JPH062345Y2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a proximity switch that is less likely to malfunction due to noise.

[Conventional technology]

A conventional proximity switch of this type is shown in FIG. In the figure, reference numeral 1 is a detection unit including an oscillation circuit, and 2 is an output unit. R1 to R5 are resistors, C1 to C3 are capacitors, and T1 and T2 are transistors. Resistance R1,
R2 and capacitor C1 form a high pass filter,
The resistor R3 and the transistor T1 form a detection circuit. The capacitors C2 and C3 and the resistor R4 form a low pass filter.

In the proximity switch having the above configuration, the output from the detection unit 1 is supplied to the base of the transistor T1 via the capacitor C1 and detected here. Then, the output is supplied to the base of the transistor T2 via the resistor R4, and the output is sent from the collector of the transistor T2 to the output unit 2.

[Problems to be solved by the invention]

In the conventional proximity switch as described above, when noise is superimposed on the output signal of the detection unit 1, the output signal including the noise is directly supplied to the base of the transistor T1, and the operating voltage of the normal transistor is Since it suffices that the base-emitter voltage V _BE (about 0.7 V) or more, there is a problem in that the base voltage changes very easily due to the weight of noise and a malfunction occurs.

The present invention has been made to solve such a problem, and an object thereof is to obtain a proximity switch that does not malfunction due to noise.

[Means for Solving Problems] A proximity switch according to the present invention is a proximity switch having a detection unit (1) that outputs a pulsating voltage when an object to be detected is detected. The proximity switch has an output terminal of the detection unit (1). A series circuit of the connected differentiating circuit (C1, R2), a resistor (R6) and a capacitor (C4) connected between terminals of the power supply circuit, and a connection point of the resistor (R6) and the capacitor (C4) , A transistor (D1) connected between the output terminal of the differentiating circuit (C1, R2) and a base terminal at the connection point, and turned off when the charge of the capacitor (C4) is discharged. (T1) and. And the resistance (R
6) and the constant of the capacitor (C4) are set so that the period of the pulsating voltage << resistor (R6) × capacitor (C4), and the diode (D1) is connected to the differentiating circuit (C1,
When the differential output is generated from R2), the charge stored in the capacitor (C4) is arranged so as to be discharged to the differential circuit (C1, R2) side. The symbols (1), (R6), (C4), etc. described above correspond to the embodiments described later.

[Operation] In the present invention, when the detection unit (1) is in the non-detection state, the detection unit (1) only outputs a signal of a constant level. Therefore, the differentiation circuit (C1, R2) outputs Only the signal of the predetermined potential is output. The potential of the capacitor (C4) at this time is the base of the transistor (T1).
Since the voltage is regulated by the voltage between the emitters, the charge of the capacitor (C4) is not discharged through the diode (D1), and the capacitor (C4) retains the charge charged from the power supply circuit as it is. However, the transistor (T1) is turned on by the potential of the capacitor (C4) at that time, and the non-detection state is grasped.

When the detection unit (1) is in the detection state, pulsating voltage is output,
A differential output is obtained from the differentiating circuit (C1, R2). When, for example, a differential output of a negative level appears at the output terminal of the differentiating circuit (C1, R2), the charge stored in the capacitor (C4) is discharged through the diode (D1), and the capacitor (C1) is discharged.
The potential of 4) changes. At this time, the cycle of the pulsating voltage <<
Since the resistance (R6) × capacitor (C4) (time constant) is set, the diode (D) is generated by the differential output of the differential circuit (C1, R2) rather than the amount of charge charged by the power supply circuit.
The discharge charge amount discharged through 1) is larger, and the charge charge of the capacitor (C4) is discharged as a whole, so that the potentials at both ends of the capacitor (C4) become low. The transistor (T1) is turned off by the change in the potential of the capacitor (C4), and it is understood that the object to be detected is detected.

〔Example〕

FIG. 1 is a circuit diagram of a proximity switch according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 indicate the same or corresponding portions.

In the circuit of FIG. 1, R6 is a resistor and C4 is a capacitor, which are connected in series, and the series circuit is connected between the circuit power supply V and the circuit ground E. D1 is a diode as a directional element, and a capacitor C1
Is connected between one terminal and the connection point of the resistor R6 and the capacitor C4. The base of the transistor T1 is also connected to the above connection point. Here, the anode of the diode D1 is connected to the circuit ground E via the resistor R2 and is arranged in the direction in which the base input of the transistor T1 is blocked.

