TCR (Temperature Coefficient of Resistance)
TCR differentiates RTDs by their resistance/temperature curves. Sometimes called alpha ( α ), it is specified in various ways by different manufacturers. In this guide TCR is the RTD’s resistance change from 0 to 100°C, divided by the resistance at 0°C, divided by 100°C:
For example, a platinum thermometer measuring 100 Ω at 0°C and 139.11 Ω at 100°C has TCR 0.00391 Ω/Ω/°C:
For a copper RTD, 10 Ω at 25°C, TCR is:
Stated another way, TCR is the average resistance increase per degree of a hypothetical RTD measuring 1 Ω at 0°C. The most common use of TCR is to distinguish between curves for platinum, which is available with TCRs ranging from 0.00375 to 0.003927. The highest TCR indicates the highest purity platinum, and is mandated by ITS 90 for standard platinum thermometers. There are no technical advantages of one TCR versus another in practical industrial applications. 0.00385 platinum is the most popular worldwide standard and is available in both wire-wound and thin-film elements. In most cases, all you need to know about TCR is that it must be properly matched when replacing RTDs or connecting them to instruments.
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