JPH02212780A - Processing apparatus of sensor signal - Google Patents

Abstract

PURPOSE:To positively supervise a sensor by providing an oscillator which oscillates at a period corresponding to a pulse period of said sensor generating a pulse in accordance with the rotation of an object to be detected, and stopping said oscillator to generate a signal of a specific level when a sensor coil is disconnected or short-circuited. CONSTITUTION:When the rotating velocity of a rotary body such as an engine is to be detected by an electromagnetic pickup as a rotary sensor 11, a pickup coil 113 is connected to a power source through a resistor R01. The sensor 11 generates a pulse of a frequency proportional to the rotating velocity, which pulse is amplified at an operating amplifier 12 and input to an oscillating circuit 13. In this circuiting when the sensor 11 is rotated normally, an oscillating signal of a period proportional to the rotating number is obtained as an output Vout. On the other hand, when the sensor 11 is not rotated, the signal is an output Vout corresponding to an internal oscillating signal of the oscillating circuit 13. If the coil 113 is disconnected or short-circuited, the output Vout becomes high level or low level, which can be easily identified.

Description

[Detailed description of the invention]

[Usability of industry-1-! ] This invention processes a pickup signal from an electromagnetic pickup constituting, for example, a rotation detection sensor, etc. 1, and processes a pickup signal from a rotation speed including a stopped state of a detected object,
The present invention relates to a sensor signal processing device that can detect and process the occurrence of a failure in a sensor 14 section. [Prior Art] As a means for detecting the rotational speed of a rotating body such as an engine, for example, a rotating disk made of a magnetic material with a large number of notches formed on the outer periphery, and a rotating disk of this rotating disk are used. (A rotation detection sensor constituted by a permanent magnet fixedly set near the circumference and an electromagnetic pickup constituted by a coil wound around the magnet) is known. In other words, a rotating disk is rotated in synchronization with the engine, which is the object to be detected, and each time the notch on the outer periphery of this disk passes close to the pickup, an electromotive force is generated in the pickup coil, which changes the output voltage to a level. Correspond to the rotational speed by discriminating 1. A pulse-like pickup signal with a certain period can now be obtained. Therefore, by counting this pickup signal, the rotational speed of the object to be detected can be measured. In a sensor that is horizontally opened like this, when no output signal is generated from the sensor, the detection output is at a low level, but when there is no sensor output, the detected My body is I! ! This also occurs in a state in which the pickup coil is disconnected or short-circuited in a state in which there is no -C and a state in which the pickup coil is in a state in which the pickup coil is disconnected or short-circuited, and these cannot be distinguished by the level discrimination means. If a disconnection or short circuit occurs in the pickup coil, even if the rotating body starts rotating from a stopped state, no output signal will be obtained from the sensor, and it will not be possible to determine whether the rotating body is rotating or not. As a means for detecting such a disconnection of the pickup sensor, a device as disclosed in, for example, Japanese Patent Laid-Open No. 62112070 has been considered. FIG. 6 shows the configuration of this wire breakage detection device.
11. This rotating disk 311 is made of a magnetic material in which 1 (number of notches) are formed on the outer periphery, and a core 31.2 made of a permanent magnet is fixed at a position close to the outer periphery of this rotating disk 311. A pickup coil 313 is wound around this core 312 to form an electromagnetic pink-up, and the pickup coil 313 of this electromagnetic pickup is provided with a rotating disc 3]1 that rotates and a cutout portion thereof. An electromotive force is generated every time the sensor approaches and passes the core 312. That is, a pulse-like voltage signal is generated in response to the rotation of the rotating disk 311. The output signal from the rotation sensor 31 is as follows. In the comparator circuit 32, level judgment is performed using a reference voltage set by dividing the voltage by resistors R31 and R32, and the output signal from the sensor 31 is waveform-shaped. The voltage is set. The output signal from the comparison circuit 32 is amplified by the transistor 33 and then supplied to the comparison circuit 34 via the resistor R34. The signal from the transistor 33 is pulled up by the resistor R35. The comparison circuit 34 compares the voltage with the reference voltage divided by the resistors R30 and R37.
When the output voltage from the transistor 33 is higher than the reference voltage, the output of the comparison circuit 34 is set to the noise level. The output from the comparator circuit 34 is passed through a charging/discharging circuit 5 consisting of a diode DI, a resistor 38 to R40, and a capacitor C1, and is then output to the collective standard γI by resistors R41 and R42.
