What is accuracy? How to improve the accuracy of the instrument?

Instrument accuracy and precision, and accuracy. Can say it's twin brother, accuracy and error because of the existence of the error, precision is the concept. Instrument accuracy in short is the accuracy of the measured values closer to the true value of the instrument, usually with relative percentage error ( Also called relative reduced error) Said. The bimetallic thermometer highest precision of instrument can achieve & plusmn; 1%. We have to improve the precision instrument error analysis. Error usually can be divided into neglect, graded error, system error and random error. Negligence error refers to man-made in the process of measuring error, a can overcome, second, and the instrument itself is no relationship. Graded error is caused by the instrument internal components ageing process, it can be used to replace components, parts or through continuous correction overcome and eliminate them. Refers to a system error to repeat the same measured parameters measurement, the error of the numerical size or symbols are the same, or change of error according to certain rule, but has not yet been know caused by accidental factors, the numerical size and nature are not fixed, it is difficult to estimate, but can be by statistical method theoretically estimate its influence on test results. Error sources mainly refers to the system error and random error. When expressed in error precision, refers to the sum of random error and system error. Any instrument has the certain error. Therefore, when using the instrument must first know the accuracy of the instrument, in order to estimate the measurement results and the conventional true value gap, which estimates the size of the measured value. The accuracy of the instrument is often used to allow the maximum error of the reference of removing percent ( %） After the Numbers to measure. The accuracy of the analogue instruments should not be commonly use absolute error ( Measured values and the real value of difference) And the relative error ( The ratio of the absolute error and the point of real value) To say, because the former could not reflect the reasonable requirements of different range instrument, which is easy to cause misunderstanding no instrument can believe in. For example, on a full scale is 100 ma, ammeter, when measuring the zero current, due to mechanical friction whose hands slightly deviation from zero in by 0. If the reading of the mA, according to the relative error of the algorithm, so that the relative error is infinity, seems to be the instrument is completely unable to use, but in engineering point of view, the measurement error is easy to understand, not surprising, it is probably a more accurate instrument! Reasonable analogue meter accuracy, should be the biggest absolute error in the measurement range and measurement range of the instrument of ratio, this ratio is called relative ( In the full scale) Percentage error. According to the provisions of the instrument industry divided into several levels, the accuracy of the instrument referred to as 'precision grade, such as 0. Level 1, 0. Level 2, 0. Level 5, 1. Level 0, 1. Level 5, 2. Level 5, etc. Thus, precision grade, the smaller the number, the higher the precision.