A simple robust dynamic leak detector suitable for vacuum proving large numbers of components down to 10^-3 1μ/s is described. The property of charcoal at low temperatures to absorb a large percentage of atmospheric gases and little hydrogen is used to eliminate irregular pressure pulses caused by impurities in the component and to increase the response of a Pirani gauge when a leak is probed with hydrogen. A charcoal trap is placed between the component and a Pirani gauge on a vacuum unit.