JPH1074104A - Input circuit fir controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save power consumption and to reduce the heat generation of an input circuit by reducing current consumption in the input circuit in which plural level judging circuits are connected in parallel between input terminals. SOLUTION: This input module 20 for the input circuit is provided with a sensor state detecting circuit 22 arranged in an energizing route from a DC power source 5 to a sensor 4a and capable of inputting a signal expressing the ON of the sensor 4a to a CPU when voltage between input terminals 20a, 20b is more than threshold voltage corresponding to power voltage and a connection state detecting circuit 24 for inputting a signal expressing the normality of wiring with the sensor to the CPU when the inter-terminal voltage is more than a threshold corresponding to a leak current ILeak allowed to flow through a main circuit in the sensor 4a and constituted so that the CPU detects the disconnection of the energizing route when both outputs from the circuits 22, 24 are low levels. When the circuit 22 judges the ON of the sensor 4a, connection between the circuit 24 and the input terminal 20a is interrupted to suppress a current flowing onto the module 20. Consequently the power consumtion of the module 21 can be saved and heat generation can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an input circuit for inputting a signal from an external device to a control device such as a controller.

[0002]

2. Description of the Related Art Conventionally, as an input circuit for inputting a signal from a sensor or a switch to a control device such as a programmable controller, a plurality of judgment circuits for judging whether a signal level of an input signal is a predetermined value or more are input. 2. Description of the Related Art There is known an input circuit which is connected in parallel to a terminal and inputs a determination result (binary signal) by each determination circuit to a control device (for example, see Japanese Patent Application Laid-Open No. 57-27310).

That is, for example, as shown in FIG. 7, in a programmable controller (hereinafter simply referred to as PC), a DC two-wire sensor (hereinafter simply referred to as “PC”) whose on / off state is switched according to a detection result. (Also called a sensor)
An input module 60 for inputting a detection signal (on / off signal) from the DC 50 supplies a DC (direct current) power 52 to the sensor 5.
0 and a negative input terminal 60a and a negative input terminal 60a which are provided on an energizing path for supplying power to the
b, a sensor state detection circuit 62 for detecting the on / off state of the sensor 50 from the voltage between the terminals, and the connection state of the sensor 50 to the input module 60 from the voltage between the terminals (that is, from the DC power supply 52 to the sensor 50). And a connection state detection circuit 64 for detecting a disconnection of the current supply path).

In the input module 60, the sensor state detection circuit 62 includes input terminals 60a, 60
b, voltage dividing resistors R1 and R2, a light-emitting diode connected in parallel to the resistor R2, and a photocoupler PC1 including a phototransistor that receives light from the light-emitting diode and is turned on. When the phototransistor of the photocoupler PC1 is on, the power supply voltage on the PC side (+5) via the phototransistor
V) to which a signal input resistor R5 is applied.
When the inter-terminal voltage is equal to or higher than a predetermined threshold voltage corresponding to the power supply voltage input from the DC power supply 52 when the sensor 50 is turned on, the light emitting diode of the photocoupler PC1 emits light to turn on the phototransistor; P for resistor R5
When the power supply voltage on the C side is applied and the resistor R5 is connected to the CPU
Operates to input a high level (+5 V) detection signal VPC1.

The connection state detection circuit 64 includes a voltage dividing resistor R connected between the input terminals 60a and 60b.
3, a light-emitting diode connected in parallel with the resistor R4, and a photocoupler PC2 including a phototransistor that receives light from the light-emitting diode and is turned on.
And a signal input resistor R to which a power supply voltage (+5 V) on the PC side is applied via the phototransistor when the phototransistor of the photocoupler PC2 is on.
6. When the inter-terminal voltage is equal to or higher than a predetermined threshold voltage corresponding to the voltage generated by the leakage current ILeak flowing through the current path when the sensor 50 is turned off, the light emitting diode of the photocoupler PC2 emits light. As a result, the phototransistor is turned on, the power supply voltage on the PC side is applied to the resistor R6, and a high level (+5 V) is applied from the resistor R6 to the CPU.
Operates to input the detection signal VPC2.

In FIG. 7, a sensor 50 includes a transistor Tr as a switching element provided in series in an energizing path, a main circuit for turning on / off the transistor Tr in accordance with an operation state of a detection target, and a transistor. Tr and a Zener diode ZD that protects the main circuit from overvoltage. When the transistor Tr is turned off, a leakage current ILeak flows through the conduction path due to the operation of the main circuit. Also, the negative input terminal 60 of the input module 60
b, a current ICircuit flowing between the input terminals 60a and 60b when a DC voltage is applied in the opposite direction between the input terminals 60a and 60b (therefore, the current ICcircuit is applied to the sensor state detection circuit 62 and the connection state detection circuit 64). A backflow prevention diode D1 is provided to prevent the input currents IIN and Iopw) flowing in opposite directions from causing the circuits 62 and 64 to fail.

