Sira Test and Certification is introducing a new facility for the calibration of standard leaks, the only one of its kind to receive accreditation from UKAS
Sira Test and Certification is introducing a new facility for the calibration of standard leaks.
The facility is the only one of its kind to receive accreditation from the UK Accreditation Service (UKAS).
The facility finally closes the long-acknowledged gap in the measurement traceability chain associated with leak detection.
The notion of a standard leak is probably an enigma to many and the fact that there is a requirement for such a thing is probably equally baffling.
However, there is such a thing and, yes, it does have a use! A standard leak is essentially a reservoir of known gas with an outlet via an element which allows a nominally fixed throughput of gas molecules.
The most common types are helium leaks where the element is a quartz capsule.
The throughput of molecules in this case depends on a number of factors, the largest of which is the helium concentration gradient across the quartz capsule.
Assuming this and the other factors can be determined with an appropriate measurement uncertainty, then the leak can be used as a transfer standard to calibrate helium leak testing apparatus.
This then allows for industrial leak detection measurements to be made in accordance with international quality standards (ie with demonstrable measurement traceability).
Standard leaks have been in wide spread use within the UK but to-date the true value of these has never been fully assessed.
In the last few months Sira Test and Certification Ltd, working in conjunction with DERA under a contract from the DTI, has built a suite of standard leak calibration facilities to accommodate the UK's traceability needs.
Some of these are already under Sira's UKAS scope of accreditation in respect of ISO/IEC 17025.
The others are on course for accreditation early in 2003.
Sira's current accredited facilities cover the calibration of standard helium leaks in the range 10-6 to 10-8 mbar l/s.
Calibration is achieved using a comparison technique based around a mass spectrometer against reference leaks calibrated in Germany by PTB (Physikalisch-Technische Bundesanstalt).
Uncertainties as low as 5% can be quoted depending on the exact value of the leak being calibrated.
Additional facilities have also been developed to increase the range such as a primary "pressure rise" technique, which allows for gases other than helium.
The facilities will also include the capability to determine the thermal dependence of the leak element - a very significant factor for many types of leak.
This leak calibration service is of particular relevance to customers from the nuclear industries (both power and re-processing), to vacuum equipment manufacturers of sealed electronic components (vacuum tubes/lights etc), to optical, decorative and tool coatings plants, pharmaceutical manufacturing and to cable and connection manufacturers.
