Abstract: A self-zeroing differential pressure signal generator. A strain gauge separates two areas of potentially differing fluid pressure and generates an electrical signal which varies as the fluid pressure difference varies. The strain gauge electrical signal is applied to the noninverting input terminal of noninverting amplifier, which develops a zeroed output signal. The noninverting amplifier includes a feedback loop which sums a feedback signal from the noninverting amplifier output with a zeroing compensation signal at the inverting input terminal of the amplifier. The zeroing compensation signal is developed by periodically eliminating the zeroing compensation signal and simultaneously exposing the strain gauge to a zero pressure difference. The output signal of the noninverting amplifier is compared to a reference output and a zeroing compensation signal is generated which, when summed with the feedback signal, brings the value of the output terminal to the value of the reference output.

Abstract: A system for controlled humidity tests wherein gas transmission through a barrier may be measured, including apparatus for controllably mixing a dry gas and wet gas, for conveying the mixed gas to a test chamber or chambers for measurement of relative humidity and gas transition through a barrier, including gas transmission conduits having a pressure drop of less than 1 percent of ambient pressure, and including conduit temperature controls to maintain a controlled first temperature in the test chamber or chambers, and controlled higher temperatures in all other gas conduits.