[0007]

However, as in the PC input module 60 shown in FIG. 7, a plurality of judging circuits are connected in parallel between input terminals, and a signal from each judging circuit is transmitted to the control device. In the input circuit configured to input to the input circuit, since all the determination circuits always operate, the amount of current flowing in the input circuit (in other words, the power consumption in the input circuit) increases,
There is a problem that the input circuit easily generates heat.

That is, in the input module 60 shown in FIG. 7, when the input terminals 60a and 60b are connected to the sensor 50 and the DC power supply 52 via a signal input cable as shown in FIG. The resistors R1 and R2 of the sensor state detection circuit 62, the photocoupler PC1, the backflow prevention diode D1, and the resistors R3 and R4 of the connection state detection circuit 64
The photocoupler PC2 and the backflow prevention diode D1 form an energization path for the sensor 50. In this path, a current IC Circuit determined by each of the resistors R1 to R4 and the internal resistance of the sensor 50 and the signal line is provided.
Flows through the circuits 62 and 64, and the input currents IIN and IOPW corresponding to the shunt ratios determined by the resistance values of the resistors R1 and R2 and the resistance values of the resistors R3 and R4 flow respectively (ICircuit = IIN + Iopw). ).

Therefore, in each of the circuits 62 and 64, the photocouplers PC1 and PC2 respond to the voltage values determined by the input currents IIN and Iopw and the resistance values of the resistors R1 and R2 and R3 and R4. Are turned on and off, and when the sensor 50 is turned off, a low level signal (sensor state detection signal VPC1) is output from the sensor state detection circuit 62 and a high level signal (connection state detection signal VPC2) is output from the connection state detection circuit 64.
) Is generated to notify the CPU that the sensor 50 is off. When the sensor 50 is turned on, a high-level signal is generated from each of the circuits 62 and 64, and the CPU is turned on by the CPU. The input module 60, the sensor 50, and the DC power supply 52
In the case where the cable connecting the cables is disconnected or broken, the outputs from the circuits 62 and 64 are both at the low level, and the CPU can be notified of an abnormality in the cable connection state.

However, such a conventional input module 6
At 0, when the sensor 50 and the DC power supply 52 are normally connected to the input terminals 60a and 60b, regardless of the ON / OFF state of the sensor 50, the sensor state detection circuit 62 and the connection state detection circuit 64 Electric current flows. Therefore, especially when the sensor 50 in which both of the circuits 62 and 64 generate a high level signal is turned on, the input current ICircuit to the input module 60 becomes extremely large.
The power consumption of the input module 60 increases, and the input module 60 is easily overheated.

In order to prevent such overheating of the input circuit, it is conceivable to dispose a plurality of decision circuits constituting the input circuit or to use large components having good heat dissipation. The circuit cannot be miniaturized (high-density mounting). In particular, in PC, it is necessary to take in a large number of signals from sensors and switches, and the input section for taking in these signals is provided with a large number of input circuits such as the above-mentioned input module. However, conventional input circuits tend to generate heat easily, and if the judgment circuits are dispersed and large-sized parts are used to prevent heat generation, the input circuit will be rather large. We cannot meet these demands.

The present invention has been made in view of such a problem. In an input circuit of a control device in which a plurality of determination circuits for determining a signal level are connected in parallel between input terminals as in the above-described input module, the input circuit includes: To reduce power consumption, reduce power consumption, and suppress the amount of heat generated by the input circuit.

[0013]

According to an aspect of the present invention, there is provided an input circuit for a control device, comprising:
A pair of input terminals for inputting a signal from an external device and connected in parallel between the input terminals, and determine whether the voltage between the terminals is equal to or greater than a threshold voltage set to different values, respectively, A plurality of determination circuits for inputting the determination result to the control device, and when there are a plurality of determination circuits having a threshold voltage equal to or lower than the terminal voltage of the input terminal, among the plurality of determination circuits, A determination circuit excluding the determination circuit having the largest threshold voltage; and a signal path blocking unit configured to block connection to the input terminal.

Therefore, according to the input circuit of the present invention, for example, there are three judging circuits connected in parallel between the input terminals, and the voltage between the terminals is equal to or higher than the threshold voltage of each judging circuit. In this case, 3
The connection between the input terminals and the two determination circuits except for the determination circuit having the highest threshold voltage among the determination circuits is cut off, and the terminal-to-terminal voltage is the threshold of the determination circuit having the highest threshold voltage. In the case where the threshold voltage is lower than the threshold voltage and equal to or higher than the threshold voltages of the other two determination circuits, the signal path cutoff means determines which of the two determination circuits has the lower threshold voltage. And the input terminal is disconnected.

