JP2019004310A - Signal repeater - Google Patents

Abstract

To provide a signal repeater for preventing misdetection on a main unit side due to current noise and performing stable long distance communication even when the current noise is input from a slave unit to the signal repeater.SOLUTION: A signal repeater 400 includes a current signal input unit 450 that outputs a current signal input from a sub unit 300 side, an AND gate 460 having an input terminal 460a, an input terminal 460b, and an output terminal, and a control unit 420 that monitors a voltage signal input from a main unit 200 side and outputs a signal to the input terminal 460b of the AND gate 460. The control unit 420 turns on the signal output to the input terminal 460b of the AND gate 460 at the time when the base unit 200 starts detecting a current signal, and turns off the signal output to the input terminal 460b of the AND gate after a predetermined time passes.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a signal repeater.

  In general, in a signal transmission system that constitutes an illumination control system or the like, adjustment is made from a master unit (for example, a lighting controller) as a first device to a slave unit (for example, a terminal device such as a lighting fixture or a wall switch) as a second device. Control data such as light rate and address setting is transmitted, and data indicating the setting status of the slave unit and lighting load status is transmitted from the slave unit to the master unit together with its own address, thereby controlling and monitoring the load. (For example, refer to Patent Document 1).

  In such a signal transmission system, control data is transmitted from the master unit to the slave unit in a voltage mode (voltage mode control) of, for example, ± 24 V, and response data is transmitted from the slave unit to the master unit as current. This is performed in the mode (current mode control). In this case, the control data transmitted from the master unit is encoded with a pulse width generated by inverting the polarity of the voltage of ± 24V in the master unit at a predetermined time, and the slave unit measures the pulse width. And decrypted. The response data transmitted from the slave unit is short-circuited by a resistor for a certain period of time so that a predetermined pulse width is obtained in synchronization with the synchronization signal transmitted from the master unit in the slave unit. Sent by. After outputting the synchronization signal, the master unit receives response data by detecting a current signal having a predetermined pulse width. The signal repeater relays the voltage signal transmitted from the master unit to the slave unit in the voltage mode and the current signal transmitted from the slave unit to the master unit in the current mode.

JP-A-3-285429

  In a signal transmission system equipped with a signal repeater for long-distance communication, the current signal pulse width becomes redundant each time the current signal output from the slave unit as the second device is relayed by the signal repeater. There is a problem that the parent device as the first device cannot detect the current signal. In addition, current noise generated when the polarity of the voltage is reversed has a redundant pulse width every time it is relayed by the signal repeater. Therefore, there is a problem that the master unit erroneously detects the current noise as a current signal.

  The present invention has been made to solve such a problem, and even when current noise is input from the second device side to the signal repeater, erroneous detection on the first device side due to current noise. It is an object of the present invention to provide a signal repeater for preventing long-distance communication.

  The signal repeater of the present invention is a signal repeater that relays a signal transmitted between a first device and a second device, and outputs a current signal input from the second device side. A current signal input section; a first input terminal connected to the current signal input section; a second input terminal; and an output terminal; a signal is transmitted to the first input terminal and the second input terminal; An AND gate that outputs a signal from the output terminal only during the input period, a first input port that monitors a voltage signal input from the first device side, and the second input terminal of the AND gate A control unit having an output port for outputting a signal to the voltage, a voltage signal input unit for outputting a voltage signal input from the first device side toward the first input port of the control unit, and the AND The current signal input from the gate is converted into the first signal. A current signal output unit that outputs the signal to a device, and the control unit outputs a signal output to the second input terminal of the AND gate when the first device starts to detect a current signal. The signal output to the second input terminal of the AND gate is turned off after elapse of a predetermined time.

  According to the present invention, even when current noise is input to the signal repeater from the second device side, erroneous detection on the first device side due to current noise can be prevented, and stable long-distance communication can be performed. .

