JPH0592638U - Display device for sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To suppress the heat generation by reducing the current flowing to the display element, and to suppress the temperature fluctuation due to heat generation by eliminating the fluctuation of the current flowing to improve the detection accuracy. [Structure] Transistors 17 and 18 are connected in series from a DC power supply terminal VCC via a constant current circuit 13, and a red LED 19 and a green LED are connected in parallel to each transistor 17 and 18.
Connect 20. At the bases of the transistors 17 and 18, the operation display signal Sa from the display output terminal X and the stable operation display signal Sb from the display output terminal Y of the detection circuit 12 are provided.
Is given. Regardless of whether or not the LEDs 19 and 20 are energized and lit, the constant current circuit 13 always applies a constant current for one of the LEDs 19 and 20, so that current consumption is reduced and fluctuations in the current are eliminated, and the temperature due to heat generation is reduced. The rise and the fluctuation are suppressed, and the detection accuracy is improved.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a sensor display device having a plurality of display elements for displaying a detection state of a sensor.

[0002]

[Prior Art]

 Some sensors, such as proximity sensors, photoelectric sensors, ultrasonic sensors, or pressure sensors, can display not only the detection and non-detection status of the detected object but also the stable detection status or abnormal detection status. A plurality of display elements such as LEDs are provided in correspondence with each of the detection states to perform lighting display.

An example of this type is shown in FIG. That is, FIG. 3 is a diagram showing an electrical configuration of a proximity sensor that detects an object M such as a metal that is in proximity, and a detection coil 1 as a sensor is connected to a detection circuit 2. The detection circuit 2 is supplied with power from the DC power supply terminal VCC (for example, + 24V), detects that the detected object M has approached due to a change in the signal from the detection coil 1, and outputs a display signal according to the detected state. Output.

The operation display circuit 3 is made up of a series circuit of a red LED 3a as an operation display lamp, an npn-type transistor 3b for lighting control and a resistor 3c, and is connected between the DC power supply terminal VCC and the ground terminal GND. There is. The stable operation display circuit 4 comprises a series circuit of a green LED 4a as a stable operation indicator, an npn-type transistor 4b for lighting control and a resistor 4c, and is connected between the DC power supply terminal VCC and the ground terminal GND. ing.

The display output terminals X and Y of the detection circuit 2 are connected to the bases of the transistors 3b and 4b, respectively, and the output terminal Z is connected to the base of the npn type output transistor 5. The output transistor 5 has an emitter connected to the ground terminal GND and a collector connected to the output terminal OUT.

According to the above configuration, when the object M to be detected is close to the detection coil 1, the detection circuit 2 detects from the output terminal X if the signal from the detection coil 1 is in the detection area. The operation display signal indicating the state is output and the detection signal is output from the output terminal Z. As a result, the transistor 3b is turned on, the red LED 3a is turned on, and the output transistor 5 is turned on to pull a load (not shown) connected to the output terminal OUT.

Further, when the signal from the detection coil 1 is in the stable detection area, the detection circuit 2 outputs a stable operation display signal from the output terminal Y in addition to the above output state. Like As a result, the transistor 4b is turned on and the green LED 4a is also energized and lit, and a stable detection state is displayed.

As described above, the detection circuit 2 performs three operation displays and outputs of a non-detection state, an unstable detection state, and a stable detection state according to the detection state of the detected object M by the detection coil 1. Is.

[0009]

[Problems to be solved by the device]

 However, in the conventional structure as described above, for example, since the LEDs 3a and 4a of the display circuits 3 and 4 are independently lit from the DC power supply terminal VCC, their energization currents are also individually. In addition to the increase in the total consumption current, there is a problem in that the total consumption current varies depending on the lighting state of each of the LEDs 3a and 4a.

That is, for example, assuming that the energization currents of the red LED 3a and the green LED 4a are about 2 mA and 4 mA, respectively, and the consumption current in the detection circuit 2 other than the LED is about 4 mA, the LEDs 3a, 4a are detected according to the detection state. When the lighting state of is changed, the total current consumption greatly fluctuates in a wide range from the minimum of 4 mA to the maximum of about 10 mA.

By the way, in recent years, such a proximity sensor has been downsized in its overall structure. For example, there is a proximity sensor which is housed in a cylindrical compact package to increase the degree of freedom of arrangement at a detection site. .. In this case, the circuit components of the detection circuit 2 and the like are integrated into an IC or the like and mounted on an internal circuit board.

