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.
Without even thinking about it, consumers depend on technology throughout the day as they send texts, turn on lights, and drive home from the office. But that technology depends on something that usually goes unnoticed until there's a problem.
I thought it would be good to continue looking at the example I gave in my last blog where we looked using fewer LDOs and combining power supply rails on an ADC while maintaining isolation with ferrite beads.
Electronic equipment and power management is becoming increasingly critical as our power grid ages and renewable energy comes on line. In response, new technologies are being developed to protect equipment from power disturbances and fluctuations.