JP6550172B2 - Object detection sensor - Google Patents

Description

  The present invention relates to an object detection sensor such as a level sensor.

  The object detection sensor is a sensor that detects the presence or absence of an object by a change in capacitance or the like. For example, it is used to determine whether powder or liquid in a container is filled to a predetermined level (Patent Document 1).

  The circuit configuration of a conventional electrostatic capacitance type level sensor is shown in FIG. The oscillation circuit 2 that oscillates a sine wave is configured by an LC oscillation circuit. The oscillation frequency fs can be changed by changing the capacitance of the variable capacitor 4 constituting the LC oscillation circuit. The output of the oscillation circuit 2 is provided between the taps a and b of the resonant transformer 8 through the coupling capacitor 6.

  The resonant coil L of the resonant circuit 10 is connected to and coupled to the opposite side of the resonant transformer 8. A resonant capacitor C is connected to the resonant coil L. The detection electrode 12 is connected to one end of the resonant capacitor C.

  If the oscillation frequency fs of the oscillation circuit 2 matches the resonance frequency of the resonance circuit 10, the impedance of the resonance circuit 10 is high, and the output of the oscillation circuit 2 appears between the taps b and c of the transformer 8. The detection circuit 14 detects this output and outputs it as a detection voltage. Therefore, the detection voltage is maximum in the resonant state.

  When an object to be detected (powder, liquid, etc.) contacts the detection electrode 12, the capacitance changes depending on the object to be detected, and the above-mentioned resonance state is broken. As a result, the impedance of the resonant circuit 10 is lowered and the detection voltage is lowered. Therefore, the presence or absence of a detection target can be determined by monitoring the detection voltage.

  By the way, when installing such a capacitance type level sensor, the oscillation frequency fs of the oscillation circuit 2 is changed to match the resonance frequency of the resonance circuit 10 in the absence of a detection object after attachment. There is a need. In the conventional example of FIG. 31, the detection voltage is measured by a tester while changing the capacitance of the variable capacitor 4 of the oscillation circuit 2 using a driver, and a resonance state is found.

Japanese Patent Application Laid-Open No. 8-292081

  However, in the conventional capacitance level sensor as described above, adjustment at the time of installation has not been easy. That is, a tester and a driver were required, and the adjustment required skill. In particular, when attached to a large tank or the like, or when attached to a narrow place, the work was caused by the high place or the closed place, which was even more serious.

  In addition, the characteristics may change due to the temperature change of the surrounding environment, and the resonance state may be shifted. Conventionally, a capacitor or the like having reverse temperature characteristics is used for temperature compensation to cope with temperature changes. However, it was difficult to find an element having an ideal inverse characteristic.

  Such problems have occurred not only in the capacitive sensor but also in other sensors such as the inductive sensor. In addition to the level sensor, the same applies to proximity sensors and the like.

  An object of the present invention is to solve at least one of the problems as described above, and to provide an object detection sensor that can be easily adjusted or an object detection sensor with high detection accuracy.

  The independently applicable features of the invention are listed below.

(1) (2) The object detection sensor according to the present invention counts the high frequency clock from the high frequency oscillation circuit, changes the output and divides the frequency each time the predetermined number of clocks are counted, and creates a rectangular shape of the desired frequency. A counter that outputs an oscillation signal, a resonant circuit that is coupled to the rectangular oscillation signal and whose resonant frequency changes according to the presence or absence of a measurement target, and an output signal of the resonant circuit when the rectangular oscillation signal is given, directly or indirectly Detection circuit that detects the presence or absence of the measurement object based on its amplitude, and changes the predetermined number for frequency division of the counter when initialization is performed in the absence or presence of the measurement object Frequency setting means for sweeping the frequency of the rectangular oscillation signal and selecting and setting the frequency of the rectangular oscillation signal such that the amplitude of the detection signal detected by the detection circuit is maximized or minimized It is equipped with a.

  Since the rectangular oscillation signal by the counter is used, the frequency can be easily controlled by changing the frequency division number, and it is easy to match the resonance frequency.

(3) In the object detection sensor according to the present invention, the counter has a frequency by dividing by a first predetermined number and a frequency by dividing by a second predetermined number adjacent to the first predetermined number. In order to realize the frequency between them, a rectangular oscillation signal is generated by temporally mixing a signal by division by a first predetermined number and a signal by division by a second predetermined number at a predetermined ratio. The frequency setting means may change the frequency based on the predetermined number for the division and the mixed ratio.

  Therefore, the frequency can be changed more finely.

(15) (16) An object detection sensor according to the present invention includes an oscillation circuit that outputs an oscillation signal of a desired frequency, and a resonance circuit that is coupled to the oscillation signal and that changes the resonance frequency depending on the presence or absence of the measurement object. An output signal of the resonance circuit when the oscillation signal is applied is directly or indirectly taken out, and a detection circuit for detecting the presence or absence of the measurement object based on the amplitude, and in a state without or with the measurement object Frequency setting means for changing and sweeping the frequency of the oscillation signal at the time of initial setting, and selecting and setting the frequency of the oscillation signal so that the amplitude of the detection signal detected by the detection circuit becomes maximum or minimum Equipped with
The frequency setting means changes the frequency of the oscillation signal at the first speed if the detection signal does not exceed the threshold at the time of the initial setting, and if the detection signal exceeds the threshold at the first speed. Change the frequency of the oscillation signal at a second speed that is slower than the speed of c to select the frequency of the oscillation signal so that the amplitude of the detection signal is maximized, or ii) the detection signal falls below the threshold For example, the frequency of the oscillation signal is changed at a first speed, and when the detection signal falls below the threshold, the frequency of the oscillation signal is changed at a second speed slower than the first speed, and the amplitude of the detection signal is It is characterized in that the frequency of the oscillation signal is selected so as to minimize.

  Therefore, even when it takes time for detection by the detection circuit, both detection accuracy and set speed can be achieved.

(17) In the object detection sensor according to the present invention, the second frequency setting means may perform the second operation if the amplitude of the detection signal acquired this time is the maximum value or the minimum value from the start of the sweep during the sweep of the frequency of the oscillation signal. Changing the frequency of the oscillation signal at a third speed that is even slower than the speed of.

  Therefore, both detection accuracy and set speed can be further achieved.

(27) (28) The object detection sensor according to the present invention includes an oscillation circuit that outputs an oscillation signal of a desired frequency, and a resonance circuit that is coupled to the oscillation signal and that changes the resonance frequency depending on the presence or absence of the measurement object. An output signal of the resonance circuit when the oscillation signal is applied is directly or indirectly taken out, and a detection circuit for detecting the presence or absence of the measurement object based on the amplitude, and in a state without or with the measurement object Frequency setting means for changing and sweeping the frequency of the oscillation signal at the time of initial setting, and selecting and setting the frequency of the oscillation signal so that the amplitude of the detection signal detected by the detection circuit becomes maximum or minimum The frequency setting means sweeps from a high frequency to a low frequency during the initial setting.

