JPH0786522B2 - Contact data reading circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a contact data reading circuit for reading an input by opening and closing a contact such as a limit switch through an isolator.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional example of this type of contact data reading circuit.

The input side of the photocoupler 31 is connected to the contact 1 of the external limit switch via the current limiting resistor 4 and the transmission circuit 3, and the DC current 33 is the power supply for the transmission circuit. The output side is connected to the high power source 12 and the ground 13 via the resistor 32,
The resistor 5 is a load voltage stabilizing resistor. When the contact 1 is opened, the photo coupler 31 is turned off, the potential of the junction point 34 between the resistor 32 and the photo coupler 31 becomes “H” at the logic level, and when the contact 1 is closed, the photo coupler 31 is turned on and joined. Since the potential of the point 34 is "L" at the logic level, the system side (not shown) can know the opening / closing of the contact 1 by the signal (5) indicating the potential of the junction point 34.

[Problems to be solved by the invention]

In the conventional contact data reading circuit described above, the photocoupler 31 is turned off even when the transmission circuit 3 is disconnected on the input side, so that the potential of the junction point 34 is the same as when the contact 1 is opened. Even if the system side reads "H" and the signal ▲ ▼ is read, it cannot be determined whether the contact 1 is open or the transmission circuit 3 is broken.

[Means for solving problems]

The contact data reading circuit of the present invention includes: an AC contact and a diode connected between both terminals thereof; an AC current when the AC contact is closed and an AC current when the AC contact is closed; and a diode when the AC contact is opened. A transmission circuit that conducts a half-wave rectified current in the forward direction via a first electric potential and a first electric potential connected in parallel between the first electric potential and the second electric potential.
And a second resistance-capacitance series circuit, a first photocoupler in which the input side is connected in the forward direction to the transmission circuit in the forward direction, and an output side is connected in parallel to the capacity of the first resistance-capacitance series circuit, and the input side is in the polarity A second photocoupler, which is connected to the transmission circuit in the opposite direction and whose output side is connected in parallel to the capacitance of the second resistance-capacitance series circuit, and the junction point of the resistance and the capacitance of each of the first and second resistance-capacitance series circuits. It has a logic gate that inputs a potential and outputs data indicating the open / closed state of the AC contact or the broken state of the transmission circuit.

[Action]

An AC power supply is used as the power supply for the transmission circuit, and the input sides of the two photocouplers are connected to the transmission circuit in opposite directions, so that when the contacts are in the closed state, the first photocoupler has a half-wave in the forward direction. The rectified current, the half-wave rectified current in the opposite direction to the second photocoupler, continuously flows in to turn on both photocouplers alternately, and when the contacts are in the open state, through the diode installed in parallel with the contacts. Only forward half-wave rectified current is applied to the transmission circuit to periodically turn on only the first photocoupler, and when the transmission circuit is disconnected, both photocouplers are turned off, which corresponds to the above three states. By determining the voltage level of the capacitance of the two resistance capacitance series circuits on the output side via the logic gate,
The system side can recognize the open or closed state of the contact and the occurrence of disconnection of the transmission circuit.

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the contact data reading circuit of the present invention, and FIG. 2 is a time chart for explaining the operation of this embodiment.

A diode 2 is connected in parallel to a contact 1 such as an external limit switch, and the input side of _two photocouplers 7 ₁ and 7 _{2 in} the transmission circuit 3 is forward to the diode 2 respectively. And are connected in the opposite direction. An AC power supply 6 is used as the power supply for the transmission circuit, and the resistors 4 and 5 are the same as those in the circuit of the conventional example described above. Two resistance-capacitance series circuits including the resistance 8 ₁ and the capacity 9 ₁ and the resistance 8 ₂ and the capacity 9 ₂ are connected in parallel with each other between the high-potential power supply 12 and the ground 13. The phototransistor collector of each photocoupler 7 ₁ and 7 ₂ is connected to the junction point 14 of the resistor 8 ₁ and the capacitance 9 _{1 and} the junction point 15 of the resistor 8 ₂ and the capacitance 9 ₂ , respectively, and the emitter is grounded 13 respectively. It is connected to the.
The negative logic OR gate 10 inputs the potentials at the junction points 14 and 15 and outputs a signal ▲ ▼ indicating the open / closed state of the contact 1.
The NAND gate 11 inputs the junction points 14 and 15 and outputs a signal ▲ ▼ which reports the disconnection of the transmission circuit 3.

It is assumed that the two resistance-capacitance series circuits have sufficiently large time constants.

Next, the operation of this embodiment will be described with reference to a time chart.

