The influence of cold traps on low-vacuum pressure measurements

An experimental investigation of the pressure difference across cold traps connected to vacuum chambers with a condensable vapour under low-vacuum conditions is presented. The chamber pressures range from 2.3 to 133 Pa with water vapour pressures ranging from 0 to 500 Pa. The measurements show that a cold-trapped gauge can cause serious errors in the low-micrometre region or where the specific humidity is sufficiently large that a substantial part of the non-condensables may be pumped out of the test chamber.