Gas sampling works by extracting a representative portion of a gas from a source for analysis. This often involves carefully controlling pressure and flow to ensure an accurate sample is obtained.
Here's a breakdown of the process, based on the reference provided:
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Source Access: Accessing the gas source, which could be a vessel, pipeline, or the atmosphere.
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Pressure Reduction: If the gas is under pressure, a pressure reducing valve is attached to regulate the flow. This valve reduces the high pressure of the source gas to a level suitable for the sampling equipment.
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Flow Control: A flowmeter is used to precisely control the rate at which the gas sample is drawn. This ensures a consistent and measurable flow, vital for accurate measurements.
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Sample Collection/Analysis: The gas then flows from the flowmeter into a detector tube (or other analytical instrument). The detector tube contains a reagent that reacts with the target gas, producing a color change or other measurable effect.
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Duration: Sampling is conducted for a predetermined time to allow sufficient interaction between the gas and the detector reagent.
Simplified Steps:
- Connect: A sampling device (often including a pressure regulator and flowmeter) is connected to the gas source.
- Regulate: The pressure reducing valve lowers the gas pressure.
- Control: The flowmeter ensures a constant flow rate.
- Collect: The gas sample passes through a detector tube or analytical instrument.
- Analyze: The detector measures the concentration of the target gas based on a color change or other reaction.
Example:
Imagine sampling air from a compressed air tank to check for carbon monoxide (CO). A pressure reducing valve and flowmeter would be connected to the tank. The valve would lower the high pressure, and the flowmeter would ensure a steady flow of air into a detector tube specifically designed to react with CO. The color change in the tube would indicate the CO concentration in the air sample.