Gas Flowmeter Calibrations Working Gas Flow Standard

1 Page 1 Gas Flowmeter Calibrations with the Working Gas Flow Standard NIST Special Publication 250-80 John D. Wright, Jean-Philippe Kayl, Aaron N. Johnson, and Gina M. Kline November 23, 2009 National Institute of Standards and... Open at page → 2 Page 2 ii Table of Contents Gas Flowmeter Calibrations with the Working Gas Flow Standard ........................... i Abstract ..................................................................................................... Open at page → 3 Page 3 1 Abstract The Working Gas Flow Standard (WGFS) uses critical venturis, critical nozzles, or laminar flowmeters as working standards to calibrate customer flowmeters. The working standards are periodically calibrated wit... Open at page → 4 Page 4 2 Meters can be tested if the flow range, gas, and piping connections are suitable, and if the system to be tested has precision appropriate for calibration with the NIST flow measurement uncertainty. The vast majority o... Open at page → 5 Page 5 3 2 Procedures for Submitting a Flowmeter for Calibration Customers should consult the web address http://ts.nist.gov/MeasurementServices/Calibrations/ to find the most current information regarding our calibration servi... Open at page → 6 Page 6 4 Figure 1. Flow ranges for gas flow standards in the NIST Fluid Metrology Group. PVTt systems are most readily applied to critical nozzles because nozzles are largely immune to the unavoidable pressure changes imposed b... Open at page → 7 Page 7 5 in pressure also occurs at the meter under test, giving non-steady state conditions. Critical nozzles are essentially immune to downstream pressure changes if the ratio of upstream to downstream pressures is greater th... Open at page → 8 Page 8 6 installed upstream from the nozzle for the calculation of flow. Pressure, differential pressure, frequency, or temperature instrumentation may be selected to acquire outputs from the meter under test. Overlapping range... Open at page → 9 Page 9 7 Table 2. Critical nozzles and the ranges of air flow they provide for pressures between 200 kPa and 700 kPa. d (inches) d (mm) Mass Flow (g/s) Volumetric Flow (L/min) min max min max 0.14234 3.615 4.85 17.0 250 875 0.2... Open at page → 10 Page 10 8 program also writes all sensor readings to a “log” file every 10 s for the entire time that the program is running. The log file is useful for diagnosing problems after a test is over, plotting the stability of test co... Open at page → 11 Page 11 9 1 1 2               r P , (4) The critical pressure ratio can also be used to calculate the Mach number, Ma. The Mach number is needed to convert static pressure ( P1) and temperature (T1) to stagnation v... Open at page → 12 Page 12 10 Here, is the gas dynamic viscosity. The discharge coefficient is calculated from the expression: th PVTt d m m C    . (10) To obtain volumetric flow V at the meter under test, the mass flow from Eq. 1 is divided... Open at page → 13 Page 13 11 Figure 4. Schematic of the arrangement used to test a Molbloc laminar flowmeter on the PVTt standard, labeled with pressures at various locations. 980 985 990 995 1000 1005 1010 1015 1020 250 260 270 280 time (min) fl... Open at page → 14 Page 14 12 A 1 L/min full scale Molbloc was calibrated on the 34 L PVTt standard and with our gravimetric standard at 0.2 L/min and at 0.8 L/min. The agreement between the two primary standards was better than 0.011 % at both fl... Open at page → 15 Page 15 13 Molblocs. Leak tests are performed with the isolation valves. In this test, after each change in flow set point or flow path, we wait 15 min for steady state conditions and then record 30 s averages of the readings fr... Open at page → 16 Page 16 14 where V  is the actual volumetric flow at the middle of the Molbloc. A second order polynomial best fit is performed on FC versus VC calibration is calculated:   2 210fit VCaVCaaFC . (13) During subsequent use... Open at page → 17 Page 17 15 where r(xi, xj) is the correlation coefficient, which ranges from –1 to 1, and equals zero if the two components are uncorrelated. As will be seen in the following analysis, some uncertainty components in the WGFS are... Open at page → 18 Page 18 16 Figure 8. Relationships between measured and calculated quantities used to obtain mass and volumetric flow from nozzle working standards. Certain components of uncertainty are common to the nozzle calibration and usag... Open at page → 19 Page 19 17 After eliminating these correlated uncertainties, the remaining significant components of uncertainty are: 1) the mass flow from the primary standard  PS um , 2) the pressure measurements Pu, 3) the temperature m... Open at page → 20 Page 20 18 thermister and cause an incorrectly low temperature measurement. The calibration uncertainties of the temperature sensors are much better: the uncertainty of the water bath temperature calibration procedure is less th... Open at page → 21 Page 21 19 this into account. If the 26 m 3 PVTt system is the source of the nozzle flow calibration, then the WGFS mass flow uncertainty increases to 0.125 % ( k = 2). The sources of uncertainty for a volumetric flow measuremen... Open at page → 22 Page 22 20 5720 5740 5760 5780 5800 5820 5840 5860 5880 5900 012345 VC / 10 6 FC N2 Air CO2 grav N2 best fit Figure 9. Flow coefficient versus viscosity coefficient for a 0.1 L/min working standard Molbloc (serial number 1851) i... Open at page → 23 Page 23 21 Density: The uncertainty of the density of air using our instrumentation and the equation of state is 0.021 %. Laminar Flowmeter Working Standard Uncertainty: The uncertainty categories and their magnitudes are summar... Open at page → 24 Page 24 NIST Test Number: 836-123456-03-01 Page 1 of 6 Calibration Date: February 24, 2007 Appendix: Sample Calibration Report REPORT OF CALIBRATION FOR A LAMINAR FLOW METER March 30, 2007 Mfg.: LFE Manufacturing Model No: asc12... Open at page → 25 Page 25 REPORT OF CALIBRATION Gas Flow Meters Flowmasters, Inc. Purchase Order No. A123 NIST Test Number: 836-274920-07 Service ID Number: 18010C Calibrated March 26-28, 2007 by Gina Kline Page 2 of 6 quantities were measured wi... Open at page → 26 Page 26 REPORT OF CALIBRATION Gas Flow Meters Flowmasters, Inc. Purchase Order No. A123 NIST Test Number: 836-274920-07 Service ID Number: 18010C Calibrated March 26-28, 2007 by Gina Kline Page 3 of 6 reprocessed using the new p... Open at page → 27 Page 27 REPORT OF CALIBRATION Gas Flow Meters Flowmasters, Inc. Purchase Order No. A123 NIST Test Number: 836-274920-07 Service ID Number: 18010C Calibrated March 26-28, 2007 by Gina Kline Page 4 of 6 1.20 1.25 1.30 1.35 1.40 02... Open at page → 28 Page 28 REPORT OF CALIBRATION Gas Flow Meters Flowmasters, Inc. Purchase Order No. A123 NIST Test Number: 836-274920-07 Service ID Number: 18010C Calibrated March 26-28, 2007 by Gina Kline Page 5 of 6 ),,,( 21 Nxxxyy  (1) and... Open at page → 29 Page 29 REPORT OF CALIBRATION Gas Flow Meters Flowmasters, Inc. Purchase Order No. A123 NIST Test Number: 836-274920-07 Service ID Number: 18010C Calibrated March 26-28, 2007 by Gina Kline Page 6 of 6 To measure the reproducibil... Open at page →