JP3207324B2 - Contact state detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact state detecting circuit, and more particularly to a contact state detecting circuit for taking in a contact state from a contact information output device constituted by a relay circuit or the like at a digital signal level.

[0002]

2. Description of the Related Art In recent years, due to demands for decentralized processing, networking, and the like, the objects of monitoring and control by a monitoring and control device have become increasingly widespread. Among them, monitoring of contact information using relays has occupied a greater weight than ever, and simplification of the circuit for capturing the contact state as digital information will greatly contribute to lowering the price of equipment. is there.

FIG. 4 shows an example of a circuit configuration of a conventional contact state detection circuit. In FIG. 4, the contact information output device 13 has a large number of relay contacts 14, which are connected 1: 1 with each contact state detection circuit 3 in the monitoring and control device. Here, each of the contact state detection circuits 3
Are all the same circuit, so the description will be made focusing on one circuit.

The contact status from the contact information output device 13 provided to the input terminal 11 of the monitoring device is determined by the contact information output device 1.
When the relay contact 14 disposed in the relay contact 3 is open, it is given to the digital control section 1 as logic "H" logic data, and when the relay contact is short-circuited, it is given as logic "L" logic data. That is, when the contacts are opened, the power supply voltage +12 V appears at the input terminal 11 of the monitoring device via the power supply ON / OFF transistor (Tr) 4, the analog switch (SW) 18, and the resistor (R 3) 6. The voltage is divided by the resistors (R1, R2) 8 and 9 to a logic voltage of + 5V. Then, the digital control unit 1 recognizes the logic voltage as logic "H" data. The power supply ON / OFF transistor 4 is always on during detection of the contact state. Further, a filter circuit (filter) 2 at the input stage in the digital control unit 1
Has a so-called Schmitt-type input determination threshold, which prevents erroneous determination of the input logic level. As described above, the contact state detection circuit 3 at the time of contact opening is in a so-called steady state without dynamically changing.

Next, the operation when the contact is short-circuited will be described.
In this case, when the relay contact 14 in the contact information output device 13 is closed, 0V is applied to the input terminal 11 of the monitoring device. Therefore, a power supply ON / OFF transistor 4-an analog switch 18-a resistor 6-an input terminal 11-a cable 12-a contact relay in the contact information output device 13 (R
L) A current of (+12 V / R3) flows through the path of 14.
Since the potential seen at the input terminal 11 of the monitoring device is 0 V as described above except for the voltage drop due to the cable 12, the voltage (0 V) divided by the bleeder resistors 8 and 9 is logic "L". Is given to the digital control unit 1.

At this time, the data of the logic "L" is also given to the Schmitt type inverter circuit 17, so that the inverter circuit 17 inverts and opens the analog switch 18. As a result, the short-circuited resistor (R4) 5 is connected in series to the resistor 3, and a current flows through the path I2 shown in FIG. Therefore, the current at the start of power supply decreases due to the increase in the resistance value of the resistor 5, and the current value is controlled to (+ 12V / (R3 + R4)). Note that the capacitor (C) 16 is connected to each of the above-mentioned resistors and C
This is to constitute an R time constant circuit and to give a certain time delay to the switching of the analog switch 18.

FIG. 5 shows an example of an operation waveform of the conventional circuit of FIG. 4 described above, and FIG. 6 shows a more detailed enlarged view of the supply current waveform shown in FIG. . The reason for switching the power supply current described with reference to FIG. 4 will be described with reference to FIGS. 5 and 6. As shown in FIGS. 5 and 6, immediately after the short-circuit, a large current ( +12 V / R3: about several mA to about several tens mA). This is because such contacts are screened in consideration of the case where an oxide film is present on the relay contacts due to non-use or the like. In contrast, FIG.
And during the subsequent stable operation of the relay shown in FIG.
From the viewpoint of reducing the power consumption of the monitoring device, the current is switched to a small current for a stable operation after a certain time (+12 V / (R3 + R4)).

[0008]

However, in the above-mentioned conventional contact state detection circuit, an analog switch circuit is used to control the switching of the supply current, and the cost and implementation of the detection circuit per one contact point are increased. There was a problem that the area became large. In particular, there is a problem in the case where a large number of contacts of 32 bits or 64 bits are accommodated on one printed circuit board, and the number of the contact state detection circuits is mounted by the number.

In view of the above problems, an object of the present invention is to provide a contact state detection circuit having a circuit configuration having the above-described relay contact screening function and as simple as possible. As a result, it is intended to simultaneously reduce the package cost and mount a large-scale circuit.

[0010]

According to the present invention, a contact state detecting circuit for detecting the contact state of an externally connected contact information output device and providing the digital contact information to a digital control section is provided by: Is connected to one potential of a power supply, the other terminal is connected to the contact information output device, and a first resistor for supplying power to the contact information output device according to opening and closing of the contact of the contact information output device. A resistor circuit comprising a series connection of a circuit and a second resistor circuit; one terminal is connected to an interconnection point between the first resistor circuit and the second resistor circuit of the resistor circuit, and the other terminal is connected to the power supply. A capacitor circuit connected to the other potential; and for comparing a potential at an interconnection point between the second resistance circuit of the resistance circuit and the contact information output device with a predetermined threshold value to convert the contact point into digital contact information. It is given by the potential conversion circuit for performing position conversion.

According to the present invention, the second resistor circuit comprises a plurality of resistors arranged in parallel, one end of which is multi-connected, and the other end of which is selectively connected. By doing so, the contact schooling current value can be variably set. Further, a power supply switch circuit is provided between the power supply and the first resistance circuit, for controlling start / stop of power supply by the power supply.

