A. Navarro-Nateras, J. C. Torres-Guzman, P. Olvera-Arana
Measurement systems development for the calibration of leaks and holes in dynamic pressure (microflow) at CENAM, Mexico
The pressure and vacuum group of the Force and Pressure Division, at the Centro Nacional de Metrologia (CENAM, Mexico) has developed two measurement systems for calibration, one for leaks and another for holes in dynamic pressure.
The leaks calibration system is based on the method of pressure increment at constant volume (and constant temperature) within the measurement range starting at 1 x 10-6 Pa·m³·s-1 up to 5 Pa·m3·s-1 with volumes of 0.5 L or 1 L (according to the leak range to be calibrated), with an operation pressure from 1 x 10-5 Pa up to 130 kPa, using helium, nitrogen or air as manometric fluids.
For the calibration of holes in dynamic pressure, the method PVTt is used. This is, pressure increments at constant volume and constant temperature during a given time. The volume used is 3.75 L with a gas flow up to 20 cm³·min-1 using nitrogen as operation fluid.
The procedure of holes calibration consists on measuring the flow through a small hole by measuring the pressure increment due to the gas accumulation in a known volume during a period of time with controlled temperature conditions. The PVTt system is formed by pressure gauges, a gas collection tank with a known volume, temperature sensors, a chronometer for time measurement, a vacuum pump, a set of valves to control the gas flow direction and the hole which will be calibrated.