Controlled monitoring signal transmission system

Abstract

The control monitoring signal transmission system of the present invention includes a parent station that performs data transmission and reception with a control unit, and a plurality of child stations that perform data transmission and reception with the parent station through a common transmission line in a transmission synchronization manner. Then, during a period between a frequency voltage region of a voltage frequency signal having a predetermined period and a predetermined duty ratio, when an impedance of a circuit formed by a plurality of internal circuits of the child station and the transmission line becomes higher than a start state before a voltage level is changed, the impedance changes to the first voltage level from a second voltage level that is lower than the first state.

Description

Technical Field

[0001] This invention relates to a control and monitoring signal transmission system that simplifies the wiring of signal lines between a master station on the control side and multiple substations on the controlled side, and transmits data via a common transmission line and a transmission synchronization method such as transmission frequency synchronization. Background Technology

[0002] In systems that centrally control multiple devices located within a facility, the reduction of wiring is widely implemented, a process known as wiring reduction. As a general method of wiring reduction, instead of directly connecting multiple machines on the controlled side to a control unit on the control side in parallel, a master station with parallel and serial signal conversion capabilities and multiple slave stations are connected to the control unit and multiple devices respectively. Data transmission and reception between the master station and the multiple slave stations are performed via serial signals through a common transmission line.

[0003] Furthermore, transmission synchronization methods, such as transmission frequency synchronization, are known as a method of transmitting and receiving data via serial signals through a common transmission line. Then, various methods for transmitting and receiving data between a master station and multiple slave stations using transmission synchronization have been proposed.

[0004] For example, Japanese Patent Application Publication No. 2002-16621 discloses a control monitoring signal transmission system in which a control signal is output from a master station in the first half of a frequency cycle in a serial pulse voltage signal region where the second half of a frequency cycle is the power supply voltage and the first half is a potential different from the power supply voltage, and in the second half of the frequency cycle, a high-frequency signal (hereinafter referred to as "frequency signal") is output from a slave station as a monitoring signal.

[0005] Furthermore, Japanese Patent Application Publication No. 2002-152684 discloses a control and monitoring signal transmission system, which divides the first half of a frequency cycle into two parts by time in a serial pulse voltage signal in which the second half of the frequency cycle is the power supply voltage and the first half is a potential different from the power supply voltage. In the divided part, a control signal from the master station and a monitoring signal from the slave station are output.

[0006] [Existing technical documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2002-16621

[0009] [Patent Document 2] Japanese Patent Application Publication No. 2002-152684 Summary of the Invention

[0010] [The problem the invention aims to solve]

[0011] In order to function as a frequency, the frequency voltage region of the serial pulsed voltage signal (hereinafter referred to as the "voltage frequency signal") used for synchronization between the master station and multiple slave stations must maintain a certain voltage level for a specified time. That is, the voltage frequency signal must have a duty cycle of a specified value or higher.

[0012] Therefore, a method was proposed to use frequency signals, similar to the prior art described above, where the duty cycle of the voltage frequency signal is maintained above a specified value while the frequency voltage region (defined in the prior art as the latter half of one cycle of the power supply voltage frequency) is used for data transmission and reception. However, once the frequency signal becomes high-frequency, around 1 MHz, the amplitude of the current change decreases due to the impedance of the transmission line, or the amplitude becomes unstable due to over-amplitude, resulting in undetectable variations. In other words, there are instances where the frequency voltage region in the voltage frequency signal cannot be used for data transmission and reception.

[0013] On the other hand, the potential changes during the period between frequency voltage regions in the voltage frequency signal have little impact on synchronization. Therefore, it is proposed to use the period between frequency voltage regions (the voltage level region different from the power supply voltage in the prior art) for data transmission and reception between the master station and the slave station, as in the prior art described above. Then, in order to perform data transmission and reception between the master station and the slave station during the period between frequency voltage regions, the voltage frequency signal used in this case has a predetermined period.

[0014] However, when the period between frequency and voltage regions is used for data transmission and reception between the master station and the slave station, the voltage level changes slowly due to circuit impedance and other factors, resulting in a so-called transition phenomenon. Due to the influence of this transition phenomenon, the accuracy of data transmission and reception will be reduced.