That is, in an input circuit in which a plurality of determination circuits are connected to an input terminal, when there are a plurality of determination circuits whose threshold voltages are lower than the inter-terminal voltage, the threshold voltage among them is the largest. Even when the output from the determination circuit is input to the control device, the terminal voltage can be notified to the control device. Therefore, in the present invention, when there are a plurality of determination circuits whose threshold voltage is equal to or lower than the terminal voltage, the connection between the determination circuit except for the determination circuit having the highest threshold voltage and the input terminal is cut off. As a result, the current flowing in the determination circuit whose connection is cut off is reduced to zero, and the amount of current flowing from the input terminal to the input circuit is suppressed.

Therefore, according to the present invention, the power consumption in the input circuit can be reduced without impairing the function as an input circuit for inputting the determination result of the voltage between terminals to the control device.
Heat generation of the input circuit can be suppressed. Further, as described above, according to the present invention, power consumption of the input circuit can be reduced and heat generation can be suppressed, so that high-density mounting of circuit elements in the input circuit can be achieved and the input circuit can be downsized. become.

In the present invention, when the inter-terminal voltage is lower than the threshold voltage of each judgment circuit, there is no judgment circuit for disconnecting the connection with the input terminal, and all the judgment circuits are connected to the input terminals. In this case, the amount of current flowing from the input terminal to each determination circuit is small, and the amount of heat generation is also small. Therefore, in the present invention, even if there is no or a small number of judgment circuits whose connection with the input terminal is cut off by the signal path cutoff means, the power consumed by the entire input circuit does not increase. Power saving of the input circuit can be favorably realized.

Here, as the input circuit of the present invention, for example, by connecting a large number of determination circuits, each having a threshold voltage set at a predetermined resolution, to an input terminal, an analog input voltage from an external device can be applied to each input terminal. The present invention can be applied to an A / D converter for converting a digital value into a digital value at the resolution of the threshold voltage of the determination circuit, or under a predetermined condition using two determination circuits as in the input module shown in FIG. The present invention is also applicable to an input circuit of a switch-type sensor device that detects an on / off state of a sensor device whose on / off state is switched and a connection state between the sensor device and an input terminal.

When an input circuit of such a switch-type sensor device is constructed, for example, a power supply is connected to the input terminal via the sensor device. A plurality of determination circuits for detecting whether the voltage between the input terminals is equal to or higher than a threshold voltage corresponding to the power supply voltage, thereby detecting an on / off state of the sensor device. By determining whether the voltage between the circuit and the terminal is equal to or higher than a threshold voltage lower than the threshold voltage of the sensor state detection circuit corresponding to the current flowing through the sensor device when the sensor device is off, A connection state detection circuit for detecting a connection state between the input terminal and the sensor device, wherein a signal path cutoff means is provided when the sensor state detection circuit detects the ON state of the sensor device; It may be configured to cut off the connection between the connected state detecting circuit.

However, when the ON / OFF state of the sensor device and the connection state between the input terminal and the sensor device are detected by using such an input circuit, the sensor device is provided with the following features. At the time of off, it is necessary to use a device through which a smaller amount of current flows than at the time of on. Therefore, if the sensor device is a DC two-wire sensor as shown in FIG. 7, there is no problem because the leak current flows even when the sensor device is turned off due to the operation of the internal circuit (main circuit). As in the case of a three-wire sensor, if the energization path of the switching element that is turned on and off in the sensor device and the internal circuit (main circuit) that turns on and off the switching element are different, the on / off state of the switching element is changed. When the input circuit is connected to the conduction path of the switching element for detecting the OFF state, it is necessary to partially modify the sensor device so that the current for detecting the connection state flows even when the switching element is OFF.

When the on / off state of the sensor device is detected as described above, if the sensor device is of the AC drive type, an AC power is input to the input terminal via the sensor device. However, in this case, for example, the determination circuit is configured to be able to determine the magnitude of the AC voltage as the threshold voltage, or a signal processing circuit for rectifying and smoothing the voltage between terminals is separately provided, What is necessary is just to input the input voltage from the processing circuit to the determination circuit for determining the DC voltage.

On the other hand, when the input circuit is configured to detect the on / off state of the sensor device and the connection state between the input circuit and the sensor device, respectively, the input circuit may be configured as follows. As described in, the sensor state detection circuit and the connection state detection circuit are connected between a photocoupler including a light emitting element and a light receiving element, respectively, and an input terminal, and a voltage obtained by dividing the voltage between the terminals is used as a light emitting element. A voltage dividing circuit that causes the light emitting element to emit light when the voltage between the terminals is equal to or higher than the threshold voltage, and a determination signal is input to the control device via the light receiving element. Good.

