JP2011232252A - Dc two-line proximity sensor having operation display lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable output voltage without synchronizing with flickering of a red LED even when the red LED is made to flicker, while cost reduction of parts is achieved by arranging a single red LED.SOLUTION: A DC two-line proximity sensor includes an operation display lamp driving system (an operation display lamp circuit 12) in addition to an output system (an output circuit 13) of a sensor output, and a single red LED 12a as an operation display lamp in the operation display lamp driving system. When a detection object 17 is in a non-detection region, the red LED 12a stops lighting. When the detection object 17 is in an unstable detection region, the red LED 12a flickers. When the detection object 17 is in a stable detection region, the red LED 12 lights continuously. Even when the red LED 12a flickers, the waveform of the output voltage from the output circuit 13 does not become a pulsed waveform.

Description

  The present invention relates to a direct current 2-wire proximity sensor with an operation indicator lamp.

  Proximity sensors can detect the presence or movement of a detection object by replacing it with an electrical signal in a non-contact state with the detection object, and there are many types and various uses. For example, there are a high-frequency oscillation type in which the detection object is a metal, and a capacitance method that can detect even if the detection object is not a metal. Such proximity sensor signal output forms include analog output and on / off output. And a proximity sensor is used as one of the input devices which detect and input the state of a control device to a programmable logic controller (PLC), for example (refer patent document 1).

  Some of the above proximity sensors are referred to as a DC 2-wire type depending on the output format. FIG. 4 shows a schematic configuration of a conventional DC 2-wire proximity sensor. The proximity sensor shown in FIG. 4 includes an internal circuit 1, an operation indicator lamp circuit 2, an output circuit 3, a power supply terminal (+ Vcc) 4, and a ground terminal (GND) 5.

  The internal circuit 1 detects a detection object (not shown) using the DC voltage between the terminals 4 and 5 as an operating voltage, and outputs a detection output to the two output units 1a and 1b included therein. When the detection position of the detection object is in the non-detection region, the red and green LED side output portions 1a and 1b are both set to the high level potential to stop the light emission, and when in the unstable detection region, the red LED side output portion. The potential of 1a is the low level of light emission, the potential of the green LED side output unit 1b is the high level of light emission stop, and when in the stability detection region, the potential of the red LED side output unit 1a is the high level of light emission stop, green LED side The potential of the output unit 1b is set to the low level of light emission.

  The operation indicator circuit 2 includes a red LED 2a that is an operation indicator having a cathode connected to the red LED side output unit 1a, and a green LED 2b that is an operation indicator having a cathode connected to the green LED side output unit 1b. . When the detection object is in the non-detection region, both the red and green LED side output portions 1a and 1b are at a high level to stop the light emission, and the red LED 2a and the green LED 2b both stop the light emission. When the detected object is in an unstable detection region, the red LED 1a emits light when the potential of the red LED side output unit 1a is low, and the green LED 2b emits light when the potential of the green LED side output unit 1b is high. It has stopped. When the detection object is in the stable detection area, the red LED 2a stops emitting light when the potential of the red LED side output unit 1a is high, and the green LED 2b is low when the potential of the green LED side output unit 1b is low. Emits light.

  When the detection object is in the non-detection area, the red and green LEDs 2a and 2b both stop emitting light and the output transistors 3a and 3b are both OFF, so that the sensor output voltage is OFF and the power supply voltage is at a high level. In this case, since it is a direct current 2-wire type, the collector potential of the output transistor 3b becomes the output of the direct current 2-wire type proximity sensor. When the detected object is either the unstable detection region or the stable detection region, one of the LEDs 2a and 2b is turned on and the output transistors 3a and 3b are ON. It becomes.

  As described above, in the proximity sensor shown in FIG. 4, both the red and green LEDs 2a and 2b are turned off or continuously turned on according to the position of the detected object.

JP 2002-076871 A

  In the proximity sensor, when the green LED 2b of the operation indicator lamp circuit 2 is continuously lit, the user can be notified that the detected object is located in the stable detection region. However, the green LED 2b has poor visibility of light emission, and it is difficult for the user to check the lighting state of the green LED 2b. In addition, since two types of LEDs, red LED 2a and green LED 2b, are used for confirmation of the detection state, the cost of parts increases, and the mounting of other parts for mounting two LEDs on the board. Space becomes narrower.

  Therefore, it is conceivable to construct an operation indicator lamp circuit with only one red LED, for example. FIG. 5 shows a proximity sensor considered by the present inventor. In the proximity sensor shown in FIG. 5, 1 is an internal circuit, 2 is an operation indicator lamp circuit, and 3 is an output circuit. The operation indicator lamp circuit 2 includes a single red LED 2c. In this proximity sensor, when the position of a detection object (not shown) is in the non-detection region, the output unit 1c of the internal circuit 1 outputs a high level output for stopping the light emission of the red LED 2c in the operation indicator lamp circuit 2. When in the unstable detection region, a plurality of pulse outputs for lighting the red LED 2c are output, and when in the stable detection region, a low level output for continuously lighting is output.

