Beckman Instruments, Inc.

Allan S Way

Thomas J Glenn

Taylor A Reid

Stanley L Pratt

Howard J Sloane

Gerald T Keahl

A double beam, optical null spectrophotometer including means for automatically determining system loop gain requirements and setting the gain to the correct value for optimum response under all operating conditions. With the system ready for operation and a sample in the sample beam path, a difference signal is generated as a function of the position of a reference beam attenuator with and without a small unbalancing signal applied to the system loop. This difference signal is compared to a desired difference signal and a loop gain adjustment is made so that the difference signal will equal the desired difference signal, thereby establishing instrument gain for optimum response.

Automatic loop gain adjustment for optical null spectrophotometers

A double beam optical null spectrophotometer having sample and reference optical beam paths, a detector common to both paths, and an attenuator feedback loop from the detector for adjusting the position of an optical attenuator in the reference beam path to balance the energy in the two paths. The slider of an attenuator transmitting potentiometer follows the position of the optical attenuator and a signal level sensitive impedance network connected to the slider calibrates the potentiometer such that an output signal therefrom indicates the true transmittance of a sample in the sample beam path over a range of transmittance values from zero to one hundred percent transmittance.

Apparatus for calibrating an optical null spectrophotometer

A variable chart format system for a recorder with a chart print out, the system having a manually selectable switch for simultaneously controlling the abscissa and ordinate formatting independent of scale expansion circuitry normally associated with the abscissa and ordinate. The abscissa formatting is digital and operable in response to a programmable or variable clock, the output of which is selectively passed through a first set of abscissa formatting frequency dividers and then serially through one of a second set of abscissa scale expansion frequency dividers to drive a chart drive stepper motor. The ordinate formatting is analog and includes ordinate scale expansion circuitry in series with the servomotor and ordinate formatting selectable compensating resistors in series with the recording pen potentiometer or slidewire, the selectable compensating resistors being selected simultaneously with the abscissa formatting dividers to thereby preselect a chart format by a single control without affecting the abscissa or ordinate expansion circuitry.

Spectrophotometer having independently controlled chart scale expansion

A tracking accuracy control system for a spectrophotometer utilizing stepper motors for controlling the wavelength drive and chart drive system. An exact ratio between the wavelength drive motor and chart drive motor is maintained under variable speed conditions by utilizing an error signal which normally operates the reference beam attenuator, this error signal being transmitted through an absolute value circuit to produce a voltage whose magnitude is the absolute value of the error signal. This absolute value is then transmitted through a fast attack, slow release hold-over circuit to control a voltage controlled oscillator in such a way as to reduce wavelength scan speed in an amount proportional to the error while simultaneously controlling chart speed in an exact ratio to the scan speed. The output of the voltage controlled oscillator is a pulse train having a frequency proportional to the magnitude of the absolute value of error signal.

Stepper motor tracking accuracy control for spectrophotometers

A spectrophotometer including a wavelength stepper motor driving a wavelength scanning mechanism and a chart stepper motor driving a chart recorder, both motors being operative in response to driving pulses received from a system clock. The upper limit of a wavelength scan interval is established by manually adjusting the wavelength scanning mechanism to the desired limit. The length of a desired scan interval is selected by the operator and loaded into a counter which decrements in response to the driving pulse input to the wavelength motor. The counter generates an output signal after a predetermined count which clocks a switching circuit for reversing, inhibiting, or otherwise controlling the wavelength and chart motors. Other inputs to the switching circuit provide for either serial or overlay chart recording and for either continuous or manually controlled scanning.

Digitally controlled repetitive scanning in a radiant energy analyzer

A spectrophotometer system having a first stepper motor driving a wavelength scanning mechanism and a second stepper motor driving a chart recorder, both motors being operative in response to pulses from a system clock. The clock frequency is successively divided by first and second cascaded, switch-selectable sets of frequency dividers. The output of the first divider is applied to the wavelength motor and determines wavelength scan speed. The output of the second divider is applied to the chart motor and determines chart scale expansion. A decoder monitors the frequency selections of the first and second sets of frequency dividers, and upon detection of a frequency selection outside the capability of the chart motor, the decoder provides an output which inhibits both motors. The decoder output additionally actuates a visual indicator to inform an operator of the invalid selection.

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Irvine, CA, United States of America

Allan S Way