RTD sensor accuracy
RTD sensor accuracy : The practical accuracy of the RTD ( pt100 sensor ) depends on the RTD tolerance, the measurement temperature, the accuracy of the coupling tool, and the effects of the connecting and installing wires. But when we talk about the accuracy of the RTD sensor, we usually refer to the degree of temperature deviation or the degree of tolerance, because its “real” tolerance depends on the temperature. There are a number of international standards that determine the tolerance and accuracy of RTDs. The most common standard used to grade RTDs is platinum (pt100 sensor) (IEC 751 1995). IEC 751 defines two performance classes for 100Ω Platinum RTDs (pt100 sensor) with alpha 0.00385, Class A and Class B:
Note: The term tolerance only applies to RTDs α = 0.00385 Pt. The symbol “| T | ” The table shows the absolute value of the sensor temperature. Other standards such as (DIN 43760, BS-1904, BS EN60751 1996) and JIS C1604 usually comply with IEC 751. While IEC 751 only shows RTDs of 100Ω platinum with an alpha of 0.00385, it is often used for temperature tolerance and accuracy in other platinums.
Types of RTD. For example, the JIS standard C1604 also adds to the alpha type detection of 0.003916 and applies the same tolerance standards. A&B performance classes are also called DIN A and DIN B according to DIN 43760. Note that Class C and Class D are sometimes used, and each class doubles the previous tolerance level. DIN Standard (DIN 43760) similarly detects three classes of temperature deviation as follows:
DIN Class A: ± (0.15 + 0.002 * | T |) ° C (Matches IEC 751 Class A)
DIN Class B: ± (0.30 + 0.005 * | T |) ° C (Matches IEC 751 Class B)
DIN Class C: ± (1.20 + 0.005 * | T |) ° C
In the United States, the ASTM E1137 specification is also referenced and defines two RTD temperature tolerances, A and B, as follows:
Grade A: ± (0.13 + 0.0017 * | T |) ° C
Grade B: ± (0.25 + 0.0042 * | T |) ° C
According to IEC 751, the degree of accuracy or tolerance of an RTD element is a function of its resistance to tolerance and temperature deviation. According to DIN 43760 and IEC 751, its class is characterized by tolerance of temperature resistance and temperature deviation at calibration temperature (usually 0 ° C) and base resistance R0 (typically 100Ω) and is divided into two main categories. Temperature tolerance and temperature resistance for platinum RTDs in each IEC 751 1995 and BS EN60751 1996
Note: It is assumed that the above tolerances apply to the connections of three- and four-wire platinum sensors, because the two connections of the RTD sensor wire require special attention due to the negative effects of lead resistance, because the two wire sensors can not These tolerances reach. Lead compensation provided by three- and four-wire sensors. Most RTD sensors use Class A or Class B according to IEC 751 International Standard and are characterized by a temperature deviation from their reference temperature: Class A, with a tolerance of 0.15 ° C at 0 ° C. Or class B, with a tolerance of 0.3 ° C at 0 ° C.
But there are a number of additional classes such as “1/10 DIN” and “1/3 DIN” that are used to indicate more accurate sensors, and they tolerate 1/10 or 1/3 of the class B specifications at 0 degrees. Respectively, while the “accuracy” of an RTD element is usually measured by the accuracy of its original element at one point, it is usually 0 ° C (32 ° F), but varies with temperature. In addition, it also depends on the resistance of the base at the calibration temperature of the element. Therefore, the effective tolerance of an RTD sensor is actually a combination of the base tolerance resistance (resistance tolerance at calibration temperature) and the coefficient of resistance tolerance temperature (TCR or characteristic slope tolerance). For most RTDs , the calibration temperature is 0 ° C, and it is understood that any temperature above or below this temperature will have a wider tolerance band and less accuracy.
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