Respiratory CO.sub.2 detector circuit with high quality waveform

Details Respiratory CO.sub.2 detector circuit with high quality waveform Respiratory CO.sub.2 detector circuit with high quality waveform

1989-02-02

1990-09-11

Cohen, Lee S.

Surgery

Truss

Pad

128725, A61B 5087

Patent

active

049559460

ABSTRACT:
A respiratory CO.sub.2 detector (10) comprising an infrared lamp source (44) and an infrared detector (50) responsive thereto forming an optical path for detecting the change in CO.sub.2 concentration, or an obstruction in a cuvette (42). The output of the infrared detector (50) provides a high and low voltage signal to be applied to a feedback control loop (12) and to an output circuit (14).
The feedback control loop (12) includes a peak detector (22), a contamination detector (24), a pulse-width modulator (26) and a low pass filter (28), the latter providing a DC bias on the infrared lamp (44). The peak detector (22) is connected to the pulse-width modulator (26) to maintain the lamp voltage constant and is connected to comparators (56,62) to compare both outputs of the peak and contamination detectors (22,24). The contamination detector (24) will respond to blockage in the cuvette (42).
The output control circuit (14) includes a sample-and-hold circuit (30) and a subtractor (32) connected to the output of said infrared detector to receive the high and low voltage signal from the infrared detector, the outputs of which produce an output signal without the DC bias which is then inverted to provide a high quality waveform.

REFERENCES:
patent: 4011859 (1977-03-01), Frankenberger
patent: 4368740 (1983-01-01), Binder
patent: 4423739 (1984-01-01), Passaro et al.
patent: 4578762 (1986-03-01), Wong
patent: 4648396 (1987-03-01), Raemer

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