The source of ranging error for photoelectric rangefinders
The ranging error of an optoelectronic distance measuring instrument is divided into two parts:
(1) Proportional error: The error that is proportional to the length of the measured distance, mainly caused by frequency error, atmospheric refractive index error, and vacuum light velocity measurement error. The influence of the error in measuring 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, proportion error, period error, and zero error are the main system errors of the photoelectric distance measuring instrument.
According to a large amount of measured data, it is shown that due to factors such as phase non-uniformity and amplitude phase error of the instrument's light-emitting and receiving tubes, there are also correction terms related to distance length in addition to frequency error and atmospheric refractive index error. Traditionally, correction numbers related to distance length are collectively referred to as multiplication constants!. The correction for zero point error is called the additive constant. System 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 distance measuring instrument mainly includes the following three items:
(1) Verification of periodic errors;
(2) Verification of additive constants;
(3) Verification of multiplication constants.
