Understand more about Various Types of PLC Input/output Modules to match with manufacturing system structure

PLC IO Modules is part of Programmable logic controllers (PLCs) that up to this time become a substantial system in the scope of industrial manufacturing. PLC is the digitally operating electronic equipment, which uses a programmable memory for the internal storage of instructions by executing specific functions just like logic, sequencing, timing, counting, and arithmetic to control via digital or analog I/O modules various types of machine or process.

PLC IO Modules has function to receive (input) and send out (output) many types of electrical and electronic signals. Therefore, a PLC has high flexibility in interfacing with computers, machines and many other peripheral systems or devices.

When we talking about input/output module, there are various types of PLC IO Modules can be implemented to a PLC including discrete input/output, analog input/output, specialty I/O modules and communication modules. Users can select the proper type to match their manufacturing system structure.

Discrete PLC IO Modules versus Analog Inputs

Discrete PLC IO Modules signals are two-state signals including Input ON or OFF, 1 or 0. Analog input signals are values as follow:

  • 0 to 10 volts DC
  • -10 to +10 volts DC
  • 4 to 20 milliamps
  • 0 to 20 milliamps
  • -20 to +20 milliamps

Typical analog signals come from pressure, position, temperature and motor speed. Analog input signals are current or voltage. The analog input modules also convert analog signals to PLC IO Modules digital words.

Example SLC 500 Combination PLC IO Modules

PLC IO Modules Allen-Bradley’s SLC 500 is the compact controller for wide array of big applications from food processing to steel fabrication. This handy tool already used by million users around the globe as its versatility and powerful stand-alone or distributed industrial control assignments.

The PLC IO Modules features:

  • Identifier as to type of module input, output and combination input or output.
  • Screw terminals for connecting field devices. Each screw terminal will have a unique identifier that calls an address. Each field device input screw terminal correlated to a status indicator.
  • Status indicators. Status indicator will be on when the input point detects an input signal. Status indicator will have same address identifier as input screw terminal.
  • Removable terminal blocks.

PLC IO Modules Binary Data Representation

Using Allen-Bradley SLC 500 controller, the PLC IO Modules can communicate to others using groups of letters arranged into words. The PLC uses groups of bits (1 or 0) called words. The different bit patterns show different information. SLC 500 series of PLCs are the 16-bit computers, which it also indicates the great measurement on computer capability because of the length of the data words on which it can operate.


There are various types of PLC IO Modules can be integrated into the PLC system. The example above shows us PLC IO Modules analog type and discrete model can be applied with Allen-Bradley SLC 500 controller. The mechanism provides versatility and easy to read information inputted and outputted by the modules. SLC 500 is the 16-bit computer that can communicate to other using bit patterns to show different information.

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