Double-beam photometer including structure to eliminate re-radiation from the output signals

Abstract

Abstract A DOUBLE-BEAM PHOTOMETRIC SYSTEM (E.G., A SPECTROPHOTOMETER) CAUSES THE RADIATION FROM THE SOURCE TO PASS THROUGH THE (FIRST) SAMPLE PATH DURING A FIRST QUARTERPERIOD TO THE DETECTOR, SO THAT THE DETECTOR RECEIVES SAMPLE-TRANSMITTED RADIATION, P, PLUS "CHARACTERISTIC" RADITION GENERATED BY THE ELEMENTS IN THE SAMPLE PATH, P0. DURING THE SECOND QUARTER-PERIOD THE RADIATION IS BLOCKED FROM THE SAMPLE PATH, WHILE THE DETECTOR "SEES" THIS SAME PATH, THEREBY OBTAINING ONLY THE "CHARACTERISTIC" SAMPLE PATH RADITION, P0. DURING THE THIRD QUARTERPERIOD BOTH THE SOURCE RADIATION AND THE PATH TO THE DETECTOR ARE SWITCHED TO THE SECOND REFERENCE PATH, SO THAT THE DETECTOR "SEES" REFERENCE TRANSMITTED SOURCE ENERGY, V, PLUS RE-RADIATION FROM THE REFERENCE PATH ELEMENTS, V0. IN THE FINAL QUARTER-PERIOD THE SOURCE RADIATION IS BLOCKED FROM THE REFERENCE PATH, SO THAT THE DETECTOR SEES ONLY THE REFERENCE PATH RE-RADIATION, V0. THUS THE FOUR QUARTER-PERIOD SIGNALS ARE: P+P0, P0 V+V0, AND V0. BY SYNCHRONOUSLY DEMODULATING THE DE TECTOR SIGNAL SO AS TO INVERT THE SECOND AND THIRD QUARTERPERIODS TOGETHER RELATIVE TO THE FIRST AND FOURTH, THE FOUR SIGNALS BECOME: +P+P0, -P0, -V -V0, AND +V0. THUS THE D.C. SUM OF THE SIGNALS IS P-V, FREE OF ALL RERADITION COMPONENTS, WHICH SIGNAL MAY THEREFORE BE UTILIZED IN A CONVENTIONAL SERVO-SYSTEM TO DRIVE A REFERENCE BEAM ATTENUATOR SO AS TO CAUSE A NULLING OF THE DIFFERENCE BETWEEN P AND THE ATTENUATED V SIGNAL. THIS SYSTEM IS RELATIVELY INSENSITIVE TO ERRORS IN PHASE SYNCHRONIZATION OF THE OPTICAL SWITCHING MEANS (E.G., ROTATING SECTOR CHOPPERS) AND THE ELECTRICAL DEMODULATOR.

Inventors

• 👤 Wolfgang Witte
• 👤 Joachim Marckmann

Bibliographic Details