[0012]

According to the present invention, the capacitor circuit is charged to the power supply potential until the contact of the contact information output device is short-circuited. Therefore, immediately after the start of the contact short-circuit, a large screening current limited by only the second resistance circuit flows. Thereafter, the potential of the capacitor circuit is reduced by the discharge of the capacitor circuit, and finally, the current during the stable operation is reduced by the series connection of the first resistor circuit and the second resistor circuit.

In the conventional detecting circuit, the schooling current immediately after the short circuit can only flow a constant current irrespective of the state of the relay contact, because the resistor (R3) of the detecting circuit is fixed. Since the film generation rate is related to the operation frequency of the relay contact (the film generation rate is small when the number of operations is large, and the film generation rate is large when the number of operations is small). The power consumption can be reduced and the reliability of the contact operation can be improved at the same time by making the value of the switch selectable according to the number of operations.

[0014]

FIG. 1 is a circuit diagram showing an embodiment of a contact state detecting circuit according to the present invention. In FIG. 1, the same components as those of the conventional circuit of FIG. 4 described above are denoted by the same reference numerals, and will not be described again here. Regarding the operation at the time of contact opening, the capacitor (C
h) Except that 10 is charged to the +12 V power supply voltage, it is the same as the conventional circuit of FIG. 4 described above, and the description thereof is omitted here.

Next, the operation when the contact is short-circuited will be described. Since the capacitor 10 functions as a +12 V battery when the contact is short-circuited, it is the resistance that limits the supply current flowing to the relay contact (RL) 14 immediately after the contact short-circuit. Vessel (R3) 6 only. Therefore, immediately after the start of power supply, a large screening current (I1) whose peak current is given by (+12 V / R3) flows. Eventually, the voltage of the capacitor 10 gradually decreases due to the discharging action of the charge, and on the contrary, a voltage difference between the voltage and the power supply voltage +12 V is applied to both ends of the resistor (R 4) 5. The current I2 flows. And finally (+
It converges to the current at the time of stable operation given by 12V / (R3 + R4)). Since the maximum value of the schooling current changes according to the value of the resistor 6 as described above, FIG.
Can be easily switched by the connection setting terminal 7 shown in FIG. The potential applied to the input terminal 11 is 0 V
In the digital control unit 1, resistors (R1, R1
2) Recognize it as logic "L" data via 8 and 9.

FIG. 2 shows an example of an operation waveform of the contact state detecting circuit of FIG. 1 described above. And FIG.
3 is a drawing in which the current waveform of FIG. 2 is enlarged in detail. As shown in the first and second stages of FIG. 2B, when the contacts are opened, no power supply current flows, so that no dynamic operation occurs in the contact state detection circuit 3 and the circuit is in a steady state. During this time, the digital control unit 1 detects a logic "H" as shown in FIG.

Next, as shown in the middle part of FIG. 2B and FIG. 3, when the contact is short-circuited, the capacitor (C
h) In 10, a voltage of +12 V is charged immediately after the contact is short-circuited, and the potential of the input terminal T becomes 0 V at the same time when the relay contact 14 is short-circuited.
-VcEXP (t / T) / R4 [T: Ch * R
3] flows. At this time, the peak value (+12 V / R3) of the current can be changed by switching the resistance value of the resistor (R3) 6 using the setting terminal 7 as shown in FIG. Then, due to the convergence of the discharge of the capacitor Ch, the power supply current becomes (+12 V / (R3 +
R4)) is stabilized.

[0018]

As described above, according to the present invention, it is possible to realize the same function with a simplified circuit without impairing the screening function of the conventional circuit. According to the present invention, large-scale mounting of the contact state detection circuit and cost reduction are achieved at the same time, which greatly contributes to improvement in reliability and cost reduction of the monitoring device itself.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a contact state detection circuit according to the present invention.

FIG. 2 is an operation waveform diagram showing an example of an operation waveform of the circuit of FIG. 1;

FIG. 3 is an enlarged view of the power supply current waveform shown in FIG. 2 in further detail;

FIG. 4 is a circuit diagram showing a configuration example of a conventional contact state detection circuit.

5 is an operation waveform diagram showing an example of operation waveforms of the conventional circuit of FIG.

FIG. 6 is an enlarged view of the power supply current waveform shown in FIG. 5 in further detail;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Digital control part 3 ... Contact state detection circuit 4 ... Power supply ON / OFF control transistor 7 ... Setting terminal 13 ... Contact information output device 14 ... Contact

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 31/02

Claims (3)

(57) [Claims] A contact state detecting circuit for detecting a contact state of an externally connected contact information output device and providing the digital contact information to a digital control unit, one terminal of which is connected to one potential of a power supply, The other terminal is connected to the contact information output device, and a series connection of a first resistance circuit and a second resistance circuit for supplying power to the contact information output device according to opening and closing of the contact of the contact information output device. A capacitor circuit having one terminal connected to an interconnection point between the first resistor circuit and the second resistor circuit of the resistor circuit, and the other terminal connected to the other potential of the power supply; And a potential conversion circuit that performs a potential conversion to compare a potential of an interconnection point between the second resistance circuit of the resistance circuit and the contact information output device with a predetermined threshold value in order to convert the potential to digital contact information. Contact status detecting circuit, characterized in that formed. 2. The contact schooling according to claim 2, wherein said second resistance circuit is composed of a plurality of resistors arranged in parallel, and one end thereof is multi-connected, and the other end thereof is appropriately connected selectively. 2. The current value can be variably set.
The contact state detection circuit as described. 3. The contact state detection circuit according to claim 1, further comprising a power supply switch circuit for controlling start / stop of power supply by said power supply between said power supply and said first resistance circuit.