JPH08146069A - Disconnection automatically detecting device - Google Patents

Abstract

PURPOSE: To provide a disconnection automatically detecting device which can automatically detect the disconnection between a three-wire-type sensor and a sensor signal input device. CONSTITUTION: A transistor circuit 22 which is turned on or off depending on whether power is supplied or not inside a sensor 20 and current is fed to a signal line 4 when a signal output contact 8 is open, thus constantly monitoring the current value in a sensor signal input device 21. And, not only the presence or absence of sensor input but also the presence or absence of the disconnection of three wires 3-5 between the sensor 20 and the sensor signal input device 21 are judged based on the current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic disconnection detecting device applied to a sensor input system using a DC three-wire type sensor used for a photoelectric tube or the like.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a conventional sensor input system. This sensor input system includes a DC three-wire sensor 1 (hereinafter simply referred to as a sensor) used for a photoelectric tube and the like, and a sensor signal input device 2 for inputting a signal from the sensor 1, both of which have three wires. , That is, the power supply positive line 3, the signal line 4, and the power supply negative line 5
Connected by.

The operation is as follows. The sensing main circuit 6 in the sensor 1 is driven by the DC power supply 7 supplied to the sensor signal input device 2 via power supply lines 3 and 5,
Similarly, the signal output contact 8 in the sensor 1 is opened / closed according to the detection result. The signal when the signal output contact 8 is opened / closed is transmitted through the signal line 4 to the signal detection unit 9 in the sensor signal input device 2.
And is input to an arithmetic processing unit (not shown) as a sensor detection signal. More specifically, in the circuit of FIG. 3, when the signal output contact 8 is closed, the transistor 10 in the signal detection unit 9 is turned on, and when the signal output contact 8 is opened, the transistor 10 is no longer biased. Since it is turned off, a signal corresponding to the on / off operation of the transistor 10 by opening / closing the signal output contact 8 is output as a sensor detection signal.

[0004]

However, in such a conventional sensor input system, for example,
When the power supply positive line 3 or the signal line 4 is disconnected, a predetermined signal cannot be sent to the signal detection unit 9 in the sensor signal input device 2 even if the signal output contact 8 in the sensor 1 is closed. The detection unit 9 determines that the signal output contact 8 is open. In other words, conversely, when the signal detection unit 9 determines that the signal output contact 8 is open, is the signal output contact 8 really open?
Or, there is a problem that it is not possible to distinguish whether the power source plus line 3 or the signal line 4 is disconnected.

The present invention has been made in view of the above problems of the prior art, and is an automatic disconnection detection device capable of automatically detecting a disconnection between a three-wire sensor and a sensor signal input device. The purpose is to provide.

[0006]

In order to achieve the above object, an automatic disconnection detection device according to claim 1 of the present invention comprises:
It is an automatic disconnection detection device that automatically detects disconnection between a three-wire sensor that has a signal output contact that opens and closes according to the detection result and a sensor signal input device that inputs the signal from the sensor through the signal line. A monitoring current supply means for supplying a monitoring current to the signal line when the signal output contact is open, and a determination means for determining the presence / absence of disconnection based on the value of the monitoring current. .

According to another aspect of the present invention, there is provided the automatic disconnection detecting device according to the first aspect, wherein the monitoring current supply means is an impedance conversion circuit whose impedance changes depending on whether power is supplied or not. Characterize.

Further, an automatic disconnection detecting device according to a third aspect of the present invention is the automatic disconnection detecting device according to the second aspect, characterized in that the impedance conversion circuit has a transistor which is turned on / off depending on whether or not power is supplied.

Further, in the automatic disconnection detecting device according to claim 4, in the automatic disconnection detecting device according to claim 3, the monitoring current is a signal current flowing through the signal line when the signal output contact is closed. It flows in the same direction as, and has a smaller value than the signal current.

According to a fifth aspect of the present invention, there is provided an automatic disconnection detecting apparatus according to the third aspect, wherein the monitoring current is a signal current flowing through the signal line when the signal output contact is closed. Characterized by flowing in the opposite direction.

