JPH01109823A - Proximity switch - Google Patents

Abstract

PURPOSE:To test the presence of a fault of a proximity switch independently of the presence of an object to be detected by storing a detection signal of a proximity switch in a test circuit, and using a test signal to feed back the detection signal to an oscillation circuit. CONSTITUTION:In closing a switch 22 when an object 13 to be detected is not approached, the output of a comparator 3, that is, a detection signal is at a low level, the signal is stored in a flip-flop 19, fed back to an oscillation circuit 1 via a buffer circuit 20, the oscillating voltage is dropped to the same state as if the object 13 to be detected were approached to a detection coil 11, circuits 2, 3 are operated and a transistor(TR) 17 is turned on. In closing a switch 22, when the object 13 to be detected is approaching, a voltage fed to a clock terminal of the flip-flop 19 rises, a high level detection signal of the flip-flop 19 is fed back, the oscillated voltage is increased, the TR 17 is turned on and a current of a relay 10 is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a proximity switch that detects the approach of a detected object by using an oscillation circuit whose oscillation voltage increases or decreases when the detected object approaches. .

[Conventional technology]

A conventional example of a proximity switch using an oscillation circuit is shown in FIG. 2, where the proximity switch includes an oscillation circuit 1, a detection smoothing circuit 2, a comparator 3, an output circuit 4, a power supply circuit 5,
It is driven by an external quantity H8 connected between the power supply terminals 6.7. For example, a relay 10 attached to a programmable controller is connected between the terminal 6 and the output end of the output circuit 4.

The oscillation circuit 1 has a resonant circuit consisting of a detection coil 11 and a capacitor 12, and oscillates at a constant voltage at the resonant frequency of this resonant circuit. When a detected object 13 such as a metal body approaches the detection coil 11, the detected object 13 consumes the energy of the oscillation circuit 1, which is detected by the path 2, smoothed, and compared with a reference value by the comparator 3. ,
This output is applied as a detection signal to the output circuit 4, turns on a transistor (not shown) of the output circuit 4, and then turns on the relay 1.
Operate 0.

(Problem to be Solved by the Invention) In the proximity switch described above, if there is a failure in the internal circuit, the ON or OFF signal will be turned off from the output terminal regardless of whether the detected object is approaching the proximity switch. The signal is
For example, if the input signal is applied via a relay driven by this proximity switch, the main '4jt' such as a programmable controller is
There was a risk that the operation of the equipment would be seriously affected. Therefore, it is necessary to test whether the proximity switch is functioning normally. Although it is possible to artificially move the object to be detected closer or further away to test the operation of the proximity switch, this method has the disadvantage that the test is time-consuming and the main device must be stopped for a relatively long time. Ta.

An object of the present invention is to provide a proximity switch having a test circuit that allows external testing of whether the function of the proximity switch is normal or not in a simple manner, regardless of whether or not a detected object is close to the detection coil. It is about providing.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention includes an oscillation circuit having a detection coil, and when an object to be detected passes near the detection coil, the oscillation of the oscillation circuit is attenuated or increased to output a detection signal. The switch has a test switch, stores a detection signal each time the test switch is operated, feeds back the stored detection signal to the oscillation circuit, and operates the oscillation circuit only while the test signal is input. A test circuit is provided to change the amplification degree of the signal.

[Effect]

The test circuit according to the present invention stores the detection signal detected and output by the proximity switch each time the test switch is operated, feeds back the stored detection signal to the oscillation circuit, and receives the input test signal from the outside. By changing the amplification degree of the oscillation circuit only while the detection coil is in contact with the detection coil, the oscillation voltage is forcibly increased even when the object to be detected approaches the detection coil and the oscillation voltage is low. By forcibly attenuating this even when the detection coil is high, the proximity switch can be tested regardless of whether or not the object to be detected is close to the detection coil.

〔Example〕

FIG. 1 shows an embodiment of a proximity switch according to the present invention, and the same parts as in FIG. 2 are given the same reference numerals as in FIG. 2, and detailed explanation thereof is omitted. In FIG. 1, 14 is a proximity switch that is exactly the same as the circuit shown in FIG. 2, and includes an oscillation circuit 1, a detection smoothing circuit 2, a comparator 3, an output circuit 4, a power supply circuit 5, and the like. In the output circuit 4, the output terminal of the comparator 3 is connected to the base of the transistor 17 via the resistor 16, and the switching transistor 17 is closed by the detection signal of the comparator 3. A relay 10 is connected to the collector of this transistor 17 as in FIG. 2.

