Trace Gas Detection Purge Gas Impurity Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Spectroscopic trace gas detection faces challenges in achieving high precision and sensitivity due to interfering absorption by atmospheric gas components and impurities in the purge gas, especially when the main gas ingredient and trace gas absorb light at identical wavelengths, as seen in the analysis of moisture in process gases like ammonia or nitrogen.
Innovation Solution
Measuring and subtracting the light absorption of the purge gas from the measuring gas, with an adjustment using a scaling factor based on the optical path lengths, effectively compensates for impurities in the purge gas, improving detection limit and accuracy even when pressure and absorption line broadening differ between the gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a purge gas is used to prevent penetration of atmospheric gas components, then interference from atmospheric gases is reduced, but impurities in the purge gas itself cause interfering absorption
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the absorption of the purge gas itself and using this information to correct the measurement. A reference channel measures the purge gas absorption, and this measurement is fed back to compensate for the interfering absorption in the main measurement channel, thereby eliminating the harmful effect of purge gas impurities
Solution Approach 2:
The patent introduces an intermediary measurement system that separately measures the purge gas absorption characteristics. This intermediary measurement acts as a mediator between the purge gas impurities and the final measurement result, allowing the system to account for and compensate the interfering absorption without directly affecting the main measurement process
2Object-affected harmful factors
If the optical path is sealed and purged with nitrogen, then atmospheric water vapor interference is prevented, but moisture in the nitrogen supply and pipe porosity introduce new interference sources
Solution Approach 1:
The system continuously monitors the absorption characteristics of the purge gas in a reference channel and feeds this information back to compensate for interference in the main measurement. This feedback approach dynamically corrects for varying levels of moisture in the nitrogen supply and pipe porosity effects, maintaining high measurement precision despite these interference sources
Solution Approach 2:
The patent extracts the interfering absorption component by separating the measurement into two independent channels: one for the measuring gas and one for the purge gas. By extracting and separately measuring the purge gas absorption, the system can remove its contribution from the final measurement, thereby eliminating the interference from nitrogen moisture and pipe porosity
3Object-affected harmful factors
If cancel gas is introduced into the reference cell to eliminate interfering absorption, then absorption spectrum subtraction is required, but this approach does not account for variations in purge gas impurities
Solution Approach 1:
Instead of using a static cancel gas approach, the patent implements a dynamic feedback system that continuously measures the actual purge gas absorption and uses this real-time information to compensate for interfering absorption. This feedback mechanism automatically adapts to variations in purge gas impurities without requiring complex manual subtraction procedures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly enhances the trace gas detection accuracy and limit by automatically compensating for impurities in real-time, ensuring precise quantification of trace gases even under conditions of differing pressure and absorption characteristics.
Implementation Method 1
the light of a light source, e.g. an infrared lamp or a tunable diode laser, is transmitted through the measuring volume to a measuring detector, e.g. an opto-pneumatic or solid-state detector, for generating a measuring detector output dependent on the light absorption in the optical path of the measuring volume
Implementation Method 2
a portion of the light of the light source is passed through a reference cell comprising the known gas component or another suitable gas component of constant concentration. Afterwards the light is detected by a reference detector, the output of which is used for self-calibration and zero point determination of the system
Implementation Method 3
In spectroscopic trace gas detection, the concentration of a known gas component, or gas components, in a gas mixture (measuring gas) is determined from a measured wavelength-specific absorption of the gas component or a measured absorption spectrum of the measuring gas, respectively
Data Source
AI summary
In spectroscopic devices the sections of an optical measuring path from a light source to a measuring volume containing a measuring gas and from there to a measuring detector are often sealed off from the ambient atmosphere and purged with a purge gas such as dry nitrogen to prevent penetration of atmospheric gas components, such as water vapor, which may interfere with the trace gas measurement. The moisture content in the nitrogen supply is usually in the range of a few ppm at the gas source and can increase dramatically at the measuring site depending on the length of the nitrogen pipe net and due to porosity of the pipe walls, leakage of seals and residual moisture trapped in so-called dead legs. In order to compensate interfering absorption of atmospheric gas components and other impurities in the purge gas the purge gas is collected after flushing the optical path sections, a portion of the light of the light source is transmitted along a second optical path to a compensation detector, the second optical path is flushed with the collected purge gas and the trace gas component in the measuring gas is determined based on a difference between the output of the measuring detector and the output of the compensation detector.