Exponential decay time constant measurement using frequency of offset phase-locked loop: system and method
First Claim
1. A system for measuring a value functionally related to an exponential decay time constant, said system comprising:
- stimulus/response means including stimulus means for stimulating a sample in response to a received stimulus signal and response means for providing a response signal reflecting a response generated by said sample;
an offset-phase locked loop including a signal generator, said generator being adapted for generating a periodic stimulus signal characterized by a frequency within a predetermined generator frequency range, said offset-phase locked loop being arranged in a feedback relation with said stimulus/response means so that said periodic stimulus signal is received by said stimulus means so as to yield a periodic response signal which is fed back to said offset-phase locked loop via said response means, said offset-phase locked loop being adapted for forcing an offset-phase angle between said periodic stimulus signal and said periodic response signal, said offset-phase angle being constant over said generator frequency range; and
conversion means for deriving from the frequency of said stimulus signal a value related to an exponential time constant for said response signal.
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Abstract
Oxygen determination based on luminescence quenching of fluorescent dye is effected by using the frequency output of an offset-phase locked loop to calculate the time constant for the exponential decay of fluorescence. An offset phase angle between a periodic stimulus signal used to excite the dye and a response signal based on fluorescence detection is predetermined to optimize signal-to-noise ratio for a wide range of time constants. An offset-phase locked loop is used to vary the frequency of a periodic stimulus signal until the predetermined phase relationship is established. Where the stimulus and response signals are substantially sinusoidal, the offset phase angle is ideally about 49.3°, although substantially optimal performance is achieved using a more conveniently generated 45°. The 45° angle offset can also be used with a square-wave stimulus signal.
42 Citations
18 Claims
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1. A system for measuring a value functionally related to an exponential decay time constant, said system comprising:
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stimulus/response means including stimulus means for stimulating a sample in response to a received stimulus signal and response means for providing a response signal reflecting a response generated by said sample; an offset-phase locked loop including a signal generator, said generator being adapted for generating a periodic stimulus signal characterized by a frequency within a predetermined generator frequency range, said offset-phase locked loop being arranged in a feedback relation with said stimulus/response means so that said periodic stimulus signal is received by said stimulus means so as to yield a periodic response signal which is fed back to said offset-phase locked loop via said response means, said offset-phase locked loop being adapted for forcing an offset-phase angle between said periodic stimulus signal and said periodic response signal, said offset-phase angle being constant over said generator frequency range; and conversion means for deriving from the frequency of said stimulus signal a value related to an exponential time constant for said response signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of measuring a parameter of a sample, said parameter being mathematically related to an exponential decay time constant characterizing a response of said sample to a stimulus, said method comprising the steps of:
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determining an offset-phase angle between a periodic stimulus signal and a resulting response signal to provide a relatively favorable signal-to-noise ratio; stimulating said sample with a periodic stimulus signal selected to periodically initiate exponential decay; detecting the resulting response signal; adjusting the frequency of said periodic stimulus signal to achieve said offset-phase angle between said periodic stimulus signal and said periodic response signal; measuring the frequency of said periodic stimulus signal; and calculating from said frequency the value of the parameter of interest. - View Dependent Claims (15, 16, 17, 18)
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Specification