A programmable logic controller (PLC) system leverages various types of sensors and feedback mechanisms to monitor and control machine or system interactions by collecting, storing, and analyzing data. Acquiring data from sensors involves precision measurement and processing of analog variables, such as voltages and currents, where there is a need to often sense very small changes. Accuracy, drift, noise rejection, and processing speed are all very important characteristics in these systems.

ADI now offers a PLC evaluation board, which is a complete industrial process control demo system. It has four isolated input channels, a microprocessor with RS-232 interface, and four isolated output channels. Total system accuracy is 0.05% at 25°C. The input channels have 24-bit resolution (using the AD8220 in-amp and the AD7793 Σ-Δ ADC); each channel can be configured to accept a wide variety of input signals, from 4 mA to 20 mA current loops to high voltage inputs of 0 V to 5 V, 0 V to 10 V, ±5 V, ±10 V. It can also accommodate low level inputs, such as from RTD/thermocouple sensors. The output module has 16-bit resolution (AD5422), which has an integrated output driver and built-in fault detection and protection. The AD5422 has the following programmable output ranges: 4 mA to 20 mA, 0 V to 5 V, 0 V to 10 V, ±5 V, ±10 V. Each range has 16 bits of resolution. The complete design uses ADI isolation technology, isolated RS-232, processors, and power management products—allowing customers to evaluate the complete signal chain.

PLC Evaluation Board Features

• Inputs selectable: 0 mA to 20 mA, 4 mA to 20 mA, 0 V to 5 V, 0 V to 10 V, ±5 V, ±10 V, RTD, TC
• Outputs programmable: 0 mA to 20 mA, 4 mA to 20 mA, 0 V to 5 V, 0 V to 10 V, ±5 V, ±10 V
• Four isolated 24-bit analog input channels
  • AD7793: 24-bit Σ-Δ ADC; 40 nV noise
  • ADR02: precision 5 V reference
  • AD8220: instrumentation amplifier, >80 dB CMRR
  • ADuM5401: isoPower® integrated, isolated dc-to-dc converter; 500 mW output power
• Four isolated 16-bit analog output channels
  • AD5422 single channel, 16-bit, serial input, current source, voltage output DAC
  • 0.01% typical at 25°C total unadjusted error (TUE)
  • Single chip solution
  • Open circuit detection and protection
  • ADR445 high accuracy voltage reference on two channels
• Power/interface/control
  • ADuC7027 analog MCU with ARM7™ core
  • ADP3339: high accuracy ultralow I/Q, LDO
  • ADM3251E: isolated single channel RS-232 line driver/receiver

	"Designing Programmable Logic Controller 4 mA to 20 mA and Voltage I/O Modules: Techniques and Solutions" available at www.analog.com/webinars.

	"Design Considerations for Industrial Instrumentation and Process Control Systems" available at www.analog.com/webinars.

Learn More About How Our Breakthrough Manufacturing Processes Enable Designers to Meet the Most Stringent PLC System Requirements

iCMOS™ process technology combines high voltage silicon with submicron CMOS and complementary bipolar technologies to make possible analog ICs capable of 30 V operation in a smaller footprint with higher performance at lower cost: www.analog.com/iCMOS.

iCoupler™ isolation technology—based on chip-scale transformers rather than the LEDs and photodiodes—can be integrated with CMOS semiconductor functions for low cost isolation: www.analog.com/iCoupler.

isoPower® technology, an extension of the iCoupler technology, offers a complete and fully integrated isolation solution for power transfer across an isolation barrier using microtransformers: www.analog.com/isoPower.

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