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[Variable Rate FEP Permeation Model (TPV)]
Variable Rate FEP Permeation Model (TPV)
The TPV model calibrated helium leak standard works equally well calibrating helium leak detectors that test under vacuum, and with helium leak detectors that sample from atmosphere utilizing a "sniffer probe". This was accomplished by designing the TPV model with both an integral KF25 (NW25) vacuum fitting and a pin-point helium source that accepts and aligns most manufacturers "sniffer probes" with virtually no "dead volume" where helium can accumulate and cause inconsistent readings. Calibrated helium leak standards with shut-off valves are designed to be used with hard vacuum systems and should not be used to calibrate a "Sniffer Type" leak detector. The FEP type leak element is not driven by differential pressure but helium partial pressure flows helium at virtually the same rate flowing into a vacuum or flowing.
Cincinnati Test Systems utilizes the finest grade of FEP available to manufacture their FEP leak elements. The leak elements have been tested at temperatures ranging from 10°C to 40°C yielding a temperature coefficient of approximately 2.5%/°C with no anomalous behavior.