[0011]

In the automatic disconnection detecting device according to claim 1 configured as described above, the monitoring current supply means applies the monitoring current to the signal line when the signal output contact in the sensor is open, The determining means determines whether or not there is a disconnection between the sensor and the sensor signal input device based on the value of the monitored current.
Therefore, when the signal line connecting the sensor and the sensor signal input device is disconnected, the monitoring current stops flowing, and the disconnection of the signal line is detected.

Further, in the disconnection automatic detection device according to the second aspect, the monitoring current supply means is composed of an impedance conversion circuit whose impedance changes depending on whether or not power is supplied. Therefore, when at least one of the two power supply lines connecting the sensor and the sensor signal input device is disconnected, the power supply is cut off, the impedance changes, and the value of the monitoring current flowing in the signal line changes, so that the signal line In addition, disconnection of the power line is also detected.

Further, in the automatic disconnection detection device according to the third aspect, preferably, the impedance conversion circuit has a transistor which is turned on / off depending on whether or not power is supplied. Therefore, when at least one of the two power supply lines is disconnected, the power supply is cut off, the transistor is turned off, and the monitoring current stops flowing, so that the disconnection of the power supply line is detected in addition to the signal line.

Further, in the disconnection automatic detection device according to the present invention, the monitoring current flows in the same direction as the signal current flowing through the signal line when the signal output contact is closed, and has a value smaller than that signal current. Since it is small, the open / closed state of the signal output contact is detected depending on the magnitude of the current value flowing through the signal line.

Further, in the disconnection automatic detection device according to the present invention, since the monitoring current flows in the direction opposite to the signal current flowing through the signal line when the signal output contact is closed, the current flowing through the signal line. The open / closed state of the signal output contact is detected depending on the direction of the.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a sensor input system incorporating an automatic disconnection detection device according to a first embodiment of the present invention.
The same parts as those in FIG. 3 are designated by the same reference numerals.

This sensor input system is, like the conventional sensor input system shown in FIG. 3, a DC three-wire type sensor 20 used for a photoelectric tube and the like, and a sensor signal input device 21 for inputting a signal from this sensor 20. And are connected by three lines, that is, a power source plus line 3, a signal line 4, and a power source minus line 5.

The sensor 20 is controlled to be opened and closed by the sensing main circuit 6 driven by the DC power supply 7 supplied to the sensor signal input device 21 through the power lines 3 and 5, and the sensing main circuit 6 according to the detection result. It has a built-in signal output contact 8. The sensor 20 also has a transistor circuit 22. This transistor circuit 22
Has a PNP-type transistor 23, the emitter of the transistor 23 is connected to the power source plus line 3 via a current limiting resistor 24, the collector of the transistor 23 is directly connected to the signal line 4, and the The bases are connected to the power source plus line 3 and the power source minus line 5 via resistors 25 and 26, respectively. Resistors 25, 2
Reference numeral 6 is a resistor for setting the value of the bias applied to the transistor 23, which is set to an appropriate value in advance. As will be described later, the transistor circuit 22 has a function of supplying a current (monitoring current) to the signal line 4 when the signal output contact 8 is open, and has a function of turning on / off depending on whether or not power is supplied. The monitoring current supply means and the impedance conversion circuit are composed of a transistor circuit 22.

The sensor signal input device 21 has a current detector 27 for detecting the current flowing through the signal line 4. The current detection unit 27 has resistors 28 and 29 connected in series, one end of the resistor 28 is connected to the signal line 4, and one end of the resistor 29 is connected to the power supply minus line 5. The resistor 28, like the resistor 24 in the sensor 20, is a current limiting resistor. The resistor 29 is a resistor for current detection, and is set to a value sufficiently smaller than the resistors 24 and 28. Both ends of the resistor 29 are respectively connected to two input terminals of an operational amplifier 30 which also constitutes the current detector 27. The output terminal of the operational amplifier 30 is, for example, a determination circuit 31 including a CPU or the like.
It is connected to the. Therefore, the operational amplifier 30 has a function of detecting the value of the current flowing through the signal line 4 and outputting it to the determination circuit 30. The determination circuit 30, as will be described later,
Based on the value of the output signal from the operational amplifier 29, the open / closed state of the signal output contact 8 in the sensor 20 and the three lines 3 to 5 between the sensor 20 and the sensor signal input device 21 according to the logic programmed in advance. It has a function to determine the presence or absence of disconnection. The determining means is composed of the current detector 27 and the determining circuit 30.

