Abstract: A self-contained automatic computer controlled system for checking and recalibrating the wavelength scale of both monochromators of a fluorescence spectrophotometer is described. No operator adjustments are required. The system sets the wavelength of each monochromator to within 0.1 nanometers. Besides automatic indexing at turn-on the operation can be repeated at any desired time. The system is applicable to single or double monochromator instruments.

Abstract: The effective range of an analog linear-log converter is extended above the number of output decades over which this converter is reasonably linear to cover several additional decades of log conversion. This is made possible by adding a variable gain amplifier having several decades of switchable gain to the input of the converter. Switching between decades to utilize the added decades of output is controlled by a microcomputer which monitors the output level. This switching restores the signal level of each of the added decades to the same level as that of an earlier decade thus maintaining the same slope accuracy and noise levels of the earlier decades throughout the whole conversion range. The microcomputer also provides slope corrections from a lookup table for each of the different output decades as well as also applying to the output corrections for offsets due to the circuit components. Ambient temperature compensation is also provided following the linear-log converter for increased precision.

Abstract: A software controlled automatic shutter is described which minimizes ultraviolet irradiation damage to optical components from a high intensity spectrophotometric light source. The shutter automatically opens when measurements are being made and closes when the photometer system is idle. The digital control system may be self contained so as to avoid complication of the main computer.

Abstract: A programmable timer controls the duration of integration with respect to time of an unknown analog signal in accordance with a programmable time period established by a microprocessor. A switching logic successively transfers an analog signal and a voltage reference signal to an integrator under logic control actuated by the programmable timer. A comparator monitors the value of the integration of the reference voltage in order to control the time-out results of an event counter initiated simultaneously with input to the integrator of the reference voltage, for providing a digital count output signal to the microprocessor.

Abstract: It has been shown that the use of a shutter to cut off the light beam entering the optical system of a fluoresence spectrophotometer will reduce UV deterioration of the components in the optical system. This invention discloses how control of the output of the light source by lowering its arc current when the shutter is closed can add significant improvement to the functioning of such a shutter system.

Abstract: A timing system for a spectrophotometer having a line driven chopper including a rotating disc with alternate open and opaque segments, index apertures in the disc spaced at invariant angular relationship to one of the open segments for providing indexing pulses having fixed time relationship to the light segments, and a programmable microcomputer assembly for generating a string of timing pulses for timing spectrophotometer operations and adjusting the rate of the timing pulses to provide a fixed number between indexing pulses in fixed phase relationship thereto.

Abstract: In a spectrophotometer having an optical beam chopped into dark and light segments, a computer controlled system is described for determining background signal due to stray light, photomultiplier dark current, offsets of photometric amplifiers and other components, and the like and for subtracting this background signal from the overall signal so as to leave only the desired light measurement. The same computer system also sets the signal level automatically for highest resolution. Furthermore, the same computer acts as an analog to digital converter by successive approximation to supply the photometric signal to the microprocessor unit. Since the same components are involved in all these functions both analog and digital offsets of the components are automatically cancelled.

Abstract: A discharge lamp firing apparatus is disclosed which includes providing only the necessary firing voltage to the lamp prior to the firing thereof. As such, the surrounding system is not subjected to transients caused by conventional mechanisms which suddenly switch an extremely high voltage across the lamp. As a result, the present apparatus protects the associated circuitry as well as prevents needless overvoltage conditions to the lamp.

Abstract: A spectrophotometer system has an optical system for transmitting a beam from a source at select wavelengths onto a detector. A plurality of filters are positioned in a tray. A stepper mechanism indexes the tray along a path. A microcomputer controls the stepper mechanism and the optical system. The wavelength is successively changed over a range, the tray is indexed to move a select filter into the beam at a predetermined wavelength and the changing is discontinued during indexing.

Abstract: 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.

Abstract: An improvement in a spectrophotometer of an improved apparatus for automatic initialization of the wavelength indexing function of the spectrophotometer. A drive mechanism drives the wavelength indexing movement of the spectrophotometer diffraction grating. The grating is initialized to a grating initialization position by physical opposition of a stop mechanism to the driving when a drive linkage reaches a drive linkage initialization position.

Abstract: A microprocessor based spectrophotometer including a memory system for providing storage locations of sets of operating parameters and correction data. The operator loads the memory via keyboard control. The memory system is battery backed-up for maintaining stored data during power shutdown of the spectrophotometer system.

Abstract: A microprocessor based spectrophotometer including manual keyboard command for sequencing a monochromatic energy beam through a spectral range of wave-lengths to a keyboard selected wavelength. A manual adjustment knob is thereafter rotatable for generating a 4-bit gray code signal which successively changes as the adjustment knob is rotated. The microcomputer senses a change in the gray code signal and indexes (steps) the wavelength of the monochromatic beam in proportion to the positional change of the adjustment knob as indicated by the changing gray code. A visual display indicating wavelength setting and spectral response, is updated conjointly with manual wavelength adjustment.

Abstract: An improved photodetector arrangement comprises positioning a photodetector having at least one semi-transparent cathode so that the light beam striking the cathode passes through it at least twice before exiting from the photodetector. In another embodiment of the invention, a second photodetector is positioned relative to a first photodetector so that the light beam, after striking the first photodetector, strikes the second photodetector. Where the two photodetectors are employed, they may be electrically connected in parallel.

Abstract: A circuit permitting an operator to accurately calibrate an instrument to indicate when a variable analog quantity being measured is zero. The analog signal is connected to the input of an operational amplifier which operates in stable mode for large analog inputs and operates in oscillation mode for very small analog inputs. The output of the operational amplifier is compared to zero and when the analog input is greater than zero, the comparator output is a logic zero. When the analog input is less than zero and not in the immediate vicinity of zero, the comparator output is a logic one. When the analog input is very small and less than zero, the operational amplifier operates in oscillation mode as the circuitry connected thereto causes it to oscillate with the duty cycle of the negative portion of the oscillation decreasing as the analog input comes closer to zero. Accordingly, the output of the comparator also oscillates.

Abstract: An improved photodetector arrangement comprises positioning a photodetector having at least one semitransparent cathode so that the light beam striking the cathode passes through it at least twice before exiting from the photodetector. In another embodiment of the invention, a second photodetector is positioned relative to a first photodetector so that the light beam, after striking the first photodetector, strikes the second photodetector. Where the two photodetectors are employed, they may be electrically connected in parallel.