Digital Input Module - Digital Output Module of Mitsubishi PLC Melsec

1. Types of Digital Input Module.
1A. Sink Type of Digital Input Module.
For the Sink Type digital Input Module, the existing driving input point runs from signaler of pilot joined, like limit switch, push-button switch, proximity switch, to inside of module, the frequent point at the module will be N pole common. And if immediacy switch is linked, the type sensor Switch of PNP Open Collector should be utilized. We call this type of Input Module as Sink Type.

1B. Source Type of Digital Input Module.
For the Digital Input Module source Type, the existing already transfers the soaking point from the P phase power linked to module and streams to signaler of pilot linked to the input module of PLC, like limit switch, switch of push-button, switch of proximity and the input point would be energized. The general point at the element would be P pole common. And if immediacy switch is linked, NPN Open-Collector Type sensor Switch should be utilized. We call this module input type as Source Type.

1C. Input Module of Digital AC.
For the Input Module of Digital AC, added resolving circuit that from AC to DC and voltage dropping circuit to robust to CMOS or TTL are live in the stage of input. The rest fundamental circuit is not so greatly different with input module of digital DC. Users should think and choose the type of sensor and common power type in case of the input module of digital DC.

2. Types of Digital Output Module.
2A. Digital Output Module Sink Type.
For the Digital Output Module Sink Type, the current from source of power P pole runs output device like Solenoid Coil, Relay that shift Actuators and the load are determined by switching device of semi-conductor in the PLC, the general point of load is + P Pole Common and switching device of semi-conductor will be Type of NPN. It calls this module output type of Sink Type.

2B. Digital Output Module Source Type.
For the Digital Output Module Source Type, the P pole power source already joins to output module of PLC, the output device like Solenoid Coil, Relay that shift Actuators is determined by PNP type semi-conductor. In this case, the output device of current drives goes out from inside PLC to loads, the loads common is N Pole Common. It calls this output module type as Source Type.

2C. Digital Output Module with Relay.
For the Digital Output Module with Relay, the relay mechanical contact driven by electronic circuits devices. The relay contact not polarities and use DC Power source / AC Power source.

2D. Digital Output Module with Solid State Relay (SSR).
Digital Output Module with Solid State Relay (SSR) can be used in the DC/AC as power driven. The Solid State Relay (SSR) Output can be used only AC power source and can not be used in the DC power source.

(source : http://program-plc.blogspot.com)