Miniaturized Ft-Ir Spectrometer For Industrial-Process Measurements

There have been made some attempts to transfer the advantages of FT-JR to industrial use. Commercially available research grade instruments have been large and rather expensive. However in many potential applications only medium resolution is required which means that the mirror displacement in a Michelson type interferometer remains short and computation of the Fourier transform can be executed by a small computer. Medium resolution gives also other advantages in spectrometer design simple source and detector optics less severe requirements for mirror transport and small size. We have used a Michelson type interferometer where the moving mirror is suspended by two flexures and driven by a coil actuator. Displacement of the mirror is monitored using moire transducer which is much smaller and has better thermal stability than the conventionally used HeNe laser. The beamsplitter is a standard CaF2/Si and a thermoelectrically cooled PbSe is used as the detector. In the present prototype data is transferred via parallel bus to a PC/AT compatible computer where the necessary mathematics is done. The spectral range is from 5000 to 1800 cm1 with resolution better than 8 cm1. Interferograins can be recorded several times per second and the computation time for a 2000 point spectrum is 10 seconds. Results of environmental tests carried out for the spectrometer will be presented. The results show that it is possible to construct a simple rugged and inexpensive FT-IR spectrometer