Before diving into the I/O modules section, this slide will help provide a perspective on where these modules fit on the overall factory automation infrastructure. The factory of today can be classified into three levels. At the very top is the operations and enterprise level. A level below is the control level, consisting of the main processing units for various systems used to control machinery and processes on the factory floor. Finally, there is the field level where the actual sensors and actuators are located. The I/O modules are mainly located at the control level in equipment such as Programmable Logic Controllers (PLC), Programmable Automation Controllers (PAC) and Distributed Control Systems (DCS). PLCs are computer based electronic control systems which consist of digital or analog I/O modules used to control machines/processes. These modules translate information to and from the field devices and the main controllers. Variations of the PLC include the PAC which has more integration and PC-like processing functions to tackle more complex operations such as machine control and the DCS (used extensively in process control). The DCS includes distributed controller elements with local control connected together by networks for communication/monitoring.