[0015] For example, when the voltage level changes through a combination of a P-channel MOS FET and a capacitor, and the voltage level in the voltage frequency signal changes from a high-potential frequency voltage region to a different voltage level (hereinafter referred to as "fall"), the voltage level change is slow. If the fall in the frequency voltage region is used as a synchronization reference point, the synchronization timing will be deviated, and a voltage level different from the voltage level that should have been detected will be detected. As a result, the data value obtained using the voltage level will become incorrect.

[0016] Furthermore, in terms of circuit configuration characteristics, the slowness of voltage level change when changing from a voltage level different from the voltage level of the high-potential frequency voltage region to the voltage level of the frequency voltage region (hereinafter referred to as "rise") is small, and its transition period is shorter than that of the fall. When data values ​​are captured using the time range from the synchronous reference point (fall) to the rise, there may be cases where the captured data values ​​become incorrect.

[0017] Moreover, the slowness of voltage level changes is not related to the period of the voltage frequency signal, but is determined by the circuit configuration. Therefore, the faster the period, the greater the impact on the accuracy of data transmission and reception.

[0018] Therefore, the object of the present invention is to provide a control and monitoring signal transmission system that can improve the accuracy of data transmission and reception during the period between frequency voltage regions using a voltage frequency signal with a specified period and a specified duty cycle.

[0019] [Technical means to solve the problem]

[0020] The control and monitoring signal transmission system according to the present invention includes a master station that transmits and receives data with a control unit and multiple substations that transmit and receive data with the master station via a common transmission line in a synchronous transmission manner. Then, during the period between frequency voltage regions of a voltage frequency signal having a predetermined period and a predetermined duty cycle, when the impedance of the circuit formed by the multiple internal circuits of the substation and the transmission line becomes higher than the initial state before the voltage level change in a first state that is set as the target of the voltage level change, the impedance changes to the first voltage level through a second voltage level that is lower than the first state.

[0021] [Comparison with the efficacy of existing technologies]

[0022] According to the present invention, when the impedance of the circuit composed of multiple internal circuits and transmission lines of the substation becomes higher than the initial state before the voltage level change in a first state that is set as the target voltage level after the voltage level change, the impedance changes to the first voltage level through a second voltage level that is lower than the first state, thereby shortening the transition period. That is, the error at the timing of synchronization caused by the transition period can be minimized. Therefore, the accuracy of data transmission and reception during the period between the frequency and voltage regions of the voltage frequency signal can be improved. Attached Figure Description

[0023] [ Figure 1 [This is a timing diagram of the transmission signal in an embodiment of the control and monitoring signal transmission system according to the present invention.]

[0024] [ Figure 2 [This is a system configuration diagram of the same embodiment.]

[0025] [ Figure 3 [This is the functional block diagram of the parent site.]

[0026] [ Figure 4 This is a schematic diagram illustrating the transmission sequence of the transmitted signals.

[0027] [ Figure 5 [This is a functional block diagram of the input substation.]

[0028] [ Figure 6 [This is the functional block diagram of the output substation.]

[0029] [ Figure 7 [This is a timing diagram of the transmission signal in another embodiment of the control and monitoring signal transmission system according to the present invention.] Detailed Implementation

[0030] An embodiment of the control and monitoring signal transmission system according to the present invention is described.

[0031] This control and monitoring signal transmission system is used to centrally control multiple devices and machines located in facilities such as factories at a control center. For example... Figure 2 As shown, it consists of a control unit 1, a host station 2 connected to common data signal lines DP and DN (hereinafter referred to as transmission lines), and multiple input substations 4, output substations 5, and input / output substations 6 configured in facilities on the controlled side and connected to the transmission lines. Furthermore, in Figure 2 In the diagram, each substation is represented as a single unit for convenience, but there is no limit to the type and number of substations connected to the transmission line.

[0032] The input section 7 connected to the input substation 4, the output section 8 connected to the output substation 5, and the input / output section 9 connected to the input / output substation 6 are devices configured in a facility serving as the controlled side.

[0033] As equivalent to input unit 7, various sensors such as reed switches, micro switches, push button switches, photoelectric switches, and others can be listed, but are not limited to these.

[0034] As equivalent to output unit 8, it can include, but is not limited to, actuators, (stepping) motors, solenoids, solenoid valves, relays, thyristors, and lamps.

[0035] Input / output unit 9 is a device that combines the functions of both input unit 7 and output unit 8. Examples of such devices include temperature controllers, timers, and counters, which also have the function of sending information to the host station 2 and performing output actions based on the data sent from the host station 2.

