DL-1200 MODEM-Finding of faults in the remote device channel
In the DL-1200 MODEM rural network transformation, almost all substations have been refitted or newly installed with telecontrol equipment. However, since the telecontrol equipment at the main station end and the remote control equipment (RTU) at the substation end are often not manufactured by one manufacturer, the transmission channels are composed of different equipments such as carrier waves, optical ends, microwaves, and spread spectrum produced by different manufacturers, and there are also thousands of passages. Meter audio cable transmission, so often in the installation and debugging barriers or high error rate issues. The problems encountered in the installation, operation and maintenance are discussed. The methods and steps for finding common faults in remote devices are introduced.
1 The role of telekinetics
The voltage, power, load, and breaker operation status of remote power plants and substations are collected, compiled into data and transmitted to the dispatch center for display. The dispatched commands are transmitted to the factory and station in data format for remote operation. These data are telecontrol signals. The use of "telemetry, remote messaging, remote control, remote adjustment" four remote to summarize the role of remote movement. The task of the transmission channel is to provide an unimpeded path for these data. Some of these data are directly connected to the channel's digital port for transmission, and some are the data through the modulator (MODEM) into an audio signal, the transmission channel audio interface to the other party, the other party to restore the original demodulator data.
2 Coordination of telecontrol equipment
In terms of telecontrol equipment, if the channel is unblocked, in addition to the stability of the equipment, the following aspects should be unified in cooperation.
2.1 The baud rate must be unified
Baud: Baud is the amount of signal change that occurs every second for a device (such as a power modem). It represents changes in the signal, not how much data is transmitted. It represents the number of times the state of the communication line changes every second.
Baud Rate: The number of bits that the serial port sends (or receives) data per second is called the baud rate.
According to the current remote system used by China's power sector, there are three types: 300Baud, 600Baud, and 1200Baud. The baud rate is not uniform, and the remote device channel is definitely not accessible. It is not only necessary to set the communication baud rate of the host station master station and the slave station lower station to be the same, but also to set the corresponding circuit breaker settings in the MODEM.
2.2 The audio frequency should be unified
The original Ministry of Electric Power stipulates that the FM frequency after MODEM is: 300 Baud 3000±150 Hz; 600 Baud 2880±200 Hz. By convention 1200 Baud 1700±500 (400) Hz. In the original power department regulations, the center frequency of 600 Baud can be set to 2880±60N (N is a positive integer) Hz according to user requirements, but the frequency deviation must be ±200 Hz. The remote manufacturer or configured MODEM shall comply with the above settings and be adjustable. The frequency is not only right, but the accuracy is higher. Frequency calibration can be used frequency meter, frequency meter, multimeter for nuclear school. Also note that the audio signal is a good sine wave and can be observed with an oscilloscope. In the on-site debugging often appears MODEM output audio frequency is not allowed, some maximum deviation reaches 50Hz; Also appeared the signal waveform is the triangle wave example. When measuring frequency or observing waveforms, try to send a single frequency. If the frequency is not correct, it will not work. Inaccurate frequency or bad waveform will cause serious error.
2.3 Positive and negative logic to be unified
The positive logic is that when it is "1", it is a high frequency, and when it is "0", it is a low frequency; if the negative logic is opposite, it is a low frequency when it is "1" and a high frequency when it is "0". Sometimes the telemetry level is normal and the waveform is good, but all received are wrong codes, and the logic of the two parties should be considered.
2.4 address code to be unified
The source and destination addresses of the two parties' messages should be unified. If one party does not set up according to the agreement, or the two parties do not agree in advance, it will not work.
2.5 Synchronizing words to be unified
The synchronization word is equivalent to the scout. If the correct synchronization word is received before each message, the channel is basically normal. Three groups of EB90 or D709 are now used as synchronization words. If the synchronization words of the two parties are not uniform and the required synchronization prefix is ​​not received, subsequent messages cannot be received.
2.6 The Statute of the Message must be unified
If the synchronization words of the two parties can be demodulated after the other party receives the data, the other data cannot be solved. That is, the telecontrol message protocols of the two parties are not the same. This requires the telecommuters of both parties to have a unified protocol, and to carefully check them, so that uploads can be collected, transmitted, displayed, and sent from the next operation command to the execution.
