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Technical Discussions
Angelo Negri
Angelo Negri
00:01 Mar-10-2003
Helium leaks measurement: ppm or mbar*l/s?

In order to perform valves Fugitive Emissions tests, we use a VARIAN sniffer probe helium leak detector, which gives readings in mbar*l/s. Our usual European reference specification (Shell MESC SPE 77/312) also gives limits in the same measurement unit.
First of all, is anybody able to explain the physical meaning of "mbar*l/s"? Is that a flow rate or a concentration?
Then, how is it possible to relate this with "ppm]"? As many leak detectors manufacturers have instruments with both scales, we think there must be a simple relation between the two units.

Johnny Darbonne
Johnny Darbonne
00:54 Apr-22-2005
Re: Helium leaks measurement: ppm or mbar*l/s?
: In order to perform valves Fugitive Emissions tests, we use a VARIAN sniffer probe helium leak detector, which gives readings in mbar*l/s. Our usual European reference specification (Shell MESC SPE 77/312) also gives limits in the same measurement unit.
: First of all, is anybody able to explain the physical meaning of "mbar*l/s"? Is that a flow rate or a concentration?
: Then, how is it possible to relate this with "ppm]"? As many leak detectors manufacturers have instruments with both scales, we think there must be a simple relation between the two units.
: Many thanks in advance, 'NGL
.
mbar*l/s is a flow rate of helium into the mass spectrometer. If you know the flow rate on your sniffer probe(measured using a precision flow measuring device) then you can convert your reading to ppm. 1 ppm = 1X10-6 of total flow. i.e. Your probe has a flow rate of 1-mbar-liter/sec and your mass spectrometer reads 5X10-6 mbar-liters/sec helium then the ppm value is 5 ppm helium.

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