[0036] Alternatively, the input unit 7 can be an integrated input substation 70 that is integrated with the input substation 4. Similarly, the output unit 8 can be an integrated output substation 80 that is integrated with the output substation 5.

[0037] The control unit 1 includes a management and judgment mechanism 11 with calculation and processing functions and an input / output unit 12. The management and judgment mechanism 11 receives data from the master station 2 through the input / output unit 12 and performs necessary calculations and processing according to the program stored inside.

[0038] <The Composition of the Mother Site>

[0039] Mother station 2 is connected to the transmission line, such as Figure 3 As shown, it includes an output data unit 21, a management data unit 22, a timing generation unit 23, a master station output unit 24, a master station input unit 25, and an input data unit 26. Then, a voltage frequency signal with a predetermined period and a predetermined duty cycle, including control data, is output. At the same time, monitoring data output during the period between the frequency and voltage regions of the voltage frequency signal is captured from the input substation 4, the output substation 5, and the output input substation 6, and output to the output input unit 12 of the control unit 1.

[0040] The output data unit 21 delivers the data received from the control unit 1 as serial data to the master station output unit 24.

[0041] Based on the data received from the control unit 1, the management data unit 22 delivers the necessary data for the instructions to the substation in the management control data area (described later) to the master station output unit 24 as serial data.

[0042] The timing generation unit 23 consists of an oscillator circuit (OSC) 31 and a timing generation mechanism 32. Based on the oscillator circuit (OSC) 31, the timing generation mechanism 32 generates the timing frequency of this system and delivers it to the master station output unit 24 and the master station input unit 25.

[0043] The main station output unit 24 consists of a control data generation mechanism 33 and a line driver 34. The control data generation mechanism 33 outputs a voltage frequency signal containing control data to the transmission line via the line driver 34 based on the data received from the output data unit 21 and the timing frequency received from the timing generation unit 23.

[0044] like Figure 1 As shown, the voltage frequency signal is formed by connecting multiple frequency voltage regions with a fixed period, where a voltage level Ep higher than the threshold Est is maintained for a specified duration. In this embodiment, the voltage level Ep is set to +24V.

[0045] Furthermore, there are no restrictions on the frequency and voltage range as long as it functions as a synchronization frequency, and it can be appropriately determined according to the usage environment and conditions. For example, a specified duration can be maintained for a negative voltage lower than the connection level.

[0046] During the period between frequency voltage regions, data values ​​are represented by a voltage level Ep that is lower than the voltage level Ep of the frequency voltage region. However, the voltage level representing the data value can be appropriately determined according to the operating environment and conditions, and a voltage level higher than the voltage level Ep of the frequency voltage region can also be used. Similarly, the voltage level Ep of the frequency voltage region is a negative voltage that is lower than the grounding level.

[0047] Furthermore, in this embodiment, the impedance of the circuit formed by the internal circuits and transmission lines of all input substations 4, output substations 5, and input / output substations 6 (hereinafter referred to as "transmission circuit impedance") is greater than that of the frequency voltage region when the voltage level representing the data value is reached (first state). Then, a transition phenomenon occurs when the voltage level Ep in the frequency voltage region changes to the voltage level representing the data value.

[0048] The period between frequency and voltage regions is divided into four regions by time. Furthermore, in the following explanation, the four regions between frequency and voltage regions are designated as region I, region V, region F, and region P, according to the order of the voltage level transitioning from the voltage level Ep of the frequency and voltage regions to the point of near-fall.

[0049] In this embodiment, in regions I, V, and F, the voltage level lower than the threshold Ect is the voltage level representing the logic data value "1", and the voltage level higher than the threshold Ect is the voltage level representing the logic data value "0". In this embodiment, the threshold Ect is set between 10V and the grounding level (approximately 6V), but its value is not limited and can be set according to the usage conditions and environment. Furthermore, the correspondence between the voltage levels representing data values ​​and the logic data values ​​is not limited and can be appropriately determined according to the usage environment and state.

[0050] In this embodiment, region P is used only for output from station 2. A voltage level lower than the threshold Ect represents the logic data value "1", and a voltage level higher than the threshold Ect represents the logic data value "0". By increasing the duration of the region with higher voltage levels—that is, by making the duty cycle larger than a set value—it becomes less susceptible to noise, thus improving the stability of the frequency function. Furthermore, similar to regions I, V, and F, the correspondence between the voltage levels representing data values ​​and the logic data values ​​is not limited and can be appropriately determined based on the usage environment and state.

