In the precision test and measurement industry, measurement accuracy (accuracy) is the soul of the instrument itself, and is one of the most important indicators of the instrument, but the accuracy of different instruments has different expressions, so only after understanding the accuracy index of the instrument can Better guide us to make measurements.
During the test and measurement process, depending on the hardware of the measuring instrument itself, the measurement conditions or the measurement method, there is a certain difference between the measured result (measured value) and the true value. This difference is the measurement error, and the measurement error may include and measure A proportional error is also a fixed error that is independent of the measured value. Usually, the accuracy index of the measuring instrument will be given by the combination of these two kinds of errors. For example, the accuracy index of the PA8000 is shown in Figure 1.
Figure 1 PA8000 accuracy index
The accuracy indicator in Figure 1 is expressed as "± (% reading + % range)", that is, reading accuracy + full scale accuracy notation. As the name suggests, the reading accuracy is an error that is only proportional to the measured value, while the full-scale accuracy is a fixed error that is independent of the measured value regardless of the measured value, that is, the error is fixed after the equivalent range is determined.
There is another way to express the accuracy of electrical measuring instruments. Before introducing the two ways of expressing the error: absolute error and relative error. The absolute error is the difference between the measured value and the standard value (the true value); the relative error is the ratio of the absolute error to the standard value (the true value). The accuracy of the readings mentioned above is expressed by the relative error, and the full-scale accuracy is expressed by the absolute error. The relative error can visually represent the quality of the measurement, while the absolute error is not as intuitive as the relative error.
Another way to express the accuracy of electrical measurement instruments is the accuracy level. When the electrical measuring instrument works under the specified conditions, the ratio of the maximum value of the absolute error to the metering range is called the accuracy level of the meter. For example, the accuracy level of a current transformer is shown in Figure 2.
Figure 2 Current transformer indicator parameters
In the "GB/T 13283-2008 industrial process measurement and control instrumentation and display instrument accuracy level", China's industrial instrument accuracy grade is planned, divided into 16 levels, of which the level in parentheses is not recommended: 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, the smaller the numerical value, the more accurate high.
If you know the accuracy level of the instrument used during the measurement, you can calculate the maximum absolute error of the measurement according to the range, and calculate the accuracy of the measurement result.
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