Measuring and testing – Sampler – sample handling – etc. – Automatic control
Patent
1991-09-18
1994-06-07
Noland, Tom
Measuring and testing
Sampler, sample handling, etc.
Automatic control
7386323, G01N 124
Patent
active
053179307
ABSTRACT:
A constant flow rate controller apparatus for an aerosol sampler using a filter includes an enclosed channel for channeling a stream of air, a filter positioned in the channel to capture and retain particles while allowing the stream of air to flow therethrough, an air or vacuum pump to pull the air through the filter, and a flow controller that maintains a constant volumetric flow rate of air through the sampler and filter, regardless of how much particulate matter is deposited on the filter or how much pressure drop across the filter changes due to particulate loading. The filter can be a substantially non-fibrous, porous, this film membrane medium, for which the flow controller of this invention is particularly beneficial, or it can be a more conventional fibrous medium. The flow controller can include a critical or choked flow orifice with a variable effective flow area, which effective flow area can be varied in response to changes in pressure drop across the filter to maintain constant volumetric flow rate. An expandable and contractible bellows with an appropriate spring constant can be used to both sense changes in air pressure drop across the filter or changes in stagnation pressure downstream of the filter and to actuate a variation in the effective flow area of the orifice in response to such changes in air pressure to maintain constant volumetric flow rate of the air. The air or vacuum pump has to have enough capacity to maintain critical or choked flow conditions in the orifice.
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Noland Tom
Wedding & Associates, Inc.
Young James R.
LandOfFree
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