The S pressure is supplied to the comparison circuit 35 where the S pressure is set, and the level is determined.). In this signal processing circuit, the L° of the sensor 31 is
Assuming that the rack coil 313 is disconnected, the capacitor CI will continue to be charged, and the terminal voltage of the capacitor C1 will exceed the reference voltage set by the resistor R41%R42, and the output of the comparator circuit 35 will be It will be set to high level.

[Thus, by monitoring the output signal from the comparison circuit 35, it is possible to detect whether the pickup coil 313 is disconnected. However, when the pickup coil 313 is short-circuited, the same output signal as the normal rotation speed "O" is obtained from the rotating section 31, and the output signal from the rotating section 31 is
It is only possible to determine the short circuit of 3. [Invention or Problem to be Solved] This invention was made in view of the above points. For example, when the rotation of a rotating body such as an engine is detected by an electromagnetic pickup, there is a possibility that the pick-up coil of this sensor may be disconnected or short-circuited. When such a problem occurs, it is possible to distinguish this from a stoppage of the rotating body and detect the occurrence of a failure such as a disconnection or a short circuit, thereby increasing the reliability of this type of detection mechanism and improving its usability. It is an object of the present invention to provide a sensor signal processing device as described above. [Means for Solving the Problem] The sensor signal processing device according to the present invention uses a big-up sensor that can obtain a pulse-like sensor signal in response to the movement of the detected object. After amplifying the output signal, it is supplied to the oscillation means. This oscillation means is designed to oscillate a signal with a period sufficiently longer than the period of the pulse-like signal generated by the pickup sensor under normal conditions, and is supplied with the amplified signal. In this state, the oscillation of a signal having a period corresponding to the period of this pulse-like pips 11, 1 is controlled. In addition, when the rotated body is in the stopped 1-state and furthermore, when a disconnection or short circuit occurs in the pick-up sensor, the output signals from the oscillation means are at different levels depending on the level of the signal given to the oscillation means. so that it is constant. [Function] In other words, in the sensor signal processing device as described above, when the object to be detected is in motion, a pulsed pickup signal with a period corresponding to the operating state is obtained from the pickup sensor. A signal having a period corresponding to this signal period is obtained from the oscillation means. By counting these oscillation signals, the operating speed of the object to be detected can be measured. In addition, when the object to be detected is in a stationary state, the oscillation means is set to a self-operating state, and corresponds to the conditions set by this oscillation means. It oscillates at the same frequency, and from this it is possible to determine whether the pickup sensor is +E or not. When the coil of the backup sensor has a fault such as a disconnection or short circuit, the oscillation means is given the maximum voltage or the minimum voltage in response to the coil disconnection or short circuit, and the oscillation means does not perform oscillation. The signal at the specified level will be output without any Therefore, based on the output signal from this oscillation means, it is possible to easily and reliably determine whether the pickup sensor M- is in a normal state, especially whether the pickup coil is disconnected or short-circuited. [Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the circuit configuration, including a rotary plate 111 made of a ferromagnetic material with a plurality of notches formed on the outer periphery, and this rotary plate 1.1. A core 112 made of a permanent magnet fixed near the outer periphery of I, and a pickup coil l1 wound around this core i12.
It is equipped with a rotation detection sensor 'J11 consisting of 3 parts. The rotary plate 111 of the rotation detection sensor 11 is driven to rotate in synchronization with an object to be detected, such as an engine, which is not shown in this figure. Every time the notch passes close to the cores 11 and 2, a pulse-like voltage signal is generated in the pickup core 13. The pulsed output voltage signal from the pickup coil 113 has the same wave number as the rotational speed of the rotating plate 11, and this output signal frequency expresses the rotational speed of the engine, which is the object to be detected. It becomes like this. this[! The ift force from the rotation detection sensor 11 is supplied to the operational amplifier circuit 12, and the pickup coil 113 of the rotation detection sensor 11 is connected to the power supply Vcc via a resistor ROI. Output Va from coil 113 is supplied to operational amplifier 121 via resistor RO2. The performance amplifier 121 is determined by resistors RO3 and RO4, and the amplifier α is set as follows, so that the output signal V b is iυ. α-(RO3+RO4) /RO3]1 When the rotation detection sensor 11 is in the W state and the rotation speed of the rotary plate III is 0, the IL'f current resistance of the pickup coil 113 and The partial voltage obtained by the resistor ROI is input to the operational amplifier 121, and the amplified output (11) obtained by α(Δ) is the output of the operational amplifier circuit 12 and Then, this output signal vb is supplied to the oscillation circuit 3. The output signal from the operational amplifier circuit 12 is supplied to the comparator 131 via the resistor RO5. The output side of the oscillation circuit 13 is connected to the input side of the comparator 131 through a resistor RO6, so that the oscillation output Vout 111 can be received from the output side of the comparator 1.31. is a resistor RO7 connected to the power supply VCC,
A capacitor C is provided which is charged via RO8 in series, and the terminal voltage VC of this capacitor C is coupled to the transfer side terminal of the comparator +31.
