JPH05227002A - Two-wire electronic switch - Google Patents

Abstract

PURPOSE:To increase current allowed to flow into a display lamp in stages correspondingly to a load current when a two-wire electronic switch is ON. CONSTITUTION:The two-wire electronic switch is provided with an output circuit 22 for opening/closing between the terminals 1, 2 of the switch in accordance with an output from a sensor circuit 5 and a display current control circuit 23 for detecting an output current outputted from the circuit 22 and controlling the display current. The circuit 23 detects the output current flowing from the circuit 22 and controls current flowing into light emitting diodes D1, D2 connected to a display circuit 21 in accordance with the output current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a two-wire photoelectric switch,
The present invention relates to an electronic switch such as a proximity switch, and more particularly to a two-wire type electronic switch characterized by its operation display.

[0002]

2. Description of the Related Art A conventional two-wire type electronic switch, for example, a direct current two-wire type proximity switch, has a pair of terminals connected in series with a load and a power source. The switch operation is performed by opening and closing the output switching element. In such a DC 2-wire proximity switch, when the output switching element is open,
Small leakage current, for example 1mA, to prevent load current
It is necessary to operate the internal circuit with a certain amount of current.
Also, when the electronic switch is on, the load is, for example, 3 mA to 100
The load current in the mA range is applied.

FIG. 7 is a diagram showing an example of a conventional DC two-wire type electronic switch, and is a circuit diagram showing in detail an output circuit and a display circuit portion. In the figure, a DC power supply 3 and a load 4 are connected in series to terminals 1 and 2. And terminals 1 and 2
A sensor circuit 5 is connected between them as shown. If the sensor circuit 5 is, for example, a high-frequency oscillation type proximity switch, it includes an oscillation circuit, a comparison circuit for comparing its amplitude with a predetermined value, a signal processing circuit, and the like. Then, the object detection signal is given to the display circuit 6 from the output terminal 5a. In the display circuit 6, a resistor R1, a light emitting diode D1, a transistor Q1, and a resistor R2 are connected in series between terminals 1 and 2, and the emitter and base of the transistor Q2 are connected to both ends of the resistor R1. The collector end of the transistor Q2 is connected to the base of the transistor Q3 of the output circuit 7 as shown in the figure,
It is also grounded via a resistor R3. The transistor Q3 is a switching element for opening and closing the output, which short-circuits the terminals 1 and 2.

If the sensor circuit 5 does not detect an object, its output terminal 5a is at L level and the transistors Q1 to Q
3 is in the off state. At this time, the sensor circuit 5 operates by the voltage applied between the terminals 1 and 2, and the load current I _L matches the current consumption I ₁ of the sensor circuit 5.

When the sensor circuit 5 is turned on, the transistor Q1 is turned on and the display current I ₂ flows. The voltage drop across the resistor R1 drives the transistor Q2 at the voltage V _BE.
When (≈0.6V) is reached, the collector current of the transistor Q2 flows, the transistor Q3 turns on, and the current I ₃ flows. The output residual voltage V _{O at} this time is expressed by the following equation. Given by _{V O = V BE (Q2)} + V F (D1) + V CE (Q1) + I 2 R2 display current I ₂ is _{I 2 = V BE (Q2)} / R1 + I B (Q2) ≒ V BE (Q2) / R1 Be done. Therefore, the residual voltage V _O is V _O = V _BE (Q2) · (R1 + R2) / R1 + V _F (D1) + V _CE (Q1). Here, it is necessary to set the resistor R1 so that the display current I ₂ has a sufficiently recognizable current value, for example, 2 mA even when the light emitting diode D1 is darkly lit. For example R1
Resistance value of 0.6V / 2mA = 300Ω.

