Specifications | ## Application Sheet for misc. SDS Attributes Tech Communications Spec |

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Specifications | ## Application Sheet for misc. SDS Attributes Tech Communications Spec |

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Specifications | ## Application Sheet for misc. SDS Attributes Tech Communications Spec |

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Content | Mass Air Flow Sensors Mass Flow Versus Volumetric Flow Application Sheet MICRO SWITCH Sensing and Control WARNING MISUSE OF DOCUMENTATION • The information presented in this application sheet is for reference only. Do not use this document as product installation information. • Complete installation, operation, and maintenance information is provided in the instructions supplied with each product. Failure to comply with these instructions could result in death or serious injury. This application note describes the difference between mass flow in terms of volumetric flow at standard conditions (760 Torr and 0°C) and volumetric flow at nonstandard conditions. Mass flow is a dynamic mass/rate unit measured in grams/minute. By referencing a volumetric flow to a standard temperature and pressure, an exact mass flow (g/min) can be calculated from volumetric flow. It is common in the industry to specify mass flow in terms of volumetric flow at standard (reference) conditions. In accordance with these standards, Honeywell mass flow sensors are specified as having volumetric flow at calibration reference conditions of 760 Torr and 0°C. This translates to a specific mass flow rate. For example, 200 cm 3/min (volumetric flow) of nitrogen at standard conditions of temperature and pressure calculates to 0.2498 g/min mass flow. The following formulae are used to find true mass flow in g/min from volumetric flow (Q): I. FINDING TRUE MASS FLOW (g/min) FROM VOLUMETRIC FLOW (Q) DEFINITIONS P = Pressure V = Volume (cm 3) n = Number of moles of gas R = Gas constant .0821 (liters • atm/mole • °K) or 82.1 (cm 3 • atm/mole • °K) T = Absolute temperature in Kelvin (°K) ρ = Gas density (g/cm 3) m = Mass in grams (g) m = Mass flow (g/min) Q = Volumetric flow Qs = Volumetric flow at standard conditions (sccm) Equation 1 Using the Ideal Gas Law, PVnRT=, solve for Volume (V): or VnRT P= Equation 2 Gas density is defined as: ρ=m V Equation 3 Substitute Equation 1 into Equation 2 to redefine gas density as: ρ=mP nRT Equation 4 Mass flow is equal to density times volumetric flow rate: m=ρ• Q Equation 5 Redefine mass flow using gas density as derived from the Ideal Gas Law. Substitute Equation 3 into Equation 4: mmP nRT= • Q Example 1 Assume a volumetric flow rate of Q = 200 cm 3/min of nitrogen (N2) at standard pressure of 760 Torr and pressure of 0°C, and solve for true mass flow (g/min): Given: Q = 200 cm 3/min m = 28.0134 grams in 1 mole of N2 n = 1 mole P = 1 atm (760 Torr) R = 82.1 (cm 3 • 1 atm)/(mole • °K) T = 273.13°K(0°C) Answer: m = .2498 (g/min) II. FINDING VOLUMETRIC FLOW (Q) FROM TRUE MASS FLOW (g/min) Microbridge products are specified in “standard” volumetric flow (Qs) such as standard cubic centimeters per minute (sccm) or standard liters per minute (slpm) which can be translated into true mass flow as indicated above. The microbridge sensor is a mass flow device rather than a volumetric one. At a constant mass flow, the microbridge device will give the same output voltage even if there are temperature or pressure changes. Because the microbridge sensor senses mass flow, confusion may result when mass |

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Following Datasheets | 008044_1 (4 pages) 008045_1 (2 pages) 008059_1 (2 pages) 008061_1 (2 pages) 008065_1 (4 pages) 00818 (12 pages) 009016_1 (2 pages) 009018_1_EN_w (4 pages) 00xi_spec_benefits (2 pages) 01-Boots-A (6 pages) |

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