  Therefore, the detection signal due to the harmonic does not appear earlier than the detection signal due to the fundamental wave, and accurate detection can be performed.

(29) The object detection sensor according to the present invention is characterized in that the oscillation signal is a periodic waveform which is not a sine wave.

  Accurate detection can be performed even on a periodic waveform in which such harmonics easily occur.

(37) (38) The object detection sensor according to the present invention includes an oscillation circuit that outputs an oscillation signal of a desired frequency, and a resonance circuit that is coupled to the oscillation signal and that changes the resonance frequency depending on the presence or absence of the measurement object. An output signal of the resonance circuit when the oscillation signal is applied is directly or indirectly taken out, and a detection circuit for detecting the presence or absence of the measurement object based on the amplitude, and in a state without or with the measurement object Frequency setting means for changing and sweeping the frequency of the oscillation signal at the time of initial setting, and selecting and setting the frequency of the oscillation signal so that the amplitude of the detection signal detected by the detection circuit becomes maximum or minimum The frequency setting means discretely changes the frequency of the oscillation signal from the sweep start frequency to the sweep end frequency, executes the sweep a plurality of times, and continuously detects a predetermined number of times. If the frequency at which the amplitude of the signal becomes maximum or minimum was identical, it is characterized by a set frequency by selecting the frequency.

  Therefore, even if noise or fluctuation occurs, the frequency can be set accurately.

(39) The object detection sensor according to the present invention is characterized in that the frequency setting means acquires the detection signal a plurality of times for each frequency, and uses the average value of the amplitude as the amplitude of the detection signal.

  Therefore, even when sudden noise is superimposed, the frequency can be set accurately.

(45) (46) An object detection sensor according to the present invention includes an oscillation circuit that outputs an oscillation signal of a desired frequency, and a resonance circuit that is coupled to the oscillation signal and that changes the resonance frequency depending on the presence or absence of the measurement object. A capacitance sensor comprising: a detection circuit for directly or indirectly taking out an output signal of a resonance circuit when the oscillation signal is given, and detecting presence or absence of an object to be measured based on the amplitude thereof, A plurality of light emitting units for displaying the operation mode are continuously arranged, and the level of the detection signal is displayed by the continuously arranged light emitting units.

  Therefore, the light emitting unit for displaying the operation mode can be used as the level display of the detection signal, and the light emitting unit having a simple configuration can perform level display that is intuitively easy to understand.

(47) In the object detection sensor according to the present invention, in the light emitting unit arranged continuously, the display mode is also displayed in which the output of the detection circuit is turned on in a display mode different from the level of the detection signal. It is characterized by having done it.

  Therefore, the threshold can be displayed together to easily know the detection margin.

(48) The object detection sensor according to the present invention is characterized in that the level of the detection signal is displayed by continuous lighting, and the threshold is displayed by blinking.

  Therefore, both can be easily distinguished.

  The "frequency setting means" refers to one having a function of changing at least the frequency of the oscillation signal to acquire the amplitude of the detection signal and setting the frequency, and in the embodiment, steps S1 to S11 correspond to this.

  "Temperature compensation means" refers to one having a function to keep the resonance state following at least the fluctuation of the resonance frequency due to temperature change, and in the embodiment, steps S41 and S42 correspond to this.

  The “program” is a concept including not only a program directly executable by the CPU but also a program in source format, a program subjected to compression processing, an encrypted program and the like.

It is a functional block diagram of an object detection sensor according to an embodiment of the present invention. It is sectional drawing of the electrostatic capacitance type level sensor by embodiment. It is an attachment example of the electrostatic capacitance type level sensor 1. FIG. 2 is a diagram showing a hardware configuration of a control circuit 32. It is a flowchart (initial setting) of a control program. It is a figure which shows the detail of the counter part 56. FIG. It is a figure for demonstrating the decision processing of a candidate frequency. It is a flowchart (at the time of operation) of a control program. It is a figure which shows the example which made two frequencies be mixed temporally. It is a circuit example for mixing two frequencies temporally. It is a functional block diagram of a target object detection sensor by a 2nd embodiment. It is a flowchart (initial setting) of a control program. It is a figure for demonstrating sweep processing. It is a figure for demonstrating sweep processing. It is a figure for showing the influence of a harmonic. It is a functional block diagram of an object detection sensor according to a third embodiment. FIG. 2 is a diagram showing a hardware configuration of a control circuit 32. It is a flowchart (initial setting) of a control program. It is a figure for demonstrating temperature compensation. It is a flowchart (at the time of operation) of a control program. It is a figure which shows the hysteresis in temperature compensation. It is an example of the temperature characteristic of coil L1. It is a figure which shows the curve of temperature compensation. It is a functional block diagram of an object detection sensor according to a third embodiment. It is an example of a display at the time of operation mode. It is an example of a display at the time of setting mode. It is an example of a display at the time of setting mode. It is an example of a display at the time of delay time setting mode. It is an example of a display at the time of sensitivity setting mode. It is an example of a display at the time of sensitivity setting mode. It is an example of a display at the time of sensitivity setting mode. It is a figure which shows the conventional electrostatic capacitance type level sensor.

1. First embodiment
1.1 Functional Configuration FIG. 1 shows a functional configuration diagram of an object detection sensor according to an embodiment of the present invention. The counter 20 counts and divides a high frequency clock and outputs a rectangular oscillation signal. The resonance circuit 26 changes capacitance and inductance and changes its resonance frequency in the presence and absence of the object 28. Also, the resonant circuit 26 is coupled to the rectangular oscillation signal.

  The detection circuit 24 acquires the output signal of the resonant circuit 26 to which the rectangular oscillation signal is given, and determines the presence or absence of the object based on the amplitude. Therefore, it can be detected whether there is an object or not.

  When installing this object detection sensor, it is necessary to match the frequency of the rectangular oscillation signal with the resonant frequency of the resonant circuit in the absence (or presence) of the object 28. In this embodiment, this process is performed as follows. The frequency setting means 22 gradually changes the frequency division number of the counter to sweep the frequency of the rectangular oscillation signal. The frequency setting means 22 acquires the amplitude of the detection signal when the frequency of the rectangular oscillation signal is thus changed. The rectangular oscillation signal is set to the frequency at which the amplitude becomes maximum (or minimum).

  In this way, the frequency of the rectangular oscillation signal and the resonant frequency of the resonant circuit are automatically matched.

