Patent GB-1153072-A (GB)
Title: Method of and apparatus for making Templates for Compensating for Systematic Absorption in Spectrophotometers
Inventor: TAPPERT JURGEN
IPC: G01J3/42
Filed: 1966-08-17
Abstract: 1,153,072. Photo-electric spectro-photometers. CARL ZEISS JENA VEB. Aug.17, 1966, No.36858/66. Heading G1A. [Also in Division G2] A template, for use in controlling the position of a compensation element in a radiation path of a spectro-photometer, is made automatically, without a sample in the radiation path. Once prepared, it can be driven in synchronism with the variation of the monochromator, so as, for example, to effect compensation for the variations in absorption of the optical elements &c. of the optical system with wavelength, and for differences in the optical elements in the two paths in a two-path system, when measurements on the sample are carried out through a particular wavelength range. In a two-path spectro-photometer, light from a source 1 is passed through the monochromator 9, whose reflex grating 6 is rotated about axle 10 by motor 48 in order to vary the wavelength continuously. The emerging beam is split by a doublerefracting calcite plate 12 into sample and reference (or compensation) beam paths. The reference beam path comprises a prism 15, diaphragm 16, the compensation element 18, which may be a grey wedge, adjustable and fixed polarizers 21, 22 and lenses 19, 20 focusing the beam via mirrors 23, 24 on to the detector 37. The sample beam comprises a prism 25, a lens 26, focusing the beam on the sample holder 29, and lenses 27 and 28 focusing an image of the sample (when present) on to the detector diaphragm at 30. An eye-piece beam path 32-34 is also provided. The beams are chopped by a rotating shutter 35 so that they arrive alternately at the detector producing an A. C. output which is amplified at 38. In the preparation of the template, the adjustable polarizer 21 is set by motor 40, cam 42 and rod 43 to give maximum intensity in the reference beam path. The switch 39 connects the detector output to motor 41 which drives a link rod 47 to cause wedge 18 to move to equalize the intensities of the two beams. At the same time the plastics disc 52 from which the template is to be made, is rotated and the monochromator adjusted, both by means of motor 48. The rod 47 carries, at the other end from the wedge 18, either a recording device to trace a curve along which the template is afterwards to be cut, or an incandescent wire which actually cuts the disc out in the required shape. In an actual measurement, the sample is located in the holder, the template and monochromator are driven in synchronism the switch 39 also being connected to the motor 40, so that an out of balance detector current results in rotation of polarizer 21, the indication of sample absorption required being that given by the index 44 mounted on the rod 43, along scale 45. In a single-path spectro-photometer, Fig. 3 (not shown), the template is cut by means under the control of error signals produced by comparison of the detector output with a reference signal representing a predetermined absorption level and provided by the recorder recording the detector output. During actual measurements using the spectro-photometer and a compensator moved under the control of the template, a switch is connected so that the error signals are not fed back to the means for cutting the template.