The quality of a measuring instrument can be reflected by its accuracy, repeatability, sensitivity, response time, zero drift, and range drift.
(1) Accuracy: also known as precision, refers to the degree to which the measurement result of an instrument closely approximates the actual value. It can be expressed as absolute error or relative error:
① Absolute error = Measured value - True value ② Relative error = Absolute error / True value
No instrument can measure the true value of a parameter with absolute accuracy; it can only strive to make the measured value as close to the true value as possible. In practical applications, the reading of a standard instrument with high accuracy is used as the true value of the measured parameter. The difference between the reading of the measuring instrument and the reading of the standard instrument is the measurement error. The smaller the error, the higher the reliability of the measuring instrument.
(2) Response time: When the measured parameter changes, the measured value indicated by the instrument always takes a certain period of time to be accurately represented. This time lag between the change of the measured parameter and the actual change is the instrument's response time. Some instruments use a time constant (such as resistance temperature measurement), while others use a damping time (such as ammeter resistance measurement).
(3) Sensitivity: The degree of sensitivity of the instrument measurement. It is usually expressed as the ratio of the change in the instrument output to the change in the measured parameter that caused the change.
(4) Zero drift and range drift: refers to the percentage of the average change relative to the range after multiple measurements of the relative zero point and maximum range confirmed by the instrument.
(5) Reproducibility: When a parameter is measured repeatedly using the same instrument under unchanged measurement conditions, the percentage difference between each measured value and the average value is relative to the maximum scale range. This is an important indicator of the stability of instruments and meters, and it is generally required to be tested during commissioning and routine calibration.
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