Next, the operation will be described. The current flowing through the signal line 4 is Is. In a normal state, the sensor 20
When the signal output contact 8 is closed by the sensing circuit 6 therein, a current (signal current) determined by the value of the resistor 28 flows through the signal line 4 and is input to the sensor signal input device 21. The value of the current at this time is A (Is = A)
And the value A of this current is the operational amplifier 3 in the current detector 27.
It is detected by 0 and output to the determination circuit 30. In this case, since the transistor 23 in the sensor 20 is not biased, the transistor 23 (or the transistor circuit 22) is turned off.

Similarly, in a normal state, when the signal output contact 8 is opened by the sensing circuit 6 in the sensor 20, the transistor 23 in the transistor circuit 22 is biased, so that the transistor 23 turns on and the signal line 4 A current (monitoring current) that depends on the values of the resistors 24 and 28 flows through. When the current value at this time is B (Is = B), the relationship of B <A is established. This current is input to the sensor signal input device 21, and its value B is detected by the operational amplifier 30 in the current detection unit 27 and output to the determination circuit 30.

Therefore, based on the value of the current flowing through the signal line 4, it is possible to determine whether the signal output contact 8 is closed or open, that is, whether or not the sensor 20 detects. The direction of the current (monitoring current) flowing through the signal line 4 when the signal output contact 8 is open is the same as the direction of the current flowing through the signal line 4 (signal current) when the signal output contact 8 is closed. Is. In other words, because the directions are the same, the present embodiment is configured so that the value of the current flowing through the signal line 4 changes depending on the open / close state of the signal output contact 8.

When the signal line 4 is broken while the signal output contact 8 is open, no current flows through the signal line 4. That is, the value of the current flowing through the signal line 4 becomes zero (Is = 0). This result is detected by the operational amplifier 30 in the current detector 27 and output to the determination circuit 30.

Similarly, in the state where the signal output contact 8 is open, even if the power source plus line 3 is disconnected, the signal line 4
No current flows through (ie, Is = 0). Sensor 20
This is because the transistor 23 in the transistor circuit 22 provided therein is not biased and the transistor 23 is turned off. This result is detected by the operational amplifier 30 in the current detector 27 and output to the determination circuit 30.

Similarly, when the signal output contact 8 is open and the power source negative line 5 is disconnected, no current flows in the signal line 4 (that is, Is =
0). This is because the base voltage of the transistor 23 in the transistor circuit 22 is hung on the positive side, no bias is applied, and the transistor 23 is turned off. This result is also detected by the operational amplifier 30 in the current detector 27 and output to the determination circuit 30.

The decision circuit 30 determines, based on the value Is of the current flowing through the signal line 4 detected by the operational amplifier 30,
Open / closed state of the signal output contact 8 in the sensor 20 (presence or absence of sensor input), and the sensor 20 and the sensor signal input device 2
Signals that match the respective determinations (sensor detection signal, disconnection detection signal) are determined by determining the presence or absence of disconnection of the three lines 3-5 between 1
Is output. Specifically, the value I of the current flowing through the signal line 4
When s is A (Is = A), it is determined that the signal output contact 8 in the sensor 20 is closed, that is, there is a sensor input,
Outputs the sensor detection signal. Further, when the value Is of the current flowing through the signal line 4 is B (Is = B), it is determined that the signal output contact 8 in the sensor 20 is open, that is, no sensor input. Further, when the value Is of the current flowing through the signal line 4 is zero (Is = 0), at least one of the three lines 3 to 5 between the sensor 40 and the sensor signal input device 41 is disconnected. It is judged that there is a break and a disconnection detection signal is output.

