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RTD PT100 - General Information

RTD PT100 - General Information
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Data sheet Date Page GENERAL INFORMATION ABOUT RESISTANCE THERMOMETERS WORKING PRINCIPLE The working principle for metal resistance thermometers, normally called thermo resistances, is based on the variation of the electrical resistance of a metal with variations in the surrounding temperature. In the industrial field the materials most frequently used are platinum and nickel which, due to their high resistivity and stability, permit the production of thermo elements which are highly reproducible, small and with excellent dynamic characteristics. The temperature measurements carried out with thermo resistances are far more precise and reliable than those carried out with other types of sensor such as thermocouples. Normally resistance thermometers are identified with the code of the material used to construct them (platinum = Pt, nickel = Ni etc.) followed by their nominal resistance at a temperature of 0°C. The range of use for industrial resistance thermometers is between -200 and +850°C. PLATINUM (Pt) RESISTANCE THERMOMETERS PCI platinum resistance thermometers comply with the international standard IEC 751; sensitive elements which conform to other standards, for example JIS C 1604 etc., may be supplied on request. According to standard IEC 751 the platinum used for the manufacture of resistance thermometers should have a temperature coefficient of alpha = 3,85x10-3 Standard IEC 751 allows for thermo resistances with a nominal value at 0 °C (Ro) of between 5 and 1000 ohm; however, the values most commonly used are 100 ohm, 500 ohm and 1000 ohm. The equation linking resistance at temperature t° (Rt) and resistance at 0° (Ro) is a follows: in the range -200°C / 0 °C Rt = Ro [ 1+At+Bt²+C ( t-100 ) t³ ] in the range 0 °C / 850 °C Rt = Ro ( 1+At+Bt² ) Where the coefficients A, B and C have the following values: -3 C = -4,183 x 10 The classes of precision for platinum resistance thermometers refer to temperature and are standardized as follows: Class A = 0,15+0,002 | t | ( °C ) Class B = 0,3+0,005 | t | ( °C ) Class A covers up to a maximum temperature of 650°C and thermometers connected to three or four wires. It is, however, possible to have more precise thermo resistances which are classified as a fraction of class B, for example class 1/3B equals 1/3 (0.3+0.005 | t |). _______________________________________________________________________________________________ PCI (Process System Solutions) Ltd, Unit 7 Slaidburn Crescent, Southport, Merseyside, PR9 9YF, UK, Tel: +44 (0) 1704 509090, Fax: +44 (0) 1704 509091, email: sales@pci-instruments.com, Website: www.pci-instruments.com

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Data sheet Date Page RESISTANCE THERMOMETER TYPES There are different methods for connecting the resistance thermometers to the measuring devices; the choice of one method rather than another basically depends on the precision required in the measurement Resistances thermometers connection techniques - The two-wire technique is the least precise and is used only in cases where the connection of the thermo resistance is carried out with short and low resistivity wires; indeed testing the equivalent electrical circuit, it can be noted that the electrical resistance measured is the sum of that...

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Data sheet Date Page TRADITIONAL INSULATION THERMORESISTANCES Traditional insulation thermo resistances comprise: 1. Sensitive element The sensitive element is the most important part of the thermo resistance, a poor quality sensitive element would jeopardize the correct functioning of the entire sensor. Once connected with the connection wires, it is placed inside the protective sheath. Sensitive elements with different degrees of precision and with double winding are available. 2. Connection wires The connection of the sensitive element can be carried out using 2, 3 or 4 wires; the wire...

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Data sheet Date Page MINERAL MgO INSULATION THERMORESISTANCES This particular construction type permits the manufacture of high performance thermo resistances with excellent mechanical characteristics. The main characteristics which differentiate this type of construction from the traditional type, in addition to those already described, are: the possibility of bending the sheath with a sharp bending radius, the possibility of soldering the sheath upon installation and the possibility of creating very long probes. 1. Sensitive element With the use of particular techniques, the sensitive...

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Data sheet Date Page thus introducing an error into the measurement. Insulation resistance can fall when the probe is used at temperatures which are too high, when there are strong vibrations or because of the influence of physical or chemical agents. The immersion depth of the sensitive element is also extremely important for correct measurements; unlike in thermocouples where measurements can be considered punctiform, if the depth is not sufficient it can cause errors in the measurement of as much as several degrees °C. This is due to the fact that the sheath, usually metallic, with which...

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Data sheet Date Page _______________________________________________________________________________________________ PCI (Process System Solutions) Ltd, Unit 7 Slaidburn Crescent, Southport, Merseyside, PR9 9YF, UK, Tel: +44 (0) 1704 509090, Fax: +44 (0) 1704 509091, email: sales@pci-instruments.com, Website: www.pci-instruments.com

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