EXPLOSION-PROOF OPTICAL ENCODER

PURPOSE:To improve resolving power and prevent the danger of explosion even with the use in a dangerous atmosphere by providing a second polarizing filter with the plane of polarization partitioned by a straight line passing a rotary shaft as a boundary so as to be formed into the plane of polarization of two directions forming an angle of 45 deg.. CONSTITUTION:The light outputted from light emitting element 17, 18 is led by optical fibers 13, 15 to irradiate polarizing filters 10, 11. The filter 10 is rotated together with a rotary shaft 4, but the filter 11 is not rotated, so that the quantity of light penetrating the filters 10, 11 becomes the maximum when the polarizing directions coincide with each other, but becomes the minimum when the polarizing directions are orthogonal. The quantity of light penetrating filters 10, 11 are therefore changed periodically according to the rotation of the filter 10. The transmitted light is led to light receiving elements 19, 20 by optical fibers 14, 16. The filter 11 is provided with the plane of polarization of two directions forming a angle of 45 deg., and the detected quantity of transmitted light is changed with 45 deg. phase difference.