Programmable Logic Controller Basic Hardware

Compact and Modular – These Two (2) are some of the major advantages brought by the utilization of PLC systems. Compact may be defined simply as being small in size yet performs so many functions. Modular on the other hand refers to the feature where a module can be installed or added at any instance as required by the system.

Sa article na ito, pag-uusapan natin kung anu-ano ang mga basic module na ginagamit sa mga PLC systems. Magandang balikan ang isa sa aming nakaraang topic, Choosing The Right PLC for your application upang makatulong na maging mas malinaw ang topic natin ngayon. .

S7-1200 PLC, isang halimbawa ng compact PLC mula sa Siemens.
S7-400 PLC mula sa Siemens, isang halimbawa ng ng Large, Modular PLC.
Modicon M340 by Schneider Electric. Isang halimbawa ng Medium, Modular PLC.





1. Rack
Rack is sometimes called Chassis or Backplane. This hardware provides mounting to the PLC system. Aside from this, it also carries the circuitry that distributes power to other modules. Depending on PLC brands, some racks can handle Four (4), Seven (7), Twelve (12) or even Sixteen (16) modules.

Small PLCs – Majority of this PLC range are mounted by means of a DIN Rail. 
Medium / Large PLCs –
Requires a PLC rack. Comes in different sizes or lengths to house different configurations.

2. Power Supply
Power Supply provides power to the system bus to energize the circuitry of any attached module to the rack. The circuitry is housed by the Rack module.

Small PLCs – Ang mga PLC na ito kadalasan ay mayroong built-in power supply.
Medium / Large PLCs – Power Supply unit for this PLC family is purchased separately. They may come in different power ratings to provide sufficient power to the bus.

3. Central Processing Unit (CPU)
Central Processing Unit is the intelligence of the PLC system. Ang module na ito ay responsable sa pag-execute ng logic at iba pang functions. Ang mga CPU rin kadalasan ay may kasama nang communication ports para magsilbing Upload / Download interface  at makipag-usap sa iba pang electronic devices through an assigned protocol.

Small PLCs – Ang mga PLC na ito ay mayroong CPU at Power supply na magkasama sa isang assembly.
Medium / Large PLCs – CPU unit for this PLC family is purchased separately. They may come in different ranges of processor speed and built in memory.

4. Signal Modules
Signal modules provide interface to signalling and actuating devices. There are different types of Input / Output modules.

Discrete Input Module – Provides interface to On/Off signal devices including majority of manually actuated switches, auxilliary contacts – Run / Stop, Remote / Local, Auto / Manual and fault conditions of motors, position feedback of valves, cylinders or any other moving equipment and other many other devices.

Pushbutton and Switches – These devices produce Discrete Signals

Discrete Output Module – Provides interface to On/Off actuating devices katulad ng mga Pilot Lamps, Direct On-Line (DOL) Motors, On/ Off Valves, Cylinders, Dampers, Fans at iba pa.

Pilot Lamps – Example of Discrete Output Devices

Analog Input Module – Provides interface to analog signaling devices such as Transmitters, converters, transducers, Thermocouple, RTDs, strain guages, etc.

Analog Input Devices – Transmitters and Transducers produces Analog signals in reference to the actual process measurement.

Analog Output Modules – Provides interface to devices that uses analog signals as the actuating reference. Ang mga devices na ito ay mas kilala sa field na “modulating”. Devices and equipment such as Variable Frequency Drives (VFDs), Modulating Valves, Positioners, Dampers and Louvers are some of the most common instruments that accepts this type of signal.

Variable Frequency Drive (VFD), Dampers and a Louver

Small PLCs – Majority of small PLCs have built in IO modules that can accommodate at least 10 Discrete Input, 10 Discrete Output, Two (2) Analog Input, One (1) Analog Output. If more IOs are needed, small PLCs can be expanded up to 128 Input 128 Outputs typically. Check your PLC datasheet to know the specific limit of your PLC.

Medium / Large PLCs – Karamihan sa mga PLC sa range na ito ay walang built-in I/O modules. Sa halip, kailangang bilhin ang mga modules depende sa pangangailangan ng system. A monitoring system can simply have an Discrete Input module only. A valve sequencing system can have both Discrete Input and Discrete Output modules. A larger system may require the use of all types of signal modules. You can use any signal module you need as long as the rack can still handle the installation.

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Next Topic: Programmable Logic Controllers Advanced Hardware

2 thoughts on “Programmable Logic Controller Basic Hardware”

    1. Hello!

      Do you mean may analog output from PLC going to VFD as reference frequency? If yes, pwede kang gumamit ng HI and LO limiter instruction sa PLC program. The function of the instruction is to limit both ends ng signal according sa limit na kailangan.

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