JP3368771B2 - Signal processing device with disconnection detection function - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing device capable of reliably detecting a disconnection state.

[0002]

2. Description of the Related Art At present, a sensor having a disconnection function is often used in a production site to improve maintenance efficiency. The connection relationship between this sensor and a signal input device such as a PLC is shown in FIG.
It is expressed as. As shown in the figure, the sensor 10 has three terminals 10A, 10B, and 10C connected to a signal line 12, a backup line 14, and a ground line 16.

In the sensor 10, for example, a sensing circuit 11 that operates when an approach of an object is detected is provided. At the time of detection, the contact 1 is closed and the contact 2 is opened. On the other hand, the signal input device 20 includes the signal line 12 and the spare line 1.
4, three terminals 20A, 20 connected to the ground wire 16
It has B and 20C.

The signal input device 20 is provided with a signal input section 22, which is based on both contact signals in the sensor 10 inputted through the signal line 12, the spare line 14, and the ground line 16. By doing so, sensing and disconnection detection are performed. In other words, when an object approaches, sensing is made by inputting that the contact 1 is closed via the signal line 12, while detecting disconnection is made by inputting that the contact 2 is opened via the spare line 14, Sensing and disconnection detection are performed by collating the logic of these contact signals.

For example, as shown in FIG.
In the case of (normally open) and the contact 2 is NC (normally closed), when the approach of an object is detected, the contact 1 is closed and the contact 2 is opened, but in the signal input unit 22, the signal line 12 is used. ON signal from the contact
When the OFF signal of the contact 2 is input via the, the object is detected, and it is determined that the disconnection has not occurred, and conversely, the OFF signal of the contact is transmitted via the signal line 12 and the spare line is also released. When the ON signal of the contact 2 is input via 14, it is determined that the object is not detected and the wire is not broken.

[0006]

However, in such a conventional device, for example, in the above-mentioned device, when the signal line 12 and the spare line 14 are both disconnected or short-circuited, the signal input section 22 receives the signal. Is OFF for contact 1 and contact 2.
Since the signal and the ON signal are input, there is a problem that the disconnection cannot be detected.

Further, when the conventional one is used, it is necessary to wire the spare line 14 for detecting the disconnection, so that the work load at the time of wiring is increased and the number of terminals is insufficient in the existing terminal block. Therefore, there is also a problem that a work load is applied when applied to the existing equipment. In addition, as a conventional one,
Some of the contacts 1 and 2 use NO (normally open), but in this case as well, if either the signal line 12 or the spare line 14 is disconnected, disconnection cannot be detected. So you will have the same problem as above.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a signal processing device having a disconnection detecting function capable of solving the above conventional problems and reliably detecting the disconnection state.

[0009]

[Means for Solving the Problems] The present invention for achieving the above object is configured as follows. The invention according to claim 1 includes a sensor that detects an environmental condition, and a detection unit that is connected between the sensor and a signal terminal and that includes an impedance adjustment unit that adjusts an impedance viewed from the signal terminal; Pulse signal output means connected to the signal terminal of the detection means via a signal line to output a pulse signal to the sensor, ON / OFF of the sensor from the peak value of the reflected pulse signal from the sensor, and the A signal input means including a determination means for determining disconnection of the signal line,
It is characterized by having.

When a pulse signal having a predetermined crest value is output from the pulse generating means, it reaches the sensor via the signal line and is reflected and returned. The crest value of the pulse that is reflected and returned, that is, the reflected pulse, differs depending on whether the sensor is in the ON state or the OFF state because the impedance of the sensor is different.
Further, at the time of disconnection, the impedance of the detecting means becomes infinite, so that the reflected pulse has a very high peak value. The discriminating means discriminates the peak value of the reflected pulse to recognize the ON state, the OFF state, and the disconnection state of the sensor. As described above, when the state of the sensor and the disconnection of the signal line are determined from the peak value of the reflected pulse, it becomes possible to reliably detect these states.

The invention described in claim 2 is the same as claim 1.
In the invention, the detecting means is attached to a production machine installed on a production site, the discriminating means is attached to a control device for controlling the production machine, and the detecting means and the discriminating means are provided in respective means. It is characterized in that they are connected by two signal lines via two signal terminals provided.

