{"id":3249,"date":"2023-05-02T06:29:55","date_gmt":"2023-05-02T06:29:55","guid":{"rendered":"https:\/\/thermibel.be\/faq\/what-is-the-alpha-coefficient-%ce%b1\/"},"modified":"2023-06-27T10:55:36","modified_gmt":"2023-06-27T10:55:36","slug":"what-is-the-alpha-coefficient-%ce%b1","status":"publish","type":"faq","link":"https:\/\/thermibel.be\/en\/faq\/what-is-the-alpha-coefficient-%ce%b1\/","title":{"rendered":"What is the alpha coefficient (\u03b1)?"},"content":{"rendered":"\n

The DIN 43760 standardised temperature coefficient of platinum wire is: \u03b1 = 0.00385. For a resistance of 100 ohms at 0 \u00b0C, this corresponds to + 0.385 ohm per \u00b0C (European \u03b1). \u03b1 is therefore the average slope from 0\u00b0C to 100\u00b0C<\/strong> $$ \\alpha = \\frac{{{R_{100}} – {R_0}}}{{ {R_0} \\times 100^\\circ C.}} $$. There is a wide range of RTDs which have different \u03b1 coefficients and ohm values at 0\u00b0C detailed in their technical properties. The most commonly used RTD is that with an \u03b1 coefficient of 0.00385 and ohm value at 0\u00b0C of 100 \u03a9. It is known as Pt100.
<\/p>\n\n\n\n

Values of some RTDs<\/strong><\/td><\/tr>
R at 0\u00b0C (\u03a9)<\/strong><\/td>\u03b1 (\u03a9\/\u03a9\/\u00b0C)<\/td>Average sensitivity (\u03a9\/\u00b0C)<\/td><\/tr>
25.5<\/strong><\/td>0.00392<\/td>0.1<\/td><\/tr>
100<\/strong><\/td>0.00392<\/td>0.392<\/td><\/tr>
100<\/strong><\/td>0.00391<\/td>0.391<\/td><\/tr>
100<\/strong><\/td>0.00385<\/td>0.385<\/td><\/tr>
200<\/strong><\/td>0.00385<\/td>0.770<\/td><\/tr>
470<\/strong><\/td>0.00392<\/td>1.845<\/td><\/tr>
500<\/strong><\/td>0.00392<\/td>1.963<\/td><\/tr>
500<\/strong><\/td>0.00391<\/td>1.955<\/td><\/tr>
500<\/strong><\/td>0.00385<\/td>1.925<\/td><\/tr>
1000<\/strong><\/td>0.00385<\/td>3.850<\/td><\/tr>
1000<\/strong><\/td>0.00375<\/td>3.750<\/td><\/tr>
10000<\/strong><\/td>0.00385<\/td>38.50<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
International standards DIN 43760 (IEC 751, BS-1904, JIS C1604)<\/td><\/tr>
Parameter<\/strong><\/td>Class A<\/td>Class B<\/td><\/tr>
R0<\/sub><\/strong><\/td>100\u03a9 \u00b10,06%<\/td>100\u03a9 \u00b10,12%<\/td><\/tr>
Alpha, \u03b1<\/strong><\/td>0,00385 \u00b10,000063<\/td>0,00385 \u00b10,000063<\/td><\/tr>
Range<\/strong><\/td>-200\u00b0C to 650\u00b0C<\/td>-200\u00b0c to 850\u00b0C<\/td><\/tr>
Res, RT<\/sub><\/strong><\/td>\u00b1(.06+.0008|T|-2e-7<\/sup>T2<\/sup>)<\/td>\u00b1(.12+.0019|T|-6e-7<\/sup>T2<\/sup>)<\/td><\/tr>
Temp, T<\/strong><\/td>\u00b1(0.3+0.002|T|)\u00b0C<\/td>\u00b1(0.3+0.005|T|)\u00b0C<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

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For a resistance of 100 ohms at 0 \u00b0C, this corresponds to + 0.385 ohm per \u00b0C (European \u03b1). \u03b1 is therefore the average slope from 0\u00b0C to 100\u00b0C $$ alpha = frac{{{R_{100}} – {R_0}}}{{ {R_0} times 100^circ C.}} $$. 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For a resistance of 100 ohms at 0 \u00b0C, this corresponds to + 0.385 ohm per \u00b0C (European \u03b1). \u03b1 is therefore the average slope from 0\u00b0C to 100\u00b0C $$ alpha = frac{{{R_{100}} – {R_0}}}{{ {R_0} times 100^circ C.}} $$. 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