Instruments for analyzing substances by determining their radiation absorption characteristics

Claim 1

An instrument for analyzing substances by determining their radiation absorption characteristics when subjected to a beam of radiation, wherein the optical components of the instrument are mounted on support members which lie in at least two intersecting planes, said support members comprising two flat plate members lying at an angle to one another in the manner of a pitched roof with the optical components being supported on each flat member, and wherein a source of infra-red radiation is mounted on one support member and the beam of radiation from the source is directed onto a beam splitting device located adjacent the apex formed by the two support members, from which beam splitting device the beam is formed into two beams which are directed in paths parallel to the apex to fall on wavelength selection devices before being reflected back along parallel paths to fall again on the beam splitter device, from which device the beams are directed along a beam path in the other support member to fall on a radiation detector, radiation chopping means being provided between the beam splitting device and the wavelength selection devices to interrupt each beam alternately so that the detector receives radiation from each beam path alternately, the sample under test being placed in the beam path on one of the support members. 2. An instrument as claimed in claim 1, wherein the wavelength selection devices are in the form of diffraction gratings with reflecting members in the Littrow arrangement.