The sensor is turned on and off based on the pulse signal.
When the FF state and the disconnection of the signal line are detected, the number of signal lines connecting the detecting means and the signal input means is two as in the case of connecting a general sensor, and the existing facility is greatly improved. It becomes possible to apply the device of the present invention without increasing (for example, increasing the number of terminal blocks or replacing the existing signal line with two from three).

According to a third aspect of the invention, in the first aspect of the invention, the impedance adjusting means is a variable resistor. By adjusting the resistance value of the variable resistor, it becomes possible to adjust the impedance, which is different depending on the type and length of the signal line, to the optimum value that can be accurately discriminated by the discriminating means. Therefore, it is sufficient to prepare only one type of circuit configuration as the discriminating means, without depending on the difference in the type and length of the signal line.

According to a fourth aspect of the present invention, in the first aspect of the invention, the peak value of the reflected pulse signal is the smallest when the detecting means is operating, and is activated when the detecting means is not operating. It is set to be larger than the peak value when the signal line is running, and is set to be the largest when the signal line is broken. Therefore, the discrimination means can surely discriminate the ON / OFF state of the sensor and the disconnection of the signal line by recognizing the level of the reflected pulse.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a signal processing device having a disconnection detection function according to the present invention.

The sensor 30 comprises a sensing main circuit 32, a switching transistor 34, and an impedance matching resistor 36. The sensor 30 is usually attached to a component of a production machine.
The sensing main circuit 32 outputs a signal when an object approaches, for example. In the present embodiment, a sensor for detecting an object will be described. However, as long as it outputs a signal when sensing, other than that, light is detected, temperature is detected, humidity is detected, and magnetic field is detected. Various things such as those for detecting

The switching transistor 34 is a transistor that is turned on when a signal is output from the sensing main circuit 32.

Impedance matching resistor 36
Is a resistor for adjusting the impedance viewed from the signal terminals 38A and 38B of the sensor 30 to a predetermined resistance value ZL. The disconnection detection by the pulse reflection method seems to be generally used in the field of power transmission and distribution, but the variation in impedance due to the type of transmission line or cable between the power transmitting and receiving ends is not considered. This is because it is possible to detect the presence / absence of a wire break without considering it.

However, in the device of the present invention, in addition to the disconnection of the signal line from the peak value of the reflected pulse, the sensor is turned on and off.
Since it is necessary to be able to detect even the above, it is difficult for the peak value of the reflected pulse to fluctuate due to the difference in the length and type of the signal line. This fluctuation changes the resistance value of the impedance matching resistor 36. It is adjusted by that.

Therefore, the signal terminals 38A, 38 of the sensor 30 are controlled by the impedance matching resistor 36.
If the impedance viewed from B is adjusted to a predetermined resistance value ZL according to the length and type of the signal line, the peak value of the reflected pulse will be a substantially constant level. Therefore, the signal input device does not need to be prepared with a plurality of types of characteristics for each difference such as the distance from the installation location of the sensor and the type of the signal line.
If you prepare only one type, it will be better,
It can be a very versatile device. The signal input device 40 includes a signal input unit 42 and a pulse generation circuit 44.
And a diode 45 and a resistor 4 that reversely block the pulse signal.
6 and 6. This signal input device is usually provided inside a control panel for controlling a production machine and incorporated in a control circuit. Usually, it is installed in the PLC.

Although details of the signal input section 42 will be described later, here, the reflected pulse is input, and the sensor outputs O from the peak value.
N state (whether an object is detected) or the sensor is O
It is detected whether the FF state (whether an object is detected or not) and whether the signal line is broken. It should be noted that the ON / OFF information of the sensor and the disconnection information are separately output.

The pulse generating circuit 44 outputs a pulse having a predetermined crest value at a constant cycle, and the cycle is slightly longer than the time required to analyze the crest value of the reflected pulse at the signal input section 42. It is set. If this is not done, accurate analysis will not be possible.

The peak value Vp of the pulse output from the pulse generating circuit 44 is the power supply voltage Vcc of the signal input device.
It is set higher than. Therefore, in order to prevent the pulse from entering the power supply, the diode 45 and the resistor 4
6 and 6 are provided.

