JPH07162280A - Proximity switch - Google Patents

Abstract

PURPOSE:To set up a proximity switch to a maximum sensitivity value in a using environment. CONSTITUTION:A sensitivity adjusting circuit 21 for adjusting the sensitivity of an oscillation circuit 2 is connected to the circuit 2. When an input signal is inputted to a setting part 24, sensitivity is continuously increased until a microcomputer or an output signal in a non-detection state reaches a detection state. The sensitivity obtained in the object detection state is set up in the circuit 21 as maximum sensitivity. Consequently the maximum sensitivity in the using state of the proximity switch can be set up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch, and more particularly to a proximity switch characterized by its sensitivity adjustment and sensitivity setting.

[0002]

2. Description of the Related Art Proximity switches of high-frequency oscillation type include an amplitude detection type that detects a decrease in oscillation amplitude when an object approaches, and a frequency detection type that detects proximity of an object based on a change in frequency. In general, an amplitude detection type proximity switch is widely used as a proximity switch for detecting magnetic metal.
FIG. 15 is a block diagram showing an example of a conventional amplitude detection type proximity switch. In this figure, an oscillating circuit 2 is configured together with a parallel resonance circuit 1 of an oscillating coil L and a capacitor C. The output of the oscillation circuit 2 is detected by the detection circuit 3,
The signal processing circuit 4 detects a decrease in the oscillation level. When the decrease in oscillation is detected, the object detection signal is output via the output circuit 5. The power supply circuit 6 supplies power to each block. Here, the oscillation circuit 2 is connected with a sensitivity adjustment resistor Re for adjusting the sensitivity.

FIG. 16 is a circuit diagram showing an example of an oscillating circuit 2 configured together with the parallel resonant circuit 1. In the figure, the parallel resonance circuit 1 includes a resistor R1 and diodes D1 and D2.
The base of the transistor Q1 is connected via. A constant current is supplied to the base of the transistor Q1 from the power source, and resistors R2, R3, and R4 are connected in series between the base of the transistor Q1 and the ground terminal. The middle point of the resistors R2 and R3 is connected to the base of the transistor Q2, and the emitter thereof is connected to the sensitivity adjusting resistor Re described above. Transistors Q3 and Q4 are provided on the collector side of the transistor Q2.
Is connected to the current mirror circuit, and a current having the same current value as that of the power supply flowing in the transistor Q2 is fed back to the parallel resonant circuit 1 via the transistor Q4 to form a positive feedback loop and oscillate. In FIG. 17A, the sensitivity adjustment resistance Re is Re1 to Re3 (Re1 <Re2 <Re
The oscillation amplitude and the distance to the detected object when changing to 3),
FIG. 17B is a graph showing the relationship between the coil loss (conductance) and the distance. In this figure, g ₁ ,
g, ₂ and g ₃ respectively indicate conductances on the oscillation circuit side when Re is Re1, Re2 and Re3. Then, as is clear from this figure, oscillation suddenly starts and stops at a specific position at a distance to the object. Such oscillation is called hard oscillation.

FIG. 18 is a graph showing the change in the loss (conductance) received by the coil of the parallel resonant circuit 1 with respect to the distance to the object. A curve is shown when there is no metal body around the proximity switch, and the proximity switch is Let B be the loss curve of the coil when attached to a metal plate. In FIG. 18, a horizontal straight line C indicates the threshold level determined by the sensitivity adjustment resistor setting on the proximity switch side. Oscillation occurs at a distance shorter than the intersection of the point on the coil loss curve determined by the distance L to the object and the threshold level indicated by the straight line C, and oscillation stops at a distance farther than this. In this way, the operation of the proximity switch greatly differs depending on the presence or absence of surrounding metal, that is, the installation environment.

[0005]

Thus, the amplitude detection type proximity switch has the following drawbacks. In order to extend the detection distance, it is necessary to lower the straight line C in FIG. 18, which is a threshold value. In this case, the influence of the surrounding metal becomes large, and if there is a surrounding metal, it is detected, and it is not possible to bring the object close to it. Therefore, the detectable distance is often set to be short with a margin so that it can be used regardless of the installation environment of the proximity switch. Therefore, there is a drawback in that a distance shorter than the maximum detection distance capability of the proximity switch is set as the maximum detection distance. Since the sensitivity adjustment is performed manually by changing the sensitivity adjustment resistance Re, there is a drawback in that the adjustment requires skill and the operator may have variations in the adjustment position. Since the rotation angle of the variable resistor of the sensitivity adjustment resistor Re is not proportional to the detection operation distance, it is difficult to adjust it to the optimum point, and it is necessary to repeat the adjustment and the operation confirmation depending on the feeling. Especially when a long-distance operating point is set, the change in the conductance of the oscillation coil becomes small depending on the presence or absence of the detection object. Therefore, there is a drawback that it is difficult to adjust to the optimum point, and the operating point changes greatly even if the position of the variable resistor is slightly displaced due to vibration or the like.

