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Field Pressure Calibration Tips Webinar with Fluke Calibration
- 1. Field Pressure CalibrationTips John Lopez, Fluke Calibration
- 2. Field Pressure CalibrationTips What are we talking about anyway? • Calibrations outside of carefully controlled conditions. Including • Onsites • Most especially in situ locations – factory floors, transmitter stations, etc
- 3. Field Pressure CalibrationTips • Pressure ranges • Accuracies • Examples of standards, pros and cons Overview
- 4. Field Pressure CalibrationTips • How I think about it • “High” pressure • “Low” pressure • “Draft” pressure • “Hard” vacuum • All of these in “quotes” because these are not solid definitions but rather categories Ranges
- 5. Field Pressure CalibrationTips “High” pressure • Depending on circumstances, >300 PSI to >3000 PSI • Often hydraulic, not always • Because of gas compressibility, higher pressure generation is easier with liquid • Because of this, it may be easier, safer, and/or more achievable to calibrate with a fluid media than with a gas/air media
- 6. Field Pressure CalibrationTips “High” pressure considerations - gas • Gas bottles • Portable gas pressure generation • Contamination • Thermal/adiabatic effects
- 7. Field Pressure CalibrationTips “High” pressure considerations - liquid • Liquid compatibility • “Buffer” arrangements – see image • Thermal/adiabatic effects
- 8. Field Pressure CalibrationTips “High” pressure standards • Traditional Deadweight • Pros: • Accurate* • Very stable – floating piston • Cons: • Not super portable - heavy • Accurate* - gravity corrections?
- 9. Field Pressure CalibrationTips “High” pressure standards • Electronic Deadweight • Pros: • Accurate • Lightweight, portable • No gravity corrections • Cons: • Thermal effects have to be dealt with • Cost
- 10. Field Pressure CalibrationTips “High” pressure standards • High pressure pneumatic pump and reference gauge/device • Pros: • Lightweight, portable • Gas pressure on demand • Cons: • Thermal effects
- 11. Field Pressure CalibrationTips • Hydraulic pump and reference gauge/device • Pros: • Lightweight, portable • Lowest cost of entry • Cons: • Thermal effects “High” pressure standards
- 12. Field Pressure CalibrationTips “Low” pressure • From the “high” pressure cutoff region down to a few PSI, plus vacuum • Consider pneumatic media here, for several reasons • Easier to generate and control low pressure • No fluid head calculations • Compatibility with pneumatic devices • Vacuum needs
- 13. Field Pressure CalibrationTips “Low” pressure considerations • Contamination • Traps, filters • Vacuum ranges • Smaller pumps on most portable standards
- 14. Field Pressure CalibrationTips “Low” pressure standards • Process calibrator • Pros: • Both pneumatic and electrical • Battery operated • Rugged • Cons: • Usually one range (may be supplemented)
- 15. Field Pressure CalibrationTips • Hand pump and reference device • Pros: • Lowest cost of entry • Battery operated • Cons: • One range (may use multiple devices) “Low” pressure standards
- 16. Field Pressure CalibrationTips “Draft” pressure • Less than a few PSI on each side of atmosphere • Often delineated in units of inches of water, sometimes mBar • Special considerations for range and stability
- 17. Field Pressure CalibrationTips “Draft” pressure considerations • Special considerations for range and stability • Range: 10 inches of water is < 1/2 a PSI. A 100 PSI, 0.05% standard is >10% equivalent at this scale – upside down against many DUTs. • Pressure generation: how to do this safely? • Stability: because of the relatively small difference from draft pressures to atmosphere, environmental influences can be significant. • Pressure “waves” • Thermal effects • Web search: “Calibrating Draft Range Pressure Sensors with a Pressure Controller/Calibrator”
- 18. Field Pressure CalibrationTips “Draft” pressure standards • Process calibrator and measurement devices • Pros • May have built in pump ranged for the application – helps prevent overpressure
- 19. Field Pressure CalibrationTips “Hard” vacuum • More specifically, a DUT that measures very low vacuum levels. Ion gauges, capacitance diaphragm gauges, etc. • How to tell? Most often, units of measure used. Torr, mTorr point towards a high vacuum DUT while PSIA, inches of mercury point towards lower vacuum accuracies. • The issue with a hard vacuum gauge isn’t accuracy, typical “good” DUT would be 0.25% to 0.1%. Issue is turndown – 100,000:1 or more. For example: • 760 Torr (atmosphere): 0.25% • 0.76 Torr (0.015 PSIA): still 0.25% • 0.0076 Torr/7.6 mTorr: still 0.25% • Not all users are taking advantage of these accuracies/turndowns, so perhaps a normal standard would suffice.
- 20. Field Pressure CalibrationTips “Hard” vacuum considerations • Usage – specifically is calibration over full range and accuracy required? • If this can be treated as a “normal” vacuum device, it makes things simpler • Large diameter tubing • Vacuum pumps, perhaps in series • Dwell time
- 21. Field Pressure CalibrationTips • Nothing from most vendors for field use • An option is to use a higher grade vacuum gauge as a comparison standard with vacuum pump(s) and metering valve • Industry options are large, expensive, not portable “Hard” vacuum standards
- 22. Field Pressure CalibrationTips Questions or Comments? Email Christina Spearman christina.spearman@transcat.com Transcat: 800-828-1470 www.transcat.com For related product information, go to: www.transcat.com/brand/fluke-calibration