[0006]

At this time, if the load current of the DC two-wire type electronic switch is 3 mA to 100 mA, the load current I _L is the consumption current I ₁ of the sensor circuit 5, the display current I ₂ ,
It is the sum of the output circuit drive current I ₃ . Since the maximum current consumption of the sensor circuit 5 is generally 1 mA, the load current I _L is 3
In the case of mA, the display current I ₂ needs to be kept within ₂ mA or less within a range where sufficient brightness can be secured. However, when the load current I _L is used at 10 mA, for example, the display current is set to 2
It is not necessary to limit it to mA or less.

In the proximity switch, as shown in FIG. 8, 100-80% of the rated detection distance is an unstable detection area, so that red light is displayed, and 80-0% is a stable detection area, which is green display. Often lights are turned on. In addition, the red color is used as the operation display, and any of 0 to 100% is lit up to 80 to 0%.
There is also a two-wire electronic switch that turns on the red and green indicators at the same time. Thus, when the display element for stable operation display is used in addition to the operation indicator lamp, the green light emitting diode is often used for stable display. However, if the minimum value of the load current is 3 mA, the indicator lamp for the operation display and the stable operation indicator can only supply a current of about 2 mA. In particular, in the case of a green light emitting diode, if the current value is small, it is dark and sufficient display cannot be performed.

As described above, in the conventional two-wire type electronic switch, the sum of the current supplied to the indicator lamp, the output current, and the current of the sensor circuit is set within the range of the minimum load current of 3 mA. Therefore, there is a drawback that the display is always dark and it is difficult to confirm even when the load current greatly exceeds 3 mA.
Particularly, the two-wire type electronic switch is often used in combination with a programmable controller, and the load current is often 8 to 10 mA. However, there is a drawback that the display is always dark even at this load current level.

The present invention has been made in view of the above-mentioned conventional problems, and makes it possible to light an indicator lamp even when the load current is at a minimum value, and a current to flow to the indicator lamp depending on the magnitude of the load current. The technical issue is to be able to increase the value stepwise.

[0010]

According to a first aspect of the present invention, there is provided a pair of terminals connected in series to an external load and a power source, a sensor circuit connected to the pair of terminals, and an output of the sensor circuit. A two-wire electronic switch comprising: an output circuit that opens and closes between a pair of terminals; and a display circuit that has an indicator lamp that displays the output state of a sensor circuit, wherein the current flowing in the output circuit is a predetermined value or more. For example, a display current control circuit that limits the current flowing through the indicator light of the display circuit to a fixed value and gradually reduces the display current flowing through the display circuit in correspondence with the drive current when the drive current flowing through the output circuit is below a predetermined value. And are provided.

In the invention of claim 2 of the present application, the output circuit is
It operates by the output of the sensor circuit, keeps the residual voltage constant by the band gap circuit, and has a switching element that opens and closes a pair of terminals.The display current control circuit is the current of the output switching switching element of the output circuit. A current detection circuit for detecting, a plurality of comparators for comparing the current value obtained from the current detection circuit with different threshold values,
The present invention is characterized by having a current control unit that controls the display current of the display circuit stepwise based on the outputs of the plurality of comparators.

In the invention of claim 3 of the present application, the current control section of the display current control circuit includes a plurality of constant current sources which are respectively driven based on the outputs of the plurality of comparators, and a current output terminal of each constant current source. Is connected to the collector of one transistor in series with the display element of the display circuit and the collector of the other transistor is connected to the current mirror circuit for controlling the display current by limiting the current flowing through the resistance of the display circuit. It is characterized by having.

In the invention of claim 4 of the present application, the display circuit comprises:
A switching element energized by an output from the sensor circuit, a series connection body of a plurality of resistors serially connected to the switching element, and a display element are included. It is characterized by having a switching element for short-circuiting different common connection ends of series connection bodies of resistors of the display circuit based on the output of the comparator.

[0014]

According to the invention of claim 1 having the above characteristics, the load current corresponds to the drive current flowing through the output circuit. Therefore, when the drive current is a predetermined value or more, the indicator light of the display circuit is displayed. The value of the current flowing through is limited to a constant value. If the current flowing through the output circuit is equal to or less than this predetermined value, the display current is gradually reduced in correspondence with the drive current. When the load current is small, the display current flowing through the display circuit is kept at a constant minimum current.

