The Perkin-elmer Corporation

Other

Autocar Equipment Limited

Michael A Ford

Larkin B Scott

Morteza M Chamran

Henry Manifold Mould

Paul B Williams

John P Coates

David Jackson

Robert W Hannah

Christopher R Bailey

Abraham Savitzky

Harry V Carter

Dieter Kolb

Brian B Leather

Bernard Brian Leather

Vapor-heated chamber

In an interferometric apparatus the path of the output beam of a rotary Optical Path Difference scanning assembly leading to an electrically responsive detector is maintained substantially fixed in space for any scan angle within predetermined limits, thus obviating a serious drawback of a prior art proposal wherein the output beam translates significantly over the detector face with changes in scan angle, with the result that the detector output is vitiated by totally spurious variations of the energy reaching it. In one embodiment, the scanning assembly comprises a beam splitter having a semi-reflective layer the output face of which cooperates with the face of an output mirror normal thereto, the axis of rotation being substantially coincident with the line of intersection between the prolongation planes of the two faces. A Fourier Transform spectrophotometer embodying the assembly is also described.

Interferometric optical path difference scanners and FT

The accuracy of the ratio between two time-varying quantities represented by electrical signals, such as the sample transmission (or absorption) signal and the reference signal in a double-beam, ratio-recording, infrared spectrophotometer, is impaired if the electrical signals are subject to inconstant phase shifts. The present invention counteracts the effect of phase shift variations, whatever their origin, by alternately reversing the order in which an elemental component of one quantity is made to occur with respect to an elemental component of the other quantity so that the said effect reverses in sign when the order is reversed and substantially cancels out when the respective elemental portions are combined to form the numerator and the denominator of the ratio. The invention is particularly described with reference to a spectrophotometer of the type referred to.

Counteracting the effect of phase shift changes between two quantities

The vitiating effect on the fluorescence measuring signal of extraneous currents flowing through the fluorescence detection means in flash spectrofluorimetry is almost completely eliminated by integrating the output of the fluorescence measuring means for the duration of the signal period, which includes a flash duration, and again for an equal period occurring between flashes which therefore does not include a flash duration. The second integral is then subtracted from the first to obtain a fluorescence measuring signal substantially unaffected by extraneous currents, such as dark current, sample phosphorescence, etc. The invention is applicable to single- and double-channel operation. In the latter, in addition to the fluorescence measuring channel there is provided a fluorescence reference channel. This enables the fluorescence measuring signal and the fluorescence reference signal to be ratioed together, the effect of extraneous currents having first been eliminated in both.

Minimizing the effect of spurious photodetector currents in flash

Disclosed herein is method and apparatus for determining the nature of an unknown substance, which includes apparatus for entering a peak table of the spectrum of an unknown substance into computing apparatus, apparatus for adjusting the peak table to a first preselected standardized format, computing apparatus for comparing the so standardized peak table of the unknown with a first library of chemical structural units contained in memory in the computing apparatus, apparatus for making a list of the possible chemical structural units most closely corresponding to the unknown substance, apparatus for readjusting the peak table to a second preselected standardized format, apparatus for forming a file for the unknown substance including data corresponding to the readjusted peak table and to the list of possible chemical structural units, computing apparatus for comparing the file of the unknown substance with a second library containing files of known substances contained in memory in the computing apparatus, each known substance having a file containing data corresponding to its respective peak table in the second standardized format and to its respective chemical structural unit, and apparatus for outputting a list of known substances which most closely correspond to the unknown substance. In a form of the invention, apparatus is provided for adding data corresponding to a known substance to the second library contained in memory in the computing apparatus.

Method and apparatus for determining the nature of an unknown chemical

A light chopper for chopping the monochromatic light beam of a spectrophotometer system, has a rotatable shaft driven by a synchronous motor at a frequency proportional to the power line frequency. An aperture bearing disc rotates with the shaft in relation to a photocell/detector array for generating digital timing signals for use by a microcomputer to control the tasks of the spectrophotometer system in synchronism with line frequency. The microcomputer monitors line frequency for responsively programming a programmable divider for generating an index signal for proportionally sequencing the wavelength of the monochromatic beam through a predetermined spectral range. The rotatable shaft is coupled to the synchronous motor via a mechanical pin drive and a set of attracting magnets which are spaced in face confronting relation at the point of coupling for providing compliance and damping between the coupled shaft and synchronous motor, thus minimizing phase jitter of the timing system and permitting rejection of time frequency stray circuit pickup.

Spectrophotometer system having power line synchronization

A cross-talk balancing circuit for double-beam spectrophotometers is disclosed. The circuit includes means to measure in four successive sample periods the sample plus sample re-radiation (S + s), reference radiation plus reference re-radiation (R + r), sample re-radiation (s) and reference re-radiation (r). The detector, however, does not respond quickly so it introduces cross-talk into each measurement. Electronic phasing circuitry selects the time when the detector output is sampled so that the cross-talk in the measurements is equalized permitting it to be subtracted out of the measurement thereby leaving a remainder which accurately corresponds to the desired quantities S and R.

