Dynamic inversion and correction of ammonia pressure within the range 6611–6614 cm−1

Abstract

Laser absorption spectroscopy is widely applied in gas concentration detection while the measurement accuracy would be affected by fluctuations in the environmental pressure (pressure fluctuations inside the gas cell under vacuum conditions). In this paper, a dynamic inversion and correction method of gas pressure without pressure sensors was proposed. Ammonia within the range of 6611–6614 cm−1 was selected as the research object. In contrast to previous reports, this method does not investigate the effect of pressure on gas concentration detection from a single point of view, or obtain pressure values from pressure sensors. Instead, the real-time temperature was measured to determine the broadening coefficient, which was then utilized along with full width at half-maximum (FWHM) of the spectral lines to calculate the real-time pressure value before correction. The directly acquired pressure has an error, and based on the error analysis, the pressure is corrected to get the corrected real-time pressure value. Finally, the effect of systematic error was eliminated by correcting the concentration using the corrected real-time pressure value and the measured real-time temperature. Experimental results show that the average residual of the corrected real-time pressure compared to the measured true values was 0.1993 torr with a standard deviation of 0.7387 torr. The correlation coefficient R2 between the inverted pressure value and the measured true value was 0.999, with a maximum fitting error of 1.19 %, error fluctuations within 2 %, and pressure uncertainty ranging from 0.545 % to 0.913 %. Furthermore, the ammonia concentration was corrected, and the maximum error compared to the standard ammonia concentration injected in the experiment was 1.025 % (with an effective optical path length of the detection gas cell of 15 cm). This work demonstrated the effectiveness of the proposed method in accurately inverting dynamic real-time pressure values and improving the accuracy of gas concentration measurement.