DC PHOTO/VOLTMETER

摘要

PURPOSE:To enable the removal of DC drift mixed into a DC output to be measured by applying a voltage to a polarizing device inverted in the polarity thereof at a fixed cycle after it is obtained by dividing DC voltage to be measured at a specified ratio. CONSTITUTION:The switching operation of a SW12 is repeated at a fixed cycle to connect a pair of electrodes 31 and 32 of a polarizing device 3 to an electrode 22 of an input capacitor 2 and a reference potential point G alternately at a fixed cycle so that only the polarity of a voltage Vi applied to the polarizing device 3 is inverted at a fixed cycle. On the other hand, beam from a laser beam source is fed to an electrooptic effect element 33 passing through a polaroid element and a 1/4 wavelength plate and a transmission beam as elliptically polarized is sent to a photo detector through a photo detecting element to obtain an alternating square wave output whose amplitude is proportional to a voltage V0 to be measured. This enable easy removal of drift components by rectification using a phase discriminator even when the output of a light modulation circuit is mixed with the DC drift components.