[0051] When the voltage level Ep in the frequency voltage region changes to the voltage level representing the data value, a voltage drop occurs until a low voltage level GND is reached (second state) where the transmission circuit impedance becomes lower than the voltage level representing the data value (first state). Then, the voltage level representing the data value changes after passing through the low voltage level GND. Furthermore, the state where the transmission circuit impedance becomes lower than the voltage level representing the data value can be created, for example, by making the low voltage level GND a level capable of clearing charge or back electromotive force retained in the circuit.

[0052] Furthermore, when the impedance of the transmission circuit in the state of representing the data value becomes smaller than that of the frequency voltage region due to circuit configuration, etc., when the voltage level representing the data value changes to the voltage level Ep of the frequency voltage region, the voltage level changes to the voltage level Ep of the frequency voltage region after the voltage level of the transmission circuit impedance becomes lower than that of the frequency voltage region.

[0053] Transmission order, such as Figure 4 As shown, the management data area, control monitoring data area, CRC area, and a series of subsequent areas between the start signal ST and the next start signal ST in the voltage frequency signal form a frame loop. Then, the control monitoring data area is used to transmit and receive stable data between the main station 2 and the input substation 4, output substation 5, and input / output substation 6.

[0054] Furthermore, unstable data not assigned to the control and monitoring data area is transmitted and received using the management data area. Additionally, the CRC area is used to determine if there are any transmission anomalies.

[0055] In the start signal ST, the voltage level Ep of the frequency voltage region in the management data area, control monitoring data area, and CRC area is maintained for a longer duration than that of the frequency voltage region. Furthermore, the duration of the start signal ST is not limited and can be appropriately determined considering usage conditions.

[0056] The mother station input unit 25 consists of a line receiver 35 and a monitoring data acquisition mechanism 36. The line receiver 35 receives voltage and frequency signals from the transmission line, performs waveform shaping, and delivers them to the monitoring data acquisition mechanism 36.

[0057] The monitoring data acquisition unit 36 ​​acquires data values ​​at the timing frequency delivered by the timing generation unit 23, based on the digital value of the voltage level of the voltage frequency signal delivered by the line receiver 35. Then, it delivers the data to the input data unit 26 as stable data DIO for the control monitoring data area and management data DEX for the management data area.

[0058] The input data unit 26 converts the serial input data received from the monitoring data acquisition mechanism 36 into parallel data, and outputs it to the input / output unit 12 of the control unit 1 as monitoring data and management monitoring data.

[0059] <Composition of Input Substations>

[0060] Input substation 4, such as Figure 5 As shown, it includes a substation input unit 40 that performs the main arithmetic processing, a substation line receiver 48 and a substation line driver 49 disposed between the substation input unit 40 and the transmission line. The substation line receiver 48 receives voltage and frequency signals from the transmission line, and the substation line driver 49 outputs monitoring signals to the transmission line.

[0061] The substation input unit 40 includes a transmission receiving mechanism 41, a management and control data acquisition mechanism 42, an address acquisition mechanism 43, an address setting mechanism 44, a management and monitoring data sending mechanism 45, an input mechanism 46, and a monitoring data sending mechanism 47.

[0062] In addition, the input substation 4 in this embodiment has a microcomputer control unit (MCU) as an internal circuit, which functions as the substation input unit 40.

[0063] The substation line receiver 48 receives voltage and frequency signals from the transmission line, performs waveform shaping, and delivers them to the transmission receiving mechanism 41.

[0064] The transmission receiving unit 41 determines the voltage level thresholds Est and Ect, and delivers the digital value of the voltage level of the voltage frequency signal delivered from the substation line receiver 48 to the management control data acquisition unit 42, the address acquisition unit 43, and the management monitoring data transmission unit 45.

[0065] The management control data acquisition unit 42 determines a start signal ST based on the digital value of the voltage level of the voltage frequency signal. Then, starting from the moment the start signal ST ends (in this embodiment, a drop), management data is acquired based on the digital value of the voltage level corresponding to the inter-pulse region of the management data region. The acquired management data is delivered to an unlabelled processing unit that performs processing based on the data.

[0066] Address acquisition mechanism 43 determines the start signal ST based on the digital value of the voltage level of the voltage frequency signal, and counts the frequency voltage region starting from the moment the start signal ST ends (in this embodiment, a falling signal). Then, it obtains the moment when this count value matches the self-station address data set by address setting mechanism 44. In addition, this moment becomes the moment when the data region (hereinafter referred to as "self-station region") allocated to the self-station in the voltage frequency signal begins (hereinafter referred to as "self-station region start moment").

