EXPERIMENTS WITH A DIFFERENTIAL PIRANI GAUGE LEAK DETECTOR
ATOMIC ENERGY RESEARCH ESTABLISHMENT HARWELL (UNITED KINGDOM)
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A differential leak detector was developed in which 2 matched Pirani gages having their filaments connected in adjacent arms of a balanced Wheatstone bridge were connected to the same point in a vacuum system. A lime soda trap was placed between the vacuum system and 1 gage to absorb the COsub2 which was used to probe the leak. The COsub2 could make its way only into the untrapped gage to cause a differential change in the indication of the 2 gages. With the detector located on the backing side of a diffusion pump where the average pressure was 15 micro Hg, the noise level of pressure fluctuations registered by the galvanometer in the detector control circuit was 7 times less than that registered by a single Pirani gage. The minimum air pressure change detected by the differential arrangement was 10 to the -5th power mm Hg. With the optimum leak-hunting conditions employed, this value corresponded to a leak on the high- vacuum side of about 10 to the -3rd power lusec 1 lusec the leak causing a pressure rise of 1 micro Hgsec in an isolated volume of 1 liter.
- Test Facilities, Equipment and Methods