It is a figure which shows schematically the structure of the signal transmission system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of a signal repeater roughly. (A) is a waveform diagram which shows the waveform of the signal input into the input port of a control part, (b) is a waveform diagram which shows the waveform of the signal output from the output port of a control part, (c ) Is a waveform diagram illustrating a waveform of a signal output from the current signal input unit, and (d) is a waveform diagram illustrating a waveform of a signal output from the AND gate. (A)-(c) is a wave form diagram which shows operation | movement of the component in the signal transmission system which concerns on a comparative example. It is a figure which shows the structure of a signal repeater roughly. (A) is a waveform diagram which shows the waveform of the signal input into the input port of a control part, (b) is a waveform diagram which shows the waveform of the signal output from the output port of a control part, (c ) Is a waveform diagram illustrating a waveform of a signal input to another input port of the control unit, and (d) is a waveform diagram illustrating a waveform of a signal output from the AND gate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to each embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram schematically showing a configuration of a signal transmission system 1 according to Embodiment 1 of the present invention.

  The signal transmission system 1 includes a two-wire communication line 100 (also simply referred to as “communication line”), a parent device 200 as a first device, a slave device 300 as one or a plurality of second devices, One or a plurality of signal repeaters 400.

  The two-wire communication line 100 connects the parent device 200 and at least one child device 300.

  The base unit 200 transmits control data to the handset 300 by voltage mode control (hereinafter referred to as “voltage mode”), for example, by inverting the polarity of the voltage of ± 24 V at a predetermined time.

  The subunit | mobile_unit 300 short-circuits the two-wire communication line 100 in the time predetermined by resistance. Accordingly, slave unit 300 synchronizes the response data with current mode control (hereinafter referred to as “current mode”) so as to have a predetermined pulse width (for example, 100 μsec) in synchronization with the synchronization signal output from master unit 200 in the voltage mode. Mode ”) to the base unit 200.

  The signal repeater 400 is connected in series with the two-wire communication line 100 between the parent device 200 and the child device 300. The signal repeater 400 relays a signal transmitted between the parent device 200 and the child device 300. Specifically, the signal repeater 400 relays a voltage signal transmitted from the parent device 200 to the child device 300 in the voltage mode and a current signal transmitted from the child device 300 to the parent device 200 in the current mode.

  The voltage value of the voltage signal output from the parent device 200 is, for example, ± 24V. However, the voltage value is not limited to ± 24 V as long as it is a voltage mode signal.

  The pulse width of the current signal output from the child device 300 is, for example, 100 μsec. However, the pulse width of the current signal may be determined in advance and is not limited to 100 μsec.

FIG. 2 is a diagram schematically showing the configuration of the signal repeater 400.
The signal repeater 400 includes a signal transmission unit 410, a control unit 420, a voltage signal input unit 430, a voltage signal output unit 440, a current signal input unit 450, an AND gate 460, a current signal output unit 470, A primary power generation unit 480 and a secondary power generation unit 490 are included.

  In the signal repeater 400, the communication circuit 40a is a part driven by the power supply Vcc1. In other words, the communication circuit 40a is driven by a power source fed from the parent device 200 via the two-wire communication line 100.

  In the signal repeater 400, the communication circuit 40b is a portion that is driven by a power source (for example, the power source Vcc2a or Vcc2b) other than the power source Vcc1. In other words, the communication circuit 40b is driven by a direct current power generated using a commercial AC power.

  The signal transmission unit 410 transmits signals between the communication circuit 40a and the communication circuit 40b connected to different power sources. The signal transmission unit 410 is a circuit or an element that can transmit signals between circuits driven by different power supply systems. The signal transmission unit 410 is, for example, an insulating circuit composed of a photocoupler and a resistor, but is not limited to such an insulating circuit.

  The control unit 420 monitors the input voltage signal input to the input port 420a from the parent device 200 side and detects an input port 420a as a first input port, and an input terminal 460b as a second input terminal of the AND gate 460. And an output port 420b for outputting a signal. The control unit 420 controls signal input at the input port 420a and signal output at the output port 420b. The control unit 420 is, for example, a microcomputer. The number of input ports 420a is not limited to one, and the number of output ports 420b is not limited to one.

