated values formed by, taken to vary slowly, even if the variation value Va exceeds the threshold Vth, exceeds the threshold Vth ₅ integrated value D if the second Will not be. Therefore, if the detection object X should be detected only once, but is based on the comparison between the fluctuation value Va and the threshold value Vth, the detection object X may be detected in a short time as in the state from time T1 to time T5 shown in FIG. Even if so-called chattering occurs in which the detection object X temporarily moves away from the detection of the time once and the second detection is performed for a long time, the detection object X 1 due to the chattering occurs.
Time of detection, since it is short, since only slowly unchanged and integral value D by comparison with a second threshold value Vth ₅ need not be detected, to be an erroneous detection due to chattering The detection object X can be reliably detected.

[0047]

According to the first aspect of the present invention, the pulse signal output from the one-shot pulse generation circuit has a predetermined width from the start of output regardless of the time when the comparison signal is "H". Therefore, in order to discriminate the noise from the noise, for example, even if a process is performed such that the noise is generated when the time during which the comparison signal is “H” is shorter than the predetermined time, a predetermined width that does not cause the noise is set. By detecting the detection object based on the pulse signal having the detection signal, the detection object can be reliably detected.

According to the second aspect of the present invention, the so-called chattering occurs, for example, in which the detected object should be detected only once, but, for example, the detected object is temporarily moved away and detected twice. When the comparison signal is output based on the detected object, the pulse signal also starts to be output, and when at least one of the pulse signal and the comparison signal is output, the logic circuit outputs the output signal once. By detecting the detection object based on the output signal, erroneous detection due to chattering can be prevented, and the effect of claim 1 that the detection object can be detected reliably can be further achieved.

According to a third aspect of the present invention, even if the fluctuation value fluctuates rapidly based on the detected object, the comparison signal output based on the comparison between the fluctuation value and the threshold value is integrated by the integration circuit. The integral value thus obtained fluctuates slowly, so that even if the fluctuation value itself exceeds the threshold value, the integral value does not exceed the second threshold value. Therefore, if the detection object is to be detected only once, but based on the comparison between the fluctuation value and the threshold value, the detection object may temporarily move away after the short-time detection has been performed once, and may not be detected. Even if so-called chattering occurs in which the second detection is performed for a long time, the first detection of the detection object by the chattering is performed in a short time, and therefore the integration value and the second value that change only slowly are calculated. Since detection is not required by comparison with the threshold value, erroneous detection due to chattering does not occur, and a detected object can be detected reliably.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a detailed circuit diagram of a one-shot pulse circuit forming a part of the above circuit.

FIG. 3 is a partial cross-sectional view of a detector main body that forms a detector together with the above circuit.

FIG. 4 is a time chart showing a state in which a high-speed detection object and a low-speed detection object are detected by the above circuit.

FIG. 5 is a circuit diagram of a second embodiment of the present invention.

FIG. 6 is a partial cross-sectional view of the detector main body showing a state where chattering of a detection object detected by the detector described above has occurred.

FIG. 7 is a time chart showing the operation of the above circuit.

FIG. 8 is a time chart showing a state in which a high-speed detection object and a low-speed detection object are detected by the above circuit.

FIG. 9 is a circuit diagram of a third embodiment of the present invention.

FIG. 10 is a time chart showing the operation of the above circuit.

FIG. 11 is a circuit diagram of a conventional example.

FIG. 12 is a partial cross-sectional view of a detector main body that forms a detector together with the above-described circuit.

FIG. 13 is a time chart showing a state in which a high-speed detection object and a low-speed detection object are detected by the above circuit.

FIG. 14 is a partial cross-sectional view of the detector main body showing a state where chattering of a detection object detected by the detector according to the first embodiment has occurred.

FIG. 15 is a time chart showing a state in which chattering of a detection object detected by the detector described above has occurred.

[Explanation of symbols]

1 periodic signal generation circuit 3 comparison circuit 4 one-shot pulse generation circuit 6 logic circuit 7 integration circuit 8 second comparison circuit X sensing object Va fluctuation value Vth threshold Vth ₅ second threshold A comparison signal B pulse signal C output signal D integral value E second comparison signal

Claims (3)

[Claims] 1. A periodic signal generation circuit for generating a periodic signal, a comparison circuit for outputting a comparison signal based on a comparison between a threshold value and a fluctuation value that fluctuates according to an amplitude change of the periodic signal based on a detected object; A detection circuit comprising: a one-shot pulse generation circuit that outputs a pulse signal of a predetermined width from the start of the output of the comparison signal. 2. The detection circuit according to claim 1, further comprising a logic circuit that outputs an output signal while at least one of the comparison signal and the pulse signal is being output. 3. A periodic signal generation circuit for generating a periodic signal, a comparison circuit for outputting a comparison signal based on a comparison between a fluctuation value that fluctuates according to an amplitude change of the periodic signal based on the detected object and a threshold value, A integrating circuit that integrates the comparison signal, and a second comparison signal that outputs a second comparison signal based on a comparison between the integration value of the comparison signal and a second threshold value by the integration circuit. A comparison circuit; and a detection circuit.