V. Digital and analog signals Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Pushbuttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC repres... [2008-12-16]

This is the first in a three-part series on programmable logic controllers by Armand L. Rogado, Senior Electrical Engineer for KEPCO/ KOPEC - Ed. I. Executive Summary The purpose of this discussion is to define the difference and to understand the specific application of programmable logic controllers(PLC) vs. distributed control systems(DCS). For the manufacturers in the process industries, the procedure for selecting the best automation technology is challenging. It is imperative to unders... [2008-11-07]