For Racine, technology keeps evolving. The company has launched its new air test stand to conduct quality airflow calibrations on gas meters. The system includes a set of seven sonic nozzles arranged in a common manifold. Each nozzle has its own control valve allowing a quick connection to the calibration manifold. The calibration manifold can accommodate wafer meters from 1/2" to 4" in diameter, along with insertion meters in a 6" diameter pipe. The complete stand can accurately measure flow rates from 0.4 to 2,800 cubic feet per minute with ±0.5% accuracy. Sonic nozzles are internationally recognized as the best secondary transfer standard for gas flow measurement and one of the most precise gas flow meters available today. The air test stand's sonic nozzles have many advantages over other devices. In a system with constant upstream pressure, sonic nozzles are a constant volumetric flow meter, but with regulated pressure supply, the sonic nozzle becomes a gas flow regulator. The test stand can therefore dial in a flow rate by setting the inlet pressure to the nozzle. They have no moving parts and offer long term accuracy and repeatability. They also create a shock wave at the throat of the nozzle. Once this shock wave exists at a fixed flow rate, downstream fluctuations cannot propagate upstream. This means they do not require differential pressure measurements across the nozzle, unlike other Venturis and orifice meters, which can lead to additional errors in flow calculations. Flow rate is not affected by downstream flow disturbances or varying downstream pressure (up to about 85% of the inlet pressure), but rather is solely a function of upstream pressure and temperature. The software developed for this technology provides more reliable and time efficient results by automating some of the calibration process. With a set of calibration target points, the software controls a pressure regulator, which sets the flow rate, and monitors inlet temperature and pressure to the nozzle that determines actual flow rate. The actual flow rate is then compared to the meter's flow rate and the amount of error between them is displayed in real time. This error is used to calculate a correction factor that can be downloaded to the meter in real time. After calibration, the software creates a detailed calibration certificate that is supplied to the customer. The combination of sonic nozzles, manifolds, and the customized software provides a test stand that is highly accurate over a wide flow range while maintaining ease of use. The air stands capabilities provide a new level of dependable and repeatable results on all of Racine's gas meter calibrations.