1.2 Appearance and Hardware Configuration FIG. 2 shows a cross-sectional view of an object detection sensor according to an embodiment of the present invention. In this embodiment, an example configured as a capacitance type level sensor is shown.

  A control circuit 32 is housed inside the housing 30. A measurement electrode 36 and a ground electrode 34 are provided to protrude from the housing 30. The measurement electrode 36 is formed in a cylindrical shape at the tip end portion, is formed thin at the root portion, and is connected to the control circuit 32. The ground electrode 34 is cylindrically provided at the root portion of the measurement electrode 36, and is insulated from the measurement electrode 36 by the insulators 44 and 46. The ground electrode 34 is connected to the ground of the control circuit 32.

  At the rear end of the housing 30, a display unit 38 in which an LED (not shown) is disposed is provided. By displaying the state on the display unit 38 at the time of switching or adjusting the mode, the worker is assisted. The display 38 is usually covered by a lid 40 so as not to be seen from the outside. When necessary, the display 38 can be viewed by opening the lid 40.

  FIG. 3 shows an attachment example of the capacitive level sensor 1. The liquid 82 is stored in the storage tank 80. The liquid 82 can be removed from the storage tank 80 by opening the valve (not shown). Further, a supply path (not shown) for supplying the liquid 82 to the storage tank 80 is provided, and the liquid 82 can be supplied to the storage tank 80. At this time, when the liquid 82 reaches the position of the capacitive level sensor 1, the capacitive level sensor 1 detects this and stops the supply of the liquid 82.

  In this manner, whether or not the liquid 82 has reached a predetermined level can be detected by the capacitive level sensor 1.

  FIG. 4 shows the control circuit 32 and its peripheral hardware configuration. The ground electrode 34 and the measurement electrode 36 are connected to the inductance L1 on the primary side of the resonant transformer L of the control circuit 32. Since the ground electrode 34 and the measurement electrode 36 are disposed close to each other as described above, they have a capacitive component C0. In this embodiment, the capacitance C0 and the inductance L1 constitute a resonant circuit.

  The rectangular oscillation signal from the counter unit 56 is given to the inductance L2 on the secondary side of the resonant transformer L via the driver 52 and the coupling capacitor 50. The counter unit 56 is controlled by the CPU 60 and can change the frequency of the rectangular oscillation signal.

  The secondary side of the resonant transformer L is also provided with an inductance L3 for extracting a signal of the resonant circuit. The amplitude of the extracted signal is converted to a direct current by the detection circuit 54 to be a detected signal. The detection signal is converted to a digital signal by the A / D converter 55, and can be acquired by the CPU 60 through the I / O port 64. In this embodiment, although the signal of the resonant circuit is indirectly taken out via the resonant transformer L, it may be taken out directly from the resonant circuit.

  A memory 62, an I / O port 64, and a flash memory 66 are connected to the CPU 60. A control program 68 is recorded in the flash memory 66.

  At the time of initialization, the CPU 60 automatically determines the frequency of the rectangular oscillation signal according to the control program 68 in a state where the liquid 82 has not reached the capacitive level sensor 1. That is, the CPU 60 controls the counter unit 56 to change the frequency of the rectangular oscillation signal to obtain a detection signal, and selects the frequency of the rectangular oscillation signal so as to match the resonance frequency of the resonant circuit.

  In use, the CPU 60 acquires a detection signal according to the control program 68, and determines whether the liquid 82 has reached the level of the capacitive level sensor 1 based on the amplitude. That is, when the liquid 82 does not reach the measurement electrode 36 and the ground electrode 34, the resonance state at the time of initial setting is maintained, and the amplitude of the detection signal becomes large. However, when the liquid 82 reaches the measurement electrode 36 and the ground electrode 34, the capacitance component C0 changes due to the liquid 82, the resonance state collapses, and the amplitude of the detection signal decreases.

  The CPU 60 detects this change to detect that the liquid 82 has reached a predetermined level, and changes the state of the output relay 61.

  The CPU 60 also controls the lighting of the LED 58 via the I / O port 64. The LED 58 displays the current mode of the capacitive level sensor 1, the amplitude of the detection signal, and the like.

1.3 Process at Initial Setting FIG. 5 shows a flowchart of the initial setting process of the control program 68. As described above, when using the capacitive level sensor 1, the resonant frequency of the resonant circuit and the rectangular oscillation signal in the absence of the liquid 82 (state not reaching the capacitive level sensor 1) It is necessary to match the oscillation frequency of This is called initialization.

  When the user operates the input device (such as an input button) 59 to enter the initial setting mode, the CPU 60 starts the initial setting process.

  First, the CPU 60 sets the frequency division ratio N given to the counter unit 56 to an initial value (step S3). Here, the details of the counter unit 56 are shown in FIG. Counter unit 56 receives a clock from clock oscillation circuit 55. In this embodiment, an operation clock (32 MHz) of the CPU 60 is used. From the viewpoint of stability, it is preferable to use a clock generated by a quartz oscillator. The oscillation frequency can be adjusted more accurately as the clock frequency is higher.

  The counter 562 counts a given clock. The count value is provided to periodic event setting register 564. The periodic event setting register 564 outputs a periodic event signal when the count value of the counter 562 becomes equal to half (N / 2) of the frequency division ratio N set by the CPU 60. This periodic event signal is provided to the reset input of the counter 562. Therefore, a periodic event signal is output from the periodic event setting register 564 every clock of the frequency division number N / 2 set by the CPU 60.

  The periodic event circuit 566 receives the periodic event signal and changes its output state (H to L, L to H). Therefore, from the periodic event circuit 566, a rectangular oscillation signal in which the clock is divided by the division number N set by the CPU 60 is output.

  Next, the CPU 60 takes in the detection signal from the detection circuit 54, and acquires its amplitude value (step S4). In this embodiment, the amplitude value is taken in continuously a predetermined number of times (five times in this embodiment) and averaged to obtain the amplitude value of the detection signal. As a result, even if instantaneous noise is superimposed, the influence can be averaged and reduced.

  The CPU 60 changes the division ratio N and sweeps the frequency of the rectangular oscillation signal (in this embodiment, it sweeps from a low frequency to a high frequency), and takes in the amplitude value of the detection signal at each frequency.

  If the acquired detection signal exceeds the maximum amplitude value so far (step S5), the CPU 60 records the maximum amplitude value and the division ratio (frequency) in the memory 62 and updates it (step S6). Therefore, when all frequencies (500 KHz to 1.7 MHz in this embodiment) are swept, the memory 62 records the maximum amplitude value and the division ratio Nmax at this time.

  FIG. 7 shows the frequency characteristics of the resonant circuit. By sweeping the frequency of the rectangular oscillation signal, the maximum amplitude of the detection signal can be found, and the frequency at this time can be detected as a resonant frequency. The CPU 60 records the division ratio Nmax (the found resonance frequency) as a setting candidate in the memory 62 (step S8).

