A custom built aerosol leakage orifice (ALO) has been developed by the US Army Primary Standards Laboratory (APSL) and the National Institute of Standards and Technology (NIST) through a Department of Defense Calibration Coordination Group project funded by the Air Force Primary Standards Laboratory. The ALO is a transfer standard used to calibrate the joint service mask leakage tester (JSMLT) with NIST traceability. The JSMLT measures the integrity of military issued gas masks by using a photometer to measure the ratio of the scattered light intensity from the ambient test aerosol and the aerosol that leaks through a gas mask. The ALO is calibrated to challenge the JSMLT with a known aerosol leakage ratio with traceability to SI units through NIST. The ALO consists of a stainless steel tube with a 30 (mu)m orifice that allows a small leakage flow of ambient aerosol to combine with a high flow of particle free air, diluting the ambient concentration by nearly the ratio of the two flow rates. The orifice is calibrated for both clean air flow rate and for aerosol leakage, which is required to account for particle loss through the assembly. A custom built test stand was developed to calibrate the ALO, using condensation particle counters as the measurement standard to measure the ambient and leakage aerosol number concentration ratio with NIST traceability. The ALO is calibrated for aerosol leakage ratio with +- 4.8percent of reading at 95percent confidence (k velence 2), at a nominal 0.008percent leakage.
展开▼