  However, in the case of the DC two-wire system, the Vf (forward conduction voltage) portion of the red LED 2c is reflected in the output voltage. Therefore, when the red LED 2c blinks when the detection object is in the unstable detection region, Since the output transistors 3a and 3b of the output circuit 3 are turned ON / OFF in synchronization with this, the output voltage becomes a pulse output.

  Therefore, the present invention reduces the number of LEDs used by using a single red LED as the operation indicator, and when the detected object is in the unstable detection region, the output voltage can be maintained even if the red LED is blinked. A stable output voltage can be output without synchronizing with this blinking lighting.

  In the proximity sensor according to the present invention, power is supplied from the host device through the power supply terminal, while the sensor output is output to the host device through the power supply terminal and the operation state of the sensor is displayed by turning on and off. A direct current 2-wire proximity sensor with an indicator lamp, comprising an operation indicator light drive system separately from an output system of sensor output, and a single red LED as the operation indicator light in the operation indicator light drive system And the red LED is turned off when the detected object is in the non-detection area, blinking when the detection object is in the unstable detection area, and continuously lit when in the stable detection area.

  According to the present invention, since the sensor output is output to the power supply terminal via an output system different from the drive system of the operation indicator lamp, the position of the detection object is in the unstable operation region, and the operation indicator light drive system is Even if the red LED is turned on and off, the sensor output waveform does not become a pulsed sensor output waveform in synchronization with the blinking and lighting of the red LED, and the waveform of the output voltage can be stabilized. Further, in the present invention, since only a single red LED is provided as the operation indicator, the number of LEDs used can be reduced to the minimum.

FIG. 1 is a diagram showing a schematic configuration of a proximity sensor with an operation indicator lamp according to an embodiment of the present invention. FIG. 2 is a diagram showing a non-detection region and a detection region (an unstable detection region and a stable detection region) according to the position of the object detected by the proximity sensor. FIG. 3 is a diagram showing an operation timing chart of the sensor output and the red LED which is the operation indicator lamp. FIG. 4 is a diagram showing a schematic configuration of a conventional proximity sensor. FIG. 5 is a diagram showing a schematic configuration of another conventional proximity sensor.

  Hereinafter, a direct current 2-wire proximity sensor with an operation indicator according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a block configuration of the entire proximity sensor. Referring to FIG. 1, 10 indicates the entire proximity sensor, 11 indicates an internal circuit for detecting a detection object, 12 indicates an operation indicator lamp circuit, 13 indicates an output circuit, and 14 indicates a power supply circuit. Reference numeral 15 denotes a power supply terminal, 16 denotes a ground terminal, and 17 denotes a detection object.

  The internal circuit 11 has two output units 11a and 11b. One output unit 11 a constitutes a drive system to the operation indicator lamp circuit 12, and the other output unit 11 b constitutes an output system to the output circuit 13. Both systems are independent from each other.

  The internal circuit 11 performs an output operation from each output unit 11a, 11b to each system in response to detection of the detection object 17. A drive signal for blinking lighting, continuous lighting, and extinction is output from the output unit 11a to the operation indicator lamp circuit 12 as a drive system, while the detection object 17 is output from the output unit 11b to the output circuit 13 as an output system. An output signal having a level corresponding to the detection is output.

  The operation indicator lamp circuit 12 incorporates a single red LED 12a and a resistor 12b in series as an operation indicator lamp, and the red LED 12a is turned off according to a drive signal from the output unit 11a of the internal circuit 11, and blinking is turned on. Turn on continuously.

  The output circuit 13 includes output transistors 13a and 13b, a Zener diode 13c, and resistors 13d and 13e, and outputs sensor output voltages of OFF and ON levels according to an output signal from the output unit 11b of the internal circuit 11.

  The power supply circuit 14 is a DC / DC converter that steps down a DC voltage of, for example, 12V or 24V applied from the power supply terminal 15 to a DC voltage of, for example, 2V.

  The power supply terminal 15 and the ground terminal 16 are connected to corresponding input terminals of an input module of a PLC (programmable controller), which is a higher-level device, as a direct current 2-wire system via a wiring not shown.

  The proximity sensor 10 is supplied with DC 12V or 24V power from the PLC side to the power supply terminal 15 from the PLC side. On the other hand, when the detection object 17 is not detected, the output circuit 13 A 24 V high level detection signal can be output from the power supply terminal 15 to the PLC side when the detection object 17 is detected, and the output circuit 13 can output a DC 3 V low level detection signal. ing.

  On the PLC side, the data of the detection state of the detection object 17 in the proximity sensor 10 is obtained from the voltage change state of the input terminal connected to the power supply terminal 15 and the ground terminal 16 of the proximity sensor 10 in the input module. Sequence control can be performed.