  In this embodiment, the CPU 60 carries out the above-described sweep process again, and similarly determines again the division ratio Nmax as a setting candidate. Then, if the frequency division ratio Nmax which is the previous setting candidate and the frequency division ratio Nmax which is the current setting candidate are equal, this is determined as the set frequency division ratio (step S11). Therefore, the counter unit 56 is set to output a rectangular oscillation signal at the resonant frequency of the resonant circuit.

  If the previous division ratio Nmax and the current division ratio Nmax are not equal, the sweep process is repeated until the division ratio Nmax becomes equal twice in a row (step S9).

  In this embodiment, since the frequency of the rectangular oscillation signal is discretely changed, it is clearly determined whether the previous oscillation frequency (division ratio) and the present oscillation frequency (division ratio) are the same. Can.

  As described above, the initial setting process by the CPU 60 is performed. The user only needs to press the input device 59 to set the initial setting mode, and does not have to perform complicated operations or delicate adjustments.

1.4 Process in Operation FIG. 8 shows a flowchart of the actual operation process (operation mode) of the control program 68.

  The user can switch to the operation mode by operating the input device 59.

  In the operation mode, the CPU 60 acquires the amplitude of the detection signal (step S51). As shown in FIG. 3, in the state where the liquid 82 has not reached the electrode of the capacitive level sensor 1, the above-mentioned initial setting is performed. Therefore, if the liquid 82 does not reach the capacitive level sensor 1, the resonant frequency of the resonant circuit matches the oscillation frequency of the rectangular oscillation signal, and the amplitude of the detection signal is in the maximum state.

  Next, the CPU 62 determines whether the amplitude of the acquired detected signal is lower than a preset detection threshold (step S52). The detection threshold may, for example, be set to 50% of the maximum amplitude. As described above, if the liquid 82 has not reached the capacitive level sensor 1, the amplitude of the detection signal exceeds the detection threshold, so the CPU 60 returns to step 51 again to detect the detection signal. Acquisition, repeat the comparison with the threshold.

  When the liquid 82 reaches the capacitive level sensor 1, the capacity of the resonant circuit changes and the resonant frequency changes. Therefore, the amplitude of the detection signal is reduced. If the CPU 60 determines that the amplitude of the detection signal falls below the detection threshold, it changes the state of the output relay 61 (step S53). Therefore, this makes it possible to detect that the liquid level of the liquid 82 has reached the capacitance type level sensor 1 and perform predetermined processing (e.g., discharge of the liquid 82).

  Note that the detection threshold can be set in advance, and setting high (setting the margin small) improves detection sensitivity, but also increases the possibility of false detection. If the setting is low (the margin is set large), although the detection sensitivity decreases, the possibility of false detection can be reduced.

  Also, how to change the state of the output relay 61 can be set in advance. It is possible to set it to be off in the initial state and to be on at the time of detection, or to be on in the initial state and to be set to be off at the time of detection.

  The setting contents are set by the user operating the input unit 59 at the time of initial setting, and the CPU 60 records the setting contents in the flash memory 66.

1.5 other
(1) In the above embodiment, the liquid 82 has been described as an example of the detection object, but if it is a substance having a detectable relative dielectric constant or conductivity, powder, fluid, a mixture of these, etc. besides liquid, etc. The same applies to

(2) In the above embodiment, initialization is performed in a state in which the detection target does not cover the electrode of the capacitance type level sensor 1, and the detection target covers the electrode of the capacitance type level sensor 1 To detect. However, initial setting is performed in a state in which the detection target covers the electrodes of the capacitive level sensor 1 so that it is detected that the detection target does not cover the electrodes of the capacitive level sensor 1. May be

(3) In the above embodiment, although the capacitive level sensor has been described as an example, the present invention can be applied to other capacitive sensors such as a capacitive proximity sensor.

(4) In the above embodiment, the capacitance type sensor has been described, but a sensor in which the inductance changes depending on the object, a sensor in which the resistance changes, a sensor in which these change collectively, etc. It can apply to the sensor which detects by.

(5) In the above embodiment, the frequency of the rectangular oscillation signal is changed by changing the division ratio. In order to precisely match the frequency of the rectangular oscillation signal with the resonant frequency of the resonant circuit, it is necessary to change the frequency of the rectangular oscillation signal in fine steps.

  However, if the frequency of the rectangular oscillation signal is changed only by the division ratio, it is difficult to finely change the frequency. If the frequency is changed in finer steps, it is necessary to increase the frequency of the original clock (the output of the clock oscillation circuit in FIG. 6), and a counter unit 56 capable of high-speed processing is required. Depending on the type of sensor and usage conditions, the use of such high-frequency clocks and counters capable of high-speed processing may be problematic.

  In such a case, in addition to changing the division ratio, it is possible to realize an intermediate frequency by temporally mixing adjacent frequency signals f1 and f2 obtained by the division ratio. .

  An example is shown in FIG. In FIG. 9A, the frequency of the rectangular oscillation signal is f1 because the frequency is f1 in all cycles. In FIG. 9B, the frequency division ratio is changed once in 16 times to obtain the frequency f2. Therefore, the frequency of the rectangular oscillation signal is (15 · f1 + f2) / 16. Similarly, in FIG. 9C, the frequency division ratio is changed twice in 16 times to obtain the frequency f2. Therefore, the frequency of the rectangular oscillation signal is (14 · f1 + 2 · f2) / 16. Similarly, in FIG. 9D, the frequency of the rectangular oscillation signal is (13 · f1 + 3 · f2) / 16.

  In this way, it is possible to realize an intermediate frequency between the frequencies f1 and f2 at adjacent division ratios. In the above, the frequencies f2 are mixed so as not to be continuous as much as possible, but how to mix them is free.

  FIG. 10 shows an example of the counter unit 56 for realizing such an intermediate frequency of the rectangular oscillation signal. The periodic event setting register 564 outputs a periodic event signal when the count value of the counter 562 becomes equal to half (N / 2) of the frequency division ratio N set by the CPU 60. The adjustment register 568 counts the output of the periodic event setting register 564, and when a predetermined number is counted, applies a carry output to the periodic event setting register 564. The periodic event setting register 564 outputs a periodic event signal when it is equal to a value obtained by adding 1 to the half (N / 2) of the set division ratio N only when the carry output is received. Therefore, a desired intermediate frequency can be realized by controlling a predetermined number of carry outputs from the CPU 60.

(6) In the above embodiment, in step S4, the detected signal is obtained five times and the average value is calculated. However, the average value may be calculated by discarding the maximum value and the minimum value among the five obtained values. Alternatively, the statistical outliers may be rejected and the average value may be calculated from among the acquired five times.