3 Inspection of transmission equipment
As far as the transmission equipment is concerned, it seems that one must first look at the road and pass it through without repairing it.
3.1 Audio transmission method
After the telecontrol signal is connected, it is necessary to use the earphone to listen to the input and output terminals first. The two frequencies are the single frequency. The two frequencies are data signals. The uplink signal is generally dual-tone; the single frequency is the test frequency, and the downlink signal is It may be a single tone, but the downlink signal is also a double tone when the command is issued at regular intervals. Some describe the signal as a two-tone sound and a single sound as a howling. Hear the audio to prove that the road has been repaired. Experienced from the audio level, purity, clarity, you can roughly determine whether the remote device can not, why not.
After listening to the audio frequency, select the frequency with the frequency selection meter and check which frequency point swings to the maximum value to determine the actual baud rate of the remote motion. It is advisable to set the test frequency for remote operation, select the frequency selection table or measure it with a frequency meter, and some multimeters also have a frequency range. If there is a difference between the frequency and the specified value, the remote device should be informed of the frequency calibration and adjustment. If you have heard or measured a third frequency, such as 300Baud 3000Hz, it is certainly a problem with the remote equipment, which often encountered in the field debugging.
The inspection of the road is not even, and that is to check the transmission quality of the transmission equipment. It is necessary to proceed from the following six aspects.
3.1.1 The convergence of transmission levels should be consistent
The general rule is 0Baud in, 0Baud out. However, there are many discrepancies in the scene, such as the remote control device output is not adjustable or the adjustment range is small, the remote control device to the transmission device access point, the audio cable is too long. Normal input is considered normal at -20 to +10 baud, and should be adjusted on the transmission equipment. For example, the power line carrier, the external line to send relative to the voice signal, 300Baud is 8dB lower than the voice; 600Baud is 3.5dB lower than the voice; when 1200Baud is transmitted, no voice is transmitted and the level is adjusted according to the voice level standard. The output should be a good sine wave at 10dB, and the range is also between -20 and +10dB, which can be adjusted according to the requirements of the telecontrol equipment. Also pay attention to some transmission equipment, the input interface rated level is not 0Baud, but -14Baud, 0 baud level access will cause overload, resulting in serious distortion.
3.1.2 Interface impedance should match
The impedance of the MODEM transceiver of the telecontrol equipment and the transceiver interface of the transmission equipment are both specified 600Ω.
3.1.3 There should be enough noise protection
The standard of the original power department is 17Baud, while the general carrier can reach 25Baud or more, and the optical transceiver is higher.
3.1.4 To Provide Sufficient Passbands According to Baud Rate
300Baud transmits 2850Hz and 3150Hz, takes 2550~3400Hz bandwidth; 600Baud transmits 2680Hz and 3080Hz, takes 2200~3400Hz bandwidth; 1200Baud occupies 300~3400Hz all voice frequency bandwidth. The power carrier should be adjustable according to the needs, such as DPLC-2000 power carrier machine, with adjustable bandwidth; and optical end, microwave, spread spectrum and other equipment generally use the four-wire E / M path in the receiving and sending paths, should be 300 ~ 3400Hz All voice bandwidth does not need to be adjusted.
Voice uses four-wire transmission, plus two lines with ground as the loop, mutual start signal transmission, interface method called four-wire E/M.
3.1.5 Transmitting and Receiving Channels shall have noise resistance of 60dB or more.
Noise Defence: The difference between the transmission signal level and the noise level is called the noise defense degree. The higher the degree of noise protection, the stronger the anti-interference ability; the lower the noise protection level, the more severe the transmission signal is.
At the scene, it was found that the optical transceiver's two-to-four-wire conversion program was set incorrectly, sending and receiving instances of serious cross-connections. There are also examples where the transmission and reception lines are connected in pairs.
3.1.6 Transmission waveform distortion is small
Observe the waveform with the oscilloscope at the input end and output end, should basically be identical. Including the waveform should be no gap or small gap.
