(1) Select the appropriate PLC model and I/O points, and select the special function module when there are special function requirements.
(2) Familiar with the selected PLC programming instructions and compilation software.
(3) Carry out soft component planning, including internal relays, holding relays, data registers, timers, counters, etc.
(4) Program planning, generally in the order of fault extraction, fault handling, manual processing, automatic processing, and output processing. Relatively large projects or equipment are processed in segments and blocks according to functional units, such as hoists, migrations, jacking and rotating devices in an automated production line, etc., they should be programmed in segments and blocks according to the above-mentioned units.
(5) A brief paragraph note should be added before the program written in sections and blocks, explaining the function of the program, and the corresponding process flow can be indicated if necessary. The order of the position of the block or segmented program in the overall program should be basically arranged in the order of the process flow, so as to facilitate the readability of the program.
(6) Before the program design, the equipment should be abstracted, such as stop, emergency stop, overload, overrun, overtime, safety light curtain, collision stop, door switch and other common factors are extracted, placed in the starting circuit or starting the main control, interlocking circuit, as the premise of the whole program structure, on this basis, the program is divided into two functional areas, automatic and manual.
(7) The common factors of the manual functional area of the program structure, such as manual, endangering the personal safety of the equipment, etc., are extracted and placed in the manual main control and interlocking circuit to protect, shield and alarm the manual control.
(8) The common factors of the automatic functional area of the program structure, such as automatic, overrun, overtime, etc., are extracted and placed in the automatic main control and interlocking circuit, and the equipment under automatic control is protected, shielded and alarmed. A general principle is that under the premise of ensuring safety, strictly restrict the entry of equipment and loosely restrict the output of equipment.
(9) When designing the program, the total reset function of the program should be designed, so that the user can restore the normal operation of the equipment as soon as possible in the case of equipment failure. The total reset should give full consideration to the safety of equipment and personnel during the reset process.
(10) When switching from automatic mode to manual mode, the program should clear the output and intermediate states in automatic mode. In particular, when the SET command is used in automatic mode, it must be cleared with the RESET command in manual mode.
(11) It is strictly forbidden to use double output in the program, that is, the same output statement or the same output coil appears 2 times or more in the program. Under different mode conditions, the output of the same output point is transferred by intermediate relays, and finally gathered together and parallel to the output point.
(12) When using the touch screen, the control area and status area common to the touch screen and the PLC shall not be programmed for other functions.
(13) For the special module of PLC, before use, it should be found out whether the control area and the status area occupy the working word, and if it is occupied, these working words shall not be programmed in other aspects.
(14) The input, output, intermediate relay, timer, counter, data register, etc. of the PLC should be annotated in Chinese. The input and output should also have component name numbers. The corresponding input point, in general, is connected to the NO contact by default for the peripheral switch, and the NC contact must be indicated in the annotation. All notes should be clear and not misleading, and generic references should be minimized.
(15) After the project debugging is completed, the system must retain the final software program, and the saved file name should include the project number/author/date information/version number, etc.
(16) About program encryption: The password of the encryption program must be saved in a special file, and the corresponding user name + password + authority must be indicated, and distributed to at least two or more people to understand the password, so as to prevent the loss of the password and the inability to open the program.
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