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Maxim > Design Support > Technical Documents > Reference Designs > Automotive > APP 3450
Maxim > Design Support > Technical Documents > Reference Designs > Measurement Circuits > APP 3450
Maxim > Design Support > Technical Documents > Reference Designs > Temperature Sensors and Thermal Management > APP 3450
Keywords: temperature sensor,RTD,platinum
REFERENCE DESIGN 3450 INCLUDES: Tested Circuit Schematic BOM Board Available Description Test Data Layout
Positive Analog Feedback Compensates PT100 Transducer
Feb 21, 2005
Abstract: This article reviews the basic characteristics of common temperature sensors, describes the RTD PT100 temperature
transducer, and explains a simple analog approach for linearizing and conditioning the output of that device.
Temperature is one of the most measured physical parameters. Thermocouple and resistance temperature detector (RTD) sensors are
adequate for most high-temperature measurements, but one should choose a sensor that has characteristics best suited for the
application. Table 1 offers general guidelines for choosing a sensor.
Table 1. Sensor Attributes
Feature Thermocouple RTD
Response time Better
Maximum temperature Higher
Ruggedness Better
Cost efficiency Better
Accuracy Better
Long-term stability
Better
Standardization
Better
RTDs offer high precision and an operating range of -200°C to +850°C. They also have an electrical output that is easily transmitted,
switched, displayed, recorded, and processed using suitable data-processing equipment. Because RTD resistance is proportional to
temperature, applying a known current through the resistance produces an output voltage that increases with temperature. Knowledge
of the exact relationship between resistance and temperature allows calculation of a given temperature.
The change in electrical resistance vs. temperature for a material is termed the "temperature coefficient of resistance" for that material.
The temperature coefficient for most metals is positive, and for many pure metals is essentially constant over a large portion of the
useful temperature range. Moreover, a resistance thermometer is the most stable, accurate, and linear device available for temperature
measurement. The resistivity of metal used in an RTD (including platinum, copper, and nickel) depends on the range of temperature
measurements desired.
The nominal resistance of a platinum RTD is 100Ω at 0°C. Though platinum RTDs are highly standardized, they conform to multiple
standards that are not identical worldwide. Therefore, problems arise when an RTD built to one standard is used with an instrument
designed to a different standard.
Table 2. Common Standards for Platinum RTDs*
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