Programmable logic controller: Difference between revisions

Revision as of 12:35, 12 December 2024

Revision as of 15:13, 18 December 2024

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[[Digital signal|Discrete (digital) signals]] can only take ''on'' or ''off'' value (1 or 0, ''true'' or ''false''). Examples of devices providing a discrete signal include [[limit switch]]es and [[photoelectric sensor]]s.<ref name=":8">{{Harvnb|Bolton|2015|pp=23–43}}</ref>

[[Analog signal]]s can use voltage or current that is analogous to the monitored variable and can take any value within their scale. Pressure, temperature, flow, and weight are often represented by analog signals. These are typically interpreted as integer values with various ranges of accuracy depending on the device and the number of bits available to store the data.<ref name=":8" /> For example, an analog 0 to 10&nbsp;V or 4-20 &nbsp;mA [[current loop]] input would be [[analog-to-digital converter|converted]] into an integer value of 0 to 32,767. The PLC will take this value and translate it into the desired units of the process so the operator or program can read it.<!--[[User:Kvng/RTH]]-->

===Redundancy===

Some special processes need to work permanently with minimum unwanted downtime. Therefore, it is necessary to design a system that is [[fault- tolerant and capable of handling the process with faulty modules]]. In such cases, to increase the system availability in the event of hardware component failure, [[Redundancy (engineering)|redundant]] CPU or I/O modules with the same functionality can be added to a hardware configuration forto prevent preventinga total or partial [[Plant process and emergency shutdown systems|process shutdown]] due to hardware failure. Other redundancy scenarios could be related to safety-critical processes, for example, large hydraulic presses could require that bothtwo PLCs turn on output before the press can come down in case one outputPLC does not turn offbehave properly.<!--[[User:Kvng/RTH]]-->

==Programming==