What is the primary purpose of purging a gas sampling line in instrumentation?

What is the primary purpose of purging a gas sampling line in instrumentation?

• A. To pressurize the line for faster sample transport.
• B. To remove ambient air, moisture, or contaminants from the line so the sample is representative.
• C. To cool the sample stream before analysis.
• D. To introduce calibration gas into the line.

Answer: (B)

Purging a gas sampling line is about making sure the sample that reaches the analyzer truly represents the process gas. By flushing the line with dry or inert gas (often the same process gas or a purge gas), ambient air, moisture, and any contaminants that have accumulated in the line are displaced. This prevents dilution, condensation, or chemical interactions on the line walls that would distort the measurement, and it eliminates the effect of dead volume so the reading reflects the current process conditions. Purging is not intended to pressurize the line for speed, cool the sample, or introduce calibration gas; those actions could introduce errors or contamination.

Purging a gas sampling line is about making sure the sample that reaches the analyzer truly represents the process gas. By flushing the line with dry or inert gas (often the same process gas or a purge gas), ambient air, moisture, and any contaminants that have accumulated in the line are displaced. This prevents dilution, condensation, or chemical interactions on the line walls that would distort the measurement, and it eliminates the effect of dead volume so the reading reflects the current process conditions. Purging is not intended to pressurize the line for speed, cool the sample, or introduce calibration gas; those actions could introduce errors or contamination.