The connection point with ll is connected to the comparator 131 via diode D.
A discharge circuit for the capacitor C connected to the output side of the capacitor C is formed. Here, the output Vb from the operational amplifier 121 is the output voltage of the diode D when the output of the comparator 13+ is at low level.
The values of resistors RO3 and RO4 are determined so that they are higher than the voltage VF applied on the node side. A transistor 141 is connected in parallel to a capacitor C forming the oscillation circuit 13. This transistor 14
Reference numeral 1 constitutes a limit circuit 14, the base of which is supplied with a voltage divided by resistors RO9, R1, and O. This limiter circuit 14 generates a voltage that prevents the terminal voltage Vc of the capacitor C from reaching the output voltage vb of the operational amplifier 121 when the output vb from the operational amplifier 121 becomes a high voltage state close to the power supply voltage Vcc. The values of resistors RO9 and RIO are set accordingly. When the output Vout of the comparator 131 becomes low level, the oscillation circuit 13 reduces the charge Vc of the capacitor C in the charged state.
is connected to comparator 13 via resistor ROB and diode D.
This discharge continues until the charge VC of the capacitor C falls below the voltage b' at the input side of the comparator 131. When VC becomes lower than Vl)', the comparator 131 is activated. Then, its output VO11t is inverted to high level. Then, the output V o of this comparator 131
When ut becomes high level, capacitor C connects to resistor RO7.
and charged via RO8. Oscillation is performed by repeating such a series of operations, and the frequency F of the oscillation signal obtained in this way is higher than the frequency of the pulsed rotation signal obtained by the normal rotation detection sensor 11. The values of capacitor C1 resistors RO7 and RO8 are determined to provide a sufficiently low frequency. To explain the operation of the device b/J configured in this way, first, while the rotation detection sensor 11 is constantly operating, the rotating plate 111 responds to the rotation of the detected object by λ. Assuming that the rotation is smooth from 1 to 2, the 2nd
As shown in figure (A), the pickup coil +13
In response to the rotation of the rotary plate Ill, its notch or core 1
12, a periodically changing electromotive force is generated and a periodically changing signal v a' is generated each time the object passes near the section 12. This signal V, is amplified to αi by the operational amplifier 121, and as shown in the figure, the signal V1 changes periodically.
．． + or i! Being ignored. Here, the oscillation a4L'8 wave number iij generated under the oscillation conditions of the t-oscillation circuit 12 is compared with the frequency of the signal Vb generated when the rotary plate 111 is rotated in a normal state. 'L is set sufficiently low. Therefore, due to the change in the C terminal j'-voltage, the operational amplifier 1
The output V out of the comparator 131 is synchronized with the frequency of the output v b of the operational amplifier 121 and is an output type L with a frequency that is 5 times higher. become. By periodically changing the output vb of the operational amplifier 121, the output of the comparator 1.3.1 is V+1 or l.
The frequency of this rectangular wave changes between the high level and the low level, and the rotation detection sensor M'
Based on the frequency of the signal Va obtained from 11 and the output Vout of the comparator 121, the rotation speed of the rotary plate Ill, that is, the rotation speed of the limb detection body is i:L 1411
It will be 1). Next, check whether the rotation detection sensor 11 is normal or not.Rotation]5 Plate 1. If we consider the state when the limb detector is in the 11-state, that is, when the limb detector is stopped, the output Va from the sensor 11 is constant, as shown in (B) in Figure 2. value is kept. That is, this voltage Va
is the DC resistance of the pickup coil 113 and the resistance ROI
This voltage Va is divided into α by the operational amplifier 121.
