JPH01261020A - Two-wire type proximity switch - Google Patents

Abstract

PURPOSE:To obtain a 2-wire proximity switch able to detect a broken coil at the controller side (load side) by detecting the broken coil and making a leakage current zero. CONSTITUTION:If a broken fault of a detection coil L takes place, no current flows to a resistor R2 connected in series with the detection coil L, a potential at a connecting pint is lower than a prescribed potential, a 2nd transistor(TR) 7 is turned off and a 1st TR 6 is turned off in response thereto. Thus, no leakage current flows to a main circuit and the current flowing to a power supply line is zero. Then when the controller side detects each current flowing to power supply lines 6a, 6b, whether the circuit is turned off normally or the detection coil L is broken is identified.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a two-wire proximity switch, and particularly to a two-wire proximity switch whose failure is easy to detect.

(b) Prior Art In recent years, DC two-wire proximity switches have been attracting renewed attention from the viewpoint of wiring savings, direct connection to a programmable controller, and the need for a dedicated power line for the proximity switch. Traditionally,
This type of well-known two-wire proximity switch consists of an oscillator circuit that includes a detection coil and a resonant capacitor, an integrator circuit that integrates the output of this oscillator circuit, a comparator circuit that compares the output of this integrator circuit with a reference level, and a comparator circuit that compares the output of this integrator circuit with a reference level. The circuit includes an output circuit that responds to the output of the circuit, and two power supply lines to each of these circuits are commonly used as signal lines.

(C) Problems to be Solved by the Invention Generally, when a proximity switch is combined with other sensors and controllers to configure a large system, high reliability is required for each component device and component, and the proximity switch also requires high reliability. This is no exception, and the demand for so-called failure diagnosis functions is increasing. In particular, in proximity switches using detection coils, it is strongly desired to output information on frequently occurring coil/coil disconnections. However, conventional two-wire proximity switches have only two output modes: ON/OFF, and it is impossible to obtain signal outputs such as coil disconnection.

This invention was made by focusing on the above problem, and when a coil breakage is detected, the leakage current is reduced to O, so that even though it is a two-wire type, it can be easily connected to the controller side (load side). The present invention aims to provide a two-wire proximity switch capable of detecting its failure.

(d) Means and Effects for Solving the Problems The two-wire proximity switch of the present invention includes an oscillation circuit (2) including a detection coil (L) and a resonant capacitor (C4), and integrates the output of this oscillation circuit. a comparator circuit (4) that compares the output of the integrator circuit with a reference level, and an output circuit (5) that responds to the output of the comparator circuit, and a power supply line to each of the circuits. (6a, 6b) are used for signal derivation, a first transistor (TR,) connected in series to the power supply line, a connecting end of the detection coil and the resonant capacitor, and one power supply Due to the resistor (R2) connected between the lines and the voltage across this resistor, ON10
FF is controlled and accordingly the O of the first transistor is
The second transistor (TRY
).

In this two-wire proximity switch, under normal operating conditions, that is, when the detection coil is not disconnected, current flows through a resistor connected in series to the detection coil and the resonant capacitor. Therefore, the connection point between the detection coil and the resistor is maintained at a predetermined potential, and the second transistor is turned on.

When the second transistor is turned on, the first transistor is also turned on, and even if the output circuit is in the OFF state, a leakage current to the main circuit section flows through the power supply line. On the other hand, when a disconnection failure occurs in the detection coil, current no longer flows through the resistor connected in series with the detection coil, the potential at the connection point becomes lower than the predetermined potential, and the second transistor becomes 0FFL, In response to this, the first transistor is also turned off. As a result, no leakage current flows into the main circuit, and the current flowing through the power supply line becomes approximately zero. Therefore, by detecting the current flowing through the power supply line on the controller side, it is possible to determine whether it is normally OFF or a disconnection of the detection coil.

(e) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a circuit diagram of a two-wire proximity switch showing an embodiment of the present invention. In the figure, the proximity switch 1 includes an oscillation circuit 2 including a detection coil L and a resonant capacitor C4;
An integration circuit 3 that integrates the oscillation output of this oscillation circuit 2, the output of this integration circuit 3 and the threshold level (reference voltage)
It is equipped with a comparator circuit 4 that compares with the output of the comparator circuit 4, and an output circuit 5 that turns ON/OFF according to the output of the comparator circuit 4, and these circuits are connected to a power supply line 6a, a two-wire power supply line 6a, and 6b is supplied with current, and the ON10 F F of the output circuit 5 is transmitted to the controller via two wires. The basic configuration described above is similar to that of a conventional two-wire proximity switch.

Further, in the proximity switch of this embodiment, transistors TR6 and TR5 are connected in series to the power supply line 6a, and the oscillation circuit 2,
Current is supplied to main circuits such as the integrating circuit 3 and the comparing circuit 4. The transistor TR is of the PNP type, and has an emitter connected to the load side and a resistor R1 connected between the emitter and the base. Further, a series circuit of transistors TR, . . . , a resistor R2°, and a transistor TR is connected between the base of the transistor TR4 and the power supply line 6b. The transistor TR is an NPN type, with the collector connected to the resistor RIG and the emitter connected to the power supply line 6.
connected to b. Further, the collector of the transistor TR7 is connected to the anode of the diode D4, and a resistor R is connected between the cathode of the diode D40 and the power supply line 6b.
8 and a parallel circuit of capacitor C7 are connected.

A resistor R2 is connected between a connection point A between the detection coil L and the resonant capacitor C4 of the oscillation circuit 2 and the power supply line 6b, and the connection point A is connected to the base of the transistor TR1.