The present invention has been made in view of the problems of the conventional method for adjusting the sensitivity of the proximity switch.
The technical issue is to be able to automatically adjust the proximity switch to the maximum detection distance in the installation environment.

[0007]

The invention according to claim 1 of the present application has an oscillation circuit, a resistor group connected to the oscillation circuit and a switch circuit for switching the resistor group, and is determined by the switch state of the switch circuit. A sensitivity adjustment circuit that adjusts the sensitivity by switching the feedback current according to the resistance value of the sensitivity adjustment resistor, a switch control unit that adjusts the sensitivity of the oscillation circuit by outputting a switch signal to the sensitivity adjustment circuit, and an output of the oscillation circuit And a signal processing unit that determines the presence or absence of an object based on the output state of the detection circuit based on the output of the detection circuit, and the switch control unit includes a sensitivity adjustment resistor that does not bring the object into proximity. The resistance value updating means for decreasing the resistance value from the non-detection state of the object to the object detection state and the object detection state by the resistance value updating means are changed. It is characterized in that it has a sensitivity setting means for setting the sensitivity adjustment resistor to the sensitivity adjustment circuit based on the resistance value of the sensitivity adjustment resistor when.

The invention of claim 2 of the present application has a power-on detection means for detecting power-on, and the switch control means is
It is characterized in that the value of the sensitivity adjustment resistor is lowered and the resistance value is updated when the power-on detection means detects the power-on.

In the invention of claim 3 of the present application, the proximity switch has a temperature detecting means for detecting an ambient temperature, and the sensitivity setting means is detected by the resistance value updated by the resistance value updating means and the temperature detecting means. It is characterized in that the resistance value set in the sensitivity adjustment circuit is calculated based on the ambient temperature.

[0010]

According to the invention of claim 1 of the present application having such characteristics, a sensitivity adjusting circuit for adjusting the sensitivity is connected to the oscillation circuit, and the output is an object when installed in an environment where a proximity switch is used. The sensitivity adjustment resistance is lowered from the non-detection state to the detection state. Then, the sensitivity adjustment resistor is set based on the resistance value of the sensitivity adjustment resistor for detecting an object. Further, in the invention of claim 2, when the power is turned on in the environment in which the proximity switch is installed, the resistance value is updated and the sensitivity is adjusted. Further, in the invention of claim 3 of the present application, the ambient temperature is detected by the temperature detecting means, and the resistance value set based on the resistance value updated by the resistance value updating means and the ambient temperature is calculated. I try to prevent the malfunction of.

[0011]

1 is a block diagram showing the configuration of a high frequency oscillation type proximity switch 20 according to an embodiment of the present invention. In the figure, the same parts as those of the conventional amplitude detection type proximity switch described above are denoted by the same reference numerals and detailed description thereof will be omitted. Also in this embodiment, the oscillation circuit 2 is provided together with the LC parallel resonance circuit 1.
Is configured. Then, the oscillation circuit 2 is provided with a sensitivity adjustment circuit 21 for adjusting its sensitivity. The sensitivity adjustment circuit 21 is an adjustment circuit for adjusting the oscillation sensitivity by changing the sensitivity adjustment resistance of the oscillation circuit based on a switch signal from the outside. The output of the oscillation circuit 2 is the detection circuit 3
Is given to the signal processing circuit 4 via. Signal processing circuit 4
Is to determine the presence or absence of an object by discriminating the output of the detection circuit 3 at a predetermined threshold level as in the conventional example, and the output is output to the outside via the output circuit 5.
In this embodiment, the output of the signal processing circuit 4 is input to the microcomputer 23 via the output signal monitor circuit 22. The microcomputer 23 is also provided with a setting unit 24 for inputting an input signal from the outside when setting the sensitivity. The setting unit 24 may use a switch provided in the proximity switch, or may receive a sensitivity adjustment activation signal input from the outside of the proximity switch via a signal line and output it as a sensitivity adjustment activation signal of the microcomputer 23. It can also be configured. Further, as shown by a broken line in the figure, a power-on monitor circuit 25 for detecting that the power of the proximity switch is turned on is provided.
It is also possible to configure the sensitivity adjustment to be started by the input signal from. The microcomputer 23 performs teaching based on these input signals as will be described later, and sets the sensitivity setting value by the switch signal to the sensitivity adjusting circuit 2
It is set to 1, and constitutes switch control means. Alternatively, the signal processing circuit 4 may not be provided, and the detection output may be directly input to the microcomputer 23 and signal processing may be performed in the microcomputer 23.