This will be multiplied to give vb. As mentioned above, this voltage vb is higher than the anode voltage Vl' of the diode D obtained when the output of the comparator 131 is at a low level, so when the output of the comparator 131 is at a high level, the capacitor C is charged through resistors R07 and RO8. Then, the charging voltage Ve of this capacitor C is the comparator 1
When the voltage Vb' on the input side of the comparator 131 is exceeded, the output VOut of the comparator 131 becomes low level. Here, Vb'
= (R(J5/ (RO5+RO8))
x(Vout -Vb) When the output of the comparator 131 becomes low level, the capacitor C is connected to the comparator 1 through the resistor RO8 and the diode D.
31 is discharged to the output side of the capacitor C, and the terminal voltage Vc of the capacitor C
When the voltage is lower than the voltage Vb', the output of the comparators 1 and 31 V o
ut or high level. Then, charging of capacitors II and C is started, and by repeating this, the oscillation is maintained in a sustained state. That is, when the rotation detection sensor 11 is in a normal state, a rectangular wave output with a frequency corresponding to the rotation speed of the rotation plate 111 is obtained while the rotation plate 11.1 is being rotated, and When the rotary plate 111 is stopped, the oscillation circuit 13 oscillates under the conditions set by itself, and a waveform output having a frequency corresponding to the oscillation frequency is obtained. Rotation detection center: If we consider a case where the pick-up coil 11 (13) is disconnected, the terminal wire of the pick-up coil 113 is disconnected, as shown in (C) in FIG. Va is caused by the power supplied through the resistor R,
IJ is set to power supply voltage VCC. l, Therefore, the amplifier 121 is intended to output this V il multiplied by α [, and V b , or this vb is VCC, l
: It won't get too expensive. Here, if "Vh';Vcc", when the output of the comparator 131 is at a high level, it becomes "vb" - vb",
Capacitor C is charged. However, this capacitor C
The terminal voltage VC cannot be less than the voltage determined by the limit circuit 14, and this terminal voltage VC can only exceed the voltage V11' on the input side of the comparator 131.・Therefore, the output VouL of the J comparator 131 is
・You will now be able to maintain a level state. Next, if we consider the case where the pick-up coil 113 of the rotation detection sensor 11 is short-circuited, the impedance of the pick-up coil 113 becomes "O" as shown in FIG. pickup coil +1
The terminal voltage Va of No. 3 becomes 0'', and the output Vb of the operational amplifier 121 also becomes 0''. Therefore, if the output of the comparator 131 is at a low level in this state, the capacitor C is connected via the resistor RO8 and the diode D. However, the end f voltage Ve of the capacitor 4f C is
The voltage does not drop below the voltage drop of diode D. Zunawaji, Vb is “(I V” and output of comparison circuit 131)
8. Since the output voltage V out is at low level (OV), the input voltage vb' of the comparator circuit 131 is also "]]V", and the terminal voltage ve of the capacitor C is equal to the input voltage Vb of the comparator 131.
', and the output Vout maintains a low level state. Therefore, if the pick-up coil 113 of the rotation detection sensor 11 is disconnected (5), the output Vout will be maintained at a high level, and if it is short-circuited, the output Vout will be maintained at a high level.
out will maintain a low level. Soshi C
1 When the same rotation detection sensor 11 is operating normally, when there is no rotation (a), the output V01Jt corresponding to the internal oscillation signal of the oscillation 1i7+path I3 is obtained, and when there is a four-way rotation white rotation, the output V01Jt is obtained. An oscillation signal with a period corresponding to the number is output V ou
It is obtained as t. The output VouL from the oscillation circuit 13 is supplied to the 1-row circuit 14, which is appropriately configured with a microcomputer, etc. In this control circuit, the output VouL is calculated from the 1-period of the internal oscillation signal frequency obtained by the oscillation circuit 13. By setting means for determining whether or not the voltage remains in the same state for a long period of time, it is possible to determine whether the output V out of the oscillation circuit 13 has been maintained in the same state for more than the specified time.
It is detected whether the rotation detection sensor 11 is abnormal. By determining the level of the output Vout based on the abnormality detection state of the lever L2, it becomes possible to determine whether the pickup coil 113 is disconnected or shorted. In addition, in a state where it is determined that the force Vout is not maintained in the same state within the specified range of 11.7, it is determined that the rotation detection sensor 11 is operating normally. In the operating state, by determining whether the oscillation cycle of the output Vout from the oscillation circuit 13 is higher than the internal oscillation frequency of the oscillation circuit 13, it is determined whether the detected object is in a rotating operating state or a stopped state. When the operating state is determined, the rotational speed of the rotated body can be calculated by counting the period of V out.
