2 error of signal analysis and processing(spirit level tool)
2.1 error of signal analysis method(spirit level tool)
The digital level adopts the correlation method for measurement. According to experience, the correlation (alignment) accuracy between the reference signal (pseudo-random code) stored in the instrument and the measurement signal (pseudo-random code) is about 1% of the symbol width (or the wavelength of the code). The symbol width of the bar code ruler is 2.025mm, so the correlation accuracy is about 0.02mm.
2.2 error of maximum correlation coefficient calculation(spirit level tool)
When the digital level is correlated, in the precision correlation search area, the measurement signal and the reference signal are correlated with all eight digits. Because the amplitudes of the two signals are different, the maximum correlation coefficient is calculated point by point in the height and distance coordinate system: the accuracy of the maximum correlation position depends on the size of the grid, and the related interpolation calculation ignores the impact caused by the loss of bar code.
2.3 error of measurement signal processing (image processing)(spirit level tool)
The measurement signal processing of digital level is the key link to obtain high-precision leveling. The imaging quality of bar code image on CCD array and the advantages and disadvantages of processing technology determine the measurement accuracy to a great extent. The main error effects causing image errors include: (1) errors caused by the physical characteristics of CCD array; (2) Error of bar code information loss caused by ruler occlusion; (3) Image resolution error caused by accurate focusing; (4) Image deformation error caused by ruler tilt; (5) Image error caused by changes in external conditions; (6) Error of electronic equipment when measuring signal formation, etc.
Obtaining stable, clear, moderate contrast and complete bar code image is the premise and key of measurement signal generation and processing. Generally speaking, the image processing is completed by the built-in software of the level. Its error depends on the advanced algorithm and technology of software.