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.
Wait a minute. Let’s see if I understand this. (Here I’m channeling you, the puzzled reader, after you’ve grabbed me in the coffee break of a Filter Wizard lecture morning). The frequency of the nth harmonic of a sinusoid is n times that of the fundamental. The nth harmonic distortion is defined as the ratio of the amplitude of the nth harmonic to the amplitude of the fundamental. So the 1st harmonic distortion is… the ratio of the amplitude of the fundamental to the amplitude of the fundamental and that’s… unity. I. Do. Not. Understand.
Single-ended signals are very common, but increasingly signal paths are being converted to differential signals as part of the signal chain. The benefits of differential signaling are particularly appealing with low supply voltage systems and for driving analog-to-digital converters (ADCs).
If you spend any time at all looking at alternative energy sources such as wind power and solar energy, you'll quickly discover one inconvenient truth: alternative energy production is both highly unpredictable and uncorrelated to energy demand.
In 2009, Time Magazine called the Iridium global satellite program a tech failure. Motorola backed it for global satellite phone usage and filed for bankruptcy in 1999 after spending $5B to build and launch the infrastructure of satellites