It is assumed that the current i flowing through the transmission circuit 3 turns from the reverse direction to the forward direction at time t ₀ with the contact 1 closed. Times of Day
photocoupler 7 ₁ If the value of the current i at t ₁ exceeds the lighting threshold input LED included in the photo coupler ₇₁ is turned on, capacitor 9 ₁ charge is rapidly discharged, the potential of the junction point 14 is grounded ( 0
Bolts). At this time (time t ₁ ), since the photocoupler 7 ₂ is in the off state, the capacitance 9 ₂ is charged from the power source 12 via the resistor 8 ₂ and the potential at the junction point 15 is increasing, before that. Since the series circuit of the resistor 8 ₂ and the capacitor 9 ₂ has a large time constant, its rising speed is slow. At time t ₂ , the optocoupler 7 ₁ turns off and charging of the capacitance 9 ₁ is started via the resistor 8 ₁ , and at time t _{3 the} input LED of the optocoupler 7 ₂ has
When the transfer threshold value of reverse current i exceeds, the photocoupler 7 ₂ is rapidly discharged, the potential of the junction 15 becomes the ground potential. At this time (time t ₃ ), the potential of the junction 15 has not risen so much for the reason described above, and the potential of the junction 14 is lower than that. After that, since the same charge and discharge operations of the capacitors 9 ₁ and 9 ₂ are repeated alternately, the potentials at the junction points 14 and 15 are always “L” at the logic input level, and the output signal ON of the negative logic OR gate 10 is at the level “ Holds "L" and reports the closed state of contact 1.

Next, when the contact 1 is opened, a half-wave rectified current flows only in the forward direction through the diode 2, only the photocoupler 7 ₁ is turned on each time, and the photocoupler 7 ₂ remains off. Thus because only capacity 9 ₁ repeats the charging and discharging operations described above, the logic input level of the potential of the junction point 14 is likewise "L", whereas, the logic at the potential of the junction point 15 that is continued to rise Exceeds the input level “H”. After that, the signal ON output from the negative logic OR gate 10 turns to the level "H" to notify that the contact 1 has turned to the open state.

When a disconnection in the transmission circuit 3 occurs not flow a current i to the photocoupler 7 ₁ and 7 _2, thus both the photocoupler 7 ₁ and 7 ₂ is turned off, the junction potential 14 and 15 high potential Continue to a value equal to 12, Nand Gate 11
Outputs a signal ALM of level "L" to notify the occurrence of disconnection.

〔The invention's effect〕

As described above, according to the present invention, a diode is connected in parallel to a contact that opens and closes by an external action, an AC power source is used as a power source of a transmission circuit, and the input sides of two photocouplers are opposite to each other. By connecting the output side in parallel to the capacitance of the resistance-capacitance series circuit, and monitoring the charge / discharge level of the capacitance using a logic gate,
The effect that the open / closed state of the contact or the disconnection state of the transmission circuit can be easily known, and the increased cost for detecting disconnection can be kept low by using the surplus gate in the IC, which is also effective in terms of mounting area. There is.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the contact data reading circuit of the present invention, FIG. 2 is a time chart for explaining the operation of this embodiment, and FIG. 3 is a circuit diagram of a conventional example of the contact data reading circuit. is there. 1 ... contact, 2 ... diode, 3 ... transmission circuit, 4,5 ... resistor, 6 ... AC power supply, 7 ₁ , 7 ₂ ...... photo coupler, 8 ₁ , 8 ₂ ...... resistor, 9 ₁ , 9 ₂ …… Capacity, 10 …… Negative logic OR gate, 11 …… Nand gate, 12 …… High-level power supply, 13 …… Grounding, 14,15 …… Junction point, i …… Current, ALM …… Disconnection signal, ON ...... Open / close signal, t _{0 to} t ₃ …… Time.

Claims (1)

[Claims] 1. An alternating current contact and a diode connected between both terminals of the alternating current contact, which is connected to the alternating current contact and which forwards an alternating current when the alternating current contact is closed and a diode when the alternating current contact is opened. A transmission circuit which conducts a half-wave rectified current in a direction and a first potential connected in parallel between a first potential and a second potential
And a second resistance-capacitance series circuit, a first photocoupler in which the input side is connected in the forward direction to the transmission circuit in the forward direction, and an output side is connected in parallel to the capacity of the first resistance-capacitance series circuit, and the input side is in the polarity A second photocoupler, which is connected to the transmission circuit in the opposite direction and whose output side is connected in parallel to the capacitance of the second resistance-capacitance series circuit, and the junction point of the resistance and the capacitance of each of the first and second resistance-capacitance series circuits. A contact data reading circuit having a logic gate that inputs an electric potential and outputs data indicating an open / closed state of an AC contact or a broken state of a transmission circuit.