Presentation on theme: "NCSLI 2007 A PRIMARY FLOW CALIBRATION SYSTEM FOR THE SUPPORT OF HIGH PERFORMANCE GAS FLOW TRANSFER STANDARDS P. Delajoud, M. Bair, C. Rombouts, M. Girard."— Presentation transcript:
NCSLI 2007 A PRIMARY FLOW CALIBRATION SYSTEM FOR THE SUPPORT OF HIGH PERFORMANCE GAS FLOW TRANSFER STANDARDS P. Delajoud, M. Bair, C. Rombouts, M. Girard
NCSLI 2007 Introduction DHI offers high performance gas flow transfer standards since 1993 Requires means to efficiently and reliably calibrate them with very low measurement uncertainty
NCSLI 2007 Introduction Product line of high accuracy LFEs Range from 0.02 to 2000 mg/s (1 Ncc min -1 to 100 Nl min -1 ) Supported by static gravimetric reference and calibration chain Calibration chain is difficult to maintain
NCSLI 2007 Introduction 2002 introduced compatible sonic nozzles Ranges from 0.2 to 100 g/s (10 to 5000 Nl min -1 ) Cannot be supported by static gravimetric reference because they cannot start from zero flow state Excellent repeatability
NCSLI 2007 Introduction Simultaneously developed dynamic gravimetric flow standard GFS2102: 0.2 to 200 mg/s (10 to 10000 Ncc min -1 ) Able to take measurements “on the fly” with flow stabilized Allows calibration of sonic nozzles that cannot start from zero flow Fully automated
NCSLI 2007 Introduction Developed extensive measurement technique to “build” traceability to higher flows Technique named “successive addition” Uses very low uncertainty contributed by repeatability from sonic nozzles to extend traceability from 0.1 to 100 g/s (5 to 5000 slm) and higher. Technique also used with LFEs below GFS range.
NCSLI 2007 GFS Gravimetric Flow Standard Objectives of developement Require less mass depletion to reduce the amount of time necessary to take a point Be able to take gravimetric points “on the fly” without having to remove bottles for weighing Reduce the total uncertainty to a level of ± 5 parts in 10 4 of reading or better.
NCSLI 2007 GFS Gravimetric Flow Standard Description of operation More complete description in the paper The Implementation Of Toroidal Throat Venturi Nozzles To Maximize Precision In Gas Flow Transfer Standard Applications, 2005 FLOMEKO
NCSLI 2007 GFS Gravimetric Flow Standard Uncertainties Technical Note 6050TN09 - Complete uncertainty analysis on DHI website of the GFS2102.
NCSLI 2007 GFS Gravimetric Flow Standard Uncertainties Uncertainties are low due to the fact that the system will start and stop after flow is stabilized Uncertainties and errors that are constants are tared out and only those that have changed from start readings to subsequent readings are relevant
NCSLI 2007 GFS Gravimetric Flow Standard Uncertainties Mass Time Air buoyancy (cylinder) Air buoyancy (regulator) Type A – Contributed by the balance Repeatability, linearity, resolution
NCSLI 2007 GFS Gravimetric Flow Standard Uncertainties Rate of change of mass Thought of as resolution due to the ability of the balance to read a mass value For example the balance can only update 23 times per second – If the flow rate is low (0.2mg/s or 10 sccm) resolution is good, if flow rate is high, resolution increases –200mg/s / 23 readings per second = resolution of 8.7 mg; 1 std uncertainty = 2.5 mg
NCSLI 2007 GFS Gravimetric Flow Standard Uncertainties Combined uncertainties at different flow rates and depletion totals to derive an equation to use as the “typical flow measurement uncertainty”. ± (3 mg + 0.035 mg/g depletion) + 1.25% of change of mass per second.
NCSLI 2007 Flow Traceability LFE Calibration Chain Sonic Nozzle Calibration Chain 10 SLM 0.001 0.01 5000 direct gravimetric
NCSLI 2007 Technique for “building” traceability to higher flows Works by taking advantage of extensive property of flow and excellent repeatability of sonic nozzles Less than 0.01% of reading under normal laboratory conditions Successive Addition
NCSLI 2007 Technique for “building” traceability to higher flows All data is traceable through precise multiples of the original reference points of 100 and 200 mg/s. Traceability can come from any point in the test. Sonic nozzles are not affected by downstream changes in pressure as long as they are choked. Successive Addition
NCSLI 2007 Uncertainties Because of the method used there is no uncertainty due to the linearity of the nozzles in the test. Uncertainties for discharge coefficients determined for each nozzle are evaluated by comparing the two separate “builds” in the calibration chain. Successive Addition
NCSLI 2007 Uncertainties Original reference flow from the GFS Transfer point pressure Transfer point temperature Repeatability of the test (Type A) Successive Addition
NCSLI 2007 Successive addition run backwards Needed method of traceability to cover range below 0.2 mg/s (10 sccm). Used laminar molblocs in one successive addition run to define flows down to 2.5 sccm. More uncertainty because of less repeatability by LFEs. Successive Addition
NCSLI 2007 GFS evaluated by comparison with existing static gravimetric reference Performed at points for optimum uncertainty for static reference and LFEs used in the test Since they are independent agreement must be inside of RSS of uncertainties Verification of Traceability and Uncertainty
NCSLI 2007 Comparisons – 2ea 1E2 LFE’s at 2 mg/s (100 Ncc min -1 ) Verification of Traceability and Uncertainty
NCSLI 2007 Calibration Chain verification Comparison between two separate successive addition builds External verification through calibration of sonic nozzle by DHI and CEESI in May 2005 using 1E4-S at various flows Verification of Traceability and Uncertainty
NCSLI 2007 Verification of Traceability and Uncertainty
NCSLI 2007 Verification of Traceability and Uncertainty
NCSLI 2007 With this system of traceability –Automation of GFS and ability to perform low mass depletions allows for an abundance of gravimetric data –Complete calibrations may be performed hands free for sonic nozzles –Uncertainties are low due to ability to measure “on the fly” Conclusion
NCSLI 2007 With this system of traceability –Successive addition eliminates uncertainty from the linearity of nozzles and primarily depends on repeatability –Range is only limited by support equipment to transport gas and availability of higher ranges of sonic nozzles Conclusion