Therefore, when the current consumption inside the LED3a, 4a is large and fluctuates due to lighting, the temperature inside the device rises due to the heat generated by the energization, and the detection circuit 2 is affected by the temperature fluctuation. Therefore, there is a problem that the detection characteristics change and the detection accuracy decreases.

Therefore, assuming that the thermal resistance from the heat generating part to the outside air is about 100 ° C./W in the circuit board and the package forming the proximity sensor main body, the LEDs 3a of the display circuits 3 and 4, The maximum value ΔT of the temperature rise due to energization of 4a can be calculated as follows. That is, ΔT = 24 (V) × (2 + 4) × 10 ⁻³ (A) × 100 (° C./W) = 14.4 () from the voltage 24 V of the DC power supply terminal VCC and the energization currents 2 mA and 4 mA of the LEDs 3 a and 4 a. (° C) ... (1) Therefore, if the lighting state of the LEDs 3a and 4a changes according to the detection state, the temperature fluctuation range exerted on the proximity sensor main body becomes a wide range of about 14.4 ° C. at the maximum.

The present invention has been made in view of the above circumstances. An object of the present invention is to reduce the current consumption and control the display state even when lighting control of a plurality of display elements is performed according to the detection state. It is an object of the present invention to provide a display device for a sensor that can suppress fluctuations in consumption current as much as possible to reduce temperature fluctuations and improve sensor detection accuracy.

[0015]

A display device for a sensor according to the present invention is connected in series with a detection unit that outputs a display signal for displaying the state of the sensor according to the detection state of the sensor. A plurality of display elements for displaying the detection state corresponding to a display signal, a constant current circuit for supplying a constant current to the plurality of display elements connected in series, and the plurality of display elements And a plurality of switch means for bypassing the current flowing to the corresponding display element when the display signal corresponding to itself is not output from the detection means. Have.

[0016]

[Action]

 According to the display device for a sensor of the present invention, a plurality of display elements are energized from a constant current circuit in a state of being connected in series. At this time, the switching means connected in parallel to each display element is connected. When the display signal is not given from the detecting means, the switch means bypasses the current flowing to the corresponding display element, and thus is not turned on. Then, when the display signal according to the detection state of the sensor is given to the corresponding switch means by the detection means, a constant current from the constant current circuit bypassed by the switch means starts to flow to the display element. Lights up.

Therefore, regardless of the lighting state of the plurality of display elements, the energizing current for display can always be a constant current from the constant current circuit, and the magnitude of the energizing current is one piece. The current value required for the minute display element can be set. As a result, it is possible to reduce the current consumption as a whole and to keep the size of the current consumption at a constant value at all times, which can reduce the heat generated by energizing the display element and suppress the temperature fluctuation as much as possible. The detection accuracy of the sensor can be improved.

[0018]

【Example】

 Hereinafter, a first embodiment in which the present invention is applied to a proximity sensor will be described with reference to FIG.

In FIG. 1 showing the electrical configuration, a detection coil 11 as a sensor for detecting an object M to be detected such as an adjacent metal is connected to a detection circuit 12 as a detection means. The detection circuit 12 is fed from a DC power supply terminal VCC of, for example, + 24V, detects the detected object M by a change in the signal from the detection coil 11, etc., and displays a plurality of displays as described below according to the detection state. For example, two types of display signals Sa and Sb are output as signals.

The constant current circuit 13 is composed of two pnp type transistors 14 and 15 and a constant current source 16. The emitters of the transistors 14 and 15 are connected to the DC power supply terminal V CC, and the bases are connected in common. It is also connected to the collector of the transistor 15. The collector of the transistor 15 is connected to the ground terminal GND via the constant current source 16.

The constant current circuit 13 has a configuration in which the same current as the constant current flowing through the constant current source 16 is also supplied to the collector side of the transistor 14 by a current mirror circuit including transistors 14 and 15, and for example, 4 mA. It is set to flow a constant current.

A plurality of, for example, two, for example, npn-type lighting control transistors 17 and 18 as switching means are connected in series between the collector of the transistor 14 of the constant current circuit 13 and the ground terminal GND. The bases of these transistors 17 and 18 are connected to the output terminals X and Y of the detection circuit 12.