  The voltage signal input unit 430 converts a voltage signal of ± 24V input from the parent device 200 side into a DC voltage, and outputs the converted voltage signal toward the input port 420a of the control unit 420. The voltage signal input unit 430 is a circuit or element that outputs a voltage signal input from the parent device 200 side toward the control unit 420. For example, the voltage signal input unit 430 is a receiving circuit including a Zener diode and a resistor, but is not limited to such a receiving circuit.

  The voltage signal output unit 440 outputs the voltage signal received from the parent device 200 side to the child device 300 side at ± 24V. The voltage signal output unit 440 is a transmission circuit including, for example, a drive circuit configured by combining a plurality of logic circuits and a full bridge circuit configured of transistors and resistors, but is limited to such a transmission circuit. Absent. The full bridge circuit is driven by the drive circuit, and switches the output voltage of ± 24 V in accordance with the output signal of the drive circuit.

  The current signal input unit 450 converts a current signal (that is, current input) input from the handset 300 side into a voltage output (specifically, a square wave (also referred to as a rectangular wave)), and the converted current Output a signal. The current signal input unit 450 is a circuit or element that outputs a current signal input from the slave unit 300 side toward the master unit 200 side (specifically, an AND gate 460). The current signal input unit 450 is, for example, a receiving circuit including a comparator and a resistor, but is not limited to such a receiving circuit.

  The AND gate 460 has an output terminal and two input terminals (specifically, an input terminal 460a as a first input terminal and 460b as a second input terminal). In the AND gate 460, one of input terminals (specifically, the input terminal 460 a) is connected to the current signal input unit 450, and the other input terminal (specifically, the input terminal 460 b) is connected to the control unit 420. It is connected to the output port 420b. As a result, the AND gate 460 compares the output signal of the current signal input unit 450 with the output signal of the output port 420b of the control unit 420, and the signal is input to both input terminals (ie, the input terminals 460a and 460b). A signal is output from the output terminal only during the specified period. That is, the AND gate 460 is controlled by the output signal of the control unit 420 so that the output signal of the current signal input unit 450 does not become the input signal of the current signal output unit 470 as it is.

  The AND gate 460 is a logic circuit that compares signals input to the input terminals 460a and 460b and outputs a signal according to the AND logic, for example, but is not limited to such a logic circuit. For example, the AND gate 460 may be configured by a circuit that outputs a signal according to logic other than AND logic, for example, NAND logic, and is configured by a circuit that is driven with negative logic with respect to the output of the current signal output unit 470. It may be. The input terminal 460 a of the AND gate 460 may not be directly connected to the current signal input unit 450. In this case, an element such as a resistor or a capacitor may be provided between the input terminal 460a and the current signal input unit 450. The input terminal 460 b of the AND gate 460 may not be directly connected to the control unit 420. In this case, an element such as a resistor or a capacitor may be provided between the input terminal 460b and the control unit 420.

  The current signal output unit 470 outputs the current signal input from the AND gate 460 via the signal transmission unit 410 to the parent device 200. Specifically, current signal output unit 470 outputs a current signal to parent device 200 according to the pulse width of the signal input from child device 300. The current signal output unit 470 is a circuit or element that short-circuits the two-wire communication line 100 with a resistor and outputs a current signal to the parent device 200 side. The current signal output unit 470 is, for example, a transmission circuit composed of a transistor and a resistor, but is not limited to such a transmission circuit.

  The primary power generation unit 480 is a circuit or element that generates power Vcc1 for driving the communication circuit 40a using power supplied from the parent device 200 side via the two-wire communication line 100. The primary power supply generation unit 480 is a power supply generation circuit including, for example, a transistor, a Zener diode, and a resistor, but is not limited to such a power supply generation circuit.