That is, if the input circuit is composed of a photocoupler and a voltage dividing circuit as in the input module shown in FIG. 7, the signal path on the sensor device side connected to the input terminal by the photocoupler, The signal path on the control device side
It is possible to completely cut off the noise and prevent noise or the like input from the sensor device from being input to the control device via the input circuit and causing the control device to malfunction.

The present invention can be applied to any input circuit for inputting a signal from an external device to a control device. In particular, in a programmable controller, a sensor, a switch, etc. When applied to an input circuit that inputs signals from external devices, the power consumption at the input section of the programmable controller can be reduced,
Heat generation at the input unit can be suppressed.

That is, as described above, in a programmable controller, it is necessary to take in many signals from sensors and switches, and an input section for taking in these signals is provided with many input circuits. According to the invention, the power consumption of each input circuit provided in the input unit can be reduced and the heat generation can be suppressed. Therefore, if the present invention is applied to the input circuit of the programmable controller, the power consumption in the input unit can be reduced. It is possible to reduce the heat generation.

Further, according to the present invention, the input circuit can be downsized while suppressing the heat generation of the input circuit. Therefore, if the present invention is applied to a programmable controller, the input section provided with a large number of input circuits can be reduced in size. In addition, the size of the programmable controller can be reduced.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic configuration diagram showing the configuration of a programmable controller (PC) 2 to which the present invention is applied and its peripheral devices.

As shown in FIG. 1, PC C2 of this embodiment is
It is used as a control device of an automation line in a factory, and includes an arithmetic unit 10 composed of a microcomputer mainly including a CPU, and a storage unit 12 in which programs and various data necessary for arithmetic operations in the arithmetic unit 10 are stored. And the digital SW, proximity SW, selector SW, push button SW, and limit SW (although S
W represents a switch) and an input unit 14 for inputting a signal from an operation / detection unit 4, and a display / drive unit including a pilot lamp, a solenoid valve, a numeric display, a motor, and the like arranged on an automation line of a factory. It comprises an output section 16 for outputting a driving signal to the section 6 and a bus line 18 connecting these sections 10 to 16.

Then, in PC2, the operation unit 10
Under the control of (1), the input unit 14 fetches signals from limit SWs, proximity SWs, and the like that constitute the operation / detection unit 4, and the arithmetic unit 10 displays based on the input signals fetched via the input unit 14. Calculate the control amount of each part constituting the drive unit 6 and make the output / output unit 16 output a drive signal corresponding to the calculation result from the output unit 16.

Next, FIG. 2 shows an input module 20 provided in the input section 14 of the PC 2 corresponding to each switch in order to individually take in signals from various switches constituting the operation / detection section 4. Represents the configuration of The input module 20 shown in FIG. 2 receives a signal from a DC two-wire sensor (hereinafter simply referred to as a sensor) 4a constituting a limit switch, a proximity switch, etc., similarly to the conventional input module 60 shown in FIG. It is designed to capture.

As shown in FIG. 2, the input module 20 of this embodiment is provided on an energizing path for supplying power from the DC power supply 5 to the sensor 4a, similarly to the conventional input module 60 shown in FIG. A sensor state detection circuit 22 for detecting the on / off state of the sensor 4a from a terminal voltage between the + input terminal 20a and the-input terminal 20b connected to the current path; And a connection state detection circuit 24 for detecting the connection state of the sensor 4a to the sensor 20.

In the input module 20, the sensor state detecting circuit 22 and the connection state detecting circuit 24
Is configured in exactly the same way as the sensor state detection circuit 62 and the connection state detection circuit 64 shown in FIG. 7, and the difference between the input module 20 and the conventional input module 60 shown in FIG. The input line of the detection signal from the resistor R5 of the circuit 22 to the CPU in the arithmetic section 10 and P
A series circuit of resistors R8 and R9 is connected between the power supply line (+ 5V) on the C2 side (in other words, between the collector and the emitter of the phototransistor constituting the photocoupler PC1). At the connection point of R9,
The base of the PNP transistor TR1 is connected, and this PN
The emitter of the P transistor TR1 is connected to the power line (+5 V) on the PC2 side, and this PNP transistor T
The collector of R1 is connected via a light emitting diode constituting the photocoupler PC3 and a current limiting resistor R7 to P ·
It is grounded to the ground line (0 V) of C2, and a phototransistor constituting the photocoupler PC3 is provided in a signal path between the + input terminal 20a of the input module 20 and the connection state detection circuit 24. .