According to the invention of claim 2 of the present application, the drive current flowing through the output circuit is detected by the display current control circuit. Then, the detected current is converted into a voltage, and it is determined whether or not this level reaches the threshold levels of the plurality of comparators. The display current of the display circuit is controlled in a stepwise manner according to the drive current based on the result of the determination.

According to the invention of claim 3 of the present application, different constant current sources are driven based on the outputs of the plurality of comparators, and the current mirror circuit is driven by the current output of the constant current sources. The current value of the series resistance with the display element of the display circuit is reduced by the mirror current of the current mirror circuit to control the display current. Further, according to the invention of claim 4 of the present application, the display current is controlled by short-circuiting the plurality of resistors connected in series to the display element of the display circuit by the outputs of the plurality of comparators.

[0017]

1 is a block diagram showing the overall construction of a DC two-wire proximity switch according to an embodiment of the present invention. In this figure, the same parts as those in the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted. Also in this embodiment, terminals 1 and 2
A DC power source 3 and a load 4 are connected in series with the. The sensor circuit 5 is provided with a constant voltage circuit 8 as shown, and the constant voltage is supplied to each part. If this proximity switch is a high frequency oscillation type proximity switch, it has an oscillation circuit 9. The oscillation circuit 9 oscillates at the resonance frequency of the resonance circuit 9 a, and its output is given to the comparison circuit 11 via the integration circuit 10. The comparison circuit 11 compares the integrated output at a predetermined threshold level, and its output is given to the signal processing circuit 12. The signal processing circuit 12 determines whether the unstable detection region or the stable detection region has been reached according to the output of the comparison circuit 11, and the output is output via the display circuit 21 and the display circuit 21. 22
Given to. The output circuit 22 short-circuits the terminals 1 and 2 based on the control output of the signal processing circuit 12,
A load current is applied to the load 4. An output residual voltage sufficient to operate the sensor circuit is generated between the terminals 1 and 2.

In the present embodiment, the display current control circuit 23 is connected to the output circuit 22. The display current control circuit 23 detects the drive current flowing in the output circuit 22, and the display circuit 21
Is used to control the display current of the indicator lamp. The display circuit 21 is a red indicator light that is lit only in the unstable detection region or when the output circuit 22 is on, that is, the light emitting diode D1.
And a light emitting diode D2, which is a green indicator light emitting in a stable operation region. The display circuit 21 changes the current flowing through the light emitting diodes D1 and D2 according to the current value of the load current detected by the display current control circuit 23.

FIG. 2 is a graph showing changes in the load current flowing through the terminals 1 and 2 and the corresponding indicator lamp current when the output circuit 22 is closed. FIG. 2 shows that when the load current is 3 to 5 mA, the current flowing through the display lamp, that is, the light emitting diodes D1 and D2 is 1.2 mA by the display current control circuit 23. When the load current is 5 to 10 mA, the current of the indicator lamp is 2.5 mA and the load current. Is 10mA or more, 5mA is made to flow to the indicator light. By thus increasing the current of the indicator lamp stepwise, it is possible to light the indicator lamp brightly corresponding to a large load current.

