JPH0548421A - Proximity switch - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the number of output terminals and prevent an increase in external wiring in proximity switches that have a detection coil disconnection detection function. An output voltage of a comparison circuit 35 for comparing the oscillation voltage of a resonance circuit 9 including a detection coil 7 with a predetermined level and an output voltage of an oscillation transistor 5 for converting the oscillation voltage of the resonance circuit 9 into a current are detected by a detection circuit. The output voltage of the voltage discrimination circuit 15 that is input via 14 is input, and when the detection coil 7 is normal, a detection signal that is turned on and off is output depending on whether or not the detection target approaches, and the detection coil 7 outputs An output / diagnosis circuit 40 is provided which outputs a diagnosis signal at an intermediate level between the ON and OFF states when the wire is broken.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency oscillation type proximity switch having a detecting coil disconnection detecting function.

[0002]

2. Description of the Related Art Conventionally, as a proximity switch of this type, FIG.
The ones shown in are known. In FIG. 3, the transistor 1 forms a current mirror circuit 3 together with the transistor 2, and a current substantially equal to the current flowing through the resistor 4 is output from the collector of the transistor 2. The base of the transistor 5 is connected to the collector of the transistor 2, and the parallel resonance circuit 9 including the detection coil 7 and the capacitor 8 is connected via the transistor 6.
The emitter of the transistor 5 is connected to the negative power supply terminal 24 via the resistor 10, and the collector is connected to the base and collector of the transistor 11, respectively. The transistor 11 and the transistor 12 together with the current mirror circuit 13
And a current substantially equal to the collector current of the transistor 5 is fed back to the resonance circuit 9. A detection circuit 14, a voltage discriminating circuit 15, and an output circuit 16 for detecting whether or not the object to be detected approaches the connection point between the emitter of the transistor 5 and the resistor 10 are sequentially connected, and are connected to the detection output terminal 21. The + input terminal is connected to the connection point between the emitter of the transistor 6 and the resonance circuit 9 (this connection point is referred to as P point), and the reference battery 36 is connected between the − input terminal and the power supply terminal. A comparison circuit 35 is provided, and the output terminal of the comparison circuit 35 is connected to the diagnostic output terminal 22.

In the resonance circuit 9, the oscillation voltage of the resonance circuit 9 is converted into a current by the transistor 5, and the current mirror circuit 1
It is fed back via 3 and continues to oscillate. At this time, to the base of the transistor 5, a voltage in which an oscillating AC component is superimposed around the current bias voltage given to the base by the transistor 6 is applied.

When the object to be detected is not close to the detection coil 7, the impedance of the detection coil 7 is high and the base voltage applied to the transistor 5 is high, so that the voltage at both terminals of the resistor 10 is high. This voltage is detected by the detection circuit 14, and the voltage discriminating circuit 15 discriminates that it is higher than the set voltage. At this time, the detection signal is not output from the output circuit 16. When the object to be detected approaches the detection coil 7, the impedance of the detection coil 7 decreases and the voltage applied to the base of the transistor 5 decreases, so that the voltage at both terminals of the resistor 10 is low and the voltage is detected by the detection circuit 14. The output discriminating circuit 15 discriminates that the output voltage is lower than the set voltage, and the output circuit 1
A detection signal is output from 6 and is taken out from the detection output terminal 21.

A failure detection operation when the detection coil is broken is shown in the time chart of FIG. Here, time t1 to t2
During this period, the proximity switch continues to operate normally, and the power supply voltage V
When s is given, the voltage Vp at the point P oscillates at the voltage Vp1. The voltage Vb is a value obtained by subtracting the voltage Vref of the reference battery 36 from the power supply voltage Vs. The oscillating voltage Vp1 changes depending on whether or not the object to be detected approaches, but the voltage Vb is set so as not to exceed the voltage Vb in any case, so the comparison circuit 35 does not output a failure signal. When the detection coil 7 is broken at time t2, the oscillation is stopped, the voltage Vp rises to a value obtained by subtracting the collector-emitter voltage Vce of the transistor 12 from the voltage Vs, and if the voltage Vref is set higher than the voltage Vce in advance, the voltage Vb. Therefore, the comparison circuit 35 outputs the failure signal Vh, which is taken out from the diagnostic output terminal 22.

[0006]

In the proximity switch having the function of detecting the disconnection of the detection coil, the detection output terminal for detecting the approach of the object to be detected and the diagnostic output terminal for detecting the disconnection of the detection coil are separately provided. Since it is provided, there is a problem that the number of external wirings connected to these output terminals increases.

An object of the present invention is to provide a proximity switch having a detection coil disconnection detecting function, in which the number of output terminals is reduced.