[0067] The address acquisition mechanism 43 obtains the timing of the I region, V region, and F region based on the elapsed time starting from the decrease of the frequency voltage region.

[0068] Then, the address acquisition mechanism 43, which obtains the start time of the self-station region, activates the monitoring data transmission mechanism 47 during the period when the self-station's I, V, and F regions are assigned. Furthermore, if the self-station region is composed of periods between multiple frequency voltage regions, then until the end of the self-station region, each time the self-station's I, V, and F regions appear, the monitoring data transmission mechanism 47 is activated during the period of their respective power supply voltage regions.

[0069] The management monitoring data transmission unit 45 determines the start signal ST based on the digital value of the voltage level of the voltage frequency signal. Then, taking the end of the start signal ST as the starting point, it outputs signals in the I, V, and F regions, which are designated for outputting monitoring signals, during the period between the frequency voltage regions corresponding to the management data region.

[0070] In addition, the monitoring signal output from the management monitoring data transmission unit 45 will only be sent if the processing unit that has not yet received the data that should be sent to the mother station 2 is delivered.

[0071] The input unit 46 delivers the data input from the input unit 7 to the monitoring data transmission unit 47.

[0072] When the monitoring data transmission mechanism 47 is enabled by the address retrieval mechanism 43, it outputs the data delivered by the input mechanism 46 as a monitoring signal to the transmission line via the substation line driver 49.

[0073] <Composition of output substations>

[0074] Output substation 5, such as Figure 6 As shown, the system includes a substation output unit 50 that performs the main computational processing, a substation line receiver 48 disposed between the substation output unit 50 and the transmission line, and a substation line driver 49. The substation line receiver 48 receives voltage and frequency signals from the transmission line, and the substation line driver 49 outputs monitoring signals to the transmission line. Additionally, Figure 6In this context, the parts that are essentially the same as input substation 4 are given the same symbols, and their descriptions are simplified or omitted.

[0075] The substation output unit 50 includes a transmission receiving mechanism 41, a management and control data acquisition mechanism 42, an address acquisition mechanism 43, an address setting mechanism 44, a management and monitoring data sending mechanism 45, a control data acquisition mechanism 51, and an output mechanism 52.

[0076] The output substation 5 in this embodiment, like the input substation 4, has a microcomputer control unit (MCU) as an internal circuit, which functions as the substation output unit 50.

[0077] The transmission receiving unit 41 of the output substation 5 delivers the digital value of the voltage level of the voltage frequency signal delivered from the substation line receiver 48 to the management control data acquisition unit 42, the address acquisition unit 43, the management monitoring data transmission unit 45, and the control data acquisition unit 51.

[0078] The address acquisition mechanism 43 of output substation 5 obtains the start time of the self-station region by counting the high-potential regions starting from the end of the start signal ST, and obtains the timing of the P region in the self-station region based on the elapsed time starting from the drop of the frequency voltage region. In addition, the timing of the I region, V region and F region is also obtained for the output from the parent station 2 to the self-station.

[0079] Then, the address acquisition mechanism 43, which determines the start time of the self-station region, activates the monitoring data transmission mechanism 47 during the period when the P region of the self-station is allocated, and during the period when the I, V, and F regions are allocated. Furthermore, if the self-station region is composed of periods between multiple frequency voltage regions, then until the end of the self-station region, each time the I, V, F, and P regions of the self-station are allocated, the monitoring data transmission mechanism 47 is activated during the period of that power voltage region.

[0080] When the control data acquisition mechanism 51 is enabled by the address acquisition mechanism 43, it acquires control data based on the digital value of the voltage level of the voltage frequency signal delivered from the transmission receiving mechanism 41 and delivers it to the output mechanism 52.

[0081] The output mechanism 52 outputs information from the control data delivered by the control data acquisition mechanism 51 to the output unit 8, causing the output unit 8 to operate or stop.

[0082] <Composition of Input / Output Substations>

[0083] The input / output substation 6 includes the functions of both the input substation 4 and the output substation 5. It has the structure of both the substation input section 40 and the substation output section 50. Its structure is substantially the same as that of the substation input section 40 and the substation output section 50, so the illustration and description are omitted.

