The programmable logic controller, more commonly known as the Plc, plays a role in practically every self-operating manufacturing process. The Plc is an electronically programmable device capable of practically infinite combinations of relays, contacts, and timing circuits used to control industrial machinery of all types and sizes. It is essentially a computer designed to withstand a harsh manufacturing environment. It was designed to replace complicated theory of relays, cam switches, and other electromechanical circuits. The first Plc's were introduced in the late 1970's and they continued to grow in popularity since the day of their release.
Plc's are produced today by numerous major manufacturers together with Siemens, Allen Bradley, Koyo, Fuji, Telemecanique, and Mitsubishi as well as a host of others. The programming of the Plc is performed through proprietary software produced by the exact manufacturer. Software among Plc's is not compatible and the logic programming, although it is very similar, has many subtle differences over the dissimilar brands. The program stored in the Plc is called the ladder logic program. Problems in the ladder program can become quite complicated and that is an entirely dissimilar subject altogether. Hardware problems however, are fairly similar and can be easy to diagnose if you know a diminutive about the singular model and it's input and production configuration.
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Hardware failure of the brain, or main processor, is rare. It can be as a matter of fact diagnosed visually most often by an illuminated fault indicator on the face of the Plc. An internal power furnish failure would be a possibility if the Plc screen or power indicator were not lit and the technician verified that the strict voltage is applied to the power terminals. Some Plc's are adequate with an internal fuse which can also fail. These problems are not quite as common as a failure of an input or production terminal.
Inputs and outputs are ready in many configurations and voltages. Both Ac and Dc are ready separately and sometimes in the same unit. These input/outputs can be both digital and analog and can be configured as a transistor production or as a dry relay contact. On both the input and production side it is essential to decide the specifications of the Plc first. Having the suitable Plc software ready at the time of troubleshooting is also necessary.
The first recommendation would be to correlate the illuminated inputs and outputs against the software in real time. An illuminated input not displaying properly as an energized input in the software is an indication of a failed or open input terminal. On the production side, an illuminated concluding not conducting the allowable production voltage can mean one of two things, the production has failed in an open position, or an improper voltage is being applied to the common production terminal. The only way to verify this would be through the use of a multimeter set on the allowable voltage scale.
Overall, Plc hardware troubleshooting is not complex, yet it needs to be approached in an orderly fashion because both hardware and software are required to work in harmony for a Plc to achieve its intended tasks.
How to Troubleshoot Plc Hardwareprogrammable logic controllers 4th edition
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