The Varian 938-41 Porta-Test Helium Leak Detector is based on the Contra-Flow principle - a proven technique that takes advantage of the differences in maximum pressure ratios produced by the diffusion pump for gases of different molecular weights.
This principle is implemented in the 938-41 leak detector by introducing helium (and other inlet gases such as those resulting from a leak in the test piece) into the diffusion pump foreline rather than into the "normal" pump inlet as in conventional leak detectors. Helium, having a much lower pressure ratio than other gases. contained in air, diffuses backwards through the diffusion pump to reach the sensing tube where it is detected as a leak in the normal manner. Although the mechanical pump is also attached to the diffusion pump foreline and removes all inlet gases, including helium, there is no appreciable loss of sensitivity in the 938-41 leak detector.
Agilent (formerly Varian) 938-41 Features
- Contra-Flow"" design allows small leaks to be detected without throttling
- No liquid nitrogen required
- Operation is controlled by rotation of only one handle through the operating cycle positions
- 50 segment, direct readout LED bar graph display with digital exponents capable of reading leaks in the 103 to 1010 atm cc/sec. range (helium)
- Only 50 pounds in a compact, well-integrated package
- Residual background switch
- Modular construction: entire vacuum system held in place by 4 bolts
- Diffusion pump thermostat offers full protection against catastrophic failures
- Optional mobile cart: optional drawer on cart provides a safe and convenient place for storing probes, tools, calibrated leaks, etc.