In the input module 20 of the present embodiment having the above-described configuration, as shown in FIG.
In the case where 0a and 20b are not connected to the sensor 4a and the DC power supply 5 via the signal input cable (unwired), the cable is disconnected, or the cable is disconnected, the input from the sensor 4a side. The current ICi
No rcuit flows in. Therefore, in this case,
The input currents IIN and Iopw of the sensor state detection circuit 22 and the connection state detection circuit 24 become zero,
The outputs VPC1 and VPC2 from the terminals 2 and 24 are both at the low level, similar to the conventional input module 60 shown in FIG.
It is possible to notify the CPU that the cable is not properly connected.

If the sensor 4a is turned off while the input module 20 is normally connected to the sensor 4a and the DC power supply 5 via a cable, the sensor state detecting circuit 22 Resistors R1, R2
Thus, an energization path for the sensor 4a is formed. And
In this case, the input current IIN of the sensor state detection circuit 22 is
Since the current becomes a small current corresponding to the leak current ILeak flowing when the sensor 4a is turned off, the photocoupler PC1 of the sensor state detection circuit 22 is turned off, and the sensor state detection signal VPC1 becomes low level.

On the other hand, if the sensor state detection signal VPC1 is at the low level, the PNP transistor TR1 is turned on, and a current flows through the light emitting diode of the photocoupler PC3 to turn on the photodiode. A current corresponding to the leak current ILeak also flows through the resistors R3 and R4. Then, the connection state detection circuit 24
In this case, the photocoupler PC2 is turned on by a very small current corresponding to the leak current ILeak.
PC2 becomes High level.

As a result, the input module 20 of this embodiment
When the sensor 4a is in the off state, the output (sensor state detection signal) VPC1 from the sensor state detection circuit 22 is at a low level, and the output (connection state detection signal) VPC2 from the connection state detection circuit 24 is at a high level. Level, and as with the conventional input module 60 shown in FIG.
The PU side can be notified that the sensor 4a is off.

Next, when the sensor 4a is turned on while the input module 20 is normally connected to the sensor 4a and the DC power supply 5 via a cable, D
Since the output voltage from the C power supply 5 is applied almost as it is between the input terminals 20a and 20b, the input current IIN of the sensor state detection circuit 22 becomes a large current due to this voltage, and the sensor state detection signal VPC1 becomes As in the case of the conventional input module 60 shown in FIG.

However, when the sensor state detection signal VPC1 is high.
When the sensor 4a is turned on, the PNP transistor TR1 is turned off, no current flows through the light emitting diode of the photocoupler PC3, and the photocoupler PC3 (specifically, the phototransistor) is turned off. The connection between the circuit 24 and the + input terminal 20a is cut off, and the resistors R3, R
4, no current flows, and the operation of the connection state detection circuit 24 is stopped.

As a result, the input module 20 of this embodiment
When the sensor 4a is in the ON state, the output (sensor state detection signal) VPC1 from the sensor state detection circuit 22 is at a high level, and the output (connection state detection signal) VPC2 from the connection state detection circuit 24 is at a low level. Level.

In this case, the input signals VPC1, VP to the CPU are
Although C2 is different from the conventional input module 60 shown in FIG. 7, on the CPU side, when the sensor state detection signal VPC1 from the sensor state detection circuit 22 is at the high level, the sensor 4a is in the on state, Since it can be determined that the connection state between the module 20, the sensor 4a, and the DC power supply 5 is normal, the control operation on the arithmetic unit 10 side is not adversely affected, and the PC 2 can operate normally.

In this case, the connection state detection circuit 24
Is disconnected from the + input terminal 20a and the connection state detection circuit 2
4, the input current Iopw becomes zero. For example, if the resistance ratio between the resistor R1 in the sensor state detection circuit 22 and the resistor R3 in the connection state detection circuit 24 is 1: 1, The current I Circuit flowing through the module 20 is approximately half (50) of the conventional input module 60 shown in FIG.
%). That is, in the present embodiment, in the conventional input module 60, the current that flows through the connection state detection circuit 64 when the sensor 50 is turned on and is hatched in FIG.
Circuit is reduced.

Therefore, according to the present embodiment, the power consumption of the input module 20 can be reduced, and the heat generation of the input module 20 can be suppressed. In addition, since the power consumption of the input module 20 can be reduced and the heat generation thereof can be suppressed, the circuit elements constituting the input module 20 can be mounted at a high density, and the input module 20 and, consequently, the PC2 can be mounted. It is also possible to reduce the size.

