The external input signal can be understood as pressing the button (PB0) and the output signal as switching on the indicator (L). The program is based on the operation of input and output relays. Generally speaking, it is a dedicated controller (computer type) that controls output devices according to a fixed program based on signals sent by input devices. The role of PLCs is to enable sequential control via the program. Use in large scale becomes impractical in terms of time and operation. Offers more flexibility and extendibility than the relay type. It is difficult to find the cause and replace when there is a relay failure. PLC modules can be replaced individually. Since relay contacts are used, they may develop poor contacts and have a limitation of life in the case of prolonged use.Įquipment failure can be monitored by peripheral software, etc. There is no alternative other than to modify wiring. They basically offer on/off control only.Ĭan be altered freely by modifying the program. In addition to original sequence control, PLCs also enable a wide variety of functions such as analog positioning, data processing and communication.Ĭomplex control using a number of relays is difficult from the standpoints of economy and reliability. Programs enable complex control to be achieved. Difficult modification of cabling after changing the control.Īs a result, PLC controllers quickly began to be used on a large scale as programmable controllers in production plants and installed in production lines in order to factory production (FA).Difficult assembly and connection of a large number of different types of elements.Inaccurate contact and high wear of components.Everything was placed in the control cabinets, so you can imagine how big they must have been. The modern ladder known from the PLC replaces wiring between contactors, relays and other special elements. Until the late 1960s machine control was based on the “relay-contactor” technique. But why they were created and what are they used in practice for? At the beginning a little bit of history… This is what the contemporary online encyclopedia claims. PLC ( Programmable Logic Controller) – a universal microprocessor device designed to control the operation of a machine or technological device.
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