FIG. 2 is a circuit diagram showing the configuration of the parallel resonant circuit 1, the oscillator circuit 2 and the sensitivity adjusting circuit 21 of this embodiment.
In this figure, the same parts as those of the conventional example described above are designated by the same reference numerals, and detailed description thereof is omitted. Also in this embodiment, the parallel resonant circuit 1 includes the diodes D1 and D2 and the transistor Q1.
The oscillator circuit 2 having Q4 is connected. The resistors R _E0 , R _E1 ... R _Em are connected in series at the position of the sensitivity adjusting resistor Re of the oscillation circuit 2 as shown in the figure. And between the resistors R _E0 and R _E1, the transistor Q _E1, Q _E2 ··· Q _Em for switching the sensitivity adjustment resistor Re as shown between the middle point ... of R _E1 and R _E2 Connected. These transistors Q _{E1 to} Q _Em are microcomputers 23
It is output as a parallel signal from the output port of. Thus, the overall sensitivity adjustment resistance Re is determined by the on or off state of each transistor. Therefore, the sensitivity of the oscillation circuit can be adjusted under the control of the microcomputer 23. Here, it is assumed that the number of transistors is m and the resistance value of R _Ei is set to R _Ei = R _{0 .2} ⁱ (i = 1 to 11). By doing this, by turning on / off the 11-bit switches of the switching transistors Q _{E1 to} Q _Em , the combined resistance value R can be obtained in 2048 steps.
e can be set.

Further, in place of Re set in this way, FIG.
Alternatively, the FET Q5 may be connected in parallel to the sensitivity adjustment resistor Re, and the current flowing through the FET Q5 may be controlled by switching the gate voltage by the switch circuit of the transistors Q _{E1 to} Q _Em .

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. First, when the operation is started, it is checked in step 31 whether an input signal is input to the setting unit 24. At the time of sensitivity setting, the object to be detected is not brought close to this with the proximity switch installed, and a sensitivity setting monitoring signal is input from the setting unit 24 by a switch input, an input signal from the inside, or power-on. If it is not entered, the process ends,
If it is input, the process proceeds to step 32, and it is checked by the output signal monitor circuit 22 whether it is in the on state, that is, whether the oscillation of the oscillation circuit 2 is stopped or is less than the threshold value of the signal processing circuit 4. When the output signal is on, it is considered that there is the threshold line C at the position shown by the broken line in FIG. At this time, the routine proceeds to step 33, where the value of the sensitivity adjustment resistor Re at this time is reduced by one step. This corresponds to raising the threshold line in FIG. Then, it waits for the oscillation to start, and proceeds to step 34 to check if the output signal is turned off. If the output does not reach the off point, the process returns to step 33 and the same processing is repeated. By doing so, the sensitivity adjustment resistance Re gradually decreases, oscillation starts at a certain position, and the output is turned off. This means that the threshold line becomes the straight line D in FIG. When the output is turned off, the routine proceeds to step 35, where it is checked whether or not margin adjustment is performed. When the margin adjustment is not performed, the processing is ended, the value of the sensitivity adjustment resistance Re at this time is set, and the actual object detection is performed. When the margin adjustment is performed, the process proceeds to step 36, the value Re of the sensitivity adjustment resistor is reduced by the set number of steps, and the process ends. In this way, as shown in FIG. 5A, the threshold level becomes high, for example, as shown by the straight line E, and the detection distance itself becomes short, but stable detection is possible. Further, the number of steps can be configured so that an arbitrary value can be input according to the usage environment.

