Position measuring instrument

摘要

The present invention is directed to a position measuring instrument having a testing device for checking the amplitude of the analog scanner signals and for testing the operation of the trigger stages. In a first preferred embodiment the trigger threshold voltage of all the trigger stages is switched simultaneously to defined various test voltages. One test voltage is within the allowable amplitude of the analog scanner signals and a further test voltage is outside. The states of the scanner signals digitized by means of the trigger stages before and after the switchover are compared with one another and as a function thereof an error signal is generated. In another preferred embodiment, the trigger threshold voltage is kept constant and either the radiation intensity of the light source or the intensity of the scanner signal is varied.