  The internal circuit 11 includes a detection circuit unit 11c and a control circuit unit 11d. The detection circuit unit 11c includes a high-frequency type oscillation circuit, a rectification circuit, a detection circuit, and the like. In the oscillation circuit, when the detection object 17 made of a metal body, a magnetic body, or the like approaches the oscillation coil, an eddy current loss occurs due to electromagnetic induction, and the impedance, which is an effective resistance value of the oscillation coil, changes. The oscillation amplitude level changes according to the proximity state of the detection object 17, and the presence or absence of the detection object 17 can be detected by oscillating or stopping oscillation. The rectifier circuit converts the oscillation output of the oscillation circuit into a direct current corresponding to the magnitude of the oscillation amplitude level and outputs it as a detection output. When the detection object 17 approaches and the oscillation amplitude level decreases, the detection output decreases. As the detected object moves away and the oscillation amplitude level increases, the detection output increases.

  In this case, the detection circuit unit 11c determines whether the detection object 17 is located in the non-detection region or the detection region as shown in FIG. 2, and whether the detection object 17 is an unstable detection region or a stable detection region in the detection region. Is output to the control circuit unit 11d. The non-detection region is a region where the detection object 17 cannot be detected by the detection circuit unit 11c, and the detection region is a region where the detection object 17 can be detected by the detection circuit unit 11c. The detection area is divided into an unstable detection area and a stable detection area. In the unstable detection area, a detection output input from the detection circuit unit 11c to the control circuit unit 11d is a change in the ambient environment (for example, a change in the ambient temperature). ), And the stable detection region can be detected stably even if the detection output input from the detection circuit unit 11c to the control circuit unit 11d changes in the surrounding environment (for example, the ambient temperature changes). It is an area.

  The control circuit unit 11d is preferably composed of a microcomputer including a CPU, a memory, and an interface, A / D converts the detection output of the detection circuit unit 11c, and based on the detection output corresponding to the position of the detection object 17 Necessary control processing is performed, and the output corresponding to the processing is D / A converted and output to the output units 11a and 11b. That is, when the control circuit unit 11d determines from the output from the detection circuit unit 11c that the position of the detection object 17 (detection distance from the proximity sensor) is located in the non-detection region, the output unit 11a emits the red LED 12a. A high level output that is not generated is output, and when it is determined that the detection object 17 is located in the unstable detection region within the detection region, a pulse output that causes the red LED 12a to blink is output from the output unit 11a. If it is determined that the red LED 12a is continuously lit, a low level output is output.

  The control circuit unit 11d also outputs a low level output from the output unit 11b to the output circuit 13 when the detection object 17 is located in the non-detection region, and the output transistors 13a and 13b in the output circuit 13 are non-conductive (OFF). When an OFF sensor output is output and the detection object 17 is located in a detection region including an unstable detection region and a stable detection region, a high level output is output to the output circuit 13 and an output transistor in the output circuit 13 13a and 13b are both conducted to output an ON sensor output. In this case, the sensor output at the time of OFF is a DC 12V or 24V output voltage at the power supply terminal 15, and the sensor output at the time of ON is the base-emitter voltage when the output transistor 13b is conductive and the resistance 13e. The voltage is about 3 V due to the drop voltage, the Zener voltage of the Zener diode 13c, and the collector-emitter voltage when the output transistor 13a is conductive. By outputting the output voltage change of the sensor output to the input module of the PLC, the detection state of the detection object 17 by the proximity sensor 10 can be determined on the PLC side, and the necessary sequence control can be performed.

  In the power supply circuit 14, as a DC / DC converter, the voltage of the power supply terminal 15 changes from 12V to 24V to 3V as described above, but a DC voltage of 2V is always supplied to the internal circuit 11. Adjust the voltage.

  As described above, in the present embodiment, power is supplied to the internal circuit 11 from the PLC, which is the host device, via the power supply terminal 15, while the sensor output is output to the PLC via the power supply terminal 15 and the operation of the sensor is performed. Since the internal circuit 11 drives the operation indicator lamp circuit 12 by a drive system different from the output system of the sensor output in the output circuit 13 in displaying the operation by turning on and off the state by the red LED 12a. The sensor output can be stably output even if the single red LED 12a in the operation indicator lamp circuit 12 is turned off, blinking, or continuously lit according to the position of the detected object.

  In the present embodiment, even if the red LED is blinked and lit, the sensor output waveform does not become a pulsed sensor output waveform in synchronization with the blinking lighting of the red LED, and the output voltage waveform is stabilized. In addition, the red light emission of the red LED is easy to visually recognize, and since only a single red LED is provided, the number of LEDs used is minimized, and the cost is low.

10 Proximity sensor 11 Internal circuit 12 Operation indicator lamp circuit 12a Red LED
13 Output circuit

Claims (1)

  While the power is supplied from the host device through the power terminal, the sensor output is output to the host device through the power terminal, and the operation state of the sensor is displayed by turning on and off the direct current 2-wire with operation indicator lamp Type proximity sensor having an operation indicator light drive system separately from an output system of sensor output, and providing a single red LED as the operation indicator light in the operation indicator light drive system, A proximity sensor characterized in that lighting is stopped when a detection object is in a non-detection area, blinking is light when it is in an unstable detection area, and light is continuously lit when it is in a stable detection area.

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