On the other hand, if the output signal is in the off state in step 32, the process proceeds to step 37 to take in the value of the sensitivity value resistor Re at that time. Then, in step 38, Re
The value of is updated to be, for example, a doubled value. This means that, for example, in FIG. 5B, the threshold line is changed from the straight line F to G. Then, the process proceeds to step 39, in which it is checked whether the output signal is off, that is, whether the oscillation has started or becomes equal to or more than the threshold value of the signal processing circuit. In this way, if the value of the sensitivity adjustment resistor Re is updated, the oscillation starts. Therefore, if the oscillation starts, the process returns from step 39 to step 33 and the same processing is repeated. In this way, the value of the sensitivity adjustment resistor can be set relatively quickly even when the output signal is in the off state. Here, the microcomputer 23 achieves the function of the resistance value updating means 23a that reduces the resistance value of the sensitivity adjustment resistance in steps 31 to 34, 37 to 39 until the object detection state changes to the object detection state. In steps 35 and 36, the sensitivity setting means 23 that sets the sensitivity adjustment resistance in the sensitivity adjustment circuit based on the resistance value of the sensitivity adjustment resistance when the object detection state is changed.
The function of b is achieved.

FIGS. 6, 7, and 8 are flowcharts showing another example of sensitivity adjustment, and FIG. 9 is a graph showing changes in conductance with respect to distance at that time. When the operation is started in these figures, first, at step 41, it is checked whether or not an input signal is inputted to the setting section.
If there is an input signal, the process proceeds to step 42 to capture the output state from the output signal monitor circuit 22 and check whether the output is on. If it is on, the procedure proceeds to step 43, where the current sensitivity setting value Re is loaded into the register and Re
(N). At this time, Re (n) is represented by the straight line A () in FIG. 9, for example. Then go to step 44 and go to R
Re (n + 1) is obtained by multiplying e (n) by α (α <1). Then, the routine proceeds to step 44, where Re (n + 1) is set as the sensitivity setting value, and it is checked whether the output is off. If the output is off at step 42, the process proceeds to step 47 to take the current value of Re and set it as Re (n). Then, in step 48, Re is multiplied by γ (γ> 1) to obtain Re (n + 1). Then, the routine proceeds to step 49, where this Re (n + 1) is set as the sensitivity setting value, and at step 50 Re (n +)
Let 1) be Re (n). Then, in step 51, it is checked whether the output is on. If the output is off, the loop of steps 48 to 50 is repeated, and if it is on, the routine proceeds to step 44. By doing so, as shown in FIG. 9, the sensitivity adjusting resistor Re whose output is once in the ON state is
(N) will be obtained.

In the loop of steps 43 to 46, Re is multiplied by the coefficient α to reduce the value, and this loop is repeated until the output is turned off. When the output is off, Re (n + 1) is represented by the curve B () in FIG. 9, for example. When the output is turned off, the process proceeds to step 52 in FIG. 7 and X is calculated by the following equation. X = {Re (n) -Re (n + 1)} / β Here, β is a positive number of 1 or more, for example, 2. Then, the routine proceeds to step 53, where Re (n + 2) is calculated by the following formula. Re (n + 2) = Re (n + 1) + X Then, the sensitivity adjusting resistor is set to the value of Re (n + 2) (step 54). In this way, Re (n + 2) is the curve A
Will be set between B and B. Then step 5
At 5 it is checked if the output is off.
If the output remains off, proceed to step 56 and Re
Insert the value of Re (n + 2) into (n + 1) (Fig. 9 →
), And returns to step 52 and repeats similar processing. In this way, when β is 2, Re (n) as shown in FIG.
Since the sensitivity adjustment resistance value is sequentially set at the intermediate point between and Re (n + 1), it is possible to change from the straight line B to the straight line C and then to the straight line D in FIG.

When the straight line D is reached, the output is turned on, so the routine proceeds from step 55 to step 57 and Re (n +
Let the value of 2) be Re (n) (→). Then, in steps 58 to 61, the same processing as steps 52 to 55 is repeated to check whether the output is off. When the output is turned off, the process proceeds to steps 62 and 63, where Re (n
+2) is multiplied by a predetermined coefficient λ (λ> 1) to obtain a new R
As e (n + 2), this is set in the sensitivity adjustment resistor. Then, the loop of steps 62 to 64 is repeated until the output is turned on, and when it is turned off, the process proceeds to step 65.
If the output is off in step 61, the process proceeds to step 65 without going through the loop of steps 62-64. Steps 65 to 68 are the same as the flowchart of step 33 and subsequent steps shown in FIG. 4, and Re is decreased step by step to check whether the output is turned off. In this way, the margin is adjusted as necessary, and the sensitivity setting is completed. Here, the microcomputer 23 achieves the function of the resistance value updating means 23a for reducing the resistance value of the sensitivity adjustment resistor until the object detection state is changed from the non-detection state to the object detection state in steps 41 to 66 without bringing the object close to each other. Therefore, the function of the sensitivity setting means 23b for setting the sensitivity adjustment resistance based on the resistance value of the sensitivity adjustment resistance when the object detection state is changed in steps 67 and 68 is achieved. By doing so, it is possible to set the value of the sensitivity adjusting resistor to the optimum value in a relatively short time regardless of the original resistance value of the sensitivity adjusting resistor.