  The secondary power generation unit 490 generates power Vcc2a and power Vcc2b that drive the communication circuit 40b using power supplied from the commercial AC power.

  Next, the operation of the signal repeater 400 will be described.

  FIG. 3A is a waveform diagram illustrating a waveform of a signal input to the input port 420a of the control unit 420. FIG. FIG. 3B is a waveform diagram showing a waveform of a signal output from the output port 420 b of the control unit 420. FIG. 3C is a waveform diagram showing a waveform of a signal output from the current signal input unit 450. FIG. 3D is a waveform diagram showing a waveform of a signal output from the AND gate 460.

  Control unit 420 monitors a voltage signal input to input port 420a from parent device 200 side. When the control unit 420 detects the synchronization signal Sg1 output from the parent device 200 (that is, the synchronization signal Sg1 input to the input port 420a) (S101), the time when the parent device 200 starts detecting the current signal (start) Time S1) can be detected. Specifically, control unit 420 detects a time point (ie, start time point S1) at which base unit 200 starts detecting a current signal based on an output signal of voltage signal input unit 430. The control unit 420 turns on the signal output to the input terminal 460b of the AND gate 460 (that is, the signal output of the output port 420b) at the start time S1 of the parent device detection section P1, and sends the signal to the input terminal 460b of the AND gate 460. Output (S102).

  The base unit detection section (section P1 or P2 in FIG. 3) is a section in which the base unit 200 detects a current signal. The section from S1 to E1 and S2 to E2 shown in FIG. It is a section. The time points when the parent device 200 finishes detecting the current signal are indicated by E1 and E2. That is, base unit 200 starts detecting the current signal at S1 shown in FIG. 3A, and ends detecting the current signal at E1. Similarly, base unit 200 starts detection of the current signal again at S2 shown in FIG. 3A, and ends detection of the current signal at E2.

  Master device 200 can detect a current signal output from slave device 300 by detecting a current signal having a predetermined pulse width in master device detection sections P1 and P2. On the other hand, when the pulse width of the current signal does not fall within the parent device detection sections P1 and P2, the parent device 200 cannot detect the current signal output from the child device 300.

  In the present embodiment, the time when control unit 420 turns on the output of output port 420b is the same as the time when parent device 200 starts detecting the current signal (that is, start time S1). However, as long as the delay of the current noise does not affect the output of the AND gate 460, the time when the control unit 420 turns on the output of the output port 420b may be a time before the start time S1.

  Subsequently, when a current signal is input to the current signal input unit 450 from the child device 300 side, the current signal input unit 450 outputs a current signal to the input terminal 460a of the AND gate 460 (S103). Even when current noise generated on the side of the slave unit 300 (for example, current noise delayed in the two-wire communication line 100) is input to the current signal input unit 450, the current signal input unit 450 is always connected to the AND gate 460. A current signal is output to the input terminal 460a.

  Subsequently, the AND gate 460 compares the input at the input terminal 460a with the input at the input terminal 460b, and during the period in which signals are input to both input terminals (ie, the input terminals 460a and 460b), A current signal Sg2 which is a shaping pulse is output to the machine 200 side (S104).

  Subsequently, the control unit 420 outputs a signal output from the output port 420b to the AND gate 460 (specifically, the input terminal 460b) after elapse of a predetermined time t1 from the start time S1 of the parent device detection section P1. Turn off (S105). In the present embodiment, this predetermined time t1 is the same as the pulse width of the current signal output from slave unit 300 (in this embodiment, 100 μsec). However, considering the signal delay in the two-wire communication line 100 and the like, if the parent device 200 can detect the current signal in the parent device detection section P1, the time t1 is equal to the pulse width of the current signal output from the child device 300. It does not have to be the same. For example, the above-described time t1 may be 90 μsec.

  After the master device 200 finishes detecting the current signal (specifically, at least after the end time E1), the control unit 420 monitors the voltage signal from the master device 200 that is input to the input port 420a. Until the machine 200 starts detecting the current signal again (that is, until the start time S2 of the next parent machine detection section P2), the signal output (ie, output) from the output port 420b to the input terminal 460b of the AND gate 460 is performed. The signal output from the port 420b is turned off (S106).