[0008]

In order to achieve the above object, the present invention relates to a resonance circuit including a detection coil for detecting the approach of an object to be detected, and an oscillating transistor for converting the voltage of the resonance circuit into a current. A first current mirror circuit that feeds back the output current of the oscillation transistor to the resonance circuit; a second current mirror circuit that supplies a base current to the transistor; and the resonance circuit and the oscillation transistor. A bias transistor that is connected to the oscillation transistor to apply a bias voltage to the oscillation transistor, a detection circuit to which the output voltage of the oscillation transistor is input, and a voltage discrimination circuit connected to the detection circuit, and the resonance circuit voltage. Is provided with a comparison circuit for comparing the output voltage of the comparison circuit with a predetermined level. Then, the output voltage of the voltage discrimination circuit and the output voltage of the comparison circuit are input, and when the detection coil is normal, a detection signal that is turned on and off is output depending on whether or not the object to be detected approaches. An output / diagnosis circuit that outputs a diagnosis signal at an intermediate level between ON and OFF when the wire is disconnected is provided.

[0009]

According to the present invention, a resonance circuit including a detection coil for detecting the approach of an object to be detected, an oscillating transistor for converting the voltage of the resonance circuit into a current, and an output current of the oscillating transistor are fed back to the resonance circuit. A first current mirror circuit, a second current mirror circuit that supplies a base current to the transistor, and a bias transistor that is connected between the resonance circuit and the oscillation transistor and applies a bias voltage to the oscillation transistor. And a detection circuit to which the output voltage of the oscillation transistor is input, and a voltage discrimination circuit connected to the detection circuit, and a comparison circuit for comparing the resonance circuit voltage with a predetermined level is provided. In the proximity switch for detecting the disconnection of the detection coil by the output voltage of, the output voltage of the voltage discrimination circuit and the comparison circuit Input voltage is input, and when the detection coil is normal, it outputs a detection signal that turns on and off depending on whether or not the detected object approaches.When the detection coil is disconnected, a diagnostic signal at an intermediate level between on and off is output. Since an output / diagnostic circuit for output is provided, the output terminal connected to this output / diagnostic circuit outputs a detection signal that turns on and off depending on whether or not the detected object approaches when the detection coil is normal. Since a diagnostic signal of an intermediate level between ON and OFF is output when the detection coil is disconnected, both the approach of the object to be detected and the detection coil disconnection can be detected only by this output terminal.

[0010]

1 is a circuit diagram showing an embodiment of a proximity switch according to the present invention. The proximity switch of the present invention shown in FIG. 1 is different from the conventional proximity switch shown in FIG. 3 in that an output / diagnosis circuit 40 is provided in place of the output circuit 16 in FIG. The output / diagnosis circuit 40 is provided with transistors 44, 45, 46 whose emitters are respectively connected to the negative power supply terminal 24, and the bases of the transistors 44, 46 are input via resistors 41, 43, respectively. The transistor 45 is connected to the terminal a, the base of the transistor 45 is connected to the input terminal b thereof via the resistor 42, the collector of the transistor 44 is connected to the collector of the transistor 45 via the constant voltage element 47, and the constant voltage element 47 and the transistor 45 are connected. Is connected to its output terminal c. The constant voltage element 47 has, for example, an anode thereof as a collector of the transistor 44 and a cathode thereof as a transistor 45.
It consists of a Zener diode connected to the collector of. The input terminal a is connected to the output terminal of the comparison circuit 35, the input terminal b is connected to the output terminal of the voltage discrimination circuit 15, and the output terminal c is connected to the output terminal 25. The load 50 is connected between the positive power supply terminal 23 and the output terminal 25.

When there is no disconnection in the detection coil 7 and it is operating normally, the failure signal Vh from the comparison circuit 35 is not output, so the transistors 44 and 46 to which this failure signal is input to their bases are turned off. ing. Therefore, the detection signal of the detected object from the voltage discriminating circuit 15 is input to the base of the transistor 45, and the transistor 45 is turned on or off. This on or off operation is taken out from the output terminal 25. Detection coil 7
When a disconnection occurs in the circuit, the comparison circuit 35 outputs the failure signal Vh, so that the transistors 44 and 46 to which the failure signal Vh is input to their bases are turned on. When the transistor 46 is turned on, the base and emitter of the transistor 45 are short-circuited and the transistor 45 is turned off. On the other hand, when the transistor 44 is turned on, the positive power supply terminal 23-the load 50-the output terminal 25-the constant voltage element 4
A circuit of 7-transistor 44-negative side power supply terminal 25 is formed, and the power supply voltage Vs and the constant voltage element voltage Ez are applied to the load 50.
The voltage of Vs-Ez of the difference is added. During normal operation, this voltage becomes an intermediate level of the voltage Vs applied to the load 50 or the voltage of 0 volt when the transistor 45 is turned on or off, and the disconnection of the detection coil 7 can be detected from the voltage applied to the load 50.

