The electrical power system movement’s security or not had the close relationship with the system running status then, regarding the electric power dispatch department, if could real-time grasp the electrical power system various part of running status comprehensively, carried on the long-distance monitor, to guarantee system’s security, stable, the economical movement had the very vital significance without doubt. The electric power long-distance monitor uses the serial mode to carry on the correspondence generally, guaranteed that the data the reliable transmission is one of its most important technical specifications. As a result of the industry scene’s adverse circumstance as well as electrical power distribution system’s long-distance transmission, the disturbance is makes the fortuitous mistake and the influence overall system reliability service primary cause. Sharpens system’s antijamming ability is an electric power long-distance monitoring important research direction.
System survey
This system is a on lower position machine form industry power distribution observation system, according to the functional need, the lower position machine selected the control function quite formidable to grind the Chinese IPC-610 industrial control computer (IPC: Industrial Personal Computer), it has nearly 20 ISA slots and the PCI slot’s passive main line ledger wall as well as the corresponding CPU board, the I/O board and so on, may transform systematic each module like A/D, video frequency gathering, the correspondence, the I/O mouth input output and so on to insert the card the form to build the building block to combine equally likely, expands a complex control system conveniently. Has selected two PC-6313 multi-purpose analog input/analog output board card, matches takes over the job which the corresponding sensor and the implementing agency complete undertake. Various lower positions machine can according to need to the multi-channel simulation quantities, the switch quantity to carry on the examination and the control. This system according to needs to 64 group simulation quantities (voltage, electric current, power factor, active power, reactive power and so on) and 16 group switch quantities (each going beyond a line switch minute switches on condition, to compensate capacitor’s condition and so on) to carry on the examination, may carry on the output control to 16 group switch quantities (switch, solenoid valve, relay). Its structure diagram as shown in Figure 1.
Figure 1 lower position machine system diagram
The superior machine may choose ordinary PC, may also act according to the system use environment, the choice and lower position machine same IPC. The superior machine may issue the instruction and any carries on the correspondence with it connected lower position machine, collects various lower positions machine transmission simulation quantity and the switch quantity information, carries on the related analysis, to compile, processing and so on report generation, and carries on the monitoring and the macroscopic dispatch to various lower positions loom system.
In the power distribution observation system, on the lower position machine is away from far, to sharpen system’s antijamming ability, has used the RS-485 serial telecommunications bus standard. The RS-485 main line uses the difference transmission, has the transmitting range far, to contact many, the segment few characteristics, has become in the distributional supervisory system the data transmission first choice standard. IPC does not have the RS-485 connection, for this reason must provide the RS-232/RS-485 connection, this system has used the deep standard company’s 7250/7521 switch. And, 7521 to have the embedded CPU intelligence communication controller, may reduce the system programming quantity, enhances system’s reliability and timeliness, what this system actual use is the 7521D module, 7521D in the module has 5 the nixietube, may use the programmed control it to extinguish brightly, supervisory system’s movement. In addition, 7521D and 7521 functions are the same. The following introduction all no longer differentiates 7521 and 7521D.
This system communication module’s segment schematic drawing as shown in Figure 2, the design is 1 superior machine control 8 lower positions machine, may also carry on the expansion according to electrical power distribution system’s actual need.
Figure 2 has the intelligence connection module network segment schematic drawing
7521 intelligence communication controller synopsis
7521 function synopses
7521 are in the deep standard company’s 752N intelligence communication controller’s one kind, may support a RS-232 equipment. In the module inlays AMD Corporation’s Am188TMES controller, is loaded with the MiniOS7 embedded operating system. May be RS-485 the network any RS-232 equipment, assigns an only address. The module contains the double watch-dog electric circuit: A hardware module watch-dog and a software main engine watch-dog, protects the main engine and 7521 modules. Simultaneously its RS-485 end has the 3000V high pressure isolation, but prevents the industrial noise disturbance effectively.
7520 modules are ordinary RS-232/RS-485 level switches, does not have the intelligent correspondence function. But its RS-485 end has the 3000V high pressure isolation similarly. No longer gives unnecessary detail in this.
7521 working patterns
7521 have two kind of working patterns, one kind is the development work pattern, one kind is the normal work pattern.
When develops the pattern, (RS-232) receives PC 7521 COM1 mouth the serial port and after establishing the good correspondence form, 7521 the PC keyboard will take its standard the input, the PC monitor takes its standard the output. Under this way, may carry on the system parameters the disposition and user program downloading.
When normal work pattern, 7521 will carry out the procedure which approaches by the AUTOEXEC.EXE document middle finger. Uses when as the intelligence communication controller, 7521 in its FLASH ROM already preassemble two documents: AUTOEXEC.EXE and 7521.EXE, after starting, may by AUTOEXEC.EXE document autoloading 7521.EXE, thus completes the intelligent correspondence the initialization disposition. The user may also download own application procedure to change 7521 functions to 7521.
7521 module function order summary
after 7521 orders divide into the master control computer transmission receives the order for the module order and the module the response two parts.
Transmission part forms of field orders: (leading character) (address) (CHK)(CR), each item explains as follows separately.
①(leading character): 1 byte, indicates the order the type. The module control command is usually divided into several different types, uses some special characters through the leading character, like $, #, ~ and so on carries on the classification.
②(address): Two bytes, indicated the order will deliver to module. The address range is 00~FF, therefore has 256 addresses.
③(order): 1 or the many bytes, assign the module execution the order. These order usual use different digit expresses the different function.
④(CHK): The redundancy check and (CheckSum), the utility program will possess the transmission the character in ASCII to according to the fixed price the address value adding together, retains a final byte, opens around two characters to do for the verification value.
