Text version of the page

W A T L O W

Sensor catalog - 7347 GeneralInformation

Thermocouples Sensors generating varying voltagesignals are thermocouples. Thermo- couples combine dissimilar metallic elements or alloys to produce avoltage.Using specific combinationsof metals and alloys in the thermo- couple’s legs produces a predict-able change in voltage based on achange in temperature.

Application Hints

General Information

Which temperature sensor is the best choice for my application?

Application Hints Thermocouples are best suited tohigh temperatures, environmentalextremes or applications requiring microscopic size sensors. They arealso recommended for high vibrationenvironments.
ThermocouplesAdvantages Disadvantages • No resistance lead wire • Non-linearproblems• Low voltage• Fastest response to • Least stable, repeatabletemperature changes• Least sensitive to small• Simple, ruggedtemperature changes• Inexpensive• High temperature operation• Point temperature sensing Thermistors are best for lowtemperature applications over limitedtemperature ranges. RTDs are best for most industrialmeasurements over a wide temperature range, especially when sensor stability is essential for proper control.
VT Voltage Temperature RTDs and Thermistors Sensors generating varyingresistance values are resistancetemperature detectors (RTDs). RTDs are further divided into two types:•RTD - resistive metallic wire or film •Thermistor (thermally sensitivemetal oxide resistor)A variation of the thermistor notcovered in this section is the integrat-ed circuit (IC). It is a thermistor that has a computer chip to condition andamplify its signal. The computer chip limits the IC’s use to a narrowtemperature range.
RTDsAdvantages Disadvantages • Most stable, accurate • Expensive• Contamination resistant• Current source required• More linear than• Self-heatingthermocouple• Slow response time• Area temperature sensing• Low sensitivity to small • Most repeatable temperature changes RT Resistance temperature measurement Temperature ThermistorsAdvantages Disadvantages • High output, fast• Non-linear • Two-wire ohms• Limited temperature range RT measurement• Fragile• Economical• Current source required• Point temperature sensing• Self-heating• High resistance• High sensitivity to smalltemperature changes Resistance Temperature 13