FIG. 2 is a circuit diagram of a sensor input system incorporating an automatic disconnection detecting device according to a second embodiment of the present invention. The same parts as those in FIGS. 1 and 3 are designated by the same reference numerals.

This sensor input system is, like the sensor input system shown in FIGS. 1 and 3, a DC three-wire type sensor 40 used for a photoelectric tube and the like, and a sensor signal input device 41 for inputting a signal from this sensor 40. Consists of
The two are connected by three lines, that is, a power source plus line 3, a signal line 4, and a power source minus line 5. Also,
In this embodiment, as will be described later, unlike the first embodiment shown in FIG. 1, the direction of the current flowing through the signal line 4 is reversed depending on the open / close state of the signal output contact 8.

The sensor 40 is controlled by the sensing main circuit 6 driven by the DC power source 7 supplied to the sensor signal input device 41 via the power lines 3 and 5, and the sensing main circuit 6 according to the detection result. It has a built-in signal output contact 8. The sensor 40 also has a transistor circuit 42. This transistor circuit 42
Has an NPN-type transistor 43, the collector of the transistor 43 is connected to the signal line 4 via a current limiting resistor 44, the emitter of the transistor 43 is directly connected to the power supply minus line 5, and The base is connected to the power source plus line 3 and the power source minus line 5 via resistors 45 and 46, respectively. Resistor 45,
Reference numeral 46 is a resistor for setting the value of the bias applied to the transistor 43, which is set to an appropriate value in advance. As will be described later, this transistor circuit 42 is provided in the signal line 4 when the signal output contact 8 is open.
In addition, it has a function of flowing a current (monitoring current) in the D direction in the figure and turning on and off depending on the presence or absence of power supply.
The monitoring current supply means and the impedance conversion circuit are composed of a transistor circuit 42.

The sensor signal input device 41 has a current detector 47 for detecting the current flowing through the signal line 4. The current detector 47 includes a set of a resistor 48 and a photocoupler 49 connected in series, and a resistor 50 and a diode also connected in series in order to detect bidirectional currents flowing through the signal line 4. 51 sets are connected in parallel. The photocoupler 49 includes a light emitting diode 52 and a phototransistor 53. The phototransistor 53 is connected to a determination circuit 55 including, for example, a CPU. The resistor 50 is a resistor for current detection, and is set to a value sufficiently smaller than that of the resistor 44. Both ends of the resistor 50 are similarly connected to the current detection unit 4
7 are connected to the two input terminals of the operational amplifier 54, respectively. The output terminal of the operational amplifier 54 is connected to the determination circuit 55. Further, in the sensor signal input device 41, a set of a resistor 56 and a Zener diode 57 connected in series is connected in parallel with the DC power supply 7 to stabilize the current. One end of the current detection unit 47 is connected to the signal line 4, and the other end is connected to the connection point of the resistor 56 and the Zener diode 57. As will be described later, when the signal output contact 8 in the sensor 40 is closed, a current (signal current) in the direction C in the drawing flows in the signal line 4, so that the current detection provided in the sensor signal input device 41 is detected. The photocoupler 49 in the section 47 is turned on, and a signal to that effect is output to the determination circuit 55. Further, when the signal output contact 8 in the sensor 40 is open, a current (monitoring current) in the direction D in the drawing flows in the signal line 4, so that the current detecting unit 47 in the sensor signal input device 41 is provided. Operational amplifier 5
The value of the current is detected by 4 and output to the determination circuit 55. The determination circuit 55 uses the photocoupler 4 according to a preprogrammed logic, as described later.
9 based on the presence / absence of a signal from the amplifier 9 and the value of the output signal from the operational amplifier 54, the open / closed state of the signal output contact 8 in the sensor 40, the sensor 40 and the sensor signal input device 41.
It has a function of determining the presence or absence of disconnection of the three lines 3 to 5. The determining means is the current detecting section 47 and the determining circuit 5.
It is composed of 5.

