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his application note addresses the calibration o snifer leak detectors.

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common leak detection method utilizes a snifer leak detector to locate leaks in a part or system that is pressurized with

tracer gas (usually helium). While very useul in pinpointing the location o a leak, snifer detectors are not as reliable in

uantiying leaks compared to other methods. Furthermore, sensitivity is much less than with hard vacuum helium leaketection, and varies among diferent types o detectors. However, with proper calibration, the snifer leak detector can be

sed as an efective tool or both production and maintenance leak location applications.

Deription

nifer leak detectors draw small amount o air through the snifer probe by means o a pump and measure the concentrati

tracer gas in the drawn sample. Calibration o the snifer can give the operator condence by providing a relative compar

the displayed leak rate to an actual leak value, and by proving that the detector is sensitive enough to detect a particular

te. It can also be helpul to illustrate correct techniques or maximizing sensitivity and success in locating existing leaks (i

ow close the probe needs to be to the leak, at what speed the probe should pass over a leak in order to detect it, the dete

sponse time).

alibration o a snifer leak detector is acilitated by a calibrated leak standard, which is a device that produces a measured

ow o gas that simulates an actual leak. Normally the leak rate value o the calibrated leak standard is at or near the minim

esired sensitivity or reject level. To perorm a snifer calibration, the background tracer gas concentration should be measu

nd veried to be below the leak rate value o the calibrated leak. This is done by taking a reading o the ambient air. I am

acer gas contamination is suspected, samples should be taken in another location. I it is determined that the test area is

ontaminated with tracer gas, then the area should be purged prior to calibration. Following verication o the tracer gas

ackground, the snifer probe is inserted into the outlet o the leak standard, and let there until the reading rom the snife

abilizes. The displayed reading is compared to the leak rate value o the leak standard, rom which a quantiying relations

an be made or uture readings (the leak detector may or may not display a value with any proximity to the value o the

ctual leak that it is reading). Some instruments allow the user to enter in a calibration actor to that will adjust the display atch the reading rom the calibrated leak standard. Additionally, calibrating will determine whether the snifer is capable

etecting the size o leak simulated by the leak standard.

any snifer leak detectors display readings in units o concentration (parts per million, or example), whereas most leak

andards are specied by leak or ow rate (typically atmcc/sec). Concentration can be correlated to leak/ow rate i the

umping speed o the snifer line o the detector is known. To correlate parts per million (ppm) to atmcc/sec:

mcc/sc = m x 106 x

where S is the pumping speed o the detector in cc/sec

note #13-10

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Deription (ontinueD)

alibration will be most successul when the amount o gas rom the leak standard that enters the probe is maximized, whi

ot impeding normal air ow into the probe. For this reason, an appropriate outlet on the leak standard is important. An

utlet that allows leaked gas to escape beyond the probe or does not allow proper air ow will result in alse readings maki

he calibration less efective. Also, the snifer probe should be very near the actual gas exit point o the leak standard so tha

he tracer gas does not become too diluted by the surrounding air. Other actors that could negatively inuence a snifer

alibration are turbulent air surroundings (such as in ront o a an), or surrounding air that is heavily contaminated with the

acer gas. Manuacturer-recommended practices that are specied in the instrument user manual (such as zeroing the bas

ading) should also be observed.alibration should be perormed regularly during any leak detection process to veriy the integrity o the process. A

commend practice is to calibrate the instrument prior to testing a system or at the beginning o the production shit, then

eriying calibration when complete.

relateD proDut

CalMasterTM Leak Standards

Gas-Check Leak Detector

miniTracerTM Portable Snifer

Mass Spec Helium Leak Detectors

referene

Application Note 07-05 Helium Sning Leak Detection

CalMasterTM Calibrated Leak Standards Manual

ASTM Standard E 499: Standard Methods o Testing or Leaks Using the Mass Spectrometer Leak Detector in the Detecto

Probe Mode.