Class of accuracy

Industrial resistance thermometers are also the subject of a number of national and international standards, which describe both cahbration constants and classes of accuracy and interchangeabihty. lEC pubhcation 751 was revised in 1976 to conform to ITS-90, and national standards will be revised to conform to this document. lEC 751 uses the fixed-poiat values of ITS-90 with the simpler algorithm of IPTS-48 ... 

Measuring voltage transformers Standard accuracy class may be one of 0.1, 0.2, 0.5, I or 3. The recommended class of accuracy will depend upon the type of metering and generally as noted in Table 15.3. 

Table 15.3 Recommended class of accuracy for different types of meters...

Nole To choose a higher class of accuracy than necessary is not desirable. 

The recommended class of accuracy will depend upon the type of application and is generally as noted below ... 

In most applications, a bar primary CT is generally used and a normal CT may be suitable. But for too small ratings, where the use of a wound primary CT is imperative, short-circuit effects must be considered, except the CTs for an LT system, where the fault level for such small ratings may be very low and may not matter (Section 13.4.1(5)). For applications on an HT system, where a wound primary CT is imperative, choice of a CT from standard wound primary CTs may still be possible, meeting the minimum requirements of class of accuracy, VA burden and short-time rating. lEC 60044-1 indicates for measuring and protection CTs the maximum short-time factors (STF) that can be obtained economically for a normal wound primary CT where... 

The class of accuracy for protection CTs is recommended to be not more than I OP as far as possible. 

The British Standards Institution (BSI) and the National Physical Loaboratory (NPL) have laid down the tolerances in the capacity of volumetric flasks (i.e., measuring flask) at 20°C by two sets of tolerances viz., Grade A and Grade B respectively, evidently to indicate the class of accuracy to which the flask has been subjected to for graduation, followed by the manufacturer s name and finally the BS standard number. However, the permitted tolerances for volumetric flasks commonly used in analytical laboratories are depicted in Table 2.8. 

Spatial accuracy—Required by tasks which are self-paced and for which time taken is of secondary or minimal importance and includes tracing (e.g., map-tracking), walking, reaching, and, in fact, most activities of daily Hving. Limitation in speed PRs should have no influence on this class of accuracy. 

Spatiotemporal accuracy The class of accuracy most required by tasks which place considerable demand on attainment of simultaneous spatial and temporal accuracy this refers particularly to paced tasks such as tracking, driving, ball games, and video games. 

In some situations we have the information about maximum measurement errors. Such maximum errors are provided by vendors of measuring instmments (sometimes as the class of accuracy). As the information about measurement accuracy must be provided in a consistent manner, the basic question concerns the relation between the standard deviation and the maximum error of measured value. The rigorous answer to this question probably does not exist. In practice we can recommend to take the standard deviation as one half of the maximum error. For more discussions about this controversial topic see (Madron, 1992). 

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