  The average value may be calculated by acquiring a predetermined number of times. Alternatively, it may be acquired only once and used as the amplitude value of the detection signal.

(7) In the above embodiment, when the frequency division ratio Nmax continuously matches, this is adopted as the set frequency division ratio. However, when they coincide with each other a predetermined number of times, this may be adopted as the set frequency division ratio.

  Alternatively, the sweep may be performed a plurality of times, and the most frequent division ratio may be adopted as the set division ratio.

  Furthermore, the sweep may be performed only once, and the division ratio Nmax at this time may be adopted as the set division ratio.

(7) In the above embodiment, sweeping from low frequency to high frequency is performed at the time of initial setting. However, it may sweep from high frequency to low frequency.

(8) Although the rectangular oscillation signal is used in the above embodiment, a triangular wave, a sine wave or the like may be used if it has periodicity.

(9) In the above embodiment, the detection signal is maximized when the resonance circuit resonates. However, even in the case of a configuration in which the detection signal is minimized at the time of resonance of the resonant circuit, the present invention can be similarly applied.

(10) In the above embodiment, the sweep is performed over 500 Hz to 1.7 MHz. This range may be determined according to the variation of the resonant frequency of the resonant circuit of the capacitive level sensor 1 in which the present control circuit is mounted (which varies depending on the length of the electrode).

(11) In the above embodiment, the oscillation signal is generated using a counter. However, any oscillator that can change frequency can be used.

(12) The above embodiment and modifications can be implemented in combination with other embodiments as long as the essence is not violated.

2. Second embodiment
2.1 Functional Configuration FIG. 11 shows a functional configuration of the object detection sensor according to the second embodiment. The basic configuration is the same as that of the first embodiment. However, in this embodiment, the speed at which the frequency setting means 22 changes the frequency is changed according to the situation.

  This is due to the following reasons. It may take time for the detection circuit 24 to detect the output signal of the resonant circuit. For example, this is the case where the detection circuit 24 is configured with a diode and a capacitor for detection. The capacitor needs time to charge and discharge, which requires time for detection. If the frequency is swept in accordance with the detection time of the detection circuit 24, it takes time for the initial setting.

  Therefore, in this embodiment, while the detection value of the detection circuit is small, the speed of the sweep is increased, and when the detection value of the detection circuit is increased (when the resonance point is approached), the speed of the sweep is decreased. That is, the frequency setting means 22 changes the frequency of the oscillation signal at the first speed if the detection signal does not exceed the threshold, and the second speed lower than the first speed if the detection signal exceeds the threshold. I try to change the frequency by the speed.

  By doing as described above, the processing speed is prevented from being lowered while the setting frequency is accurately determined.

2.2 Appearance and Hardware Configuration The appearance and hardware configuration when the object detection sensor is configured as a capacitance type level sensor are the same as those in FIGS. 2 and 3. The details of the counter unit 56 are the same as those shown in FIG.

2.3 Process at Initial Setting FIG. 12 shows a flowchart of an initial setting process of the control program 68. The same processes as in FIG. 5 in the first embodiment are assigned the same step numbers.

  When the user operates the input unit 59 to enter the initial setting mode, the CPU 60 starts the initial setting process.

  The CPU 60 sets the delay time when changing the frequency of the rectangular oscillation signal to the minimum (0 in this example) (step S10). That is, in the initial state, the rectangular oscillation signal is swept at high speed.

  The CPU 60 sets the frequency division ratio N given to the counter unit 56 to an initial value (step S3). Therefore, the counter unit 56 outputs a rectangular oscillation signal in which the clock is divided by the division number N set by the CPU 60. In this embodiment, the sweep is performed from high frequency to low frequency.

  Next, the CPU 60 determines whether the set delay time has elapsed (step S11). Here, since the delay time is set to 0, the process of the next step S4 is performed without providing the delay time.

  In step S4, the CPU 60 takes in the detection signal from the detection circuit 54, and acquires its amplitude value. In this embodiment, the amplitude value is taken in continuously a predetermined number of times (five times in this embodiment) and averaged to obtain the amplitude value of the detection signal. As a result, even if instantaneous noise is superimposed, the influence can be averaged and reduced.

  Subsequently, the CPU 60 determines whether the amplitude of the detection signal exceeds a threshold (step S12). FIG. 13 shows the relationship between the threshold value and the detection signal. The threshold value is preferably set to a value (approximately 1/5 to 1/10) sufficiently lower than the peak value of the expected detection signal.

  Since the sweep start frequency is set higher than the update frequency, the detection signal is below the threshold at the start of the sweep. Therefore, the CPU 60 sets the next division ratio in the counter unit 56 (step S3). Then, the amplitude of the detection signal is acquired (step S4), and it is determined whether the threshold is exceeded (step S12).

  The above processing is repeated, and when the detected signal exceeds the threshold (point A in FIG. 13), the CPU 60 sets the delay time to medium (1 ms in this example) (step S13). Furthermore, if the amplitude of the detection signal has updated the maximum value so far (step S5), the CPU 60 sets the delay time to the maximum (100 ms in this example) (step S14). Here, since the amplitude of the detection signal updates the maximum value, the delay time is set to the maximum.

  Subsequently, the CPU 60 records and updates the current amplitude as the maximum value, and records the current division ratio (step S6).

  As described above, while the amplitude of the detection signal is updating the maximum value (between time point A and time point B in FIG. 13), the delay time is maximized (slow speed) in order to obtain the amplitude accurately. I do.

  When the frequency of the rectangular oscillation signal falls below the resonance frequency, the CPU 60 proceeds from step S5 to step S7, so the delay time will be set to medium. That is, the sweep is performed at a medium speed between time point B and time point C in FIG. Since the maximum value is not updated during this period, it can be determined that the resonance frequency has passed. However, because it exceeds the threshold, for safety, it is sweeping at medium speed instead of high speed. Note that this section may also be swept at high speed instead of medium speed.

  The CPU 60 further performs a sweep, and sets the delay time to be small when the amplitude of the detection signal falls below the threshold (step S15). Therefore, the sweep is performed at high speed.

  When the CPU 60 continues the sweep further, there is a portion where the amplitude of the detection signal appears due to the harmonic component of the rectangular oscillation signal (from the point D to the point E in FIG. 13). In this embodiment, since a rectangular wave which is easy to control is used, harmonic components are generated with respect to the oscillation frequency. The amplitude of the detection signal generated by the harmonic component is smaller than the amplitude of the detection signal at the original oscillation frequency. Therefore, the maximum value of the amplitude is not updated, and the sweep is performed at medium speed.

  When the CPU 60 continues sweeping further, the amplitude of the detection signal falls below the threshold, so the CPU 60 sweeps at high speed. Then, when the sweep end frequency is reached, the sweep is ended.

