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The primary dust concentration reference value is obtained from the weight increase of the two filters due to the dust collected over a measured period of time, at a constant and known flow rate. The two master real-tune monitors are then adjusted to agree with the reference mass concentration value (obtained from averaging the measurements of the two gravimetric filters) to within±1%. Three primary,NIST traceable,measurements are involved in the determination of the reference mass concentration: the weight increment from the dust collected on the filter, the sampling flowrate, and the sampling time. Additional conditions that must be met are: a) suspended dust concentration uniformity at all sampling inlets of the mixing chamber;b) identical sample transport configurations leading to reference and instrument under calibration; and c) essentially 100% collection efficiency of filters used for gravimetric reference for the particle size range of the test dust. The test dust used for the MIE factory calibration of the personalDataRAM is SAE Fine (ISO Fine) supplied by Powder Technology,Inc. It has the following physical characteristics (as dispersed into the mixing chamber): • Mass median aerodynamic particle diameter: 2 to 3 µm • Geometric standard deviation of lognormal size distribution: 2.5 • Bulk density: 2.60 to 2.65 g/cm3 • Refractive index: 1.54 13.2 Field Gravimetric Calibration If desired,the personalDataRAM can be calibrated gravimetrically for a particular aerosol(dust,smoke,mist, etc.) under field conditions (actual conditions of use). To effect such calibration in the particle environment of interest, proceed as indicated below. For field calibration of the model pDR-1000AN, a personal type filter sampler is placed side-by-side (collocated) to the pDR-1000AN to be calibrated, and the two units should be started simultaneously. For the model pDR-1200,its own filter and attached pump can be conveniently used for the same purpose. • Weigh and load into filter holder a fresh membrane filter. • Start pump. • Immediately turn on personalDataRAM and start a run such that the pump and the personalDataRAM are started nearly simultaneously. The duration of this comparison run should be sufficient to collect a mass of at least 1 mg on the reference filter (in order to permit accurate weighing of the collected mass by means of an analytical balance). The time-weighted average (TWA) reading of the personalDataRAM can be used to estimate the required sampling time to collect the above-mentioned mass on the filter.To estimate the required sampling time (ET as measured on the personalDataRAM) in minutes,read the TWA value 30