Regensburg 2002 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

VA: Vakuumphysik und Vakuumtechnik

VA 3: Vakuummesstechnik

VA 3.1: Talk

Monday, March 11, 2002, 15:10–15:30, H47

The influence of the evaluation model on the resultant uncertainty of the helium leak secondary standards calibration in the Czech Metrology Institute — •Dominik Prazak, Jiri Tesar, and Frantisek Stanek — Czech Metrology Institute, Okruzni 31, 638 00 Brno, Czech Republic

Mass spectrometers as helium leak detectors are traditionally used for accurate measurement of vacuum leaks. The critical point of their accuracy is their low long-term stability. It is necessary to calibrate them with very short recalibration periods. Secondary helium leak standards are used for these calibrations. But, of course, they need calibration to.

That means the traceability to a primary standard or better to two primary standards. Their leak rates must be lower and higher than the leak rate of device under test is. The principle of the traceability method is to reach an equilibrium state in a dynamical system, pumped and by the same time filled with a gas, that does not contain helium, and by a leak from a standard leak. This equilibrium state is defined by constant partial pressure of helium. Knowing the partial pressures for two leak rates of two primary standards, it is simple to calculate an unknown leak rate from its partial pressure of helium.

The evaluation procedures and their uncertainties are discussed. And the results reached in the praxis of CMI will be shown.