Here, in the above embodiment, when the output voltage of the DC power supply 5 is applied to the input terminals 20a, 20b substantially as it is while the sensor 4a is on, the photocoupler PC
1, only the sensor state detection circuit 22 having a high threshold when the PC2 is turned on is operated, and the connection state detection circuit 24
A signal path cutoff circuit including a PNP transistor TR1, a photocoupler PC3, and resistors R7 to R9 is used as a signal path cutoff means for cutting off the connection with the side input terminal 20a. When the output (sensor state detection signal) is at the high level, the connection state detection circuit 24 and the + side input terminal 20a
It was configured to cut off the connection with

However, in order to realize such a function as the signal path cutoff means, it is not always necessary to use the output from the sensor state detection circuit 22.
a, 20b according to the voltage between the terminals.
4 and the input terminal 20a (or 20b) may be disconnected.

Hereinafter, based on the inter-terminal voltage of the input terminals, the connection state detecting circuit 24 and the + input terminal (or-
An input module configured to cut off connection with the input terminal will be described with reference to FIGS. First, similarly to the input module 20 of the above embodiment, the input module 30 shown in FIG. 4 is provided on an energizing path for supplying power from the DC power supply 5 to the sensor 4a, and the + input terminal 30a connected to the energizing path. A sensor state detection circuit 32 for detecting the on / off state of the sensor 4a from a voltage between terminals between the input terminal 30b and the negative input terminal 30b, and a connection state of the sensor 4a to the input module 30 from the voltage between the terminals. And a connection state detection circuit 34.

In the input module 30, the sensor state detection circuit 32 and the connection state detection circuit 34
Is configured in exactly the same way as the sensor state detection circuit 22 and the connection state detection circuit 24 of the above-described embodiment. The difference from the input module 20 of the above-described embodiment is that the output from the sensor state detection circuit 22 is at a high level. At one time, a PNP transistor TR1 and a photocoupler PC for cutting off the connection between the connection state detection circuit 24 and the + side input terminal 20a.
3 and resistors R11 to R15 and a PNP transistor TR11 provided between input terminals 30a and 30b, a connection state detection circuit 34, and a + side input terminal 30a, instead of an energization path cutoff circuit including resistors R7 to R9. This is the point that an energization path cutoff circuit composed of a PNP transistor TR12 provided between the circuit and the PNP transistor TR12 is provided.

That is, in the input module 30 of FIG. 4, the resistors R11 and R12 are connected between the input terminals 30a and 30b via the diode D1, and the connection point of the resistors R11 and R12 is connected to the PNP. The base of the transistor TR11 is connected. The emitter of the PNP transistor TR11 is connected to the + input terminal 30a, and the collector is connected to the resistor R13 and the diode D1.
Is connected to the negative input terminal 30b.

The collector is connected between the connection state detecting circuit 34 and the + input terminal 30a.
4, the emitter is connected to the + input terminal 30a, respectively, and the base is connected to the PNP transistor TR11 and the resistor R.
13 is provided with a PNP transistor TR12 which is connected via a resistor R14 to a connection point with the input terminal 13 and connected to a + input terminal 30a via a resistor R15.

In the input module 30 of FIG. 4 configured as described above, if the PNP transistor TR11 is off, the PNP transistor TR12 is turned on, and the connection state detection circuit 34 and the + input terminal 30a are connected. Connected, if the PNP transistor TR11 is on, the PNP transistor TR12 is off,
The connection between the connection state detection circuit 34 and the + input terminal 30a is cut off.

Since the base of the PNP transistor TR11 is connected to the connection point between the resistors R11 and R12, the threshold voltage between the terminals is such that the output VPC1 of the sensor state detection circuit 32 becomes high. When the voltage is equal to or higher than a predetermined voltage near the value voltage, the PNP transistor TR
11 are turned on so that each of the resistors R11, R12
Is set.

That is, the PNP transistor TR11 is turned on only when its base-emitter voltage VBE
(In other words, when the voltage across the resistor R11) becomes equal to or higher than a predetermined voltage of about 0.7 V, the sensor 4a is turned on in the input module 30 of FIG. When the output of the circuit 32 is at the high level, the resistance values of the resistors R11 and R12 are set such that the voltage across the resistor R11 is also equal to or higher than the voltage at which the PNP transistor TR11 is turned on. For example, when the lower limit of the inter-terminal voltage Vin at which the output of the sensor state detection circuit 32 becomes High level is 5 V, and the lower limit of the DC power supply 5 is 10 V, the lower limit of the inter-terminal voltage Vin required for the PNP transistor TR11 to be turned on. Is set to 7V, P
VBE at which the NP transistor TR11 is turned on is -1.
Assuming that the forward voltage V.sub.F of the diode D1 is 1 V, the voltage across the resistors R11 and R12 is 6V (= 7V).
−VF), the resistance ratio of R11 and R12 is set to R11: R11 so that the PNP transistor TR11 is turned on.
R12 may be set to 1: 5.

