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1. (WO1998018019) DEVICE FOR CALIBRATING DISTANCE-MEASURING APPARATUS

Pub. No.:    WO/1998/018019    International Application No.:    PCT/EP1997/005735
Publication Date: Apr 30, 1998 International Filing Date: Oct 17, 1997
IPC: G01S 7/497
Applicants: LEICA GEOSYSTEMS AG
GIGER, Kurt
Inventors: GIGER, Kurt
Title: DEVICE FOR CALIBRATING DISTANCE-MEASURING APPARATUS
Abstract:
The invention concerns a device for calibrating distance-measuring apparatus. A transmitter (1) emits high-frequency modulated optical radiation which is reflected by an object to be measured and is received by a measurement receiver (2). Part of the transmitter radiation is always decoupled as reference radiation and guided via a calibration path to a reference receiver (3) whose electrical signals are fed to a frequency mixer (4). The frequency mixer (4) and the avalanche photodiodes acting as measurement receivers (2) of the measuring radiation are interconnected directly via an electrical connection line (5) upon which a mixer frequency acts. As a result thereof, optoelectronic calibration which completely compensates the temperature-dependent phase shifts of the avalanche photodiodes is possible. Since, in addition, the phase shifts generated in the reference and receiver signals by the temperature drifts of the transmitter (1) compensate one another, the overall accuracy of the distance measurement is increased, in particular for short measuring times and immediately after the apparatus has been switched on. Furthermore, in comparison with a successive mechanical calibration process, the measuring times are halved and advantages in terms of weight, cost and reliability are afforded since a mechanical change-over device is dispensed with.