  The processing after finishing the first sweep in this way is the same as that of step S8 and subsequent steps in FIG. That is, if the frequency division ratio obtained as the setting candidate is the same two consecutive times, this is determined as the setting frequency division ratio.

  In the above, the sweep process is performed from high frequency to low frequency. This is because, as shown in FIG. 15A, when the sweep process is performed from low frequency to high frequency, harmonic components appear first, and this part is swept at low speed. That is, the sweep is performed at a speed as shown in FIG.

  It is useless even if it determines correctly about a harmonic component. Therefore, it is preferable to perform a sweep process from high frequency to low frequency as shown in FIG. 15B.

2.4 Process at the time of operation The process at the time of operation is the same as that of the first embodiment.

2.5 other
(1) In the above embodiment, only the division ratio is changed to perform the sweep. However, as shown in FIG. 10, intermediate signals may be realized by temporally mixing adjacent frequency signals f1 and f2 obtained by the division ratio.

(2) In the above embodiment, while the amplitude of the detection signal is updating the maximum value, the sweep is performed at a low speed. However, the sweep may be performed in such a manner as to be slow if it exceeds the threshold and to be fast if it is below the threshold.

(3) The above embodiment and modifications can be implemented in combination with other embodiments as long as the essence is not violated.

3. Third embodiment
3.1 Functional Configuration FIG. 16 shows a functional configuration diagram of an object detection sensor according to the third embodiment. The process at the time of initialization is the same as that of the first embodiment or the second embodiment. However, in this embodiment, a configuration is employed which compensates for the fluctuation of the resonance frequency due to the temperature change of the surrounding environment at the time of operation.

  The measurement electrode 36 and the ground electrode 34 have their capacitance C0 as an air condenser (see FIG. 4). Since the dielectric constant of the air hardly changes with temperature, the capacitance C0 is almost constant even if the temperature changes. However, the inductance (coil) L1 used for the resonant circuit 26 has positive temperature characteristics (inductance increases with temperature rise). For this reason, even if the frequency of the rectangular oscillation signal is made to coincide with the resonant frequency of the resonant circuit in the initial setting, there is a possibility of a shift due to a temperature change during use.

  Therefore, as shown in FIG. 17, a compensation capacitor Cc having a negative temperature characteristic (capacitance decreases with temperature rise) is connected in parallel to the electrode capacitance C0 so as to cause resonance due to temperature change, as in the prior art. It is intended to offset the frequency shift.

  However, the lengths of the measurement electrode 36 and the ground electrode 34 differ depending on the use site and application. Therefore, the capacitance C0 between the electrodes also differs depending on the length of the electrodes. When the electrode is long, the capacitance C0 also increases, and when the electrode is short, the capacitance C0 also decreases.

  Although it is preferable to prepare the compensation capacitor Cc in accordance with the size of the electrostatic capacitance C0, it is complicated because it is necessary to prepare various types of control circuits 32 having different electrostatic capacitances of the compensation capacitor Cc. Therefore, in this embodiment, an object detection sensor capable of performing temperature compensation is realized using the compensation capacitor Cc having the same capacitance regardless of the length of the electrode.

  In FIG. 16, a resonance circuit 26 is provided with a compensation capacitor Cc. However, if the electrode lengthens and the electrostatic capacitance C0 increases, temperature compensation by the compensation capacitor Cc does not work well. This is because of the following reasons.

  Since the inductance L1 is the same regardless of the length of the electrode, the variation ΔL of the inductance due to the temperature change is the same. The resonance frequency is determined by the product of (L1 + .DELTA.L) and (C0-.DELTA.C), where .DELTA.C is the variation of the capacitance of the compensation capacitor. Therefore, compensation can not be performed unless the capacitance of the compensation capacitor changes (ΔC) so that ΔC / C0 becomes a ratio of the same degree to the ratio ΔL / L1 of ΔL to L1 due to temperature change. .

  However, when the electrode lengthens and the capacitance C0 increases, the ratio decreases even if ΔC has the same capacitance. For this reason, even when the capacitance C0 is small, even if the compensation can be appropriately performed, there arises a problem that the compensation can not be completed when the capacitance C0 becomes large.

  Therefore, in this embodiment, when it is not possible to compensate by the compensation capacitor, temperature compensation is performed by changing the oscillation frequency of the rectangular oscillation signal.

  In FIG. 16, the oscillation circuit 20 generates an oscillation signal of a frequency that matches the resonance frequency of the resonance circuit 26 and supplies the oscillation signal to the resonance circuit 26. The detection circuit 24 detects a change in the output of the resonant circuit 26 by the object 28 and outputs a detection output.

  The resonant circuit 26 includes a compensation capacitor. The temperature compensation means 27 receives the temperature detected by the temperature detector 29 and controls the oscillation circuit 20 so that the lack of temperature compensation by the compensation capacitor is compensated by the frequency of the rectangular oscillation signal. That is, the frequency of the oscillation signal of the oscillation circuit 20 is changed so as to coincide with the resonant frequency of the resonant circuit 26 which has not been compensated by the compensation capacitor due to the temperature change.

  As described above, it is possible to perform more accurate detection in response to the variation of the resonant frequency of the resonant circuit with respect to the temperature change.

3.2 Appearance and Hardware Configuration The appearance when the object detection sensor is configured as a capacitance type level sensor is the same as that shown in FIG. The hardware configuration is shown in FIG. A compensation capacitor Cc is provided in parallel with the electrostatic capacitance C0 between the electrodes. Further, the small signal diode D is provided in the vicinity of the coil L1, and the ambient temperature is measured by the forward voltage. The forward voltage is converted to a digital signal by the A / D converter 63 and input to the I / O port 64 of the CPU 60. The CPU 60 measures the temperature by the magnitude of the forward voltage. A temperature sensor may be provided instead of the small signal diode D. Further, a temperature sensor built in the CPU 60 may be used.

  The details of the counter unit 56 are the same as those shown in FIG. 6 or FIG.

3.3 Process at Initial Setting FIG. 18 shows a flowchart of the initial setting process of the control program 68. In FIG. 18, only the part regarding setting of the parameter regarding temperature compensation among initializations is shown. The frequency setting and the like of the rectangular oscillation signal are the same as in the first embodiment and the second embodiment.

  The CPU 60 determines a compensation curve in accordance with the determined frequency of the rectangular oscillation signal (step S31). As described above, the degree to which the compensation capacitor Cc can compensate varies depending on the magnitude of the electrostatic capacitance C0 due to the electrode. When the electrode is short and the capacitance C0 is small, the compensation by the compensation capacitor Cc is performed well. When the electrode is long and the capacitance C0 is large, the compensation by the compensation capacitor Cc is relatively small.