A plurality of, for example, two display elements, a red LED 19 and a green LED 20, are provided for operation display and stable operation display, respectively. The red LED 19 is connected in parallel with the transistor 17 to the connection terminal 17a, The green LED 20 is connected to the transistor 18 in parallel via connection terminals 18a and 18b.

In this case, the red LED 19 and the green LED 20 have energization currents of about 2 mA and 4 mA, respectively, when they are turned on with appropriate brightness, and the red LED 19 has a shunt resistor 21 for shunting a current of about 2 mA. Are connected in parallel so that an appropriate energizing current can be applied. Further, the red LED 19 having a smaller energizing current is connected to the side closer to the power source side, and the green LED 20 having a larger energizing current is connected to the ground terminal GND side.

The npn-type transistor 22 for external output is used as an open collector. The collector is connected to the output terminal OUT, the emitter is connected to the ground terminal GND, and the base is the output terminal of the detection circuit 12. It is connected to Z.

It should be noted that, in the above-mentioned overall configuration, the portion excluding the sensor 11, the LEDs 19 and 20, and the shunt resistor 21 is configured as an integrated circuit as the sensor circuit 23, which is integrally formed. The whole is housed in a cylindrical compact package (not shown).

Next, the operation of this embodiment will be described.

In the non-detection state of the detected object M, the detection circuit 12 sets the display output terminals X and Y to the “H” level output state and turns on the transistors 17 and 18. As a result, the constant current from the constant current circuit 13 flows through the transistors 17 and 18 in the ON state having low impedance, and the LEDs 19 and 20 are not energized. Further, the detection circuit 12 keeps the output terminal Z at the “L” level state in the non-detection state of the object to turn off the transistor 22.

When the detected object M approaches and the signal from the detection coil 11 enters the detection area, the detection circuit 12 outputs the operation display signal Sa of “L” level indicating the detection state of the object from the display output terminal X. And a detection signal Sc of “H” level is output from the output terminal Z. In this case, the stable operation area is not entered, and this detection state is referred to as an unstable detection state.

As a result, when the transistor 17 is turned off and its impedance becomes high, the constant current from the constant current circuit 13 is no longer bypassed, so that the constant current flows from the connection terminal 17a through the red LED 19 and the shunt resistor 21. Flow through the energization path to the connection terminal 17b. Therefore, the constant current of 4 mA from the constant current circuit 13 is shunted to the red LED 19 by about 2 mA and shunted to the shunt resistor 21 by about 2 mA, so that the red LED 19 for operation display has an appropriate current. Will come on.

On the other hand, the transistor 22 turns on when the base receives the “H” level detection signal Sc, and sets the output terminal OUT to the “L” level. Therefore, the transistor 22 connected from the outside is not shown. Get the load working.

Further, when the signal from the detection coil 11 is in the stable detection area, the detection circuit 12 outputs the operation display signal Sa of “L” level from the display output terminal X and outputs it from the display output terminal Y. The stable operation display signal Sb of "L" level is output, and the detection signal Sc of "H" level is further output from the output terminal Z.

As a result, when the transistor 18 is turned off and its impedance becomes high, a constant current from the constant current circuit 13 is no longer bypassed, and a current path from the connection terminal 18a to the connection terminal 18b via the green LED 20 is established. It comes to flow. Therefore, the constant current of 4 mA from the constant current circuit 13 is applied to the green LED 20, and the green LED 20 for stable operation display is turned on with an appropriate applied current.

Therefore, the constant current from the constant current circuit 13 flows through the parallel circuit of the red LED 19 and the shunt resistor 21 and the green LED 20, whereby the LEDs 19 and 20 can be turned on together. it can.

In this case, the temperature rise of the entire device due to heat generation due to lighting of the LEDs 19 and 20 can be calculated as follows. That is, assuming that the terminal voltage of the DC power supply terminal VCC is 24 V and the thermal resistance is 100 ° C./W, ΔT = 24 (V) × 4 × 10 ⁻³ (A) × 100 (° C./W)=9.6. (° C) ... (2) Since the constant current circuit 13 is constantly energizing 4 mA regardless of the lighting state of the LEDs 19 and 20, the temperature rise of the entire device due to the heat generation is always constant at 9.6 ° C.