The sensor 30 and the signal input device 40 are respectively provided with two signal terminals 38A, 38B, 48A and 48B, and these terminals are connected by a signal line 50. As shown in the figure, the signal terminals 38A, 38B
When the internal impedance of the sensor 30 as viewed from above is ZL and the transmission impedance of the signal line is Z0, ZL is Z0.
The impedance can be matched by adjusting the impedance matching resistor 36 so as to be equal to.

When it is attempted to apply the device of the present invention to existing equipment, the sensor and the PLC are mostly connected via two signal lines. Therefore, the sensor and the signal input device are connected to this signal line. Need only be connected and the impedance matching resistor 36 is adjusted (calibrated to a predetermined value).

FIG. 2 shows a specific circuit configuration of the signal input section 42 shown in FIG. This signal input section 42
Is composed of a disconnection detection comparator 60, an ON / OFF determination comparator 70, amplification transistors 61 and 71, and pulse holding circuits 62 and 72.

A reflected pulse is input to the disconnection detection comparator 60, and the peak value of this reflected pulse is the reference voltage V.
Compared with p + α. If the peak value of the reflected pulse is larger than the reference voltage Vp + α, the pulse is output from the comparator 60. The peak value of this pulse is amplified by the amplifying transistor 61 by a predetermined factor and held in the pulse holding circuit 62 for a certain period of time. Therefore, the signal line 50
While the disconnection is detected, a voltage of 5V is output from the output terminal of the pulse holding circuit 62.

On the other hand, the ON / OFF judgment comparator 7
The same reflected pulse is also input to 0, and the peak value of this reflected pulse is compared with the reference voltage Vp. If the peak value of the reflected pulse is larger than this reference voltage Vp (sensor OFF
In the case of, or when the signal line is disconnected), a pulse is output from the comparator 70. Conversely, if it is small (when the sensor is ON), no pulse is output. The peak value of this pulse is amplified by the amplifying transistor 71 by a predetermined factor and held in the pulse holding circuit 72 for a certain period of time.
Therefore, while the sensor is OFF, the voltage of 5V is output from the output terminal of the pulse holding circuit 72.

In this way, when the signal is output from the output 1, it can be determined that the signal line 50 is broken,
Further, if the signal is output from the output 2, it can be determined that the sensor 30 is OFF, and if the signal is not output, the sensor 30 is ON.

FIG. 3 is a circuit diagram of the pulse generation circuit 4 shown in FIG.
4 is a diagram showing waveforms of respective parts when a pulse oscillation pulse is output from 4 and then the pulse is reflected and returned. FIG. The operation of the device of the present invention will be described in more detail with reference to this figure.

First, the pulse generation circuit 44 outputs a pulse having a peak value Vp as shown in FIG. 3 at a constant cycle.
This pulse is input to the sensor 30 via the signal line 50, and returns from here as a peak value according to the impedance of the sensor 30.

When the sensor 30 is ON, since the switching transistor 34 is ON, the value of the internal impedance of the sensor 30 is close to zero. On the other hand, when the sensor 30 is OFF, since the switching transistor 34 is OFF, the value of the internal impedance of the sensor 30 is ZL, and normally ZL is adjusted to the transmission impedance Z0 of the signal line 50. As a result, the impedance value becomes Z0.

Therefore, when the sensor 30 is ON, since there is no reflection, the peak value of the reflected pulse is naturally lower than the initial oscillation pulse voltage Vp, and ON / OF
No pulse is output from the F determination comparator 70 (see the waveform in the 3D portion of FIG. 3). Therefore, the pulse holding circuit 7
No signal is output from the output terminal of No. 2 (see the waveform in FIG. 3E).

On the other hand, when the sensor 30 is OFF, the value of the internal impedance of the sensor 30 is Z0, so that the pulse of the peak value in which the reflection pulse and the oscillation pulse are superposed is the ON / OFF judgment comparator. It is input to 70. This pulse is, of course, the original oscillation pulse voltage Vp.
Becomes higher than the ON / OFF judgment comparator 70
Will output a pulse (see waveform in FIG. 3D). Therefore, a signal is output from the output terminal of the pulse holding circuit 72 (see the waveform of the portion E in FIG. 3).

As described above, when the signal is output from the output terminal of the pulse holding circuit 72, it is determined that the sensor is OFF and the object is not detected, and the output of the pulse holding circuit 72 is output. When no signal is output from the terminal, the sensor is ON, and it is determined that an object is being detected.