Cross-talk balancing circuit for spectrophotometers

In a plotting apparatus such as a spectrophotometer having a modifying system which introduces a phase lag between the occurrence of a change in a dependent variable quantity and plotting thereof against an independent variable quantity, in one embodiment, a cam is used to provide a quantity representing the dependent phase lag and the output of the cam is coupled to the driving system for the plotter so as to introduce therein a phase shift to compensate for the phase lag. In another, electrical embodiment the same object is accomplished by digitizing the phase lag and using the digital value to offset the wavenumber stepper motor and the chart stepper motor in the spectrophotometer with respect to each other.

Apparatus for compensating ordinate phase lag in a plotting apparatus

There is described an improvement for an apparatus employing a plurality of operational elements adapted to cooperate for producing an electrical signal representing the variation of an ordinate quantity with respect to an abscissa quantity changing at a controlled rate. At least one of said elements requires an adjustment during operation such as is capable of causing spurious transients in the electrical signal. The apparatus further comprises a filter for filtering the electrical signal before feeding the signal to a suitable utilization device such as a recorder. The improvement includes control means which operate to interrupt the ordinate quantity signal and cut off the filter response prior to any element adjustment. There is disclosed means for storing the output of the filter at cut off and for memorizing the point along the impulse characteristic of the filter at which cut off takes place. There is further disclosed means for sensing the completion of the element adjustment and for applying a predetermined time delay before the reinstatement of system operation. This eliminates the effect of transients at this point.

Transient suppressor network for spectrophotometers and the like

A tunable electrical filter is disclosed wherein an RC (resistor-capacitor) network comprising a plurality of switchable capacitors among the components determining the time constant of the filter provides a given minimum value of filter time constant and, therefore, a given minimum bandwidth, when all the capacitors are continuously connected in the network. Each capacitor is coupled to the network through the output means of an electronic switching means. A pulse generator connected to the input means of said switching means provides a train of pulses having an adjustable ON-time to OFF-time ratio. When all the capacitors are periodically switched by the output of the pulse generator, the effective filter time constant increases from said given minimum value as the ON-time compared with the OFF-time decreases. The pulse generator is provided with control means for adjusting the ON-time to OFF-time ratio. Operation of the control means will, therefore, enable the filter to be tuned within a predetermined range.

Tunable electrical filter network

A double-beam, time-sharing, ratio-recording spectrophotometer in which the reference signal data is evaluated both in an actual demodulation cycle and in a different cycle, which may be either a preceding or a following cycle. The two evaluations are combined to produce derived reference signal data. Ratioing means are included for extracting the ratio between the sample signal data evaluated in an actual demodulation cycle and the derived reference signal data. Predetermined multiplying factors may be used in arriving at the derived reference signal data. The interpolation of reference signal data from actual and non-actual demodulation cycles enables the effect of uncompensation on photometric accuracy to be minimized. Uncompensation results from the fact that in a time-sharing spectrophotometer sample and reference signal data do not occur at the same time and do not therefore relate to the same environment and the same wavelength.

Ratio-recording spectrophotometer with suppression of uncompensation

In a device such as a spectrophotometer with an associated chart recorder in which the speed ratio between a first displaceable member and a second displaceable member may be selectively changed within a predetermined range of speed ratios, in a first embodiment of invention which is mechanical in nature, a number of gear trains in constant mesh with each other are provided to obtain the different speed ratios. Each of the gear trains has associated therewith a rotary disc with circumferentially even spaced apertures, the gear train obtaining an input from the first displaceable member by means of arms rotatable concentric with the discs, the arms carrying a pin adapted to enter into positive engagement with any one aperture, the number apertures depending on the scale served by the associated gear train. In a second, electrical embodiment equivalent operation is obtained by maintaining counts in counters of the position where the second displaceable member would be for each of the given scales along with maintaining a count of the actual position with comparator means used to bring the actual count into correspondence with the desired count when a scale change takes place.

Apparatus for changing the speed ratio between first and second

Disclosed is a fluorescence spectrometer having an intermittently activated sample irradiating source, such as a UV lamp, the periods of activation being short (e.g., 100 microseconds) in comparison to the intervening inactive periods (e.g., 20 milliseconds). Fluorescence radiation emitted by the sample is detected by a photomultiplier, the output signal of which is supplied to an integrating amplifier for utilization. A field effect transistor (FET) in the output circuit of the photomultiplier has its gate coupled to a control unit which determines the activation periods of the lamp and, in timed relation thereto, cuts off the FET to interrupt the output circuit during periods that the lamp is inactive. A dual channel fluorescence spectrometer is also described.

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Maidenhead, United Kingdom

Michael A Ford