According to the present embodiment as described above, the detection circuit 12 switches to the three detection states of the non-detection state, the unstable detection state, and the stable detection state according to the detection state of the detected object M by the detection coil 11. When performing the corresponding operation display and output, the LEDs 19 and 20 are always lit while a small constant current is constantly supplied from the constant current circuit 13 regardless of whether or not the operation display signal Sa and the stable operation signal Sb are output. Since the control of turning on and off can be performed, the total current consumption can always be a constant current for one LED.

As a result, since the heat generated by the consumed current can be kept constant and at a low level, the temperature rise of the whole can be suppressed and the temperature fluctuation can be suppressed, and the detection operation can be performed stably and accurately. ..

Further, according to the present embodiment, when the LEDs 19 and 20 having different optimum energizing currents are connected, a constant current of 4 mA is applied to the green LED 20 having the largest energizing current to supply the energizing current. Since the red LED 19 having a current of 2 mA is provided with a shunt resistor 21 so as to flow an optimum current, the brightness of each of the LEDs 19 and 20 can be made uniform and lighted.

FIG. 2 shows a second embodiment of the present invention. The difference from the first embodiment is that a constant current circuit 24 is provided instead of the constant current circuit 13.

That is, in the constant current circuit 24, the collector of the npn-type transistor 25 is connected to the direct current power supply terminal VCC, the emitter is connected to the collector of the transistor 17 via the resistor 26, and the base is connected to the resistor 27 via the resistor 27. It is connected to the DC power supply terminal VCC. In the npn-type transistor 28, its collector is connected to the base of the transistor 25, its emitter is connected to the collector of the transistor 17, and its base is connected to the emitter of the transistor 25.

The constant current circuit 24 is adapted to supply a constant current of, for example, 4 mA. Therefore, the second embodiment as described above has the same effect as that of the first embodiment. In addition to being able to obtain the constant current, it is possible to supply a constant current with a current smaller than the energizing current of the constant current circuit 13 in the first embodiment.

In each of the above embodiments, the case where the two LEDs 19 and 20 are used as a plurality of display elements has been described, but the present invention is not limited to this, and for example, an LED for alarm display or an abnormality may be used. It can also be applied to a structure in which three or more LEDs are used as display elements, including LEDs for status display.

In this case, when the optimum energization current of the display element is different, it is preferable to connect the one having a smaller energization current closer to the power supply terminal VCC side. This is because as the distance from the power supply terminal VCC side increases, the current added with the base current from the transistor as the switch means flows.

In each of the above embodiments, the case where the LEDs 19 and 20 having different energizing currents are used as display elements has been described, but the present invention is not limited to this. For example, the detection level of the detection circuit 12 can be set to a large number of LEDs. It may be applied to a level indicator that displays depending on the number of lights.

Further, although the above embodiments have been described with respect to the case where the present invention is applied to a proximity sensor, the present invention is not limited to this, and can be applied to a display device of various sensors such as a photoelectric sensor, an ultrasonic sensor or a pressure sensor. It is a thing.

[0046]

[Effect of the device]

 As described above, according to the sensor display device of the present invention, a plurality of display elements are connected in series to supply power from a constant current circuit, and each display element is provided with a switch means in parallel to supply the current. By controlling the lighting by bypassing, it is possible to reduce the energizing current due to lighting of the display elements, and to generate heat by constantly flowing a constant current regardless of whether the display elements are on or off. This has an excellent effect that the temperature fluctuation can be reduced and the detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is an electrical configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 3 is a view corresponding to FIG. 1 showing a conventional example.

[Explanation of symbols]

11 is a detection coil (sensor), 12 is a detection circuit (detection means), 13 is a constant current circuit, 17 and 18 are npn type lighting control transistors (switch means), 19 is a red LED (display element) for operation display. ), 20 is a green LED (display element) for stable operation display, 21 is a shunt resistor, 22 is an npn-type transistor for external output, 23 is a sensor circuit, 2
4 is a constant current circuit.

Claims (1)

[Scope of utility model registration request] 1. A detection unit for outputting a display signal for displaying the state according to the detection state of the sensor, and for displaying the detection state corresponding to the display signal from the detection unit connected in series. A plurality of display elements, a constant current circuit for supplying a constant current to the plurality of display elements connected in series, and a plurality of display elements connected in parallel to each of the plurality of display elements and connected to each other by the detection means. A display device for a sensor, comprising: a plurality of switch means for bypassing a current passing through the corresponding display element when the corresponding display signal is not output.