Next, a third embodiment of the present invention will be described. In the third embodiment, the temperature compensation process is performed after the maximum sensitivity value is set in step 34 or step 66 of the first and second embodiments. That is, in the flowchart of FIG. 10, the process proceeds to step 71, the value of Re is taken in, the margin of Re is calculated by the temperature correction arithmetic expression, and the value of Re after correction is switched and set. For example, assuming that the change in the conductance of the coil with respect to the distance at room temperature is represented by the curve A as shown in FIG. 11, generally, at high temperature, the curve rises as shown by a broken line curve B, and the proximity switch has a surrounding metal. It will be in the same state as when it was installed in the environment. Therefore, in step 72, Re is multiplied by a predetermined coefficient k (0 <k <1), for example, k = 0.72, so that the value becomes lower than the value of Re that provides the maximum sensitivity. Then, the corrected value is set as a new sensitivity setting value. This makes it possible to provide a proximity switch capable of detecting at the maximum detection distance in the entire temperature range including the case of the highest temperature.

Next, a fourth embodiment of the present invention will be described. In this embodiment, in addition to the blocks of the first to third embodiments,
The temperature detection circuit that detects the temperature and the correction is performed based on the detected temperature. That is, as shown in FIG. 12, a temperature sensor, for example, a thermistor, and a CR oscillation circuit 72 including the thermistor 71 are provided in the proximity switch. C
The output of the R oscillation circuit 72 is input to the counter 74 via the frequency dividing circuit 73. Further, the output of the clock oscillator 75 for generating the reference clock signal is input to the counter 74, and the temperature information is output to the microcomputer 23A by counting the frequency-divided output. Thermistor 71, CR oscillator circuit 72, frequency divider circuit 73, counter 7
4 and the block of the reference clock oscillator 75 constitute a temperature detecting means for detecting the ambient temperature. The temperature detecting means is not limited to the structure of this embodiment, but may have any structure for detecting the temperature. In addition, the microcomputer 23
A table memory 76 for storing the correction coefficient k for the ambient temperature at that time is connected to A. FIG. 13 is a graph showing an example of changes in the correction count k with respect to the ambient temperature.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. Then, following steps 34 and 66 in FIGS. 4 and 8, when the output signal is turned off, the value of Re is taken in at step 81. Then, in step 82, the count value of the counter 74 is read and converted into the current temperature. Next, in step 83, the coefficient value corresponding to the current temperature is read from the temperature compensation table, and the value of the current sensitivity adjustment resistance Re obtained is multiplied to calculate the value of the sensitivity adjustment resistance at room temperature (for example, 20 ° C.). . Then, in step 84, the value of Re is corrected by the correction calculation formula. This correction calculation is performed in step 7 of the third embodiment described above.
Similar to 2, the calculation is performed by multiplying Re by a predetermined coefficient k, for example, 0.72. Then, the value of Re after correction is switched to complete the processing. In this way, regardless of the ambient temperature at the time of teaching, the sensitivity can always be set with a margin without malfunction in all temperature ranges.

Further, in the present embodiment, the high frequency oscillation type proximity switch has been described, but the teaching according to the present invention can be applied to other types of proximity switches. For example, even in a capacitance type proximity switch, if the operating distance can be continuously changed by the sensitivity adjusting resistor, the teaching according to the present invention can be applied.