Next, the operation of the two-wire proximity switch of this embodiment will be explained.

When a controller is connected to the power supply lines 6a and 6b and the power is turned on, a voltage is applied to the transistor TR0 via the emitter/base of the transistor TR and the resistor R1, which is composed of the transistor TR11 and the resistor R2°. Constant current circuit operates. This constant current is the diode D4
The current flows to the capacitor C1 via the capacitor C1, and charging of the capacitor C1 is started. During this time, the constant current hf of the transistor T Rlr and the resistor R1°, and the double current of the transistor T R
It has the ability to flow to the emitter and collector of h. Therefore, the constant current circuit of transistor TR operates, and the power supply voltage of the main circuit increases to the Zener voltage of Zener diode D.

Upon application of the power supply voltage, the oscillation circuit 2 starts oscillating operation.

This oscillation output is integrated by the integration circuit 3 and input to the comparison circuit 4. However, when there is no detection object, the oscillation output is large and the input terminal is larger than the threshold, so the comparison circuit 4 Transistors TR,, TR,, TR, of the output circuit 5 at low level. Turn off. Therefore, only the leakage current of the main circuit flows through the proximity switch 1.
This leakage current flows through the two-wire line to the controller, resulting in a normal OFF output.

When a detection object exists, the oscillation output of the oscillation circuit 2 decreases,
The input voltage to the comparator circuit 4 is below the threshold,
The output of the comparator circuit 4 becomes high level, and the output circuit 5 and the transistors TR,, TR,, TR,. turns on. As a result, an ON current flows through the proximity switch 1 to the output circuit 5 through the two-wire line, resulting in a normal ON output.

As mentioned above, the oscillation output changes depending on the presence or absence of the detection object, but in any case, the detection coil L is not disconnected.
When the oscillation circuit is operating normally, a current flows through the resistor R2, and the potential at the connection point A becomes higher than the power supply line 6b, so that the transistor TR is turned on. Even if capacitor C7 finishes charging when the power is turned on, transistor TR still remains.

is ON, the transistor T R+ + and the resistor R9° cause the constant current to flow through the transistor TR. Therefore, the ON state of transistor TRb is maintained.

When the detection coil L is disconnected, no current flows through the resistor R2, so the potential at the connection point A becomes low, and the transistor T R
'r turns off. Since the resistance value of the resistor R6 is selected to be sufficiently large, the capacitor C1 remains charged and the constant current circuit of the transistor TR8 and the resistor RIG does not operate. Therefore, transistor TR, is 0FFL,
The constant voltage of the main circuit decreases, the output circuit 5 turns FF, and the leakage current also becomes zero. In this case, the current flowing through the two-wire line and the controller is approximately 0 because the leakage current is also 0, unlike the case where the normal output is OFF.

Next, an example in which the controller detects a coil disconnection failure by detecting leakage current O will be described with reference to FIG. The proximity switch 1 and the controller 7 are connected by two-wire lines 8a and 8b. The two-wire lines 8a and 8b are connected to the power supply lines 6a and 6b on the proximity switch 1 side, and on the controller side, the line 8b is grounded, and the line 8a is connected to a photocoupler LED 9, a resistor R11, and a current mirror circuit transistor. It is connected to the power supply V via TR8.

Transistor T R of one current mirror circuit = 2
Detect leakage current from. A normal ON10FF output is derived from a phototransistor 10 and an amplifier 11 in response to turning on/off the LED 9. In addition, normally OFF
Sometimes, a leakage current flows in the proximity switch l, so a leakage current flows in the transistor TR11, and therefore,
A current equal to its leakage current flows through the transistor T R,t. However, when the detection coil is disconnected, the transistors TR, . . . , TR12 stop flowing, so that a coil disconnection failure is detected.

(f) Effects of the Invention According to the present invention, a first transistor connected to a power supply line, a resistor connected between a connection end of a detection coil and a resonant capacitor, and the other power supply line, and a resistor connected to a first transistor connected to a power supply line; Since it is provided with a second transistor that is ON10FF controlled by the voltage across it and controls the 0N10FF of the first transistor accordingly, when the detection coil is disconnected, the current flowing through the first transistor, that is, Since the leakage current can be set to 0, disconnection of the detection coil can be detected without increasing the number of lines, distinguishing it from a normal OFF state in which leakage current exists. .

[Brief explanation of the drawing]

Fig. 1 is a circuit connection diagram of a two-wire proximity switch showing an embodiment of the present invention, and Fig. 2 shows an example of leakage current detection when the same two-wire proximity switch is connected to a controller. It is a circuit diagram. 1: Two-wire proximity switch, 2: Oscillation circuit, 3: Integrating circuit, 4: Comparison circuit, 5: Output circuit, 6a/6b
: Power supply line, L: Detection coil, C4: Resonant capacitor, R2: Resistor, TR, :) Transistor (first), TR, : Transistor (second). Figure 2

Claims (1)

[Claims] (1) An oscillation circuit that includes a detection coil and a resonant capacitor, an integration circuit that integrates the output of this oscillation circuit, a comparison circuit that compares the output of this integration circuit with a reference level, and an output that responds to the output of this comparison circuit. a two-wire proximity switch, wherein the power supply line to each of the circuits is used for deriving a signal, the first wire connected in series to the power supply line;
ON/OFF control is performed by the transistor, a resistor connected between the connection end of the detection coil and the resonant capacitor, and one power supply line, and the voltage across this resistor, and the ON/OFF of the first transistor is controlled accordingly. 2nd to control OFF
A two-wire proximity switch characterized by comprising a transistor.