  Therefore, when the capacitance C0 is small and the resonance frequency is high, as shown in FIG. 19A, since the compensation by the compensation capacitor Cc is sufficient, it is not necessary to compensate by the frequency change of the rectangular oscillation signal. As the capacitance C0 is large and the resonance frequency is low, as shown in FIG. 19B, the degree of compensation by the compensation capacitor Cc decreases, and the necessity of compensation due to the frequency change of the rectangular oscillation signal also increases. Therefore, the direction of the compensation curve becomes larger as the resonance frequency becomes larger.

  In this embodiment, the inclination of the compensation curve is recorded in advance in accordance with the frequency of the rectangular oscillation signal (corresponding to the resonant frequency of the resonant circuit) set by the initial setting process. The CPU 60 reads this out and records it as a set value (step S32).

  In this embodiment, the frequency of the rectangular oscillation signal is discretely changed. Therefore, the slope of the compensation curve is recorded as the temperature width until changing to the next frequency.

  As described above, the curve for the temperature compensation process is set.

3.4 Process in Operation FIG. 20 shows a flowchart of the temperature compensation process of the control program 68. This temperature compensation process is performed in parallel with the process at the time of actual operation. The CPU 60 acquires the voltage of the diode D, and determines the ambient temperature based on the prerecorded relationship (step S41).

  Next, based on the set temperature compensation curve, the frequency division number given to the counter unit 56 (and the mixing ratio of adjacent frequencies) is changed to change the frequency of the rectangular oscillation signal (step S42).

  FIG. 21 shows an example of the compensation curve. The frequency of the rectangular oscillation signal is changed stepwise in accordance with the ambient temperature. At this time, in order to prevent the frequency from being complicatedly fluctuated by a small change in the ambient temperature, a hysteresis is provided in the vicinity of the boundary. For example, in FIG. 21, when the ambient temperature is set to T1 when the frequency is set to f1, the frequency is changed to f2. Thereafter, even if the ambient temperature again exceeds T1, the frequency does not return to f1 until the ambient temperature T2 is reached. In this way, chattering that occurs near the threshold temperature boundary is prevented.

  According to this embodiment, when the compensation by the compensation capacitor becomes insufficient due to the fluctuation of the ambient temperature, the frequency of the rectangular oscillation signal is fluctuated to maintain the coincidence with the resonance frequency. Therefore, even if there is a change in ambient temperature, accurate detection can be performed.

3.5 other
(1) In the above embodiment, the frequency of the rectangular oscillation signal is changed by changing the division ratio (and further changing the temporal mixing ratio of two frequencies). However, the frequency of the rectangular oscillation signal may be changed by changing L and C of the oscillation circuit.

(2) In the above embodiment, the compensation capacitor is used, and the compensation shortage due to this is compensated by changing the frequency of the oscillation signal. However, the variation due to the temperature change may be compensated only by changing the frequency of the oscillation signal without using the compensation capacitor.

(3) The above embodiment has described the case where the coil L1 has a linear temperature characteristic. However, as shown by curves k and j in FIG. 22, there are many coils having such characteristics that the frequency characteristics can be flat and approximated from a certain point. When such a coil is used, it is preferable to use a compensation curve as shown in FIGS. 23A and 23B.

  FIG. 23A shows the case where the electrode is short (the resonant frequency is high), the slope G of the curve is also small, and the range over which the compensation due to the change of the oscillation frequency has to be performed is narrow. On the other hand, FIG. 23B shows the case where the electrode is long (the resonance frequency is low), the slope G of the curve is also large, and the range over which compensation due to the change of the oscillation frequency has to be performed is wide. As described above, as the resonance frequency decreases, the slope G of the curve is increased to widen the range in which the compensation due to the change in the oscillation frequency has to be performed.

  A plurality of such compensation curves are recorded in advance and selected and used according to the resonance frequency.

(4) The above embodiment and modifications can be implemented in combination with other embodiments as long as the essence is not violated.

4. Fourth embodiment
4.1 Functional Configuration FIG. 24 shows a functional configuration of the object detection sensor according to the third embodiment. The oscillation circuit 20 provides an oscillation signal to the resonance circuit 26. Since the resonant frequency of the resonant circuit 26 changes when the object 28 exists, the detection circuit 24 determines the presence / absence of the object 28 based on the change in the output of the resonant circuit 26, and outputs a detection output.

  The setting unit 21 receives an input from the setting input unit 25 by the operator, and sets an operation mode, a detection level, and the like. The display control means 23 performs display for mode selection in the light emitting sections P1, P2,... Pn at the time of initial setting.

  For example, when the detection circuit 24 detects an object 28, there are a mode in which an “on” detection output is output and a mode in which an “off” detection output is output. In order to indicate which mode the current setting is in, display is performed on the light emitting units P1, P2,.

  Furthermore, when setting the detection level, the display control means 23 displays the threshold and the level of the detection signal using the light emitting units P1, P2,. This makes it possible to easily know the threshold for detection and the detection margin.

4.2 Appearance and Hardware Configuration The appearance and hardware configuration when the object detection sensor is configured as a capacitance type level sensor are the same as those in FIGS. 2 and 3. The details of the counter unit 56 are the same as those shown in FIG. 6 or FIG.

4.3 Configuration and Display Process of Light Emitting Unit At the time of initial setting, the user opens the lid 40 shown in FIG. 2 and operates the input button and the input knob provided on the display unit 38. The details of the display unit 38 are shown in FIG. LEDs 58a, 58b,... 58j, which are light emitting portions P1, P2,. On the left side of the LEDs 58a, 58b,... 58j, numerals “1” to “10” for displaying the level are displayed. On the right side, a display for displaying the mode is shown.

  An input knob 591 is provided at the center. The input knob 591 can change an input value by rotating it. In addition, a press switch for generating a signal by pressing the input knob 591 itself is also provided.

  Below the input knob 591, an LED 581 indicating the state of the output relay 61 is provided. The LED 581 is configured to light when the output relay 61 is turned on and to turn off when the output relay 61 is turned off.

  On the right side, a mode selection button 592 and mode display LEDs 582a, 582b,... 582e are provided. "Operation" "Sensitivity" "Delay Timer" "Setup" "Test" indicating the content of the mode is displayed on the right side of the mode display LEDs 582a, 582b,... 582e. "Operation" is the actual operation mode, "Sensitivity" is the sensitivity adjustment, "Delay Timer" is the delay time setting from detection to the output relay output change, "Setup" is the other initial setting, and "Test" is the operation test It shows.

  The contents of operations performed by the input knob 591 and the mode selection button 592 are taken into the CPU 60 via the I / O port 64. Further, lighting of the LEDs 58a, 58b,... 58j, the LED 581, the LEDs 582a, 582b,... 582e is controlled by the CPU 60 via the I / O port 64.

