Patent GB-735035-A (GB)
Title: Improvements in or relating to apparatus for recording and reproducing variables
IPC: G01J3/28
Filed: 1951-09-14
Abstract: 735,035. Recording apparatus. BECKMAN INSTRU - MENTS, Inc. Sept. 14, 1951 [Sept. 15, 1950], No. 21629/51. Class 106 (4). [Also in Groups XXXVIII and XL (b)] A variable is recorded by causing it to vary the phase of a cyclical function which is then recorded. Recording (Figs. 3 and 5).- The variable to be recorded is translated by known means into the angular displacement of a drum 61 on the surface of which are marked three sine functions 66 displaced from each other by 120 degrees as shown in the development of the drum in Fig. 5. Two functions displaced by 90 degrees may be used. A narrow strip 83 on the edge of the drum is defined by a mask and illuminated by lamps 84 such as fluorescent tubes. An image of the strip is projected on to a moving film 75 which thus bears a record of the angular position of the drum. A length of the developed film strip is shown in Fig. 6. Reading the strip (Fig. 7).- The film 75 is fed over sprockets 102, 103 past a narrow slit 110 illuminated by a light source 111. In the path of the light to the slit is situated a rotating disc 115 of polarizing material and behind the slit and film are three pieces 117 of polarizing material with their axes of polarization inclined at 60 degrees to each other. One such piece is associated with each trace 90 on the film (Fig. 6). The light passing through these pieces of polarizing material is focused on to a photo-electric cell 114 and it is shown in the Specification that the output of the photo-cell is an alternating current the phase of which varies in proportion to the angular rotation of the recording drum. A reference voltage is generated by directing part of the light passing through the-rotating polarizer on to a photo-cell 122 and fixed polarizer 121 by means of mirror 120. Reproducing the variable (Fig. 9).-The output of photo-cell 114 varying in phase with the value of the variable is fed to a phase discriminator 132. The reference signal from photo-cell 122 is split into two quadrature components by a phase splitter 127 which components are amplified in amplifiers 128, 129 and applied to the field windings of a Selsyn 130. The output of the Selsyn rotor also feeds the phase discriminator. The output of the discriminator is connected through a servo amplifier 133 to a rotor 134 which rotates the Selsyn rotor 130 to reproduce the angular deflection of cylinder 61. Spectrophotometer (Fig. 13).-The invention is applied to indicating the relation between the position of the wavelength adjusting means and the light intensity means. As shown, light from a Nernst lamp 269 is interrupted by a lowfrequency chopper 264, a gas cell 267 and a liquid cell 268. The beam then passes through a narrow slit 270 to a condensing mirror 271 and a dispersing prism 272 on to a rotatable mirror 273 by means of which the wavelength under inspection is selected. The radiation is reflected back from the mirror to an exit slit situated below the entry slit finally impinging on a radiation detector 278. The size of the entrance and exit slits may be adjusted by a motor 280, the mirror position by a motor 274. In use, with no sample present in either of cells 267 or 268, as the wavelength is varied by motor 274 the cell output is maintained constant by adjustment of the slits by motor 280. The motor 274 also drives the tape of the recording apparatus shown in Fig. 3 while motor 280 adjusts the recording drum. Thus the tape bears a record of slit position against wavelength selector position. To determine the transmissivity of a sample the tape is fed through the reproducing apparatus already described, the Selsyn adjusting motor 134 being replaced by the slit adjusting rotor which thus reproduces the slit position during the recording process. The output of the detector 278 then indicates transmissivity directly. Reproducing a relation between two variables. (Fig. 17). This application of the invention is concerned with modifying the movement of the chart of a recording spectrophotometer so that it is in accordance with wavelength rather than position of the wavelength selector. In this case a tape of the kind shown in Fig. 6 must be made, the longitudinal position of the tape indicating wavelength adjuster position and the phase of the sine waves on it, wavelength. The apparatus of Fig. 3 is suitable for this purpose except that tape and drum drive are from the same motor or cam adjusting the drum rotation, or the correct relationship between the movements may be achieved by means of a non-linear potentiometer. In use, the tape prepared as indicated above is advanced by the motor 274 which also adjusts the wavelength selector. The reproducing arrangement is as described in paragraphs 2 and 3. Motor 311 which adjusts the rotor of Selsyn 130 drives the chart through Selsyns 312, 313. The pen position is adjusted by the radiation detector of the spectrophotometer. Modifications.-More than a single record may be made on a tape and the Specification describes apparatus (Figs. 10, 11, 12, not shown), in which two variables are impressed on a single tape. The apparatus is as shown in Figs. 3, 7 and 9 duplicated but only a single reference cell and phase splitter is necessary. A device is described (Fig. 18) in which recording and reproduction are effected on a magnetic tape. As shown, the variable to be recorded is converted into a rotation of shaft 330 which is split into two quadrature components by the known linkage shown and which appears as vertical movements of the magnetic recording heads 335 which then produce two sine waves on the tape out of phase with each other by 90 degrees. The phase of these waves with respect to a reference is a measure of the angle of rotation of shaft 330. During reproduction servomotors 345 which are swung into engagement with the recording heads are fed by the leads through a detector amplifier discriminator and power amplifier 348 so that the head follows the curve. Shaft 330 then repeats its original movement.