As will be described later, the oscillation voltage of the oscillation circuit 1 is controlled by feeding back the detection signal of the proximity switch. The test circuit 1B is a D-type flip-flop 19
and a three-state buffer circuit 20, the input terminal of the flip-flop 19 is connected to the output terminal of the comparator 3, and the clock terminal T is connected to the external voltage a! through a test terminal 21 and a test switch 22. connected to the negative pole of 8,
The output terminal Q is connected to the input end of a three-state buffer circuit 20, and the output end of this three-state buffer circuit 20 is connected so as to feed back this output to the oscillation circuit 1. Also, is the limit of 20 buffers per circuit? The clock terminal T of the flip-flop 19 is connected to the terminal 11, and a test signal is applied thereto. flip flop 19
When the test signal 11 is applied to the clock terminal T, the detection signal applied to the input terminal at that time is outputted to the output terminal Q and inputted to the buffer circuit 20. Buff 1
In the circuit 20, the detection signal inputted to the input terminal is transmitted to the output terminal only when the test signal is applied to the control terminal a, and when the test signal is not inputted to the control terminal, the output circuit is not connected to the input terminal. It becomes a high impedance without affecting the amplification degree of the oscillation circuit 1.

When an object to be detected approaches the detection coil 11 and the oscillation voltage of the oscillation circuit 1 decreases, this voltage is applied to the comparator 3 via the detection smoothing circuit 2, and a high-level detection signal is output from the output terminal of the comparator 3. do. Therefore, transistor 17 is turned on and relay 10 is energized. Switch 2 to test this proximity switch in this state.
2 is closed, the voltage applied to the clock terminal of the flip-flop 19 falls, and at the time of this falling, a high-level detection signal is applied to the input terminal of the flip-flop 19, so the flip-flop 19 receives this high-level detection signal. is stored, and a high level signal is output to output terminal Q. At this time, the negative applied voltage is applied to the control terminal of the buffer circuit 20 and the inhibition input is canceled, so the high level detection signal is output as is, and this signal is fed back to the oscillation circuit 1. As a result, the oscillation circuit 1
The amplification degree of is increased, and this oscillation voltage is increased to the same state as when the detected object 13 is not approaching. Therefore, transistor 17 is turned off and the current in relay 10 is cut off. At this time, the signal at the input terminal of the flip-flop 19 is inverted to low level, but if the signal applied to the clock terminal T does not fall, that is, the second test switch 22 is not operated, the output terminal The Q signal remains unchanged. When the switch 22 is opened, the output circuit of the buffer circuit 20 becomes high impedance, and the oscillation circuit 1 returns to its normal state.

When the switch 22 is closed when the detected object 13 is not approaching, the output of the comparator 3, that is, the detection signal is at a low level, and this signal is stored in the flip-flop 19 and fed back to the oscillation circuit 1 via the buffer circuit 20. , since this signal is at a low level, the amplification degree of the oscillation circuit 1 is reduced, the oscillation voltage is reduced to the same state as when the detected object 13 is approaching the detection coil 11, and each circuit 2.3 is The transistor 17 is activated and turned on.

If there is a failure such as a disconnection or a short circuit between the detection coil 11 and the transistor 17, turn the test switch 22 on in one of the two modes: approach of the object to be detected and 11-turn as described above. When closed, the energization of the relay 10 does not reverse, indicating that the proximity switch is faulty. Note that similar results can be obtained even if the test circuit 18 itself fails. Furthermore, if the switch 22 causes chattering at a relay contact or the like, the test result may be erroneous, but this can be solved by providing a timer circuit between the output of the comparator 3 and the flip-flop 19.

[Effects of the Invention] According to the present invention, the detection signal of the proximity switch is stored in the test circuit, and this signal is fed back to the oscillation circuit as a test signal, thereby inverting the detection signal regardless of the presence or absence of the detected object. By checking loads such as externally connected relays, it is possible to test whether there is a failure in the proximity switch. Therefore, the operation of this proximity switch can be easily tested just before starting operation of a device using this proximity switch, or when an abnormality occurs in the device.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a proximity switch according to the invention,
A block diagram including a wiring diagram of main parts. FIG. 2 is a block diagram showing an example of a conventional proximity switch. 1: Oscillation circuit, 11: Detection coil, 18: Test circuit,
22: Test switch. I. Attorney without agent Iwao Yamaguchi

Claims (1)

[Claims] 1) A proximity switch comprising an oscillation circuit having a detection coil, and in which when an object to be detected passes near the detection coil, the oscillation of the oscillation circuit is attenuated or increased to generate a detection signal, and the proximity switch includes a test switch, A test circuit is provided that stores the detection signal each time the switch is operated, feeds back the stored detection signal to the oscillation circuit, and changes the amplification degree of the oscillation circuit only while the test signal is input. A proximity switch characterized by: