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REFERENCE SCHEMATIC 5817

Novato (MAXREFDES16#): 4-20mA Loop-Powered Temperature

Sensor with HART

By:

Yuriy Kurtsevoy, Strategic Applications

Engineer

Whitney Scott, Strategic Applications Engineer

Jan 30, 2014

Abstract: The Novato reference design (MAXREFDES16#) is a 16-bit, high-accuracy, loop-powered temperature transducer that transmits

temperature information from a remote object to the central control unit over a 4–20mA current loop and using the highway addressable

remote transducer (HART) communication protocol.

Introduction

Temperature is one of the most widely measured parameters in industrial process control and automation. This reference design provides

a complete signal-chain solution that works with any type of RTDs, from PT100 to PT1000. The Novato PT100 2-wire, loop-powered smart

temperature transmitter guarantees a low-power, easy-to-use, reliable solution of temperature measurement from -200°C to +850°C with

accuracy better than 0.1% or 1.0°C, whichever is more accurate, over the entire operating range.

The Novato MAXREFDES16 smart sensor transmitter reference design features:

2-, 3-, or 4-wire RTD sensor input

-200°C to +850°C measured temperature range

-40°C to +85°C operating range

0.03°C temperature resolution

< 0.05% span error or ±0.2°C at +23°C (whichever is greater)

< 0.1% span error or ±1.0°C over operating range

12V to 40V supply voltage range

200µA RTD excitation current

Auto compensation of wire resistance for 3-wire RTD

4–20mA current loop output

10½ to 1k½ loop load

Highway addressable remote transducer (HART) communication protocol requires minimum load of 230½

Sensor burnout detection

NAMUR down scale: < 3.2mA

NAMUR up scale: programmable from 20.5mA to > 24mA

Loop current limiter: 30mA ±5mA

HART protocol compatible

Detailed Description

Block diagram of the Novato smart sensor transmitter is shown in Figure 1.

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