Next, a second embodiment of the present invention will be described. This embodiment is basically the same as the first embodiment, the same parts are designated by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, the display circuit is 21A, and the display circuit 21A has only an operation indicator lamp. Then, the display circuit 21A, the output circuit 22A and the display current control circuit 2 of the second embodiment.
A detailed configuration example of 3A will be described with reference to FIGS. 3 and 4. In this embodiment, as shown in FIG. 3, the output terminals 5a and 5b of the sensor circuit 5 are transistors Q1 and Q.
It is connected to each of the two bases. The transistor Q1 is Darlington-connected with the transistor Q3, and the emitter terminal thereof is connected to the base of the transistor Q3. A light emitting diode D1 for operation display and a resistor R1 are connected between the collector end of the transistor Q3 and the terminal 1, and the emitter end is grounded via a resistor R2. On the other hand, in the output circuit 22A, the emitter of the transistor Q2 is grounded and the collector end is connected to the bandgap circuit 24. The bandgap circuit 24 includes a resistor R3, a transistor Q4, and a resistor R4 connected in series to the terminal 1 and a resistor R as shown in the figure.
5, a transistor Q5 and a resistor R6 are connected in series, and a resistor R7 and a transistor Q6 are connected in parallel. The collector of the transistor Q5 is the transistor Q
4 and the base of the transistor Q5 is commonly connected to the base and collector ends of the transistor Q6.

Now, the collector end of the transistor Q4 is PN
It is connected to the base of a P-type transistor Q7. The emitter of the transistor Q7 is at the terminal 1, and the collector end is the resistor R8.
Is connected to the terminal 2 through the base of the transistor Q8. The collector of transistor Q8 is terminal 1
In addition, the emitter is connected to the terminal 2 via the resistor R9 and further connected to the base of the transistor Q8. The collector of the transistor Q9 is connected to the terminal 1 and the emitter is connected to the terminal 2 via the resistor R10. The transistor Q9 is a switching transistor that short-circuits the terminals 1 and 2, and its base end is commonly connected to the base of the transistor Q9.

The display current control circuit 23A has a transistor Q10 for detecting the current of the output transistor Q9 as shown in FIG. The transistor Q10 has a collector connected to the terminal 1 and an emitter connected to the terminal 2 via the resistor R11.
Connected to. The transistor Q10 is a transistor for current detection, and comparators 25 and 26 are connected to its emitter end as shown in the figure. The comparator 25 has a resistor R12
It is composed of a voltage dividing circuit of ~ R14, a comparator 25a and a transistor Q11. When this threshold value is Vref1, the constant current circuit 27 is driven when a voltage exceeding this level is given. Similarly, the comparator 26 has a resistance R
It is composed of a voltage dividing circuit of 15 to R17, a comparator 26a, and a transistor Q12, and hysteresis is provided in the threshold value determined by this voltage dividing circuit. When the input of the comparator 26 exceeds the threshold value Vref2, the constant current circuit 28 is driven. The constant current drive circuits 27 and 28 generate predetermined constant currents I ₅ and I ₆ , respectively, and apply these currents to the transistor Q13 via the resistor R18 shown in FIG. The transistors Q13 and Q14 are current-mirror connected, the emitter of the transistor Q14 is grounded, and the collector is connected to the common connection end of the resistor R2 and the emitter of the transistor Q3. Here, the constant current sources 27 and 28 and the current mirror circuit of the transistors Q13 and Q14 form a current control unit that controls the display current of the display circuit 21A.

Next, the operation of this embodiment will be described. First, when the sensor circuit 5 does not detect an object, the output terminals 5a and 5b are at the L level, and the transistors of the display circuit 21A, the output circuit 22A, and the display current control circuit 23A are in the off state. At this time, the current I _L (O
FF) is equal to the sensor current I ₁ of the sensor circuit 5.

When the sensor circuit 5 detects an object, the output terminals 5a and 5b become H level. Then, the transistor Q2 is turned on, and the band cap circuit 24 is also turned on. With this bandgap circuit 24,
An output residual voltage V _O (generally 3 V or less) for driving the sensor circuit 5 is generated. The output residual voltage V _O is expressed by the following equation. V _O = V _R5 + V _BE (Q4) + V _R4 + V _CE (Q2) = V _R5 + V _BE (Q4) + V _BE (Q7) · R4 / R3 + V _CE (Q2) = V _R5 + V _BE · (R3 + R4) / R3 + V _CE (Q2) Then, the transistors Q7, Q8, Q9 are turned on, and the drive current I ₂ flows through the transistor Q9. At this time, the transistor Q10 also turns on at the same time, but its collector current I
₃ is determined by the emitter area ratio of the transistors Q9 and Q10. For example, if it is 50: 1, the current 1/50 of I ₂ becomes I ₃ .

