Abstract: A spectrophotometer using a charge coupled device array as an image receiver characterised in that an image of its entrance slit is tilted with respect to columns of pixels in the charge coupled device array and in which the height of the image of the entrance slit on the charge coupled device array is arranged to extend over two or more rows of pixels so that the image of the entrance slit is skewed over pixels in two adjacent columns. Means are provided to analyse the output of the pixels to provide information on the intensity distribution of each spectral line with respect to wavelength having a resolution greater than that of the pitch of the pixels in each row of the charge coupled device array.

Abstract: A method of analysis by liquid chromatography and liquid chromatograph apparatus are disclosed. The method and apparatus are arranged to enable a chromatographer to locate an optimum solvent composition for a particular analysis. A display is produced which shows simltaneously a contour map of chromatogram quality across an isoeluotropic plane and a predicted chromatogram corresponding to a selected point on the isoeluotropic plane.

Abstract: Rigid supporting structures for the components of high precision optical instruments, such as interferometers or monochromators, have hitherto been based on massive castings. Such castings suffer from residual non-recoverable changes of shape during temperature cycling, due to the differential temperatures set up in the castings. The invention provides a rigid structure assembled from a number of flat sheet structural elements. Each sheet element is substantially rigid in its own plane and is attached to one or more other sheets at points of contact which are such that the edge of one sheet bears against the surface of another sheet with the planes of the two sheets being perpendicular in the region of the points of contact. An open ended rectangular box structure may be assembled from two sheets, each with a single right angled fold. Each point of contact and attachment may be formed as a foot standing proud from the remainder of the sheet edge.

Abstract: In beam splitting interferometers for use in Fourier transform spectrometers working in the infra-red region from 2.5 microns to 50 microns wavelength, it is impossible to provide a single beam splitting assembly which is efficient over the whole wavelength range, due to the limitations of available materials. In a set of interchangeable beam splitters it is difficult to ensure sufficiently accurate registration of each beam splitter after a change. The invention provides a set of beam splitters held stationary in separated locations and radiation directing means which passes an input beam through a beam splitter, which selects the recombined beam emerging from a desired beam splitter, and which passes it to a detector in a fixed location.

Abstract: A method and apparatus is provided for adjusting the direction of a beam of radiation by a mirror mounted on a shaft so that the normal to the mirror is inclined relative to the longitudinal axis of the shaft. The shaft is mounted in a bearing for rotational adjustment relative to a supporting structure. This technique and structure may be applied to monochromators or interferometers in which radiation beams must be adjusted in direction to very close tolerances, such as seconds of arc, and maintained in direction with a corresponding stability. The shaft is rigidly secured in the bearing after adjustment by an adhesive so that a stress-free structure is realized in which hysteresis effects due to temperature cycling are minimized.

Abstract: A cam and follower arrangement in which the cam consists of a track carried by a rotatable member. The track has one or more abrupt directional transitions (17) and the follower (17) is biassed to engage one wall or the other (21) of the track (21) appropriate to the direction of rotation of the member by means including a direct-current electric motor operated in a stalled condition. The arrangement may be employed in a monochromator for spectrophotometric apparatus to drive a filter-holder to position one of a number of optical filters arranged in the incoming beam of light.

Abstract: An Ebert monochromator for a spectrophotometer in which the diffraction grating is positioned off of the central optical axis of the collimator mirror by interpositioning a plane mirror between the collimator mirror and the diffraction grating. The plane mirror may be movable to select one of several diffraction gratings. By arranging the diffraction grating about an axis parallel with the central optical axis, a simple mechanical wavelength drive system with a common cam shaft driving the grating, a filter holder, and a rotatable slit plate can be provided. Further gratings may be driven from the cam shaft as may also the movable plane mirror which selects them.

Abstract: A dual-beam ratio recording spectrophotometer has signal processing circuitry for determining the transmittance of a substrate. The signal processing circuitry has a bandwidth which is dependent on the magnitude of the radiation passing through a reference cell and includes control logic circuitry which produces a pulse whose width is proportional to the square of the magnitude of the radiation detected when the beam passes through the reference cell. A sample and hold circuit whose sample time is controlled by this pulse samples the output of an integrator which produces at regular intervals a signal representative of the transmittance of a substance. Thus, the response time of the sample and hold circuit and hence the bandwidth of the signal processing circuitry depends on the magnitude of the radiation passing through the reference cell.

Abstract: A dual beam spectrophotometer includes a radiation chopper, a monochrometer, and a diffraction grating moved by a stepper motor. The chopper includes a gate pulse generator which produces gate pulses G.sub.S and G.sub.R corresponding to periods during which radiation from the source passes through a sample cell and a reference cell respectively. A stepper motor drive circuit produces pulses to step the stepper motor which are synchronized with the chopping cycle by means of the G.sub.R and G.sub.S pulses. The stepper motor is arranged to step an equal number of times in each half of a chopping cycle. A further condition which is preferably satisfied is that the first pulse of a sequence should start in the opposite half of the chopping cycle from that in which the first pulse started in a previous chopping cycle. At low stepping rates the motor will step twice in one chopping cycle and then pause for several cycles before again stepping twice.

Abstract: A dual beam spectrophotometer includes signal processing circuitry for producing sample-dark and reference-dark signals. The dark signals substracted from the sample and reference signals are the average of the dark signals produced on each side of the sample and reference pulses. The signal processing circuitry may comprise four sample and hold circuits which store the sample signal, reference signal and first and second dark signals, a resistive combining network for the two dark signals and first and second substractor circuits. The first substractor circuit provides the sample-dark signal at its output while the second substractor circuit provides the reference-dark signal at its output.