3.2 Digital transmission method
The digital interface usually uses an RS-232 interface. It should be noted that the connection distance between the device interfaces cannot be too long. The standard is 15m, preferably two devices are adjacent, or in the same room. The farthest is the neighboring engine room, which cannot exceed the standard too much. If more than tens of meters, apply RS-422 or other interface to convert.
For the RS-232 interface, remote devices (including other terminal devices, such as computers) should send energy to the voltage, generally should be ± (2 ~ 12) V or so, when receiving less than the voltage; carrier, optical and other transmission The device is unable to detect the voltage, and the receiver should be able to measure the voltage of ± (2~12)V. The connection method is:
Telecontrol equipment - transmission equipment
Send, receive, and receive
Transmission equipment - transmission equipment
Send receive and receive hair
Regardless of the connection between devices, pay attention to the ground to be connected to the same ground. RS-232 standard plugs, whether they are 9-pin or 25-pin, have a ground wire and must be connected.
In general, the connection port is: there is no electricity, no electricity, no electricity, no Mo. The total land is the key.
Through the inspection of the above several steps, the telecontrol still fails or the bit error rate is high. Finally, a segmented self-loop method can be used to determine the range of the compression fault. The method is to send a synchronization word, a timing command or a message at one end, and observe the data with the computer at the receiving end. The received data should be consistent with the issued data. If no or error is received, the failure is within the loop. Remote data cannot be uploaded. The MODEM at the station side can be restarted. The scope of inspection is:
• MODEM output self-loop input: check MODEM itself;
• The input line of the transmission device is self-looped on the output line: check the connection line;
• The local transmission equipment has high-frequency self-loop: check the local transmission equipment;
• The opposite transmission device outputs the input-to-input large loop loop: Check the channel and the peer transmission device.
Since the big loop is self-looped, it will be the addition of the two uplink and downlink channels, so the error rate will be superimposed. However, it is also one of the frequently used methods for on-site debugging.
DL-1200 MODEM DL-1200 Power Modem Power Modem Power Line Modem Power Line Modem Remote Modem
In the DL-1200 MODEM rural network transformation, almost all substations have been refitted or newly installed with telecontrol equipment. However, since the telecontrol equipment at the main station end and the remote control equipment (RTU) at the substation end are often not manufactured by one manufacturer, the transmission channels are composed of different equipments such as carrier waves, optical ends, microwaves, and spread spectrum produced by different manufacturers, and there are also thousands of passages. Meter audio cable transmission, so often in the installation and debugging barriers or high error rate issues. The problems encountered in the installation, operation and maintenance are discussed. The methods and steps for finding common faults in remote devices are introduced.
1 The role of telekinetics
The voltage, power, load, and breaker operation status of remote power plants and substations are collected, compiled into data and transmitted to the dispatch center for display. The dispatched commands are transmitted to the factory and station in data format for remote operation. These data are telecontrol signals. The use of "telemetry, remote messaging, remote control, remote adjustment" four remote to summarize the role of remote movement. The task of the transmission channel is to provide an unimpeded path for these data. Some of these data are directly connected to the channel's digital port for transmission, and some are the data through the modulator (MODEM) into an audio signal, the transmission channel audio interface to the other party, the other party to restore the original demodulator data.
2 Coordination of telecontrol equipment
In terms of telecontrol equipment, if the channel is unblocked, in addition to the stability of the equipment, the following aspects should be unified in cooperation.
2.1 The baud rate must be unified
Baud: Baud is the amount of signal change that occurs every second for a device (such as a power modem). It represents changes in the signal, not how much data is transmitted. It represents the number of times the state of the communication line changes every second.
Baud Rate: The number of bits that the serial port sends (or receives) data per second is called the baud rate.
According to the current remote system used by China's power sector, there are three types: 300Baud, 600Baud, and 1200Baud. The baud rate is not uniform, and the remote device channel is definitely not accessible. It is not only necessary to set the communication baud rate of the host station master station and the slave station lower station to be the same, but also to set the corresponding circuit breaker settings in the MODEM.