I will be receiving I+. If the control circuit 15 is configured to perform the determination operation as described in -4- and to enter a predetermined abnormality control mode after determining the abnormality of the sensor 11, it will be possible to prevent danger in the event of a sensor abnormality. control conditions can be effectively avoided. In the embodiment described in l-, a diode D is provided in the oscillation circuit 13 for setting the lower limit that operates when detecting a short circuit in the sensor 11, and a limit for setting the upper limit voltage that operates when detecting a disconnection of the sensor 11. Circuit 14 can now be used. FIG. 3 shows an embodiment configured without using such a limit means, in which a control circuit 2I configured by a digital processing circuit such as a microcomputer controls disconnection of the coil 11.3 of the rotation detection sensor 11. Or to detect short circuits. ing. That is, in this device, there is one J rotation detection sensor I.
The detection signal obtained by I (tj, ) is amplified by the operational amplifier +21 as in the previous embodiment, and the operational amplified output is supplied to the comparator circuit 22. In this comparison circuit 22, a resistor R2
Based on the voltage Vg divided by 1 and R22, the level of the output from the operational amplifier +21 is determined by I11,
The determination result is supplied to the input terminal 21+ of the control circuit 21. The control circuit 21 determines whether or not the signal input from this terminal 21.1 has a predetermined frequency or higher, and determines whether the rotation detection sensor 11 is in a rotation stop state or not. When it is determined, the output terminal 212
After a predetermined time TI, the output signal is set to a low level, and the transistor 23 is controlled to be in an on state. A resistor R2g is connected in series with this transistor 23, and when this transistor 23 is in an on state, this resistor R23 is connected in parallel with the resistor R21. After the signal that reaches the level below the time T1 is output in this way, the output terminal 213 of the control circuit 2 is kept at a high level for a predetermined time T2, and the transistor 24 is turned on. . This l transistor 24
A resistor R24 is connected in series with , and when the transistor 24 is on, this resistor R24 becomes the resistor R22! 112 columns are connected. That is, the control circuit 21 has a built-in oscillation circuit that oscillates a signal with a period set by times T1 and T2, so that the output from the comparison circuit 22 reaches a predetermined value of 0. +J between L'l
In the absence of I change 1:, the J transistors 23 and 24 are controlled on and off reciprocally. In this device N, when one rotation detection sensor 11 is in the i+j state and one is rotating,
The output of the operational amplifier 121 has a period of 1"l and 'l-1
), and the output of the comparison circuit 22 changes accordingly. Then, when the C1 sensor 11 is in the normal and stopped state, the rotation detection sensor 11 is further disconnected or ((J circuit abnormality occurs), the outputs 1 and 1 from the comparator circuit 22 are The operating state is explained as follows. First, rotation detection 1 (1 sensor 11 is in normal state, [1
When the rotation speed is 5 degrees, as shown in Fig. 5, the operational amplifier 12+ generates a signal with a period corresponding to the same rotational speed, and the comparison circuit 22 outputs a signal synchronized with this signal whose period changes. A rectangular wave signal is generated, and this signal is supplied to the control circuit 21. Therefore, the control circuit 21 does not turn on the transistors 23 and 24;
The comparison reference voltage set in the comparison circuit 22 is kept constant. If the rotation is stopped under such normal conditions, the comparator circuit 2
The output from the control circuit 21 does not change, and the output terminal of the control circuit 21 outputs a signal that is at the front-level of the time TI, and the transistor 23 is turned on and connected in parallel to either the resistor R23 or the resistor R21. Therefore, the 1λ voltage Vg of the comparator circuit 22 increases,
The level of this voltage and the voltage from the operational amplifier 12+ is determined. Then, after this time T I has elapsed, the output terminal 213 or 11. During the interval T2, the transistor 24 is turned on and the resistor R24 is connected to the resistor R22.