  3A to 3D, the operation of the signal repeater 400 in the above-described S101 to S106 is shown stepwise to show the signal output from the AND gate 460 in time series. However, the monitoring of the voltage signal performed by the control unit 420 (that is, the detection of the signal input to the input port 420a) and the comparison of the input at the input terminal performed by the AND gate 460 are always performed regardless of the operation shown in FIG. It may be.

The effects of the first embodiment will be described below.
FIGS. 4A to 4C are waveform diagrams showing the operation of the components in the signal transmission system according to the comparative example. Specifically, FIG. 4A is a waveform diagram showing a waveform of a signal (specifically, a voltage signal) output from the master unit to the signal repeater in the signal transmission system according to the comparative example. . The parent device in the signal transmission system according to the comparative example corresponds to the parent device 200 in the present embodiment. FIG. 4B is a waveform diagram showing a waveform of a signal (specifically, a current signal) output from the slave unit to the signal repeater in the signal transmission system according to the comparative example. The handset in the signal transmission system according to the comparative example corresponds to handset 300 in the present embodiment. FIG. 4C is a waveform diagram showing a waveform of a signal (specifically, a current signal) output from the signal repeater to the master unit in the signal transmission system according to the comparative example. The signal repeater in the signal transmission system according to the comparative example corresponds to the signal repeater 400 in the present embodiment.

  As in the comparative example and the present embodiment, in a signal transmission system using a signal repeater, the longer the communication line (for example, two-wire communication line), the longer the signal delay. In particular, since the current signal transmitted from the slave unit to the master unit is easily affected by the impedance of the communication line, as shown in FIG. Pulse width becomes redundant. For example, as shown in FIG. 4B, the pulse width of the current signal becomes redundant due to the falling delay D1 of the current signal having a predetermined pulse width W1. Furthermore, when the polarity of the voltage of ± 24V is reversed every time a voltage signal is output from the parent device, current noise (for example, inrush current) generated on the child device side due to the polarity inversion is also shown in FIG. As shown, the fall is significantly delayed by the impedance of the communication line.

  In the signal transmission system according to the comparative example and the present embodiment, when a current signal is input from the slave unit to the signal repeater, the signal repeater shapes the waveform of the current signal and converts the shaped current signal into the current mode. To output to the main unit. However, when the pulse width of the current signal output from the slave unit is redundant (FIG. 4 (b)), as shown in FIG. 4 (c), the current signal output from the signal repeater to the master unit side. The pulse width W2 of the current signal becomes redundant, and the pulse width W2 of the current signal output from the signal repeater does not fall within the parent device detection sections P1 and P2, and the parent device cannot detect the current signal.

  On the other hand, according to the signal transmission system 1 according to the first embodiment, the current signal delayed in falling (specifically, the output signal of the current signal input unit 450) is sent from the slave unit 300 side to the AND gate 460. Even when the signal is input, the signal repeater 400 (specifically, the AND gate 460) receives the current signal Sg2, which is a shaped pulse shaped so as to have a predetermined pulse width, on the parent device 200 side. Can be output. Thereby, even when the current signal delayed in falling is input from the slave unit 300 side to the signal repeater 400 (specifically, the AND gate 460), the signal repeater 400 (specifically, Since the pulse width (FIG. 3 (d)) of the current signal Sg2 output from the AND gate 460 is within the parent device detection sections P1 and P2, it is possible to prevent the current signal detection failure in the parent device 200. As a result, stable long-distance communication can be performed.

  Further, the control unit 420 monitors the output signal of the voltage signal input unit 430 and turns off the signal output to the input terminal 460b of the AND gate 460 until the start time S2 of the parent device detection section P2 comes next. To do. Thus, even when current noise is input from the slave unit 300 side to the signal repeater 400, current noise is not output to the master unit 200 side until the next start time S2 of the master unit detection section P2 comes. Therefore, it is possible to prevent erroneous detection on the base unit 200 side due to current noise and perform stable long-distance communication.