[0084] In this embodiment, the data values ​​in regions I, V, F, and P are acquired based on the voltage level detected at a predetermined time within each region. That is, data transmission and reception are performed by aligning the voltage level of the voltage frequency signal with the data value, but data transmission and reception can also be performed by aligning the duty cycle of the voltage frequency signal with the data value.

[0085] Figure 7 This is a timing diagram of the transmission signal in an embodiment where data is transmitted and received by making the duty cycle of a voltage frequency signal correspond to the data value. Additionally, in... Figure 7 In the description of the illustrated embodiments, regarding the... Figures 1 to 6 The embodiments shown assign the same symbols to substantially the same parts and simplify or omit their descriptions.

[0086] Figure 7 In the illustrated embodiment, the duration of the frequency voltage region, i.e., the duty cycle of the voltage frequency signal, corresponds to the data value. Furthermore, the duration of the frequency voltage region can be obtained by measuring the elapsed time from the decrease to the increase of the frequency voltage region.

[0087] exist Figure 7 In the illustrated embodiment, since the decrease in the frequency voltage region that serves as the reference point for synchronization has a fixed period, when the duration of the frequency voltage region is long, the elapsed time from the decrease to the increase in the frequency voltage region is short, and when the duration of the frequency voltage region is short, the elapsed time from the decrease to the increase in the frequency voltage region is long. Therefore, the duration of the frequency voltage region can be determined by the length of the elapsed time.

[0088] exist Figure 7 In this context, an elapsed time TL longer than the specified threshold represents a data value "1" corresponding to a short time length, while an elapsed time TS shorter than the specified threshold represents a data value "0" corresponding to a long time length. There are no restrictions on the correspondence between the time length of the frequency voltage region and the data value; it can be set appropriately according to the usage conditions. However, the time length of the frequency voltage region must be at least a certain length necessary for it to function as a frequency signal; that is, the duty cycle must be greater than the set value of the voltage frequency signal.

[0089] [Symbol Explanation]

[0090] 1. Control Department

[0091] 2 Mother Station

[0092] 4. Input Substation

[0093] 5 Output Substation

[0094] 6 Input / output substations

[0095] 7 Input Section

[0096] 8 Output Section

[0097] 9 Input / Output Section

[0098] 11. Management Judgment Body

[0099] 12 Input / Output Units

[0100] 21 Output Data Section

[0101] 22 Management Data Department

[0102] 23. Timing Generation Department

[0103] 24 Mother Station Output Department

[0104] 25. Mother Station Input Department

[0105] 26 Input Data Section

[0106] 31. Oscillator Circuit (OSC)

[0107] 32. Timing-generating mechanism

[0108] 33 Control data generation mechanism

[0109] 34 Line Drivers

[0110] 35 Line Receiver

[0111] 36 Surveillance data collection agencies

[0112] 40 Substation Input Department

[0113] 41 Transmission and Receiving Mechanism

[0114] 42 Management and Control Data Acquisition Organization

[0115] 43 Address Scraping Agencies

[0116] 44 Address Setting Agency

[0117] 45. Management and monitoring of data transmission agencies

[0118] 46 Input mechanism

[0119] 47. Surveillance data transmission agency

[0120] 48 Substation Line Receiver

[0121] 49 Substation Line Driver

[0122] 50 Substation Output Department

[0123] 51 Control Data Acquisition Mechanism

[0124] 52 Output Mechanism

[0125] 70 Input Department Integrated Substation

[0126] 80 Output Unit Integrated Substation

Claims

1. A control and monitoring signal transmission system, comprising: a master station for transmitting and receiving data with a control unit, and multiple slave stations for transmitting and receiving data with the master station via a common transmission line and in a synchronous transmission manner. in, During the period between frequency voltage regions of a voltage frequency signal with a specified period and a specified duty cycle, When the impedance of the circuit consisting of the multiple internal circuits of each substation and the transmission line becomes higher than the initial state before the voltage level change in the first state, which is set as the target voltage level after the voltage level change, the voltage level change is passed through the second voltage level of the second state, which makes the impedance lower than the first state, and then changes back to the first voltage level.

2. The control and monitoring signal transmission system as claimed in claim 1, wherein the period between the frequency voltage regions is time-divided into three or more regions.

3. The control and monitoring signal transmission system as claimed in claim 2, wherein during the period between the frequency voltage regions, there is a region that allows the timing of voltage level changes toward the frequency voltage region to be earlier and has a larger duty cycle than the prescribed duty cycle.

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