Why gas calibrators with sonic nozzle show unbeatable accuracy and stability?

The SONIMIX 2106 uses the sonic nozzle principle. A sonic nozzle is a restriction where the critical flow is reached. When a flowing gas passes through a restriction, such as the throat of a convergent-divergent nozzle, under specific conditions it reaches the supersonic speed at the critical flow. At this state any downstream conditions changes like temperature or pressure will not affect the flow. The use of sonic nozzles is described in the ISO 6145-6 norm 'Gas analysis – Preparation of calibration gas mixtures using dynamic volumetric methods – Part 6. Critical orifices'.

This principle provides several benefits:

• Simplicity: the mechanical setup includes a high precision pressure regulator at the inlet and a nozzle with small diameter. No electronic signal measurement or flow regulation are needed as flow condition are blocked by gas physics conditions.
• Long-time stability: the pressure regulator is a 750 grams full metal device capable of maintaining the inlet pressure within pressure variations of less than 2 mbar. The nozzle is made of nickel or gold with unaffected dimensions or surface properties even for corrosive gas applications.
• Metrological superior performances: With both above mentioned features the uncertainty reached is better than 0.5% and across the entire dilution range of the device. Unlike Mass Flow Controllers, working below 10% of the dilution range is possible within the specifications.
• Extended dilution capability – By combining several nozzles up to 1024 mixtures ratios can be generated. The a dilution ratio range goes from 1/1 up to 1/1000.
• Proven performances: Finally accuracy performances of each are identified and reported into our accredited ISO 17025 laboratory.

Today more than 500 units of Sonimix 2106 are installed worldwide. By tracking their performances into our ISO 1702, it shows the long term stability and accuracy even for devices having more than 15 years.

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