System for detecting a first light transmissive substance, such as for instance blood, in a second light transmissive, different substance

A detection system for automatically detecting a first light transmissive substance in a second and different light transmissive substance, comprising:

• light emitting means for alternately producing light beam flashes of light having a first wavelength and light having a second wavelength;
• support means for temporarily supporting a volume containing said first and said second substance respectively in the light beam path;
• opto-electric detecting means for converting light beam flashes directed along said light beam path into corresponding electric voltages;
• an electric detecting arrangement comprising a controllable gain amplifier with a control input through which its gain is controlled in dependence of a gain control signal, a control loop circuit for deriving said gain control signal from voltages corresponding to light beam flashes which at said second wavelength are transmitted directly (in the absence of said volume in front of the opto-electric detecting means) to said opto-electric detecting means and including comparator means for regulating said gain in such a manner that in response to said light beam flashes which at said second wavelength are directly applied to said opto-electric detecting means, a constant voltage corresponding to a reference voltage is produced at the output of said amplifier, a sample and hold circuit which is selectively activated during time intervals at which light beam flashes at said first wavelength are transmitted through said volume under inspection, in order to produce a first voltage proportional to the ratio between light transmitted through said volume under inspection at said first wavelength and light transmitted through said volume under inspection at said second wavelength, and another sample and hold circuit which is selectively activated during time intervals corresponding to light beam flashes which at said first wavelength are transmitted directly to said opto-electric detection means, so as to produce a second voltage proportional to the product of a detection threshold and the quotient of light transmitted directly to said opto-electric detecting means at said first wavelength and light directly transmitted to said opto-electric detecting means at said second wavelength;
• and comparator means for comparing said first voltage and said second voltage for providing a decision signal indicating whether or not the ratio between the transmission through said volume under inspection at said first wavelength and the transmission through said volume at said second wavelength exceeds said detection threshold.

A detection system for automatically detecting a first light transmissive substance in a second and different light transmissive substance, comprising light emitting means for alternately producing light beam flashes of light having a first wavelength and light having a second wavelength;

• support means for temporarily supporting a volume containing said first and said second substance respectively in the light beam path;
• opto-electric detecting means for converting light beam flashes directed along said light beam path into corresponding electric voltages;
• an electric detecting arrangement comprising means for producing a first voltage proportional to the ratio between light transmitted through said volume under inspection at said first wavelength and light transmitted through said volume under inspection at said second wavelength, and means for producing a second voltage proportional to the product of a detection threshold and the quotient of light transmitted directly to said opto-electric detecting means at said first wavelength and light directly transmitted to said opto-electric detecting means at said second wavelength, and a controllable gain amplifier with a control input through which its gain is controlled independence of a gain control signal, a control loop circuit for deriving said gain control signal from voltages corresponding to light beam flashes which at said second wavelength are transmitted directly and through said volume under inspection as well to said opto-electric detecting means and including comparator means for regulating said gain in such a manner that in response to said light beam flashes which at said second wavelength are applied to said opto-electric detecting means, a constant voltage corresponding to a reference voltage is produced at the output of said amplifier, said comparator means for regulating the gain of said controllable gain amplifier comprises a sample and hold circuit which is selectively activated during time intervals corresponding to light beam flashes at said first wavelength;
• and further comparator means for comparing said first voltage and said second voltage for providing a decision signal indicating whether or not the ratio between the transmission through said volume under inspection at said first wavelength and each transmission through said volume at said second wavelength exceeds said detection threshold.