Determining null intensity for respiratory gas analyser used during patient care using a function that approximates the sensor reference value as a function of temperature

摘要

The null intensity for each gas channel is approximated with the reference channel intensity multiplied by a function that approximates the reference value for the sensor as a function of temperature. A method for continuously determining the null intensity (I0) of a gas analyser comprising an IR emitter (1), a reference filter (3), an optical band pass filter (4), channels for the gases being analyzed, a measuring cuvette (5) for the gases (i), and an IR detector (6) for the amount of radiation absorbed in the cuvette, comprises approximating the null intensity for each channel with the reference channel intensity multiplied by a function K(i) that approximates the reference value for the sensor as a function of temperature (T). The function is defined by the following equation: K(i) = k(i) x T + l(i), k(i) = proportionality factor ; and l(i) = offset value. During the time immediately following start-up, the offset value is approximated using the following function : l0(i) + t x [l(i) - l0(i)]/tal, l0(i) = offset value determined by a reference measurement immediately after start-up ; t = time after start-up ; and tal = thermal time constant for sensor.