| |  Temperature (air, soil, grass, leaf) - 4wire RTD
Overview The PT1000 RTD (Resistance Temperature Detector) probe is a rugged, reliable temperature sensor. The probe consists of a platinum type RTD element mounted inside a stainless steel sheath which protects the element from environmental factors. When to use RTDs or thermocouples The two most common ways of measuring industrial temperatures are with resistance temperature detectors (RTDs) and thermocouples. But when should control engineers use a thermocouple and when should they use an RTD? The answer is usually determined by four factors: Factors: - Temperature, time, size, and overall accuracy requirements. What are the temperature requirements? If process temperatures fall from -328 to 932°F (-200 to 500°C), then an industrial RTD is an option. But for extremely high temperatures, a thermocouple may be the only choice.What are the time-response requirements? If the process requires a very fast response to temperature changes--fractions of a second as opposed to seconds (i.e. 2.5 to 10 sec)--then a thermocouple is the best choice. Keep in mind that time response is measured by immersing the sensor in water moving at 3 ft/sec with a 63.2% step change.
What are the size requirements? A standard RTD sheath is 0.125 to 0.25 in. dia., while sheath diameters for thermocouples can be less than 0.062 in. What are the overall requirements for acuracy? If the process only requires a tolerance of 2°C or greater, then a thermocouple is appropriate. If the process needs less than 2°C tolerance, then an RTD is the only choice. Keep in mind, unlike RTDs that can maintain stability for many years, thermocouples can drift within the first few hours of use. (above: 'When to use RTDs or thermocouples' extract from wiki: Resistance thermometer, 20/02/2009, http://en.wikipedia.org/wiki/Resistance_temperature_detector) Variations Air Temperature - 4 wire RTD element in a radiation shield
Soil Temperature - standard 4 wire RTD probe
Grass Temperature - 4 wire RTD element on plate covered by a mattingLeaf Temperature - 4 wire RTD element on leaf frame  Specifications Measurement | Specification Range | Class A (1/2B) | | Tolerance Range | -30 to +350 °C | Tolerance accuracy | <2°C | Temperature Deviation | t = ±(0.15+0.0025|t|) | Resistance at 0 °C | 1000Ω | Change of resistance | 0.385 ohms/°C | Absolute range | -270 °C - +660 °C | Standard | DIN43760 |
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