FIG. 2 is a circuit diagram showing another embodiment of the proximity switch of the present invention. The proximity switch of the present invention shown in FIG. 2 differs from the proximity switch of the present invention shown in FIG. 1 in that the constant current element 4 is used instead of the constant voltage element 47 in FIG.
8 is provided. In the constant current element 48, the constant current value Iz is the power supply voltage Vs and the resistance value of the load 50 is R.
When it is set to 1, it is set to be smaller than Vs / Rl. Accordingly, when the detection coil 7 is disconnected, a current of Iz> Vs / Rl flows through the load 50, and this current is Vs / Rl or Vs / Rl applied to the load 50 when the transistor 45 is turned on and off during normal operation. The disconnection of the detection coil 7 can be detected from the current flowing through the load 50 at an intermediate level of the current of 0 ampere.

The current mirror circuits 13 and 3 are connected to the first and second current mirror circuits, the transistor 44 and the transistor 44, respectively.
45 and 46 are referred to as first, second and third transistors, respectively, and resistors 41, 42 and 43 are referred to as first, second and third resistors, respectively.

[0014]

In the proximity switch of the present invention, when the detection coil is normal from its output terminal, a detection signal of ON and OFF is output depending on whether or not the object to be detected approaches, and when the detection coil is disconnected. A diagnostic signal of an intermediate level between ON and OFF is output, and both the approach of the object to be detected and the disconnection of the detection coil can be detected only by this output terminal, and the number of external wires can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a proximity switch of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the proximity switch of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional proximity switch.

FIG. 4 is a time chart of the failure detection operation of the conventional proximity switch shown in FIG.

[Explanation of symbols]

 3 Second Current Mirror Circuit 5 Oscillation Transistor 6 Biasing Transistor 7 Detection Coil 9 Resonance Circuit 13 First Current Mirror Circuit 14 Detection Circuit 15 Voltage Discrimination Circuit 35 Comparison Circuit 40 Output / Diagnostic Circuit 41 First Resistance 42 Second Second resistor 43 Third resistor 44 First transistor 45 Second transistor 46 Third transistor 47 Constant voltage element 48 Constant current element

Claims (3)

[Claims] 1. A resonance circuit including a detection coil for detecting the approach of an object to be detected, an oscillation transistor for converting a voltage of the resonance circuit into a current, and an output current of the oscillation transistor is fed back to the resonance circuit. A first current mirror circuit,
A second current mirror circuit that supplies a base current to the transistor, a bias transistor that is connected between the resonance circuit and the oscillating transistor and applies a bias voltage to the oscillating transistor, and an output voltage of the oscillating transistor. Is provided, and a voltage discriminating circuit connected to the detector circuit is provided, and a comparator circuit for comparing the resonance circuit voltage with a predetermined level is provided, and the detection coil is disconnected due to the output voltage of the comparator circuit. In the proximity switch for detecting the, the output voltage of the voltage discrimination circuit and the output voltage of the comparison circuit are input, and when the detection coil is normal, a detection signal that is turned on and off depending on whether the detected object approaches Features an output / diagnosis circuit that outputs a diagnostic signal at an intermediate level between ON and OFF when the detection coil is disconnected Proximity switch to. 2. The proximity switch according to claim 1, wherein the output / diagnosis circuit is provided with first, second and third transistors whose emitters are respectively connected to the negative power supply terminals, and the first and second transistors are provided. The base of the third transistor is connected to the output terminal of the comparison circuit via the first and third resistors, respectively, and the second transistor is connected to the voltage discrimination circuit via the second resistor. A collector of the first transistor is connected to a collector of the second transistor via a constant voltage element, and a detection signal and a diagnostic signal are output from a connection point between the collector of the second transistor and the constant voltage element. Proximity switch characterized by. 3. The proximity switch according to claim 1, wherein the output / diagnosis circuit is provided with first, second and third transistors whose emitters are respectively connected to the negative power supply terminals, The base of the third transistor is connected to the output terminal of the comparison circuit via the first and third resistors, respectively, and the second transistor is connected to the voltage discrimination circuit via the second resistor. A collector of the first transistor is connected to a collector of the second transistor via a constant current element, and a detection signal and a diagnostic signal are output from a connection point between the collector of the second transistor and the constant current element. Proximity switch characterized by.