2.2 The audio frequency should be unified
The original Ministry of Electric Power stipulates that the FM frequency after MODEM is: 300 Baud 3000±150 Hz; 600 Baud 2880±200 Hz. By convention 1200 Baud 1700±500 (400) Hz. In the original power department regulations, the center frequency of 600 Baud can be set to 2880±60N (N is a positive integer) Hz according to user requirements, but the frequency deviation must be ±200 Hz. The remote manufacturer or configured MODEM shall comply with the above settings and be adjustable. The frequency is not only right, but the accuracy is higher. Frequency calibration can be used frequency meter, frequency meter, multimeter for nuclear school. Also note that the audio signal is a good sine wave and can be observed with an oscilloscope. In the on-site debugging often appears MODEM output audio frequency is not allowed, some maximum deviation reaches 50Hz; Also appeared the signal waveform is the triangle wave example. When measuring frequency or observing waveforms, try to send a single frequency. If the frequency is not correct, it will not work. Inaccurate frequency or bad waveform will cause serious error.
2.3 Positive and negative logic to be unified
The positive logic is that when it is "1", it is a high frequency, and when it is "0", it is a low frequency; if the negative logic is opposite, it is a low frequency when it is "1" and a high frequency when it is "0". Sometimes the telemetry level is normal and the waveform is good, but all received are wrong codes, and the logic of the two parties should be considered.
2.4 address code to be unified
The source and destination addresses of the two parties' messages should be unified. If one party does not set up according to the agreement, or the two parties do not agree in advance, it will not work.
2.5 Synchronizing words to be unified
The synchronization word is equivalent to the scout. If the correct synchronization word is received before each message, the channel is basically normal. Three groups of EB90 or D709 are now used as synchronization words. If the synchronization words of the two parties are not uniform and the required synchronization prefix is ​​not received, subsequent messages cannot be received.
2.6 The Statute of the Message must be unified
If the synchronization words of the two parties can be demodulated after the other party receives the data, the other data cannot be solved. That is, the telecontrol message protocols of the two parties are not the same. This requires the telecommuters of both parties to have a unified protocol, and to carefully check them, so that uploads can be collected, transmitted, displayed, and sent from the next operation command to the execution.
3 Inspection of transmission equipment
As far as the transmission equipment is concerned, it seems that one must first look at the road and pass it through without repairing it.
3.1 Audio transmission method
After the telecontrol signal is connected, it is necessary to use the earphone to listen to the input and output terminals first. The two frequencies are the single frequency. The two frequencies are data signals. The uplink signal is generally dual-tone; the single frequency is the test frequency, and the downlink signal is It may be a single tone, but the downlink signal is also a double tone when the command is issued at regular intervals. Some describe the signal as a two-tone sound and a single sound as a howling. Hear the audio to prove that the road has been repaired. Experienced from the audio level, purity, clarity, you can roughly determine whether the remote device can not, why not.
After listening to the audio frequency, select the frequency with the frequency selection meter and check which frequency point swings to the maximum value to determine the actual baud rate of the remote motion. It is advisable to set the test frequency for remote operation, select the frequency selection table or measure it with a frequency meter, and some multimeters also have a frequency range. If there is a difference between the frequency and the specified value, the remote device should be informed of the frequency calibration and adjustment. If you have heard or measured a third frequency, such as 300Baud 3000Hz, it is certainly a problem with the remote equipment, which often encountered in the field debugging.
The inspection of the road is not even, and that is to check the transmission quality of the transmission equipment. It is necessary to proceed from the following six aspects.
3.1.1 The convergence of transmission levels should be consistent
The general rule is 0Baud in, 0Baud out. However, there are many discrepancies in the scene, such as the remote control device output is not adjustable or the adjustment range is small, the remote control device to the transmission device access point, the audio cable is too long. Normal input is considered normal at -20 to +10 baud, and should be adjusted on the transmission equipment. For example, the power line carrier, the external line to send relative to the voice signal, 300Baud is 8dB lower than the voice; 600Baud is 3.5dB lower than the voice; when 1200Baud is transmitted, no voice is transmitted and the level is adjusted according to the voice level standard. The output should be a good sine wave at 10dB, and the range is also between -20 and +10dB, which can be adjusted according to the requirements of the telecontrol equipment. Also pay attention to some transmission equipment, the input interface rated level is not 0Baud, but -14Baud, 0 baud level access will cause overload, resulting in serious distortion.