Connect in parallel. Then, the reference voltage Vg is set low. Here, the values of resistor R2] and R22 are set to a resistance value that is the center of the peak value of the output obtained when the sensor 11 is normal, and the resistor R23 is connected in parallel to the resistor R21. Then, the reference voltage Vg is set so that the reference voltage Vg is set to be greater than the maximum peak value of the output obtained when the sensor 11 is normal, and lower than the output voltage obtained at the disconnection 11j of the sensor 11. The resistance value is set. Also, when the resistor R24 is connected to the resistor R22 in the d14 column, it is lower than the peak value of the output i'7 when the sensor 11 is normal, and higher than the output voltage obtained when one sensor 11 is short-circuited. The resistance value is set so that a reference voltage Vg of .) is obtained. Therefore, when the sensors 11 are normal and 11 are in a stopped state, the comparison circuit 22 is disconnected between TI and T2.
It changes to high level and low level as shown in Figure 5. Then, when the sensor 11 is short-circuited, the inputs of the comparator circuit 22 are both at a low level between TI and T2, and the outputs of the comparator circuit 22 are both at a low level. In a state where 1 for sen→no is disconnected, the output from the comparator circuit 22 is at the 21 level for both periods ]1 and T2, and the logic shown in FIG. 4 comes to hold. Therefore, by determining this logic in the control circuit 2I, it is possible to determine whether the rotation detection sensor is in a normal state or in an abnormal state such as a disconnection or short circuit. [Effects of the Invention] As described above, according to the sensor signal processing device according to the present invention, when the pickup sensor is in a normal state, when the limb detection body is in the operating state and when it is in the stopped state, Also, a pulse-like oscillation signal with a predetermined cycle or more can be obtained, and it can be clearly determined whether the sensor is in a normal state. In addition, if the pick-up coil of the sensor is in an abnormal state such as disconnection or short-circuit, a signal with a level corresponding to the content of the abnormal state can be obtained, and monitoring of the sensor's pick-up coil in particular is the output signal. This type of i1+ can be easily and reliably determined based on
The reliability and ease of handling of the 11-station device are significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram for explaining a sensor signal processing device according to an embodiment of the present invention, and FIG. 2 is a -1-2 unit W.
FIG. 3 is a circuit configuration diagram illustrating another embodiment of the present invention, and FIG. 4 is a diagram illustrating the operating state of this actual example. FIG. 5 is a diagram illustrating the relationship between signals 1 and 1, FIG. 5 is a signal lIυ11 diagram illustrating the operating state, and FIG. ■...Rotation detection sensor, Ill... Rotation plate, ■2.
・Core (ferromagnetic material), 113・ Pickup coil, 12... operational amplifier circuit, 13 oscillation circuit, +31-
...Comparator, 14...Limit circuit, C...Conde>
The.

Claims (4)

[Claims] (1) A pickup sensor that generates a pulsed pickup signal in response to the motion of the detected object, an amplification means that amplifies the sensor signal corresponding to the potential difference between both ends of a pickup coil that constitutes the pickup sensor, and the detected object. oscillation means that oscillates at a cycle sufficiently longer than the cycle of the pickup signal obtained from the pickup sensor in the operating state of the detection object; the oscillation means is supplied with the output signal from the amplification means; An oscillation output is obtained from the oscillation means in response to an output signal from the amplification means corresponding to the pickup signal having a cycle sufficiently shorter than the oscillation signal cycle, and the output signal from the amplification means is in the maximum state or A sensor signal processing device characterized in that the oscillation operation of the oscillation means is stopped in a minimum state. (2) The oscillation means includes a capacitor and a charging/discharging circuit for the capacitor, and the capacitor is controlled to be charged and discharged based on a pulse-like output signal from the amplification means, and the capacitor is Claim: wherein a limit means is set to prevent the terminal voltage from being charged to a voltage higher than the maximum output from the amplification means and from being discharged to a voltage lower than the minimum output from the amplification means. 1. A sensor signal processing device. (3) The sensor signal processing device according to claim 2, wherein the output of the amplifying means is set to the maximum voltage state when the pickup coil is disconnected, and is set to the minimum voltage state when the pickup coil is short-circuited. (4) The output from the amplification means is supplied to a comparison means in which a specified reference voltage is set, and the output signal from the comparison means is supplied to a digital processing circuit, which The apparatus further comprises a stop determining means for determining that the output signal from the comparing means is equal to or lower than a specified frequency, and the stop determining means corresponds to the oscillation period of the oscillating means in a state determined to be stopped by the stop determining means. The sensor according to claim 1, wherein the reference voltage of the comparison means is switched and set to a state higher than a maximum voltage of the output of the amplification means or a state lower than a minimum voltage generated by the disconnection or short circuit of the pickup coil. Signal processing device.