The source of ranging error of photoelectric rangefinder
The ranging error of photoelectric rangefinder is divided into two parts:
(1) Proportional error: the error proportional to the measured distance length is mainly caused by frequency error, atmospheric refractive index error and vacuum light speed measurement error. Among them, the influence of the error of light speed measurement on the ranging value can be ignored.
(2) Fixed error: the inherent error of the instrument has nothing to do with the measured distance length, including the calibration error of zero error, the alignment error between the instrument and the reflector, the phase measurement error, the amplitude-phase error, the phase unevenness error of the LED and the periodic error. The periodic error mainly comes from the same frequency interference of photoelectric signals inside the instrument, and the magnitude of the error is repeated with the length of the precision ruler as the cycle.
Among them, proportional error, period error and zero error are the main system errors of photoelectric rangefinder.
According to a large number of measured data, it is shown that due to the phase inhomogeneity of the light-emitting tube and the receiving tube of the instrument, amplitude and phase errors and other factors, the instrument still has correction terms related to the length of the distance besides frequency error and atmospheric refractive index error. Traditionally, the correction numbers related to the length of the distance are called multiplication constants! . The correction number of zero error is called adding constant. System error can be eliminated by obtaining system error value in verification and applying correction. Therefore, the verification of the system error of photoelectric rangefinder mainly includes the following three items:
(1) periodic error verification;
(2) Verification of adding constants;
(3) Verification of multiplication constant.
