Quad 16-Bit Voltage-/Current-Output DACs Save Space, Cost, and Power in Multichannel PLCs from Analog Devices

By Colm Slattery - Analog Devices

Overview

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.

System

The levels of communication in a typical industrial control system are shown in Figure 1. Until recently, the distributed input/output (remote I/O and PLC) would typically be connected using such open or proprietary protocols as Modbus, PROFIBUS (process field bus), or Fieldbus. Nowadays, there is an increasing interest in using PROFINET, a form of industrial Ethernet protocol that is designed for the fast exchange of data between Ethernet-based devices.

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About Analog Devices

Innovation, performance, and excellence are the cultural pillars on which Analog Devices has built one of the longest standing, highest growth companies within the technology sector. Acknowledged industry-wide as the world leader in data conversion and signal conditioning technology, Analog Devices serves over 60,000 customers, representing virtually all types of electronic equipment. Celebrating over 40 years as a leading global manufacturer of high-performance integrated circuits used in analog and digital signal processing applications, Analog Devices is headquartered in Norwood, Massachusetts, with design and manufacturing facilities throughout the world. Analog Devices' common stock is listed on the New York Stock Exchange under the ticker “ADI” and is included in the S&P 500 Index.

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Editor's Contact Information:

Howard Wisniowski

781/937-1517

howard.wisniowski@analog.com