What is measurement error? What are some ways to express measurement error?

In the process of electrical measurement, measurement errors will certainly occur due to various reasons. The existence of measurement errors is inevitable and universal. People can only limit them within a certain range according to needs and possibilities, but it is impossible to completely eliminate them.

The difference between the measured value and the actual value of a measuring instrument or meter is called measurement error. Usually, electrical measurement errors are expressed in the following three forms.

(1) Absolute error (△). The actual difference between the value (i.e., measured value) Ax measured by the instrument and the actual value A0 of the measured object is called the absolute error, which is represented by the symbol △. That is, the absolute error is expressed as

The unit of absolute error is the same as the unit of the measured value, and the sign of absolute error can be positive or negative. When calculating the absolute error △, the standard meter indication value is often used as the actual value of the measured value. The absolute error reflects the degree and direction of deviation between the measured value and the actual value of the measured object, and it cannot reflect the accuracy of the measurement.

(2) Relative error (γ). In order to reflect the accuracy of the measurement, it can be judged based on the relative error. The percentage of the absolute error △ to the actual value A0 is called the relative error, which is represented by the symbol γ. That is, the relative error is expressed as

Relative error has no unit and is expressed in %. In actual use, because the reading value of the instrument is close to the actual value, Ax is often used instead of A0 in engineering measurements to facilitate calculation. The relative error at this time is called the nominal relative error, which is represented by the symbol γx. That is, the nominal relative error is expressed as

(3) Maximum reference error (γm). Relative error can only indicate the accuracy of a certain measurement result, but cannot indicate the accuracy of the measuring instrument itself. The relative error of the same measuring instrument will gradually increase as the measured value decreases, so the maximum reference error can be used to indicate the accuracy of the measuring instrument itself. Under normal working conditions, the absolute error of the measuring instrument. The accuracy level of direct-reading indicating measuring instruments is determined based on the maximum reference error. For example, a 2.5-level measuring instrument indicates that its maximum reference error is less than or equal to 2.5%.