Method and apparatus for measurement of the fluorescence relaxation period of a fluorescent substance

A method for measuring the fluorescence relaxation period of fluorescence radiation from a fluorescent substance having a fluorescence relaxation period dependent upon a physical parameter, said method comprising the steps of:

• repeatedly subjecting the substance to excitation radiation in the form of oscillations from an oscillator of a regulating circuit having a regulating parameter corresponding to the physical parameter during time intervals in an excitation phase to produce fluorescence radiation from the substance, said oscillations having substantially uniform frequency;
• generating a radiation output signal representative of the fluorescence radiation from the fluorescent substance;
• alternately, only during the relaxation phase, phase-sensitively rectifying the radiation output signal in two different polarities to provide rectified output signals in two corresponding polarities;
• integrating the rectified output signals and providing integrated signals in said two polarities;
• and
• controlling the relative durations of rectification in each polarity so that a summation of the integrated signals in said two polarities substantially equals zero to determine the regulating parameter corresponding to the physical parameter.

An apparatus for measuring the fluorescence relaxation period of fluorescence radiation from a fluorescent substance having a fluorescence relaxation period dependent upon a physical parameter, said apparatus comprising:

• means for repeatedly subjecting a substance to excitation radiation during time intervals in an excitation phase to produce fluorescence radiation from the substance during a relaxation phase;
• a photoelectric receiver for receiving the fluorescence radiation from the fluorescent substance and providing a radiation output signal indicative thereof;
• a phase-sensitive rectifier receiving the radiation output signal for alternately, only during the relaxation phase, phase-sensitively rectifying the radiation output signal in two different polarities with the total time of rectification in each polarity being equal to provide rectified output signals in each of said two polarities, said rectifier including a differential amplifier having an inverting input, a non-inverting input and an output, and a plurality of switches for selectively connecting said inputs of said amplifier to said photoelectric receiver or, during the excitation phase, to a reference potential;
• an integrator connected to said rectifier for integrating the rectified output signals and providing integrated signals therefrom in said two polarities;
• and
• a regulating circuit having a regulating parameter corresponding to the physical parameter, said regulating circuit including a voltage controlled oscillator responsive to a summation of the integrated signals for controlling said excitation radiation, a scan and hold circuit connecting said oscillator to said integrator, and a logic circuit for controlling said plurality of switches for said rectifier.

An apparatus for measuring the fluorescent relaxation period of fluorescence radiation from a fluorescent substance having a fluorescence relaxation period dependent upon a physical parameter, said apparatus comprising:

• means for repeatedly subjecting the substance to excitation radiation in the form of oscillations having substantially uniform frequency during time intervals in an excitation phase to produce fluorescence radiation from the substance;
• a photoelectric receiver for receiving the fluorescence radiation from the fluorescent substance and providing a radiation output signal indicative thereof;
• a phase-sensitive rectifier receiving the radiation output signal for alternatively, only during the relaxation phase, phase-sensitively rectifying the radiation output signal in two different polarities to provide rectified output signals in each of said two polarities, said rectifier including a differential amplifier having an inverting input, a non-inverting input and an output, and a plurality of switches for connecting said inputs of said amplifier to said photoelectric receiver or, during the excitation phase and during predetermined pauses, for connecting said inputs to a reference potential;
• an integrator connected to said rectifier for integrating the rectified output signals and providing integrated signals in said two polarities;
• and
• a regulating circuit having a regulating parameter corresponding to the physical parameter and determined by the relative durations of rectification in each of said polarities;
• said regulating circuit including a discriminator connected to said integrator for receiving the integrated signals therefrom and a logic circuit connecting said discriminator to an output, said logic circuit having a counter for counting substantially uniform frequency clock pulses, said logic circuit comparing the count of said counter with predetermined values and controlling said switches of said rectifier to set the relative durations of rectification in each polarity so that a summation of the integrated signals in said two polarities substantially equals zero.