The miniPDD pulsed discharge detector (PDD) is said to be both small and cost effective. It uses about one fifth (20%) the amount of helium as the company’s D-3 and D-4 versions, giving up only a bit of sensitivity and dynamic range in return. It is approximately one half the size of the D-4, but has nearly the same sensitivity, about 100 ppb for fixed gases. A datasheet is available at http://www.vici.com/instr/pdd-mini.pdf
Valco Instruments Co. Inc.