As a result, in the input module 30 of FIG. 4, the signal VPC1 is output without using the output (sensor state detection signal) VPC1 from the sensor state detection circuit 32.
When it is at the high level, the input current Iopw can be prevented from flowing through the connection state detection circuit 34, and the same effect as the input module 20 of FIG. 2 can be obtained.

On the other hand, the input module 40 shown in FIG.
Input module 2 of the above embodiment shown in FIG. 2 or FIG.
Like 0 and 30, the DC power supply 5 is provided on an energizing path for supplying power to the sensor 4a, and a voltage between terminals between the + side input terminal 40a and the − side input terminal 40b connected to the energizing path. It is composed of two determination circuits: a sensor state detection circuit 42 for detecting the on / off state of the sensor 4a, and a connection state detection circuit 44 for detecting the connection state of the sensor 4a to the input module 30 from the voltage between its terminals. Is done.

In the input module 40, the sensor state detection circuit 42 and the connection state detection circuit 44
Is configured in exactly the same way as the sensor state detection circuit 22 and the connection state detection circuit 24 shown in FIG. 2, and is different from the input module 20 shown in FIG. 2 in that the output from the sensor state detection circuit 22 is high. When the level is at the level, the connection between the connection state detection circuit 24 and the + input terminal 20a is cut off.
And a resistor R2 provided between the input terminals 40a and 40b instead of the current path cutoff circuit including the resistors R7 to R9.
1 to R25 and an NPN transistor TR21, and an energization path cutoff circuit including an NPN transistor TR22 provided between the connection state detection circuit 44 and the negative input terminal 40b.

That is, in the input module 40 of FIG. 5, the resistors R21 and R22 are connected between the input terminals 40a and 40b via the diode D1, and the connection point of the resistors R21 and R22 is connected to the NPN. The base of the transistor TR21 is connected. The collector of the NPN transistor TR21 is connected to the +
Side input terminal 40a and a resistor R24,
-Side input terminal 40b via R25 and diode D1
, And the emitter of the NPN transistor TR21 is connected to the negative input terminal 40b via the diode D1.

The collector is connected between the connection state detecting circuit 44 and the negative input terminal 40b.
4, an NPN transistor TR22 having an emitter connected to the negative input terminal 40b and a base connected to a connection point between the resistor R24 and the resistor R25.

In the input module 40 of FIG. 5 configured as described above, if the NPN transistor TR21 is off, the NPN transistor TR22 is turned on, and the connection state detection circuit 44 and the negative input terminal 40b are connected. Connected, if the NPN transistor TR21 is on, the NPN transistor TR22 is off,
The connection between the connection state detection circuit 44 and the negative input terminal 40b is cut off. Since the base of the NPN transistor TR21 is connected to the connection point between the resistors R21 and R22, the inter-terminal voltage Vin becomes close to the threshold voltage at which the output VPC1 of the sensor state detection circuit 42 becomes high. NPN transistor TR
Each resistor R21, R22 is turned on so that the resistor 21 is turned on.
Is set.

As a result, in the input module 40 shown in FIG. 5, similarly to the input module 30 shown in FIG. 4, the output (sensor state detection signal) VPC1 from the sensor state detection circuit 42 is obtained.
When the signal VPC1 is at the high level, the input current Iopw can be prevented from flowing through the connection state detection circuit 34, and the same effect as the input module 20 of FIG. 2 can be obtained.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various embodiments can be adopted. For example, in the above-described embodiment, a case has been described in which the signal from the DC two-wire sensor 4a is taken into the PC2 using the input module 20 (30, 40). The input module 20 (30, 40) described in the above embodiment can also be used as it is when capturing the signal from the expression sensor 4b.

However, in this case, as shown in FIG. 6, the input module 20 (30, 40) is not arranged on the power supply path from the DC power supply 5 to the main circuit of the DC three-wire sensor 4b. Since the power supply 5 is arranged on a conduction path from the power supply 5 to a switching element (transistor Tr in the figure) which is turned on / off by the main circuit, when the transistor Tr is turned off, the conduction path is completely cut off and the input module 20 ( 30, 40), the current for detecting the connection state may not flow.

Therefore, in such a case, in order to allow a current for detecting the connection state to flow, the transistor T of the sensor 4b is used.
r, a leakage resistor Ro for flowing a leakage current is provided in parallel with the input module 2 even when the transistor Tr is turned off.
It is necessary to allow a current for connection state detection to flow at 0 (30, 40). The direct current three-wire sensor 4b shown in FIG. 6 has a reverse current preventing diode Do for regulating the direction of current flowing from the DC power supply 5 into the sensor 4b so that no reverse current flows. Is provided.