[0023]

As described in detail above, according to the invention of claim 1 of the present application, it is possible to automatically set the maximum sensitivity in the environment in which the proximity switch is installed. Therefore, it is not necessary to set the sensitivity with a margin so that it can be used in all usage environments and mounting conditions, and the maximum sensitivity value can be set in the environment where the detection switch is actually used. Further, in the invention of claim 2 of the present application, since such sensitivity adjustment is performed every time the power is turned on, an optimum maximum sensitivity value can be set according to the environment and temperature in the usage state. Further, in the invention of claim 3 of the present application, since the ambient temperature is calculated and the sensitivity value is set, there is an effect that it is possible to set the maximum sensitivity that does not malfunction in the entire operating temperature range in the operating environment. Therefore, the operability is good, and the optimum sensitivity can be easily adjusted without depending on the feeling or experience of the operator. Further, even if there is a metal or a background object in the surroundings, the sensitivity can be set to the optimum point under the environment. Further, it does not use a variable resistor as in the prior art, and has excellent vibration resistance.

[Brief description of drawings]

FIG. 1 is a block diagram of an amplitude detection type proximity switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an oscillation circuit and a sensitivity adjustment circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing configurations of an oscillation circuit and a sensitivity adjustment circuit according to another embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the first embodiment.

FIG. 5 is a graph showing a change in coil loss with respect to a distance to a detection object according to the present embodiment.

FIG. 6 is a flowchart (1) showing a teaching process according to the second embodiment of the present invention.

FIG. 7 is a flowchart (part 2) showing the teaching process according to the second embodiment of the present invention.

FIG. 8 is a flowchart (No. 3) showing the teaching process according to the second embodiment of the present invention.

FIG. 9 is a graph showing a change in conductance with respect to a detection distance during a sensitivity adjusting operation in the second embodiment of the present invention.

FIG. 10 is a flowchart showing the operation of the third embodiment of the present invention.

FIG. 11 is a graph showing changes in conductance with respect to a detection distance according to the third embodiment of the present invention.

FIG. 12 is a block diagram showing an overall configuration of a proximity switch according to a fourth embodiment of the present invention.

FIG. 13 is a graph showing changes in the correction coefficient k with respect to ambient temperature.

FIG. 14 is a flowchart showing the operation of the fourth embodiment of the present invention.

FIG. 15 is a block diagram showing an overall configuration of a conventional amplitude detection type proximity switch.

FIG. 16 is a circuit diagram showing an oscillation circuit of a conventional amplitude detection type proximity switch.

FIG. 17: Work setting distance L of amplitude detection type proximity switch
5 is a graph showing the amplitude of the oscillation circuit and the conductance of the coil with respect to FIG.

FIG. 18 is a graph showing a change in the loss that the coil receives with respect to the distance to the object of the conventional proximity switch.

[Explanation of symbols]

 1 parallel resonance circuit 2 oscillation circuit 3 detection circuit 4 signal processing circuit 5 output circuit 20 proximity switch 21 sensitivity adjustment circuit 22 output signal monitor circuit 23 microcomputer 23a resistance value updating means 23b, 23c sensitivity setting means 24 setting section 25 power-on monitor Circuit 71 Thermistor 72 CR oscillation circuit 73 Frequency divider circuit 74 Counter 75 Reference clock oscillator 76 Table memory

Claims (3)

[Claims] 1. An oscillation circuit, a resistance group connected to the oscillation circuit, and a switch circuit for switching the resistance group, the feedback current being switched according to a resistance value of a sensitivity adjustment resistor determined by a switch state of the switch circuit. A sensitivity adjusting circuit for adjusting the sensitivity thereof, a switch control unit for adjusting the sensitivity of the oscillation circuit by outputting a switch signal to the sensitivity adjusting circuit, a detection circuit for detecting the output of the oscillation circuit, and the detection circuit. Signal processing means for determining the presence or absence of an object based on the output of the circuit based on the oscillating state, wherein the switch control means sets the resistance value of the sensitivity adjustment resistor to the non-object Resistance value updating means for decreasing until the detection state changes to the object detection state, and an object detection state changed by the resistance value updating means Proximity switch, characterized in that those having a sensitivity setting means for setting a sensitivity adjustment resistor to said sensitivity adjustment circuit based on the resistance value of the sensitivity adjustment resistor can. 2. A power-on detection means for detecting power-on, wherein the switch control means lowers the value of the sensitivity adjustment resistor and updates the resistance value when the power-on detection means detects the power-on. The proximity switch according to claim 1, which is a switch. 3. The proximity switch has a temperature detecting means for detecting an ambient temperature, and the sensitivity setting means has a resistance value updated by the resistance value updating means and an ambient temperature detected by the temperature detecting means. The proximity switch according to claim 1 or 2, wherein a resistance value set in the sensitivity adjustment circuit is calculated based on