3.1.2 Interface impedance should match
The impedance of the MODEM transceiver of the telecontrol equipment and the transceiver interface of the transmission equipment are both specified 600Ω.
3.1.3 There should be enough noise protection
The standard of the original power department is 17Baud, while the general carrier can reach 25Baud or more, and the optical transceiver is higher.
3.1.4 To Provide Sufficient Passbands According to Baud Rate
300Baud transmits 2850Hz and 3150Hz, takes 2550~3400Hz bandwidth; 600Baud transmits 2680Hz and 3080Hz, takes 2200~3400Hz bandwidth; 1200Baud occupies 300~3400Hz all voice frequency bandwidth. The power carrier should be adjustable according to the needs, such as DPLC-2000 power carrier machine, with adjustable bandwidth; and optical end, microwave, spread spectrum and other equipment generally use the four-wire E / M path in the receiving and sending paths, should be 300 ~ 3400Hz All voice bandwidth does not need to be adjusted.
Voice uses four-wire transmission, plus two lines with ground as the loop, mutual start signal transmission, interface method called four-wire E/M.
3.1.5 Transmitting and Receiving Channels shall have noise resistance of 60dB or more.
Noise Defence: The difference between the transmission signal level and the noise level is called the noise defense degree. The higher the degree of noise protection, the stronger the anti-interference ability; the lower the noise protection level, the more severe the transmission signal is.
At the scene, it was found that the optical transceiver's two-to-four-wire conversion program was set incorrectly, sending and receiving instances of serious cross-connections. There are also examples where the transmission and reception lines are connected in pairs.
3.1.6 Transmission waveform distortion is small
Observe the waveform with the oscilloscope at the input end and output end, should basically be identical. Including the waveform should be no gap or small gap.
3.2 Digital transmission method
The digital interface usually uses an RS-232 interface. It should be noted that the connection distance between the device interfaces cannot be too long. The standard is 15m, preferably two devices are adjacent, or in the same room. The farthest is the neighboring engine room, which cannot exceed the standard too much. If more than tens of meters, apply RS-422 or other interface to convert.
For the RS-232 interface, remote devices (including other terminal devices, such as computers) should send energy to the voltage, generally should be ± (2 ~ 12) V or so, when receiving less than the voltage; carrier, optical and other transmission The device is unable to detect the voltage, and the receiver should be able to measure the voltage of ± (2~12)V. The connection method is:
Telecontrol equipment - transmission equipment
Send, receive, and receive
Transmission equipment - transmission equipment
Send receive and receive hair
Regardless of the connection between devices, pay attention to the ground to be connected to the same ground. RS-232 standard plugs, whether they are 9-pin or 25-pin, have a ground wire and must be connected.
In general, the connection port is: there is no electricity, no electricity, no electricity, no Mo. The total land is the key.
Through the inspection of the above several steps, the telecontrol still fails or the bit error rate is high. Finally, a segmented self-loop method can be used to determine the range of the compression fault. The method is to send a synchronization word, a timing command or a message at one end, and observe the data with the computer at the receiving end. The received data should be consistent with the issued data. If no or error is received, the failure is within the loop. Remote data cannot be uploaded. The MODEM at the station side can be restarted. The scope of inspection is:
• MODEM output self-loop input: check MODEM itself;
• The input line of the transmission device is self-looped on the output line: check the connection line;
• The local transmission equipment has high-frequency self-loop: check the local transmission equipment;
• The opposite transmission device outputs the input-to-input large loop loop: Check the channel and the peer transmission device.
Since the big loop is self-looped, it will be the addition of the two uplink and downlink channels, so the error rate will be superimposed. However, it is also one of the frequently used methods for on-site debugging.
DL-1200 MODEM DL-1200 Power Modem Power Modem Power Line Modem Power Line Modem Remote Modem
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