This blog is about choosing a particle counter for gas applications. First, determine whether your process gas is reactive or non-reactive. Then decide its pressure range.
Reactive Gases
Examples of reactive gases include hydrogen and oxygen. These gases require a special particle counter stored inside a containment vessel. In addition, they require careful evaluation that the wetted materials of the particle counter are compatible with the gas. Also consider additional precautions such as leak monitoring, purge flow monitoring, and other safety measures that ensure safe operation.
Sampling gases at pressure is best. Therefore, gas instruments employ mass flow controllers to provide constant, volumetric flowrates when connected to gas line pressures between 40 – 150 psig. Particle sizing can differ with pressure and the composition of gas. Gas particle counters must account for these variables. A gas constant entered into the instrument’s data system provides correction factors for different gases. It also allows the mass flow controller to increase or decrease the flowrate based on the chemistry of the gas.
If the gas is reactive and falls within the specified pressure range, you may sample the gases using a Ultra High Purity Gas Particle Counter (HPGP). The HPGP™ 101-C offers 0.1 µm sensitivity, 0.1 CFM flowrate, and can accommodate line pressures up to 150 psig.
Non-reactive Gases
Non-reactive gases such as argon, helium, neon, nitrogen, and xenon have different monitoring requirements. The option with the lowest initial cost is a connection from a standalone particle counter to a high-pressure diffuser (HPD). HPD’s dilute gas samples with ambient air and provide humidity. Humidity prevents degradation in a particle counter’s optics and plumbing. The HPD III accommodates pressures from 40 – 100 psig.
Takeaway: Dedicated gas particle counters should be used for critical applications and any measurement of reactive gases. HPDs should be used for less critical applications or occasional monitoring of non-reactive gases.
Conclusion
While the purchasing choices may seem endless, evaluating your particular application will help you focus on your requirements. Still have questions about what you’re looking for? Click here for expert assistance.
To learn about more considerations for buying aerosol particle counters, download the full paper here.
Want to read more? Jump to other released posts in this series:
Part 1 of 4: Terminology and Standards
Part 2 of 4: Types of Monitoring
Part 3 of 4: Number of Monitoring Locations
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