Next, the operation of the proximity switch configured as described above will be described with reference to the time chart of FIG.

In the non-detection state, there is no output from the detection unit 1, and in this state, the output at the point A is a low potential. At this time, the capacitor C4 is charged through the resistor R6 to have a high potential, the high potential is applied to the base of the transistor T1, and the transistor T1 is turned on. Therefore, the potential at the point a on the cathode side of the diode D1 is lower than the potential of the capacitor C4 by the forward voltage of the diode D1. Since the transistor T1 is on, the potential at the point C, which is the collector of the transistor T1, is at "0" level. As a result, the transistor T
2 is turned off, and the potential at point D, which is its collector, is at "1" level. Then, the potential at the point D is sent to the output unit 2 and taken out as an output, and it is grasped that it is in the non-detection state.

Next, in the detection state, a high frequency output is obtained from the detection unit 1. In this state, the potential at the point a pulsates as shown in the figure, and the potential at the point a also oscillates accordingly. That is, when the pulsating voltage is input to the differentiating circuit composed of the capacitor C1 and the resistor R2, the potential of the point a, which is the output of the differentiating circuit, also pulsates with positive and negative voltages as shown by the differential operation. When the pulsating voltage is high, the current is blocked by the diode D1 and the capacitor C4
Is charged through the resistor R6, and when the pulsating voltage is low, the charge in the capacitor C4 is discharged through the diode D1. In this way, charging and discharging are repeated according to the amplitude of the pulsating voltage. At this time, the cycle of the pulsating voltage << C4.
When the pulsating voltage is R6 and the pulsating voltage is a low voltage, the voltage drops to a negative voltage.
A large amount of electric charge is discharged through the transistor B, and the potential B is almost at the “0” level (base-emitter voltage V _{BE of the} transistor T1).
Below). Therefore, the transistor T1 is turned off. The upper limit of C4 and R6 is determined in consideration of the response time.

When the transistor T1 is turned off, the potential at the point C, which is its collector, becomes "1" level. As a result, the transistor T2 is turned on, and the potential at the point D, which is its collector, is at the "0" level. Then, the electric potential at the point D is sent to the output unit 2 and taken out as an output to grasp the detection state.

By the way, in this embodiment, even if noise is superposed on the output of the detection unit 1 in the non-detection state, the signal is not directly applied to the transistor T1, and as described above, the differentiating circuit, the diode D1 and the capacitor C4. The potential of the capacitor C4 does not fluctuate unless the noise is supplied for a certain period of time as the pulsating voltage at the time of detection, so that the transistor T1 is not affected at all.

Although the transistor T1 is of the NPN type in the above embodiment, a PNP type may be used in the present invention, in which case the direction of the diode D1 must be reversed.

[Effect of device]

As described above, according to the present invention, the output of the detection unit is applied to the switching transistor through the differentiating circuit, the diode and the capacitor, so that an excellent effect of not malfunctioning due to a noise signal is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a proximity switch according to an embodiment of the present invention, FIG. 2 is a time chart showing the operation of each part thereof, and FIG. 3 is a circuit of a conventional proximity switch. D1 ... Diode, R6 ... Resistor, C4 ... Capacitor, T
1 ... Transistor.

Claims (1)

[Scope of utility model registration request] 1. A proximity switch having a detection unit (1) for outputting a pulsating voltage when an object to be detected is detected, the differentiation circuit (C being connected to an output terminal of the detection unit (1).
1, R2) and a series circuit of a resistor (R6) and a capacitor (C4) connected between terminals of a power supply circuit, a connection point of the resistor (R6) and the capacitor (C4), and the differentiation. A diode (D1) connected between the output terminal of the circuit (C1, R2) and a base terminal connected to the connection point, and a transistor (turned off when the charge stored in the capacitor (C4) is discharged ( T1) and the constants of the resistor (R6) and the capacitor (C4) are set so that the period of the pulsating voltage << the resistor (R6) x the capacitor (C4), and The diode (D1) is arranged in a direction in which the charged electric charge of the capacitor (C4) is discharged to the differentiating circuit (C1, R2) side when the differentiating output from the differentiating circuit (C1, R2) is generated. Near Switch.