Embodiment 2. FIG.
The second embodiment of the present invention will be described below. The signal transmission system according to Embodiment 2 includes a two-wire communication line 100 (also simply referred to as “communication line”), a parent device 200 as a first device, and a child as one or a plurality of second devices. Machine 300 and one or more signal repeaters 400a. That is, the signal transmission system according to the second embodiment is basically the same as the configuration of the signal transmission system 1 shown in FIG. 1, but a signal repeater 400 a is used instead of the signal repeater 400.

  In the second embodiment, the configuration and operation of the signal repeater 400a are different from the configuration and operation of the signal repeater 400 in the first embodiment. Specifically, the configuration and operation of the control unit 421 of the signal repeater 400a are different from the configuration and operation of the control unit 420 of the signal repeater 400 in the first embodiment. In the second embodiment, a configuration and operation different from those of the first embodiment will be described.

  FIG. 5 is a diagram schematically showing the configuration of the signal repeater 400a. In the signal repeater 400a, the control unit 421 includes an input port 420a as a first input port that monitors and detects a voltage signal input to the input port 420a from the parent device 200 side, and a second input of the AND gate 460. An output port 420b that outputs a signal to an input terminal 460b as a terminal, and a current signal input from the handset 300 side (specifically, the current signal input unit 450) (that is, an output signal of the current signal input unit 450) And an input port 420c as a second input port for monitoring and detecting. In the signal repeater 400a, the configuration other than the control unit 421 is the same as that of the signal repeater 400 in the first embodiment. The control unit 421 is, for example, a microcomputer.

  Next, an operation different from that of the first embodiment in the signal repeater 400a will be described.

  FIG. 6A is a waveform diagram illustrating a waveform of a signal input to the input port 420a of the control unit 421. FIG. 6B is a waveform diagram illustrating a waveform of a signal output from the output port 420 b of the control unit 421. FIG. 6C is a waveform diagram illustrating a waveform of a signal input to the input port 420 c of the control unit 421. FIG. 6D is a waveform diagram showing the waveform of the signal output from the AND gate 460.

  When a current signal is input to the current signal input unit 450 from the child device 300 side, the current signal input unit 450 outputs a current signal to the input terminal 460a of the AND gate 460 and the input port 420c of the control unit 421 (S203). . Even when current noise generated on the side of the slave unit 300 (for example, current noise delayed in the two-wire communication line 100) is input to the current signal input unit 450, the current signal input unit 450 is always connected to the AND gate 460. A current signal is output to the input terminal 460a.

  Subsequently, when the control unit 421 detects a current signal (that is, an output signal of the current signal input unit 450) input to the input port 420c within the parent device detection section P1 (S203), the control unit 421 The signal output from the output port 420b to the AND gate 460 (specifically, the input terminal 460b) is turned off after elapse of a predetermined time t2 from the time when the current signal input to 420c is detected (S205). .

  The monitoring of the voltage signal performed by the control unit 421 (that is, detection of the signal input to the input port 420a) and the comparison of the input at the input terminal performed by the AND gate 460 are the operations shown in FIGS. 6A to 6D. Regardless, you may always go.

  The signal repeater 400a is the same as the operation of the signal repeater 400 in the first embodiment except for the above-described operation.

  In signal repeater 400 in the first embodiment, control unit 420 detects a time point (ie, start time point S1) at which base unit 200 starts detecting a current signal based on an output signal of voltage signal input unit 430. The controller 420 turns off the signal output from the output port 420b to the AND gate 460 (specifically, the input terminal 460b) after a predetermined time t1 has elapsed from the start time S1 (S105). That is, in the first embodiment, control unit 420 determines the period of signal output to AND gate 460 based only on the output signal of voltage signal input unit 430. In this case, if the rise of the current signal input to the signal repeater 400 (specifically, the AND gate 460) is delayed, the signal repeater 400 (specifically, the AND gate 460) outputs the signal to the parent device 200 side. The pulse width of the current signal is shortened, and the master device 200 may not be able to detect the current signal.

