ABSTRACT
In many processes, mass ow rate, rather than volume ow rate, is the desired parameter because volumetric ow measurements are less reliable than are mass ow measurements. Since changes in gas temperature and pressure will aect the density of a xed volume of gas, thermal mass ow meters and controllers, unlike rotameters, turbine meters, and other volumetric ow devices, are relatively immune to changes in inlet temperature and pressure. Because these instruments directly measure molecular ow, they provide the most reliable, repeatable, and accurate method for delivering material from a supply volume to a process at a desired rate. Features, such as direct electronic readout, fast response, exceptional sensitivity at low ow rate, negligible pressure drop, no moving parts, simple installation, unobstructed straight through ow path, absence of temperature or pressure corrections, and superior retain accuracy over a wide range of ow rates, make thermal mass ow meters a superior alternative to conventional ow meters in many important applications. Some other advantages of this type of ow meter are accuracy in a 2% range, low ow sensitivity, reliability, and long life with advances in electronic technology; in a sense, these ow meters are getting smarter and more capable with microprocessor computing power, thus expanding the range of their usage.