The reflected pulse is also input to the disconnection detecting comparator 60. Since the comparison voltage of this comparator is Vp + α, the sensor 30 is turned on and off.
No signal is output when the peak value of the reflected pulse changes due to the FF state.

When the signal line 50 is disconnected, the impedance becomes infinite, so the peak value of the reflected pulse becomes very high, and the reflected pulse having a high peak value as shown in FIG. Is input to the disconnection detection comparator 60. This pulse is, as shown in FIG. 3, a reference voltage V
Since it is higher than p + α, a pulse is output from the disconnection detection comparator 60 (refer to the waveform of the portion B in FIG. 3). For this reason, a signal is output from the output terminal of the pulse holding circuit 62 (see the waveform in the portion C of FIG. 3).

As described above, in the signal processing device having the disconnection detection function of the present invention, the ON / OFF state of the sensor and the disconnection state of the signal line can be reliably detected from the peak value of the reflected pulse.

In order to make such detection accurate, it is necessary to make accurate impedance matching. For example, the crest value of the reflected pulse when the sensor is OFF in the state where the signal line is not broken is adjusted to be slightly higher than the value of the reference voltage Vp, and is adjusted not to exceed the value of the reference voltage Vp + α. Keep it.

[0040]

According to the first aspect of the invention, since the ON / OFF state of the sensor and the disconnection of the signal line are discriminated from the peak value of the reflected pulse, the discrimination can be surely performed.

In the invention described in claim 2, since the detecting means and the discriminating means are connected by two signal lines through two signal terminals provided for each means, it is used in the existing equipment. The device of the present invention can be equipped by replacing the existing sensor with the detection means of the device of the present invention.

According to the third aspect of the invention, since the impedance can be adjusted by the variable resistor,
As the determining means, it is sufficient to prepare only one type of circuit configuration without depending on the difference in the type and length of the signal line. Moreover, if the impedance is adjusted to the optimum impedance on a regular basis, it is possible to prevent the determination accuracy from deteriorating due to aging.

In the fourth aspect of the invention, the peak value of the reflected pulse signal is the smallest when the detecting means is operating, and is larger than the peak value when the detecting means is not operating. Since the maximum value is set when the signal line is broken, the discrimination means recognizes the level of the reflected pulse, and the O of the sensor is detected.
The N, OFF state and the disconnection of the signal line can be reliably determined.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a signal processing device according to the present invention.

FIG. 2 is a circuit diagram of a signal input unit of the signal processing device shown in FIG.

3 is a timing chart showing a signal waveform of each part of the signal input part shown in FIG.

FIG. 4 is a schematic configuration diagram of a conventional signal processing device.

[Explanation of symbols]

30 ... Sensor, 32 ... Sensing main circuit, 34 ... Switching transistor, 36 ... Impedance matching resistor, 40 ... Signal input device, 42 ... Signal input section, 44 ... Pulse generating circuit, 50 ... Signal line.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01D 5/00-5/62 G01B 7/00-7/34 G01R 31/02 G08C 25/00

Claims (4)

(57) [Claims] 1. A detection unit including a sensor for detecting an environmental condition and an impedance adjustment unit connected between the sensor and a signal terminal for adjusting an impedance viewed from the signal terminal, and a signal of the detection unit. A pulse signal output means connected to the terminal through a signal line to output a pulse signal to the sensor, ON / OFF of the sensor from the peak value of a reflected pulse signal from the sensor, and disconnection of the signal line A signal processing device having a disconnection detecting function, which comprises: 2. The detecting means is attached to a production machine installed on a production site, the discriminating means is attached to a control device for controlling the production machine, and the detecting means and the discriminating means are respectively provided. The signal processing device having a disconnection detecting function according to claim 1, wherein the signal processing device is connected by two signal lines via two signal terminals provided in each of the two. 3. The signal processing device having a disconnection detecting function according to claim 1, wherein the impedance adjusting means is a variable resistor. 4. The crest value of the reflected pulse signal is the smallest when the detecting means is operating, and is larger than the crest value when the detecting means is not operating, and the signal line is disconnected. The signal processing device having the disconnection detection function according to claim 1, wherein the signal processing device is set to the largest value when the signal processing is performed.