| 摘要 |
<p>A capnometer includes a light sourse for irradiating an infrared radiation to respirtory gas, a thermal detector for sensing the transmission of the infrared radiation, switch device for turning the radiation source on and off in a predetermined period, memory device for storing output from the thermal deterctor, and control device for picking up a maximum value of the detection signal from the thermal detector for the present inspiration phase, for storing the maximum value in the memory device and calculating the difference between a subsequently issued detection signal and the stored maximum value, for compensating a drift occurred on the basis of the thermal detector charachteristic to determin a varying density signal, for picking up a minimum output value, corresponding to an offset value, of the detection signal from the thermal detector when the radiation source is turned off momentarily, for calculating the difference between the minimum value and the stored maximum value for the present inspiration phase, for storing the calculated difference in the memory device as a reference value corresponding to carbon dioxide concentration of zero and with a maximum reception of infrared radiation at that time, for storing the reference value in the memory device, for calculating the ratio of the density signal to the reference value, and for determining the concentration of carbon dioxide through compensation of a sensitivity corresponding to an amplitude. <IMAGE></p> |