When the load current I _L is, for example, about 3 mA, the terminal voltage of the resistor R11 is low and the comparators 25 and 26 are turned off. At this time, the display current I ₄ flowing through the light emitting diode D1 is expressed by the following equation. _{I 4 = {V O -V F} (D1) -V CE (Q3)} / (R1 + R2) which is the minimum current value that does not depend on the load current I _L.

If the load current I _L is increased to a value of 5 mA as shown in FIG. 5B, the transistor Q10
Is turned on and a current I ₃ flows. When the terminal voltage of the resistor R11 exceeds the threshold value Vref1 of the comparator 25, the comparator 25 is turned on and the constant current I ₅ flows out from the constant current circuit 27. A mirror current I ₇ (= I ₅ ) of this current also flows through the transistor Q14 via the current mirror circuit of the transistors Q13 and Q14. Therefore, the current flowing through the resistor R2 becomes I ₄ -I ₇ , and the voltage drop at the resistor R10 decreases. Therefore, as shown in FIGS. 5A and 5B, the display current I
₄ increases and at the same time the drive current I ₂ decreases. At this time, the resistance R10, so that the display current I ₄ becomes 2.5 mA, for example,
The value of Vref1 can be selected. At this time, a hysteresis is applied by the transistor Q11 so that chattering does not occur, and the drive current I ₂ (≈) shown in FIG.
By a decrease in the terminal voltage of the resistor R11 corresponding to I _3/50), the output of the comparator 25 is kept so as not inverted.

When the load current I _L exceeds 10 mA and the current I ₃ · R11 exceeds the threshold value Vref2, the comparator 26 is turned on and the constant current circuit 28 operates. Therefore, the current I ₅ + I ₆ flows through the transistor Q13. Therefore, the mirror current I flowing through the transistor Q14 by the current mirror
₇ also becomes I ₅ + I ₆ . Therefore, the voltage drop across the resistor R2 becomes smaller and the display current I ₄ becomes larger. That is, as shown in FIGS. 5A and 5B, the display current I ₄ increases when the load current I _L exceeds 10 mA. At this time, the drive current I ₂ flowing through the output transistor Q9 decreases. Therefore, it is assumed that the transistor Q12 has a hysteresis so that the output of the comparator 26 does not reverse even if the current I ₂ decreases. By doing so, as shown in FIGS. 5A and 5B, the display current I ₄ can be changed stepwise in correspondence with the load current I _L.

In this embodiment, only the operation indicator lamp is current-controlled and turned on, but it is also possible to simultaneously turn on the display elements for stable operation and operation display.

Although the present embodiment describes the DC 2-wire proximity switch, it may be an electronic switch of another type such as a photoelectric switch, and is not limited to DC but an AC 2-wire electronic switch. The present invention can also be applied to.

FIG. 6 is a circuit diagram showing one embodiment of the display circuit 21B and the display current control circuit 23B according to the third embodiment of the present invention. In the second embodiment described above, the resistor R2 of the display circuit is used.
The display current is controlled by controlling the voltage drop of the display current, but in the present embodiment, the display current is directly controlled. That is, as shown in FIG. 6, resistors R21, R22, and R23 are connected in series between the emitter of the transistor Q3 and the terminal 2 in place of the resistor R2, and the resistors R21, R22, and R23 are connected in series.
22 and R23, R21 and R22, and switching transistors Q21 and 22 for short-circuiting the terminals 2 are provided, and these transistors are connected to the first and second comparators 25 and 25, respectively.
It is controlled by the output of 26. Here transistor Q2
1, Q22 and the resistor R21~R23 constitute a current control unit for controlling the display current I _4. In this way, the display current I ₄ of the display circuit 21B can be controlled with a simple structure, and the stepwise current control can be performed as in the second embodiment.

