Beam modulator for optical systems in gas analysers - has compact transparent drum with mask as chopper in front of diaphragm

摘要

The beam modulator, esp. for gas analysers, comprises a hollow cylinder (1) which is driven by a motor (3) and which acts as an optical chopper. The cylinder is transparent to radiation with the exception of a strip (7) which interrupts the beam twice for every revolution of the drum. The chopper is placed between the object being measured (4) and the aperture (5) of the detector (6). Compared with a flat disc type of chopper operating at the same frequency, the drum with its strip is half the size. The drum can be fitted with several such strips if necessary in which case: where dz = the diameter of the cylinder, a = the number of strips and dB = the width of the aperture.