What are the Different Parts of a PLC?

Опубликовано: 17 Июнь 2024
на канале: RealPars
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https://www.realpars.com/blog/parts-o...

⌚Timestamps:
00:00 - Intro
00:14 - Power supply
01:13 - Central Processing Unit (CPU)
01:59 - Memory
03:10 - Isolation bus
04:03 - Network card/interface
04:38 - Programming interface
04:50 - Inputs and outputs
05:58 - Conclusion

PLC parts include the power supply, central processing unit, memory, isolation bus, network card, input and output cards, and programming interfaces.

The power supply converts power that will be used by the central processing unit (CPU), memory, and the rest of the components. It normally is fused. It may be a specific line voltage and varies by country. In the United States, it's typically 120 VAC and 60 Hz.

Many companies have gone toward supplying the PLC with 24 volts due to safety. Thus, the source power coming in could be 220 VAC at 50 Hz and then converted to 24 Volts AC.

A PLC has a controller that is a CPU. The CPU will be able to take a “program” and convert the program into machine language.

There will also be an interface such as an external PC for programming so that an executable program may be downloaded to the controller.

A program is downloaded into the CPU, and signals based on decisions are sent out to the field. The program's purpose is to monitor the inputs and make decisions based on the application the PLC is being used for.

Memory may be part of the CPU or located on a separate card. Wherever the memory is located, it stores data. The program is stored in memory as a run-time executable file. Each input and output will have a register or a location where the CPU keeps its values.

Output registers are used to correlate to physical output locations that will receive a signal once the program decides what to do with the input feedback.

Understanding how your PLC memory is configured will influence how tag assignments are made and help you understand register assignments for inputs and outputs.

The power supply provides source power to drive the CPU and the input and output cards, or any kind of power on the PLC rack.

Power and communication can be bussed on the PLC backplane. Think about it as where the “cards” are seated on a bus. The cards on the PLC rack share power. They get the power off the bus.

When sizing a fuse or circuit breaker for the PLC rack, the power consumption across the whole rack should be understood.

The PLC has to be able to be networked or programmed so there needs to be some physical communication port.

This communication port may be an Ethernet IP port, a USB port built into the CPU, or a separate card type that connects to the bus.

There are other protocol types as well, like Profibus, serial communications, and sometimes wireless radio interfaces. Another type of interface is IO-Link , and this RealPars IO-Link video explains IO-Link in more detail.

PLCs’ have a programming interface where a connection may be made via Ethernet or a USB port. This port is used to connect the software design environment to the PLC.

The PLC chassis has slots that are allocated in the rack for the input and output (IO) cards. Field terminal blocks are wired to the IO cards.

These allow versatility due to being discrete, analog, high-speed counter, or thermocouple inputs. There are many types of cards and card configurations.

Power, space on the rack, and application needs will determine what kind of cards are required for a PLC to execute and meet the application requirements successfully.

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IO-Link: https://www.realpars.com/blog/io-link

PLC Programming Made Easy course series: https://www.realpars.com/courses?*=PL...

Remote IO:    • What is Remote I/O?  

PLC Fundamentals for Control Systems: https://www.realpars.com/courses/plc-...

PLC Hardware Fundamental: https://www.realpars.com/courses/plc-...

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