[0031]

As described in detail above, according to the present invention, when used as a two-wire electronic switch, it is possible to change the display current stepwise as the load current increases. Therefore, for example, when the load current is about 8 to 10 mA, the current flowing through the display circuit can be increased, so that the display can be made clear. Therefore, when a bright indicator lamp is required, it can be dealt with by increasing the load current, and the brightness of the indicator lamp can be selected by one electronic switch.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of a two-wire electronic switch according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a load current and a display current according to the first embodiment of this invention.

FIG. 3 is a circuit diagram (part 1) showing details of a main part of a second embodiment of the present invention.

FIG. 4 is a circuit diagram (No. 2) showing details of a main part of the second embodiment of the present invention.

5A is a graph showing a change in a display current I ₄ with respect to a load current I _L , and FIG. 5B is a graph showing a change in a current I ₂ flowing through an output switching element with respect to a load current in the second embodiment.

FIG. 6 is a circuit diagram of a display circuit and a display current control circuit according to a third embodiment of the present invention.

FIG. 7 is a circuit diagram showing an output circuit and a display circuit portion of a conventional two-wire electronic switch.

FIG. 8 is a diagram showing a relationship between an electronic switch and an object and a change in output of an indicator light thereof.

[Explanation of symbols]

 1, 2 terminals 3 power supply 4 load 5 sensor circuit 21, 21A, 21B display circuit 22, 22A output circuit 23, 23A, 23B display current control circuit 24 bandgap circuit 25, 26 comparator 27, 28 constant current circuit

Front page continuation (72) Inventor Ishikawa Nobugen 10 Ouron, Hanazono-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture Omron Co., Ltd. (72) Inventor Yasushi Matsuoka 10 Odoron-cho, Hanazono, Ukyo-ku, Kyoto City Kyoto Prefecture Omron Corporation

Claims (5)

[Claims] 1. A pair of terminals connected in series to an external load and a power source, a sensor circuit connected to the pair of terminals, and an output circuit that opens and closes between the pair of terminals by the output of the sensor circuit. In a two-wire electronic switch including a display circuit having an indicator light for displaying the output state of the sensor circuit, a current flowing in the indicator light of the display circuit if the current flowing in the output circuit is a predetermined value or more. And a display current control circuit that reduces the display current flowing through the display circuit stepwise in correspondence with the drive current when the drive current flowing through the output circuit is a predetermined value or less. Two-wire electronic switch characterized by. 2. The output circuit includes a switching element that operates according to the output of the sensor circuit, keeps a residual voltage constant by a bandgap circuit, and opens and closes the pair of terminals. The circuit includes a current detection circuit that detects a current of the output switching switching element of the output circuit, a plurality of comparators that compare current values obtained from the current detection circuit with different threshold values, and outputs of the plurality of comparators. The two-wire electronic switch according to claim 1, further comprising a current control unit that controls the display current of the display circuit stepwise based on the above. 3. The current control unit of the display current control circuit comprises a plurality of constant current sources which are respectively driven based on outputs of a plurality of comparators, and a current output terminal of each of the constant current sources is one transistor. A current mirror circuit in which a collector connected to a display element of the display circuit in series is connected to the collector of the other transistor, and the display current is controlled by limiting the current flowing in the resistance of the display circuit. The two-wire type electronic switch according to claim 2. 4. The display circuit includes a switching element energized by an output from a sensor circuit, a series connection body of a plurality of resistors serially connected to the switching element, and a display element. The current control unit of the current control circuit has a switching element that short-circuits different common connection ends of series connection bodies of resistors of the display circuit based on outputs of the plurality of comparators. The two-wire electronic switch according to claim 2. 5. The display circuit includes a pair of switching elements energized by different outputs from the sensor circuit, and an operation display element and a stable operation display element energized by the respective switching elements. The two-wire electronic switch according to claim 1, wherein the two-wire electronic switch is provided.