  In the initial state, as shown in FIG. 25, the LED 582a is turned on to indicate that it is in the actual operation mode. Every time the user presses the mode selection button 592, the mode is switched, and the corresponding 582b to 582e are lighted.

  Here, assuming that “Setup” is selected, the state in which the LEDs 58i and 58j are lit (“Tuning” oscillation frequency automatic setting mode) is performed by rotating the input knob 591 in order to select further details. It is possible to switch between the LED 58 d and 58 e (the output setting mode) in the lighted state (“Output”).

  When the user presses the input knob 591, the mode at that time is selected. When the input knob 591 is pressed with the LEDs 58i and 58j turned on as shown in FIG. 26a, the oscillation frequency automatic setting mode is set. In this state, when the user further rotates the input knob 591 and blinks the LED 58h and presses the input knob 591 as shown in FIG. 26b, for example, the automatic adjustment of the oscillation frequency as shown in the first embodiment To be executed.

  When the input knob 591 is pressed in a state where the LEDs 58 d and 58 e are lighted, a mode for setting the output method of the output relay 61 is set. In this mode, when the input knob 591 is rotated, switching is performed so that any one of the LEDs 58a, 58b, and 58c blinks.

  When the LED 58 c is selected (when the input knob 591 is pressed in a lit state), a delay time can be provided between the detection of the object 28 by the output relay 61 and the turning on of the detection output. Similarly, when the LED 58b is selected, a delay time can be provided between the output relay 61 not detecting the object 28 and the detection output being turned off. Furthermore, when the LED 58a is selected, the output relay 61 can be set to be turned off (usually turned on) when the object 28 is detected.

  As shown in FIG. 27, when the mode selection button 592 is pressed to turn on the LED 582c, the above-mentioned delay time is set. In this mode, when the input knob 591 is rotated to the right, one of the LEDs 58a to 58j blinks in the order. When the left rotation is performed, one of the LEDs 58 j to 58 a blinks in the order.

  FIG. 27 shows a state in which 58 d is blinking. In this state, when the input knob 591 is pressed, the delay time is set to a value (delay of 4 seconds) corresponding to 58 d. Since this value is displayed on the left side of each of the LEDs 58a to 58j, the user can easily grasp the delay time.

  In this embodiment, the user can intuitively grasp how long the set delay time of 4 seconds is. In this state, when the detection electrode 36 is touched, the CPU 60 detects this. Four seconds after the detection, the CPU 60 turns on the LED 581 indicating the state of the output relay 61. At this time, the CPU 60 turns on the LED 58a one second after the detection, turns on the LED 58b two seconds later, and turns on the LED 58c three seconds later, thereby indicating a state of delay so that the bar graph extends. ing.

  As shown in FIG. 28, when the mode selection button 592 is pressed to turn on the LED 582b, the sensitivity adjustment mode is set. In this mode, when the input knob 591 is rotated to the right, one of the LEDs 58a to 58j blinks in the order. When the left rotation is performed, one of the LEDs 58 j to 58 a blinks in the order.

  FIG. 28 shows a state in which the LED 58 e is blinking. In this state, when the input knob 591 is pressed, the threshold for outputting the detection output from the output relay 61 is set to the level "5". Since this level is displayed on the left side of each of the LEDs 58a to 58j, the user can easily grasp the threshold level. The larger the level number, the higher the threshold, and the smaller the level, the lower the threshold.

  In this embodiment, it is possible to know whether the set threshold is appropriate in relation to the amplitude of the detection signal (whether there is a sufficient margin). In this state, when the hand approaches the detection electrode 36, the CPU 60 sequentially displays the LEDs 58a to 58j in a bar graph according to the amplitude level of the detection signal. FIG. 29 shows a case where the hand approaches and the detection signal becomes level “3”. At this time, since the threshold value is displayed in a blinking state and the amplitude of the detection signal is displayed in a lighted state, it can be easily distinguished.

  Furthermore, when the hand is brought into contact with the detection electrode 36, the detection signal exceeds the threshold value "5" (level "8" in this example) as shown in FIG. 30, and the LED 581 is lit. Therefore, it can be seen that the threshold value set this time operates properly. Also, it can be seen that the margin of the amplitude of the detection signal at the time of detection is three levels.

  As described above, the sensitivity can be easily set.

4.5 other
(1) In the above embodiment, in order to distinguish between the set value of the delay time and the elapsed time, the light emission form (one blinks and the other lights on) is changed. However, the emission color may be changed. The same applies to the threshold and the level of the detection signal.

(2) The above embodiment and modifications can be implemented in combination with other embodiments as long as the essence is not violated.

Claims (4)

An oscillation circuit that outputs an oscillation signal of a desired frequency;
A resonant circuit which is coupled to the oscillation signal and whose resonant frequency changes depending on the presence or absence of a measurement object;
A detection circuit that directly or indirectly takes out an output signal of the resonance circuit when the oscillation signal is given, and detects the presence or absence of a measurement object based on the amplitude of the output signal ;
A temperature detector for detecting a temperature near the resonance circuit;
Temperature compensation means for changing the frequency of the oscillation signal of the oscillation circuit in accordance with the temperature detected by the temperature detector so as to follow the fluctuation of the resonance frequency of the resonance circuit due to a temperature change;
Object detection sensor with. In the object detection sensor of claim 1,
The detection circuit has a capacitor for temperature compensation,
The temperature compensation means changes the frequency of the oscillation signal in a predetermined relationship with the temperature change in order to compensate for the deviation of the temperature compensation by the temperature compensation capacitor.
The object detection sensor characterized in that the predetermined relationship is set according to a resonance frequency. An oscillation circuit that outputs an oscillation signal of a desired frequency, and an output signal when the oscillation signal is applied to the resonance circuit that is coupled to the oscillation signal and whose resonance frequency changes according to the presence or absence of the measurement object, directly or indirectly A sensor program for realizing an object detection sensor by controlling the detection circuit for taking out and detecting the presence or absence of the measurement object based on the amplitude of the output signal , and realizing the object detection sensor,
Temperature compensation means for changing the frequency of the oscillation signal of the oscillation circuit in accordance with the temperature detected by a temperature detector provided near the resonance circuit so as to follow the fluctuation of the resonance frequency of the resonance circuit due to a temperature change Sensor program to make it work. In the sensor program of claim 3,
The detection circuit has a capacitor for temperature compensation,
The temperature compensation means changes the frequency of the oscillation signal in a predetermined relationship with the temperature change in order to compensate for the deviation of the temperature compensation by the temperature compensation capacitor.
The sensor program characterized in that the predetermined relationship is set according to a resonant frequency.

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