The sources of ranging errors in photoelectric rangefinders
The ranging error of a photoelectric rangefinder is divided into two parts:
(1) Proportional error: an error proportional to the length of the measured distance, mainly caused by frequency error, atmospheric refractive index error, and vacuum light speed measurement error, resulting in errors in the ranging results. The influence of the measurement error of the speed of light on the ranging value can be ignored.
(2) Fixed error: The inherent error of an instrument, independent of the length of the measured distance, including calibration error of zero point error, alignment error between the instrument and the reflector, phase measurement error, amplitude and phase error, phase non-uniformity error of the light-emitting tube, and periodic error. The periodic error mainly comes from the same frequency interference of the internal photoelectric signal of the instrument, and the magnitude of the error is repeated in cycles of the length of the precision measuring ruler.
Among them, proportional error, periodic error, and zero error are the main systematic errors of the photoelectric rangefinder.
According to a large amount of measured data, it is shown that due to the phase non-uniformity and amplitude and phase errors of the instrument's light-emitting and receiving tubes, there are also correction terms related to distance, in addition to frequency errors and atmospheric refractive index errors. Traditionally, correction factors related to distance are collectively referred to as multiplication constants!. The correction for zero point error is called the additive constant. Systematic errors can be eliminated by applying corrections to the system error values obtained during calibration. Therefore, the calibration of the system error of the photoelectric rangefinder mainly includes the following three items:
(1) Verification of periodic errors;
(2) Verification of additive constants;
(3) Verification of multiplication constants.
