1 Internal mark M: The “internal mark†in Siemens plc is marked with the English letter M, which is equivalent to the “internal relay†often mentioned in PLCs of other companies. It is used to register the intermediate operation result of the PLC program. In the PLC program, the contents of the internal flag bits can be continuously updated and changed during execution as the program is executed.
2 Special internal flag SM: The special internal flag of PLC is marked with the English letter SM. The difference between it and the internal flag is: the special flag SM has a special meaning, it can reflect the working status and control information inside the PLC, and Used by the PLC user program.
The special flag SM is divided into two parts: "read only" and "read and write". The "read-only" signal is automatically generated by the PLC, and only the results can be used in the program, and the "write" (or output) operation cannot be performed.
3 accumulator AC: S7.200 and S7-400 have four 32-bit accumulators ACCU0 ~ ACCU3: S7-300 has two 32-bit accumulators ACCU0, ACCU1. The contents of the accumulator can also be processed in the form of bytes, words or double words, with AC0 to AC3 as absolute addresses. When the accumulator is accessed in bytes (or words), the lower 8 bits or lower 16 bits of the accumulator are used.
4 Sequence control relay S (S7-200 only): In the S7-200 PLC, a sequence control relay (SCR) can be used, which is marked with the English letter S, used to organize the PLC program operation or enter the corresponding program step.
5 data block DB/DI (S7-300/400 only): In S7-300/400 series PLC, you can use the data block DB to store the processing result or data of the program. The data block can be in the address of DB (or DI). The following is specified in decimal form.
The contents of the data block can also be used in the form of binary bits, bytes, words, double words. For binary bits, the address is DBX+. + (or DIX *.*) form specification; for bytes, words, double words in the data block, the address is DBB**, DBW**, DBD** (DIB ̈+, DIW**, DID*** Form specification.
The IDA system is a new product that Sinco has put on the market in recent years. IDA is an abbreviation for Intelligent Data Collection. The main components of the system are: sensors, multi-channel modules, interface repeaters, terminal boxes, I/R modules, power supplies, personal computers, sensing cables, buses, various lightning protectors, bus power controllers, overvoltages Protector, manual reading adapter and portable reading display, etc. The multi-channel module converts the sensor signal into a digital form and transmits it to the personal computer on site via the IDA bus. The PC will convert the data obtained from the engineering unit and save it to a floppy disk. If necessary, the PC can also analyze and compare the input data to preset alarm limits and issue alarms. Data can be printed, displayed, and can be repeatedly returned from the front PC to the rear PC for many times. The front PC is used for data recording and the rear is used for data analysis, and the data is transmitted by modem or floppy disk. The rear PC is responsible for data archiving, data analysis, drawing and report generation of the database. The Tennessee Engineering Administration (TVA) in the United States adopted IDAS in the monitoring of the Fontena Dam. The system works well and can also be used for the monitoring of landslides and tailings dams.
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