PSN-L Email List Message

Subject: Re: Microbarograph ??
From: ChrisAtUpw@.......
Date: Tue, 15 Feb 2000 14:20:46 EST

From experiments on capacities for gliding applications, you can expect the 
'response time' of the gas in a 1 L bottle to changes in the wall temperature 
to be of the order of 1.5 to 2 minutes. The response to external pressure 
changes will be limited by the mass of the fluid in the column, by it's 
viscosity which is also strongly temperature dependant and by the forth power 
of the bore of the tube.  I would expect the response rate to be limited to 
small fractions of a Hertz. For every 1 C Deg change in the bottle 
temperature, the internal pressure changes by about 3.5 milli Bar. To be able 
to measure pressure changes of the order of micro Bars, would require 
temperature tracking of the whole bottle to milli degree level. How stable is 
your external air temperature? The first thing that you notice when observing 
microbarograph traces are the large fluctuations in pressure due to wind and 
air turbulence. In looking for pressure changes, the sluggish response of the 
manometer will be beneficial here, but what do you actually want to measure?  


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Larry Cochrane <cochrane@..............>