Further, in the above embodiment, the case where the input circuit of the present invention is applied to the input module of P · C2 has been described. However, the present invention relates to an input circuit of a signal to a control device other than P · C2. It can also be applied to Also,
In the above embodiment, the ON / OFF state of the sensor device whose ON / OFF state changes, such as the proximity SW and the limit SW, is determined as the determination circuit.
The input circuit provided with two determination circuits, a sensor state detection circuit for detecting an OFF state and a connection state detection circuit for detecting a disconnection of a cable or the like, has been described. A large number of determination circuits are connected in parallel between input terminals. Even with such an input circuit, the present invention can be applied to reduce the power consumption of the input circuit.

[Brief description of the drawings]

FIG. 1 shows a programmable controller (P
FIG. 3C is a schematic configuration diagram illustrating the configuration of peripheral devices.

FIG. 2 is an electric circuit diagram showing a first configuration example of a PC input module to which the present invention is applied.

FIG. 3 is a time chart for explaining the operation of the input module of FIG. 2;

FIG. 4 is an electric circuit diagram illustrating a second configuration example of the PC input module to which the present invention is applied.

FIG. 5 is an electric circuit diagram illustrating a third configuration example of the PC input module to which the present invention is applied.

FIG. 6 is an explanatory diagram illustrating a configuration of a DC three-wire sensor and a connection state of an input module to the DC three-wire sensor.

FIG. 7 is an electric circuit diagram illustrating a configuration example of a conventional PC input module.

FIG. 8 is a time chart for explaining the operation of the input module of FIG. 7;

[Explanation of symbols]

2 ... PC (programmable controller) 4 ...
Operation / detection unit 4a: Sensor (DC 2-wire sensor) 5: DC power supply
6 display / drive unit 10 arithmetic unit 12 storage unit 14 input unit 1
6 Output unit 18 Bus line 20, 30, 40 Input module 20a, 30a, 40a + input terminal 20b, 30b, 40b-negative input terminal 22, 32, 42 Sensor state detection circuit 24, 34 44 Connection state detection circuit PC1, PC2, PC3 Photocoupler R1-R9, R11-R15, R21-R25 Resistor TR1, TR11, TR12 PNP transistor TR21, TR22 NPN transistor 4b Sensor (DC 3-wire type) Sensor) Ro… Leak resistance

Claims (4)

[Claims] 1. A pair of input terminals for inputting a signal from an external device, connected in parallel between the input terminals, and determining whether or not the voltage between the terminals is equal to or higher than a threshold voltage set to a different value from each other. A plurality of determination circuits for making respective determinations and inputting the result of the determination to the control device, wherein in the input circuit of the control device comprising: a plurality of determination circuits in which the threshold voltage is equal to or less than the inter-terminal voltage. An input circuit of a control device, comprising: a determination circuit excluding the determination circuit having the largest threshold voltage among the plurality of determination circuits; and a signal path interrupting unit for interrupting connection with the input terminal. . 2. An on / off state is switched to the input terminal under a predetermined condition as the external device, and a power supply is connected to the input terminal via a sensor device capable of supplying a smaller current than the on state when the device is off. A sensor state detection circuit that detects an on / off state of the sensor device by determining whether the inter-terminal voltage is equal to or higher than a threshold voltage corresponding to a power supply voltage; By determining whether or not the inter-terminal voltage is equal to or higher than a threshold voltage lower than a threshold voltage of the sensor state detection circuit corresponding to a current flowing through the sensor device when the sensor device is off. A connection state detection circuit for detecting a connection state between the input terminal and the sensor device, wherein the signal path cutoff means is configured to detect the connection state of the sensor device by the sensor state detection circuit. When the down state is detected, the input circuit of the control device according to claim 1, characterized in that interrupting the connection between the input terminal and the connection status detection circuit. 3. The sensor state detection circuit and the connection state detection circuit are connected between the input terminal and a photocoupler including a light emitting element and a light receiving element, respectively, and a voltage obtained by dividing the voltage between the terminals is provided. A voltage dividing circuit that, when applied to the light emitting element, causes the light emitting element to emit light when the voltage between the terminals is equal to or higher than the threshold voltage, and inputs a detection signal to a control device via the light receiving element. The input circuit of the control device according to claim 2, wherein 4. The control device according to claim 1, wherein the control device is a programmable controller that executes a predetermined control operation according to a preset program in response to an input from the external device. An input circuit of the control device according to any one of the above.