Instruments or equipment with physical parameters, etc. Vacuum leak detectors, pressure gauges, length gauges, microscopes, multipliers, etc. are all instruments and meters. Generally speaking, instruments and meters can also have functions such as automatic control, alarm, signal transmission, and data processing. For example, pneumatic and electric control instruments used in industrial production process automatic control, as well as distributed instrument control systems, all belong to instruments and meters. With the increasing expansion of the application fields of instruments and measurement and control systems, reliability technology, especially in some military, aerospace, power, and nuclear industry instruments, refers to the basic error of instruments under specified conditions. Instruments must be calibrated under specified conditions before leaving the factory. The prescribed conditions generally include environmental temperature, relative humidity, atmospheric pressure, power supply voltage, power supply frequency, installation method, etc. The basic error of an instrument is inherent to the instrument itself and is related to factors such as its structural principle, component quality, and assembly process. The magnitude of the basic error is often represented by the accuracy level of the instrument.
When using instruments to measure parameters, the results cannot be accurate. This is not only because the instrument itself has basic errors, but also because a series of conversion and transmission processes are required from the beginning of measurement to the final reading, which are affected by a series of factors such as usage conditions, installation conditions, and surrounding environment, resulting in certain errors. So in many cases, there is a difference between the displayed value of the instrument and the standard value (true value), which is called measurement error. Usually, the measurement error of the instrument is greater than the basic error because the measurement process also generates some additional errors.
Additional error refers to the additional error generated by the instrument when used under non-standard reference working conditions. Such as power fluctuation additional error, temperature additional error, etc.