How to determine the class of accuracy of the instrument

Determining the accuracy class.

To enjoy high-quality equipment for the measurement of various quantities necessary to know the accuracy with which it carries out the measurement device.Technical characteristics of any measuring device include indicators that usually point to the scale:

• unit values, which specifies the device;
• system operating principle (magnetoelectric, electromagnetic, induction and other)
• accuracy class of the instrument;
• position of the device scale (horizontal, vertical or inclined);
• voltage at which the test was carried out insulation casing;
• serial number and year of manufacture.
• type of current at which the measurement should be carried out (DC, AC).

One of the characteristics of the technical means of measuring accuracy is class - the value determined by several errors, namely their limits.The formula for determining the characteristics of this device is as follows:

γ = ΔXnaib / Xpr⋅ × 100%, where

ΔXnaib - maximum absolute error of measurement;

Xpr - the highest value on the scale of the device.

class precision instrument is also called a reduced error.For this indicator, all measuring devices are divided into eight classes:

1. 0,05;
2. 0,1;
3. 0,2;
4. 0,5;

devices having such a group of errors, called precision, from the English word «precision», meaning in Russian - accuracy.This is the most accurate devices and their use in laboratory research.

following four classes of accuracy:

1. 1,0;
2. 1,5;
3. 2,5;
4. 4.

used in the tech industry, and they are called - technical.

Manufacturers of measuring technical devices affix its accuracy class on the scale, if the mark is not present - the unit is considered to be extra-curricular, and his error in measurements greater than 4%.

Accuracy of instruments is a characteristic of accuracy in relation to the devices themselves, but this figure does not determine the accuracy of the measurements.For example, precision ammeters class is characterized by boundaries of the absolute error and does not guarantee that these statements are not will make adjustments such factors as the effect of the magnetic field, AC frequency and temperature extremes, as well as other external stimuli.

Accuracy classes of devices can be marked as the letters, and Arabic or Roman numerals.Arabic Numeric values ​​mean that the main indicator of the accuracy is reduced error and should be considered the largest and smallest values ​​of a number of measurements.Roman numeral in the designation of accuracy class suggests that the accuracy of the device was determined from the value of the relative error.If

marking instrument accuracy class indicated on the scale a fractional number (for example - "0.01 / 0.02"), this means that the reduced maximum error in the scale is ± 0.01%, and at the beginning ± 0, 01%.This applies to the high-frequency electrical devices.

All values ​​are errors of any standardized instruments and accepted standards and must not exceed these values.These indicators may have different values, depending on the operating conditions of the measuring device, but in general, limiting the boundaries of these errors should not go beyond the normalized value.Methods for determining the rules of permissible errors and accuracy classes marking instruments installed GOST.