Programmable logic controllers (PLCs) use fast, deterministic functions, such as logic, sequencing, timing, counting, and arithmetic algorithms, to control machines and processes. They use analog and digital signals to communicate with end nodes (reading sensors and controlling actuators, for example). Typical methods of communication include current/voltage loops, Fieldbus, and industrial Ethernet protocols.
The industry has a continuing tendency to increase the number of sensor and control nodes in the remote area, causing a corresponding increase in the number of I/O module nodes in the controller—and some distributed control systems (DCS) can handle thousands of nodes. This concentration of nodes brings increased temperature-related challenges, especially for systems that implement the 4-mA to 20-mA loop communications standard.
Perhaps the biggest and most relevant challenge to the system designer is the need for greater efficiency and reduced power consumption, as the inefficiency of existing systems results in wasted power and increased operating costs. This article explains the challenges of designing such systems for greater efficiency and introduces the AD5755, a versatile, 4-channel, 16-bit digital-to-analog converter (DAC) as a more integrated solution to help resolve these issues.
The article is presented as a pdf file, in two parts (no registration required):
Part 1: System overview, and power dissipation concerns, click here.
Part 2: System error checking and diagnostics under fault conditions, flexible output-range programmability, communicating additional information over the 4- to 20-mA current loop, AD5755 complete solution, click here.
About the author
a system applications engineer for the Industrial and Instrumentation segment
at Analog Devices, Inc. (Limerick, Ireland). After working in test-development
engineering at Microsemi, he joined ADI in 1998. He spent three years in an
applications role in Shanghai. He graduated in 1995 from the University of
Limerick, Ireland, with a bachelor's degree in electronic engineering.
The last and final day of the show is usually has the most relaxed atmosphere and this year that proved to be the case once again. It is the shortest day of the show lasting from just 9:00 AM to 3:00 PM.
After having a pretty good first day of the show, I was looking forward to a good second day and it did not disappoint. The second day of the show on Wednesday is the longest day of the show as the exhibit hours go from 9:00 AM until 6:00 PM (day one is 9:00 AM to 5:00 PM and day three is 9:00 AM to 3:00 PM).
It sure doesn’t seem like it has already been a year since IMS2014! Well, technically, it hasn’t been since IMS2014 was in June last year. Once again this year IMS (International Microwave Symposium) is in a state known for its sunshine albeit this time sans the humidity. This year the show visits sunny Phoenix, Arizona.