What does the designation 1/3 DIN mean in resistance thermometers?
"1/3 DIN, 1/5 DIN, and 1/10 DIN are all divided value based on accuracy Class B. However, it is important to note that these classifications are not standardized and are, in fact, superfluous. Some background: Before May 2009, when DIN EN 60751 was introduced, there was no standardized accuracy class better than Class A. Some manufacturers of resistance thermometers, including WIKA, used these fractional DINs to describe thermometers with a higher accuracy than Class A. What began as a useful addition to traditional standard designations has, upon closer inspection, proven to be inadequate. The typical question “1/3 DIN from what?” has the answer “from Class B.” Unfortunately, defining “1/3 DIN B” makes the situation even less clear, as there are two ways of looking at what “from Class B” means: 1. Set the increased accuracy to a specific temperature point, such as 1/3 DIN B at 0°C. 2. Define a range in which this accuracy is valid: 1/3 DIN B 0 ... 50°C. The representation described in #2 carries an additional uncertainty. If one uses a Class B measuring resistance, its characteristic curve has a defined pitch. In the example of 0 .. 50°C, a Class A measuring resistor would already deliver, at about 20°C, a better result than 1/3 DIN B, and the user would be better off using a Class A measuring resistor. This confusion ultimately led to the introduction of a new accuracy class, Class AA, in DIN EN 60751 of May 2009. As a result, the non-standardized 1/3 DIN, 1/5 DIN, and 1/10 DIN accuracy classes are no longer necessary."
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