Patent GB-1501883-A (GB)
Title: Devices for use in monitoring chemical reactions
IPC: G01N21/25
Filed: 1975-02-07
Abstract: 1501883 Photometric analyzers NATIONAL RESEARCH DEVELOPMENT CORP 7 Feb 1975 [7 Nov 1973 7 May 1974] 4741/75 and 4742/75 Heading G1A Apparatus for monitoring chemical reactions has a turn-table I, Fig. 1, carrying many cuvettes 3 in a circular array; the turn-table can be stepped about its axis by a motor 6 so that the cuvettes pass in sequence through filling, monitoring and emptying zones. While in the monitoring zone the cuvettes are scanned many times by a light beam which is directed down the axis from unit 9, then outwardly to the cuvettes by reflector 26 which rotates rapidly about the axis. The light passes through the cuvettes and is reflected back to the axis by mirrors 27 associated with the cuvettes to strike a further rotating reflector 30 which directs the light to a photo-multiplier 32. Because both the turn-table and the reflectors 26, 30 rotate (at different rates) timing signals have to be generated to allow the photo-multiplier signal to be demodulated so that information is given about individual cuvettes. Also, since the light from unit 9 alternates rapidly between a measuring and a reference wavelength, further timing signals are needed. The turn-table position is found by vanes 54 which are associated with respective cuvette positions and which can block a path between light source and detector 57, 58. The rotating reflectors are mounted in a tube 33 driven via a gear 46 by motor 48; this tube is fixed to a bearing tube 38 which carries a disc 43. The latter rotates relative to a timing light source and detector 42, 44 held in a housing 41 which rotatably supports the bearing tube. The remaining timing signals come from detectors associated with the two beams produced by a chopper 14 in unit 9, and from a source and detector 50, 52 which gives a signal once per revolution of the tube 33 (typically every 2 secs); a similar detector 53 (not shown) also co-operates with source 50 to give another signal once per revolution, the signals being used to indicate that the cuvettes being viewed are those in the measuring zone. The unit 9 has a lamp 10, Fig. 3, whose light is split at 12 and passes along two paths; the first path is via chopper 14, lens 17, filter plate 20, reflector 21 to beam combiner 22, and the second path is via reflector 13, chopper 14, lens 17, filter plate 20 to combiner 22. The paths are alternately chopped by the chopper, and the filter plate has two different filters so that at combiner 22 a beam is produced which alternates between measuring and reference wavelengths. Two detectors 19a, 19b give the above-mentioned timing signals. The combined beam exits through aperture 24 which is on the turn-table axis as seen in Fig. 1. The beam passes down to lens 25, Fig. 4, prism 26 and the cuvettes 3; reflectors 27 behind the cuvettes return the beam to prism 30, lens 31 and the photo-multiplier. The cuvettes may be in two concentric, staggered rings on the turn-table, hence the two radially different cuvette positions in Fig. 4. The photo-multiplier signals are gated into one or other of two inegrators depending on the measuring/reference timing signals. The timing signals from detector 44 representing the scanning assembly position indicate which cuvette is being examined, and read-out of the integrators is controlled by these signals via a counter and logic circuit, Fig. 9 (not shown). The integrator signals are determined either in an analogue manner by finding the log of their ratio, Fig. 7 (not shown), or in a digital manner by discharging the capacitor of the reference integrator until its voltage is the same as that of the measuring integrator, clockpulses being counted during the discharge period, Fig. 8 (not shown).