Next, the operation will be described. The current flowing through the signal line 4 is Is. In normal times, the sensor 40
When the signal output contact 8 is closed by the sensing circuit 6 inside, a current (signal current) flows through the signal line 4 in the direction C in the figure.
Is input to the sensor signal input device 41. This current turns on the photocoupler 49 in the current detector 47 provided in the sensor signal input device 41, and the output signal of the phototransistor 53 is input to the determination circuit 55. In this case, since the transistor 43 in the sensor 40 is not biased, the transistor 43 (or the transistor circuit 42) is turned off.

Similarly, in the normal state, when the signal output contact 8 is opened by the sensing circuit 6 in the sensor 40, the transistor 43 in the transistor circuit 42 is biased, so that the transistor 43 is turned on and the signal line 4 is turned on. A current (monitoring current) determined by the value of the resistor 44 flows in the direction D in the figure. The current value at this time is E
And This current is input to the sensor signal input device 41, and its value E is detected by the operational amplifier 54 in the current detector 47 and output to the determination circuit 55.

Therefore, the photo coupler 49 or the operational amplifier 5 is exclusively used depending on the direction of the current flowing through the signal line 4.
4 outputs a signal, and based on this, whether the signal output contact 8 is closed or open, that is, the sensor 2
The presence or absence of detection by 0 can be determined.

When the signal line 4 is broken while the signal output contact 8 is open, no current flows through the signal line 4. That is, the value of the current flowing through the signal line 4 becomes zero (Is = 0). Therefore, the sensor signal input device 41
The photocoupler 49 in the current detector 47 provided therein is not turned on, and the above result (Is = 0) is detected by the operational amplifier 54 in the current detector 47, and the determination circuit 5
5 is output.

Similarly, when the power source plus line 3 is disconnected while the signal output contact 8 is open, the signal line 4
No current flows through (ie, Is = 0). Sensor 40
This is because the base voltage of the transistor 43 in the transistor circuit 42 provided inside is zero and no bias is applied, so that the transistor 43 is turned off. Therefore,
Also in this case, the photocoupler 49 in the current detector 47 is not turned on, and the result (Is = 0) is detected by the operational amplifier 54 in the current detector 47, and the determination circuit 5
5 is output.

Similarly, when the signal output contact 8 is open and the power source negative line 5 is disconnected, no current flows through the signal line 4 (that is, Is =
0). This is because the transistor 43 in the transistor circuit 42 is not biased and the transistor 23 is turned off. Also in this case, the photocoupler 49 in the current detector 47 is not turned on, and the result (Is = 0) is obtained.
Is detected by the operational amplifier 54 in the current detector 47 and output to the determination circuit 55.

The decision circuit 55 inputs the output signals of the photocoupler 49 and the operational amplifier 54, respectively, and determines the signal in the sensor 40 based on the presence or absence of the signal from the photocoupler 49 and the value of the output signal from the operational amplifier 54. Open / closed state of output contact 8 (presence or absence of sensor input), and sensor 4
The presence or absence of disconnection of the three lines 3 to 5 between 0 and the sensor signal input device 41 is determined, and signals (sensor detection signal, disconnection detection signal) that match each determination are output. Specifically, when there is an output signal from the photocoupler 49 (photodiode 53), it is determined that the signal output contact 8 in the sensor 40 is closed, that is, there is a sensor input, and a sensor detection signal is output. In addition, there is no output signal from the photocoupler 49 and the current value I detected by the operational amplifier 54
When s is E (Is = E), it is determined that the signal output contact 8 in the sensor 40 is open, that is, there is no sensor input. Further, when there is no output signal from the photocoupler 49 and the current value Is detected by the operational amplifier 54 is zero (Is = 0), the three lines 3 to 5 between the sensor 40 and the sensor signal input device 41 are connected. It is determined that at least one of them is disconnected, and a disconnection detection signal is output.

Therefore, according to the above embodiment, the transistor circuits 22 and 42 are provided in the sensors 20 and 40, respectively.
Since the current (monitoring current) is passed through the signal line 4 when the signal output contact 8 in the sensor 20, 40 is open, and the value of the monitoring current is changed depending on the presence or absence of power supply, monitoring It becomes possible to determine the presence or absence of disconnection based on the value of the current, and the disconnection between the three-wire sensor 20, 40 and the sensor signal input device 21, 41 is automatically detected in the sensor signal input device 21, 41. can do.