  On the other hand, in the second embodiment, the base unit detection sections P1 and P2 are detected by detecting the output signal of the current signal input unit 450 input to the input port 420a of the control unit 421, and the control unit 421 When the current signal input to the input port 420c is detected within the parent device detection section P1 (S203), the control unit 421 has elapsed a predetermined time t2 from the time when the current signal input to the input port 420c is detected. Later, the signal output to the AND gate 460 (specifically, the input terminal 460b) is turned off (S205). As a result, even when a current signal delayed in rising and falling is input from the handset 300 side to the signal repeater 400a (specifically, the AND gate 460), the signal repeater 400a (specifically, The AND gate 460) can output a current signal having a pulse width shaped so as to be within the parent device detection sections P1 and P2 to the parent device 200 side. As a result, it is possible to prevent a current signal detection failure in the parent device 200 and to perform stable long-distance communication.

  Further, the control unit 421 monitors the output signal of the voltage signal input unit 430 and turns off the signal output to the input terminal 460b of the AND gate 460 until the start time S2 of the parent device detection section P2 comes next. To do. Thus, even when current noise is input from the slave unit 300 side to the signal repeater 400a, current noise is not output to the master unit 200 side until the next start time S2 of the master unit detection section P2 comes. Therefore, it is possible to prevent erroneous detection on the base unit 200 side due to current noise and perform stable long-distance communication.

  The present invention is used in, for example, a signal transmission system for transmitting a current signal from a child device to the parent device, for example, a lighting control system, but can also be used in a signal transmission system other than the lighting control system.

  1 signal transmission system, 40a, 40b communication circuit, 100 2-wire communication line, 200 master unit (first device), 300 slave unit (second device), 400, 400a signal repeater, 410 signal transmission unit, 420 , 421 control unit, 430 voltage signal input unit, 440 voltage signal output unit, 450 current signal input unit, 460 AND gate, 470 current signal output unit, 480 primary side power generation unit, 490 secondary side power generation unit.

Claims (5)

A signal repeater that relays a signal transmitted between a first device and a second device,
A current signal input unit that outputs a current signal input from the second device side;
It has a first input terminal, a second input terminal, and an output terminal connected to the current signal input unit, and only during a period when a signal is input to the first input terminal and the second input terminal An AND gate that outputs a signal from the output terminal;
A control unit having a first input port for monitoring a voltage signal input from the first device side, and an output port for outputting a signal to the second input terminal of the AND gate;
A voltage signal input unit that outputs a voltage signal input from the first device side toward the first input port of the control unit;
A current signal output unit that outputs a current signal input from the AND gate toward the first device;
The control unit turns on signal output to the second input terminal of the AND gate when the first device starts detecting a current signal, and the AND gate is turned on after a predetermined time has elapsed. The signal relay to turn off the signal output to the second input terminal.   2. The signal repeater according to claim 1, wherein the control unit detects a time point at which the first device starts detecting a current signal based on an output signal of the voltage signal input unit.   After the first device finishes detecting the current signal, the control unit goes to the second input terminal of the AND gate until the first device starts detecting the current signal again. The signal repeater according to claim 1, wherein the signal output is turned off. The control unit has a second input port for monitoring an output signal of the current signal input unit,
After the first device starts detecting the current signal, when the control unit detects the output signal of the current signal input unit, the control unit detects the output signal of the current signal input unit. The signal repeater according to claim 1, wherein the signal output to the second input terminal of the AND gate is turned off after elapse of a predetermined time.   After the first device finishes detecting the current signal, the control unit goes to the second input terminal of the AND gate until the first device starts detecting the current signal again. 5. The signal repeater according to claim 4, wherein the signal output is turned off.

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