How to determine the accuracy class of the device

Definition of the accuracy class.

In order to use high-quality equipment for measuring various quantities, it is necessary to know the error with which this device is measuring it. The technical characteristics of any measuring instrument include the following indicators, which usually indicate on the scale: the

• unit of measurement that is determined by the device;
• operating principle system( magnetoelectric, electromagnetic, induction and others)
• accuracy class of the device;
• position of the scale of the device( horizontal, vertical or inclined);
• voltage at which the insulation test of the housing was conducted;
• serial number and year of manufacture.
• type of current, in which it is necessary to carry out measurements( constant, variable).

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

γ = ΔXinab / Xpr⋅ × 100%, where

ΔXnab is the maximum absolute measurement error;

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

The accuracy class of the device is also called the 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 that have such groups of errors are called precision, from the English word "precision", meaning in translation into Russian - accuracy. These are the most accurate devices and they are used in laboratory studies.

The following four accuracy classes:

1. 1.0;
2. 1.5;
3. 2.5;
4. 4.

is used in the technical industry, and they are called technical.

Manufacturers of measuring technical devices put its accuracy class on a scale, if there are no notes - the device is considered extra-curricular, and its error in measurements is more than 4%.

The accuracy class of the instruments is a characteristic of the accuracy with respect to the devices themselves, but this index does not determine the accuracy of the measurements. For example, the accuracy class of ammeters is characterized by the boundaries of absolute error and does not guarantee that such indications as the action of the magnetic field, the frequency of alternating current and temperature differences, and also other external stimuli will not make corrections.

The accuracy classes of instruments can be marked with either a Latin letter or Arabic or Roman numerals. Numerical Arabic values ​​mean that the main accuracy factor is the reduced error and the largest and smallest values ​​of a series of measurements should be taken into account. The Roman numeral in the designation of the accuracy class indicates that the accuracy of the instrument was determined from the value of the relative error.

If a fractional number is indicated on the scale when marking the accuracy class of the device( eg "0.01 / 0.02"), this means that the resulted error at the maximum scale is ± 0.01%, and at the beginning ± 0,01%.This is applicable in high-frequency electrical measuring instruments.

All values ​​of the errors of any measuring instruments are normalized and accepted standards and should not exceed these values. These indicators may have different values, depending on the operating conditions of the measuring device, but in general the marginal limits of these errors should not exceed the limits of the normalized value. The methods for determining the norms of tolerable errors and marking the accuracy classes of devices are established by GOST.