In particular, according to the first embodiment, the open / closed state (presence or absence of sensor input) of the signal output contact 8 in the sensor 20 is detected by the value of the current flowing through the signal line 4 (Is = A or Is = B). Therefore, the sensor signal input device 2
The current detection unit 27 in 1 can be configured relatively easily.

Further, particularly according to the second embodiment, the open / closed state (presence or absence of sensor input) of the signal output contact 8 in the sensor 20 is detected by the direction of the current flowing through the signal line 4 (direction C or D). By doing so, it becomes possible to determine the open / closed state of the signal output contact 8 only by the presence or absence of the input signal, and the determination logic programmed in the determination circuit 55 can be configured relatively easily.

In the above embodiment, the impedance conversion circuit is the transistor circuit 2 in order to simplify the structure.
However, the present invention is not limited to this, and any configuration may be used as long as the impedance changes depending on the presence or absence of power supply and the value of the monitoring current flowing through the signal line 4 changes. It may have any configuration. This is because it is possible to determine the presence / absence of disconnection based on the value of the monitoring current.

[0042]

As described above, according to the automatic disconnection detection device of the first aspect of the present invention, the monitoring current is passed through the signal line when the signal output contact in the sensor is open, and the current is passed through. Since the value is constantly monitored, the disconnection of the signal line connecting the sensor and the sensor signal input device can be detected.

Further, according to the automatic disconnection detection device of the second aspect, the impedance conversion circuit whose impedance changes depending on the presence or absence of power supply is provided to change the value of the monitoring current flowing through the signal line. In addition to the signal line, the disconnection of two power supply lines can be detected.

Further, according to the automatic disconnection detection device of the third aspect, the impedance conversion circuit is composed of the transistors which are turned on / off depending on the presence / absence of power supply, so that the structure of the impedance conversion circuit can be simplified.

According to the automatic disconnection detector of the fourth aspect, the open / close state of the signal output contact in the sensor is detected by the value of the current flowing through the signal line. Can be simplified.

According to the automatic disconnection detection device of the present invention, the open / closed state of the signal output contact in the sensor is detected by the direction of the current flowing through the signal line. Can be converted.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a sensor input system incorporating an automatic disconnection detection device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a sensor input system incorporating an automatic disconnection detection device according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional sensor input system.

[Explanation of symbols]

3 ... Power source positive line 4 ... Signal line 5 ... Power source negative line 6 ... Sensing main circuit 7 ... DC power source 8 ... Signal output contact 20, 40 ... Three-wire type sensor 21, 41 ... Sensor signal input device 22, 42 ... Transistor circuit ( Monitoring current supply means, impedance conversion means) 23, 43 ... Transistors 28, 48 ... Current detection section (determination means) 30, 54 ... Operational amplifier 31, 55 ... Determination circuit (determination means) 49 ... Photocoupler

Claims (5)

[Claims] 1. A disconnection that automatically detects a disconnection between a three-wire sensor having a signal output contact that opens and closes according to a detection result and a sensor signal input device that inputs a signal from the sensor through a signal line. An automatic detection device, comprising a monitoring current supply means for supplying a monitoring current to the signal line when the signal output contact is open, and a determination means for determining the presence or absence of disconnection based on the value of the monitoring current, An automatic disconnection detection device having. 2. The automatic disconnection detection device according to claim 1, wherein the monitoring current supply means comprises an impedance conversion circuit whose impedance changes depending on whether or not power is supplied. 3. The automatic disconnection detection device according to claim 2, wherein the impedance conversion circuit has a transistor that is turned on and off depending on whether or not power is supplied. 4. The monitoring current flows in the same direction as the signal current flowing through the signal line when the signal output contact is closed, and has a smaller value than the signal current. Automatic disconnection detection device. 5. The disconnection automatic detection device according to claim 3, wherein the monitoring current flows in a direction opposite to a signal current flowing through the signal line when the signal output contact is closed.