DUAL WAVELENGTH PHOTOMETER RESPONSE CIRCUIT

• US 3,804,535 A
• Filed: 10/13/1972
• Issued: 04/16/1974
• Est. Priority Date: 10/13/1972
• Status: Expired due to Term

• Current Assignee: SLM Instruments Incorporated
• Original Assignee: Rodolfo R. Rodriguez
• Inventors: Rodriguez, Rodolfo R.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Morrison, S. K.
• Application Number:
  US05/297,279
• Time in Patent Office: 550 Days
• Field of Search: 356/246,201,39,40,41,229,217,205
• US Class Current: 356/217
• CPC Class Codes: G01J 1/16 using electric radiation detectors G01J1/20 takes precedence
• CPC Class Codes: G01N 21/27 using photo-electric detection G01N21/31 takes precedence; circuits for computing concentration logarithmic circuits G06G7/24; photometric circuits in general G01J
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

An apparatus to measure the difference in intensity between periodically recurring reference and measure light pulses of different wavelength reaching a photomultiplier tube, the apparatus having alternately keyed steady voltage-generating circuits keyed in synchronism with the light pulses and generating concurrent steady d.c. electrical signals with amplitudes corresponding to the light pulse intensities which are furnished to the respective inputs of a differential amplifier. The output of the differential amplifier is therefore a steady signal representing the difference in intensity between the reference and measure light pulses.

Claims

1. In a photometer, a source of time-shared sequential light reference and measure beams recurring cyclically at a predetermined fixed rate, cuvette means included in the path of said beams, a photosensitive device located to receive said beams and generating respective time-shared sequential electrical pulse signals in accordance with the intensities and durations of said beams after they have passed through the cuvette means, means to generate respective substantially concurrent steady electrical signals having amplitudes in accordance with said response signals, and means to measure the difference in the amplitudes of said steady signals, wherein the means to generate the respective steady signals and to measure the difference in their amplitudes comprises a differential amplifier, respective steady signalgenerating devices connected to the inputs of said differential amplifier, respective alternately keyed circuit means drivingly connecting the photosensitive device to said steady signalgenerating devices, means to key said keyed circuit means at said predetermined rate, and indicating means connected to the output of said differential amplifier, and wherein each of the steady signal-generating devices comprises an amplifier, the associated keyed circut means including an electronic switch connected in series with the input of said last-named amplifier, and a parallel-connected resistor and capacitor connected in parallel through said electronic switch, the capacitor being connected directly across the input and output terminals of the last-named amplifier, and means closing said electronic switch at said predetermined rate so that the resistor forms a discharge circuit for the capacitor when the electronic switch is closed, whereby to allow the capacitor to adjust its charge with changing amplitudes of input pulses and to thereby control the voltage level at the output of the last-named amplifier.

2. The apparatus of claim 1, and respective additional keyed circuit branches for said reference and measure beams connected between said photosensitive device and said first-named keyed circuit means, one of said additional circuit branches including adjustable attenuator means for balancing the signals furnished to said steady signal-generating devices at the beginning of a test, and means to key said respective additional keyed circuit branches synchronously with said respective first-named keyed circuit means.

3. The apparatus of claim 1, and wherein said keying means comprises a periodic synch generator operating at the same rate as said reference light beam, circuit means operatively connecting said synch generator to one of said keyed circuit means, and means to operate the other keyed circuit means after a time delay corresponding to the time spacing between the reference and measure light beams.

4. The apparatus of claim 3, and wherein the means to operate the other keyed circuit means comprises a timed signal generating circuit connected to the output of said synch generator having means to generate an output signal at a time delay after excitation thereof corresponding to the time spacing between the reference and measure light beams, and circuit means operatively connecting the output of said timed signal generating circuit to said other keyed circuit means.

5. The apparatus of claim 4, and a logarithmic amplifier connected between said photosensitive device and said Steady signal generating devices.

6. The apparatus of claim 5, and respective additional keyed circuit branches for said reference and measure beams connected between said photosensitive device and said logarithmic amplifier, one of said additional circuit branches including adjustable attenuator means for balancing the signals furnished to the logarithmic amplifier at the beginning of a test, and means to key said additional circuit branches synchronously with said respective steady signal-generating devices.