⑤the (CR):Enter key, in VB was vbCr, the expression order conclusion.
after 7521 receive the order, in the most situations will return gives a main engine response string of character. This response string of character form: (leading character) (address) (data) (CHK)(CR)
The response string of character (data) is only different with the order string of character form, other parts same. The data part must act according to the concrete order explanation.
7521 have 30 practical orders, has provided the more perfect driver. The user does not need oneself to compile the communication protocol, only need install good 7521.exe and the related archive file according to the operating manual on the master station computer, connects the computer and 7521 modules correctly, after the initialization, namely may start to work.
On lower position machine communications system antijamming design
Although the RS-485 main line standard has the strong antijamming ability, but in actual use process, as a result of the scene environment bad, situations and so on electromagnetic interference, still will affect the correspondence the reliability, the most typical question was the data transmission presents the error code, serious possibly appeared halts. Therefore, adopts essential enhances reliable and the antijamming ability measure is very important. In this system, has carried on the antijamming design from the hardware line and the software design two aspects.
System communication hardware antijamming measure
On the hardware line, is mainly from aspects and so on isolation, interface standard and wiring considered:
(1) this system’s RS-485 connection is uses is balanced the driver and the difference receiver’s combination, simultaneously uses the shield the twisted pair line, the anti-noise jamming performance is good.
in (2) course of communications, because the impedance does not match not continuously with the impedance, possibly will cause the signaling, will affect the signal the transmitting range. Twisted pair line characteristic impedance generally in 110~130 OMEGA, this system in a transmission line end termination 120Ω matched impedance by erasure signal reflection.
(3) this system selects 7520/7521 has 3000V the isolation RS-232/RS-485 transformation connection, as shown in Figure 3.
Figure 3 7520/7521 module internal circuit schematic drawing
May see by Figure 3, RS-485 end and power source end with place a region, what RS-485 end use turns on the power source. The RS-232 end is the module interior after the transformation power source, the power source has the 3000V quarantine measures around the transformation. Because the noise origin mostly comes from the power source end, the formidable noise will follow the power line to enter in the module, so long as but this disturbance in the extent of protection, then guaranteed that the RS-232 end the equipment is not damaged, will thus serve the protection master control computer’s purpose.
7521 protection principles and 7520 are the same, may protect the lower position computer not the RS-485 network in noise jamming.
System communication software antijamming measure
In the reality system design, must guarantee that the data transmission the reliability, cannot leave the hardware and software’s coordinated work. For guarantee data transmission accuracy, when software design must take certain measure.
the (1)7521 intelligence communication controller has the CheckSum verification function. Uses in the data transmission process accumulates and verifies the way, might cut the data transmission error ratio greatly. The CheckSum computational method like chart 4 and shown in Figure 5.
Figure 4 time output command accumulation and verification flow
Figure 5 inspection returns result accumulation and verification flow
For example the transmission order string of character is $012 [Enter], the leading character ($), the address (01), orders (2) three ASCII value adding together, the result to be as follows separately:
CheckSum=0×24 0×30 0×31 0×32=0×B7
Finally the final two characters are “B” and “7″, them and in routing directive’s behind, [Enter] front, the string of character which finally transmits is $012B7[Enter], so completed one to have the CheckSum order string of character.
When the main engine uses CheckSum the way will order the transmission, must in advance calculate this CheckSum the value, receives the string of character which the order the module will also receive to carry on time CheckSum again the computation, when the two’s result will be consistent, this time transmission was then considered that will be correct; If the two’s result is inconsistent time, the module will return to the corresponding error message.
Similarly, the main engine when CheckSum activates the situation which receives the module returns the string of character, must to the Checksum value carry on the verification, confirms the transmission process the accuracy.
7521 leaving the plant establish for activate CheckSum. In order to guarantee that the data transmission the accuracy, this system design to activate CheckSum, available orders the $AAKN activation.
the (2)7521 module contains two kind of watch-dog mechanisms. The first kind of mechanism is the hardware watch-dog which monitors 7521 modules, it belongs to the hardware reset line, after the starting, automatic movement, its watch-dog fixed time time is 1.6s. This line can monitor the module the operation condition, when the module is under the bad working conditions to cause the work is not normal, this monitoring wire can cause the module automatic reset. When system normal work, should “feed the dog” at least in 1.6s one time, avoids repositioning. If 7521 replacements, may transmit “$AA5″ the order to make it to restore normally. Its flow as shown in Figure 6.
Figure 6 7521 hardware watch-dog replacement post-processing means
The second kind of mechanism is the software main engine watch-dog. The software main engine watch-dog may monitor main engine’s condition. If the main engine halts, all 7521 output module will return to their preinstall the safe mode to carry on the safekeeping of security. When main engine normal operation, once in a while should transmit “the main engine is normal” the order to avoid the watch-dog replacement. Its flow as shown in Figure 7
Figure 7 software main engine watch-dog flow
Experiment test data and analysis
According to the system design and the laboratory condition, have carried on the serial communication data test, as shown in Table 1.
May see from the above analysis result, joins the CheckSum verification which and the watch-dog mechanism in the RS-485 serial communication system the intelligence communication controller has, may reduce serial communication effectively the error rate, enhances the correspondence data the success ratio. System’s antijamming ability had enhanced greatly.
Concluding remark
This system has made the perfect antijamming design from the hardware and the software two aspects, because the intelligence communication controller brings the CheckSum verification and the software and hardware watch-dog function, only needs the corresponding order activation then. Reduced the hardware cost and the software work load, system’s extendibility and the maintainable enhancement. The experiment proved that this system has the good timeliness and the reliability, the data error rate is low. Again auxiliary by measures and so on software filter and redundancy check, may further enhance the system performance. Therefore this article has certain theory and the practice reference value to the similar design.
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