Instrument accuracy

This post was last edited by hxch150804 on 2022-4-2 at 11:49. In fact, the precision can be expressed numerically, that is, maximum error/maximum range × 100% = ? It is not scientific to express the error of magnetic flap switches in XX mm; an error of 10 mm for a range of 10 meters is very different from an error of 10 mm for a range of 1 meter – the latter case may make the device unusable due to the excessive error.

Let’s talk about temperature measurement: thermal resistors and thermocouples have different ways of expressing accuracy； Thermal resistors, Class A/B; thermocouples, Class 1/2. Thermal resistors Pt100 in accordance with IEC60751; thermocouples in accordance with IEC60751

Under normal operating conditions, the degree of accuracy of the measurements taken by an instrument is referred to as the instrument’s accuracy. The smaller the reference error, the higher the accuracy of the instrument. Since the reference error is related to the instrument’s range, when using instruments with the same level of accuracy, it is common to reduce the range in order to minimize measurement errors. In industrial measurement, to facilitate the indication of an instrument’s quality, its accuracy level is commonly used to represent the degree of accuracy of the instrument. The accuracy grade is the maximum reference error with the plus and minus signs and percent sign removed. The accuracy class is one of the important indicators for measuring the quality of instruments. I. The accuracy grades for industrial instruments in our country include: 0.005, 0.02, 0.05, 0.1, 0.2, 0.35, 0.4, 0.5, 1.0, 1.5, 2.5, 4.0, etc. The smaller the order, the higher the precision (accuracy). II. The accuracy grades for measuring and indicating instruments used in industrial process measurement and control are: 0.01, 0.02, (0.03), 0.05, 0.1, 0.2, (0.25), (0.3), (0.4), 0.5, 1.0, 1.5, (2.0), 2.5, 4.0, 5.0 ； There are 16 in total, of which the 5 in parentheses are not recommended for use. The standard referred to is \"GBT 13283-2008 Accuracy Grades for Measuring and Control Instruments and Displays Used in Industrial Processes.\"

Precision refers to the degree of closeness between an observed value and the true value. Since the true value cannot be obtained, a reference value (a value that can be displayed by standard instruments) is usually used in its place, and this is referred to as error. Error: the measured value minus the reference value. The accuracy of a measuring instrument (meter) refers to the maximum error that may occur, or in other words, the maximum allowable error (tolerance) for that product. The common ways of representation are as follows: 1. When the maximum allowable error of a measuring instrument does not change with the value displayed, it is expressed in absolute terms. 　　For example, for a 1-meter ruler, the tolerance at 1 mm and the tolerance at 1000 mm are both 0.1 mm; its precision can be expressed as ±0.1 mm. 2. When the maximum allowable error of the measuring instrument varies linearly with the magnitude of the indicated value, it is expressed in absolute terms, or it is represented by several accuracy grades based on the size of the allowable tolerance. 　　For example: the accuracy of a thermal resistor is expressed as the basic tolerance plus the tolerance at the measurement location, such as ±(0.15+0.002|t|)℃ ； Depending on various requirements, thermocouples/thermoresistors with different precision levels can be classified into several accuracy grades such as AA, A, B, and C. (For details, see Floor 3.) 3. When the maximum allowable error of the measuring instrument is expressed as a referenced error, it is represented as a relative error. 　　Relative error refers to the value obtained by multiplying the absolute error caused by the measurement by the (agreed) true value of the quantity being measured, and then multiplying the result by 100%, expressed as a percentage. 　　The accuracy of a gauge is expressed as a percentage, calculated by taking the ratio of the absolute error to the gauge’s range and multiplying it by 100%. 　　The accuracy class of the instrument is expressed as the percentage accuracy of the instrument, without the percent sign. Different instrument accuracy grades can form a series. (For details, see Floor 4.) Note: The relative error mentioned here refers to the concept of error, while precision and precision grades refer to the concept of tolerances; these can be confusing. Tip: The precision grades indicated as “2,” “3,” etc. above are different concepts and are easy to confuse ； 　　There are also instruments corresponding to the different grades of metering stations; for example, the instruments required for grade 1, grade 2, and grade 3 metering stations are referred to as grade 1, grade 2, and grade 3 metering instruments respectively. But it is only a grade that meets the technical requirements of the measurement system; it is not the same as the accuracy grade of the specific instrument.