畢業(yè)論文設(shè)計(jì)-基于plc的水廠濾池自動(dòng)控制系統(tǒng)設(shè)計(jì)-預(yù)覽頁(yè)
【正文】 are code This will ensure that data from one area cannot accidentally be used in the wrong area Similarly by merely looking at an address one can tell whether the data es from a radio telemetry system another PLC a SCADA system or whether it was generated within the software code External devices such as SCADA systems radio telemetry systems and other PLCs on a work can then also be configured in a standard way for data exchange All these factors contribute to quality control as well as the ease and speed with which software can be evaluated andor modified Flags outputs or coils generated internally should be annotated to describe the function it actually performs and not the function it will eventually perform For example if a bit has to be set when several interlocks are healthy and this bit is then later used to start a pump the bit should be annotated as All Interlocks Healthy rather than Start Pump This will ensure that when someone else evaluates the software he can see what causes that particular bit to be on or off rather than having to search for the code which controls it to establish how it functions Annotation of program files works All program files works segments etc should be annotated with a description of the actual logic it contains For example Water Treatment Plant Controls Pump Station Level Controls Mass of Balance Calculations etc This same annotation along with the description of the program structure and database structure should form part of the final documentation for that project Literally hours of time could be saved if the next person not the software design engineer has to find a specific area of logic control with properly annotated software and documentation Furthermore the original software design engineer might be called back to this project long after missioning and handover eg to do modifications and he would then be grateful that the software and documentation was annotated properly if he can save face in front of the client by quickly and effectively being able to implement the necessary changes Annotation of the PLC software logic This is one of the most important parts of PLC annotation because it gives the next person an insight into how the design engineer thought and reasoned when he designed the software No two people think alike PLC software is almost like a persons signature because each person writes it in his own unique way The next person to work with this software therefore has to establish how the designer thought and reasoned before he can effectively understand and evaluate the software Even ones own thoughts and reasoning change as one grows in experience If the original design engineer therefore has to make changes to his own software long after it was designed even he would save hours if he can easily determine the reasoning behind the relevant sections of PLC logic It is for these reasons that every section work etc of the PLC logic must be clearly described The description should explain the objective of the software logic eg Pump 1will start if the discharge valve is open and the gland seal water is on but not if the sump level is low or it will start if Bypass is selected and the sump level is not low rather than duplicate the ladder logic in verbal terms eg If bit 00320 is on and bit 00321 is on and bit 00322 is off or if bit 00323 is on output 00024 will be on This will provide the user of the software with an insight into how the controls should work as well as with the logical implementation thereof The same applies to software used to perform calculations Show the calculation being done Maintain data integrity PLC software always involves the transfer of data either from the field to the PLC from The PLC to the field between PLCs between PLC and between PLC and radio telemetry systems and so on Any of these systems can fail One must therefore never merely assume Where analogue inputs are read from the field this data should be read into a buffer area first and only if one is sure there were no problems with the data transmission should this data be transferred to the relevant areas in the PLC software where valid data is then used If an error in the data transmission has occurred or if a fault occurred in the analogue input module data which might be corrupted should not be transferred for use in the PLC control logic and the failure must be alarmed so that action can be taken In the event of such a failure one needs
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