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Calibration Intervals - Best Practices in Maintaining Pressure Transmitters
- 1. Copyright © Yokogawa Corporation of America 1 Calibration Intervals Best Practices in Maintaining Pressure Transmitters Michael Keller Product Manager – Temperature and Multivariable Transmitters May 24, 2016
- 2. Copyright © Yokogawa Corporation of America 2 Why?
- 3. Copyright © Yokogawa Corporation of America 3 Agenda
- 4. Copyright © Yokogawa Corporation of America 4 Pressure Basics
- 5. Copyright © Yokogawa Corporation of America 5 Pressure Definitions
- 6. Copyright © Yokogawa Corporation of America 6 Reference Accuracy
- 7. Copyright © Yokogawa Corporation of America 7 Zero Point Errors
- 8. Copyright © Yokogawa Corporation of America 8 Zero Point Errors Adjusted
- 9. Copyright © Yokogawa Corporation of America 9 Full Scale Errors
- 10. Copyright © Yokogawa Corporation of America 10 Full Scale Errors Adjusted
- 11. Copyright © Yokogawa Corporation of America 11 Linearity
- 12. Copyright © Yokogawa Corporation of America 12 Repeatability
- 13. Copyright © Yokogawa Corporation of America 13 Hysteresis
- 14. Copyright © Yokogawa Corporation of America 14 ±3 Specification Conformance
- 15. Copyright © Yokogawa Corporation of America 15 What is Real World Performance?
- 16. Copyright © Yokogawa Corporation of America 16 Real World Performance = Total Probable Error (TPE)
- 17. Copyright © Yokogawa Corporation of America 17 Real World Performance = Total Accuracy (TA)
- 18. Copyright © Yokogawa Corporation of America 18 Overpressure Effect
- 19. Copyright © Yokogawa Corporation of America 19 Total Accuracy Calculation Example
- 20. Copyright © Yokogawa Corporation of America 20 Total Accuracy Calculation Example
- 21. Copyright © Yokogawa Corporation of America 21 Total Accuracy Calculation Example
- 22. Copyright © Yokogawa Corporation of America 22 Total Accuracy Calculation Example
- 23. Copyright © Yokogawa Corporation of America 23 Total Accuracy Calculation Example
- 24. Copyright © Yokogawa Corporation of America 24 Total Accuracy Calculation Example
- 25. Copyright © Yokogawa Corporation of America 25 Total Accuracy Calculation Example
- 26. Copyright © Yokogawa Corporation of America 26 Total Accuracy Calculation Example
- 27. Copyright © Yokogawa Corporation of America 27 Total Accuracy Calculation Example
- 28. Copyright © Yokogawa Corporation of America 28 Total Accuracy Calculation Example
- 29. Copyright © Yokogawa Corporation of America 29 Total Accuracy Calculation Example
- 30. Copyright © Yokogawa Corporation of America 30 Total Accuracy Calculation Example
- 31. Copyright © Yokogawa Corporation of America 31 Total Accuracy Calculation Example
- 32. Copyright © Yokogawa Corporation of America 32 Total Accuracy Calculation Example
- 33. Copyright © Yokogawa Corporation of America 33 Total Accuracy Calculation Example
- 34. Copyright © Yokogawa Corporation of America 34 Total Accuracy Calculation Example
- 35. Copyright © Yokogawa Corporation of America 35 Total Accuracy Calculation Example
- 36. Copyright © Yokogawa Corporation of America 36 Total Accuracy Calculation Example
- 37. Copyright © Yokogawa Corporation of America 37 Calculating Calibration Interval
- 38. Copyright © Yokogawa Corporation of America 38 Calculating Calibration Interval Example
- 39. Copyright © Yokogawa Corporation of America 39 Calculating Calibration Interval Example
- 40. Copyright © Yokogawa Corporation of America 40 Calculating Calibration Interval Example
- 41. Copyright © Yokogawa Corporation of America 41 Calculating Calibration Interval Example
- 42. Copyright © Yokogawa Corporation of America 42 Calibration Interval Calculator http://www.dpharp.com/index.php/performance- calculator
- 43. Copyright © Yokogawa Corporation of America 43 Calibration Interval Takeaway
- 44. Copyright © Yokogawa Corporation of America 44 Thank you very much Questions?
Editor's Notes
- Pressure thermometer Pressure transmitters in almost any industry Industrial plants need to ensure that all of their instrumentation is measuring accurately within a certain tolerance. Poor performance from instruments can cause problems concerning safety, production downtime and issues with quality.
- P = f/a , psi , lbs typically expressed as a force, mg, square inch (inH20, rho * g * h , rho = m/V = m/h^3 , -> f/a) Abs – not affected by atm pressure changed, barometer if left open
- Capsule for various pressure ranges
- Need to define before we talk about real world performance The reference accuracy guaranteed on specification sheets is just an accuracy based on laboratory conditions. Typical/common reference conditions might be: - Temperature: 25 o C or 77 o F - Static Pressure: Zero psi - Relative Humidity: 10 to 55% Manufacturing – characteristic (calibration) curve, raw sensor has unique output, characterization curve created and tested, optimized, turn characterization curve to ideal is goal, always some error out of scale % of span typically IEC 61298-2 – not defined standard for pressure transmitter accuracy, but defines factors that make up accuracy - must include effects of linearity, repeatabilty and hysteresis We define reference accuracy as the maximum deviation from an ideal characteristic line including the effects of zero point errors, full scale errors, linearity, repeatability, and hysteresis; expressed in % of span.
- Assuming characteristic curve is linear, transition to linearity
- How close characteristic curve is to a straight line IEC does not define how quantified Terminal based – straight line through actual zero point and full scale values, it is max deviation of characteristic curve Best fit straight line – straight line to limit max deviation, generally = ½ * TB Terminal based more conservative,, be aware
- Repeatability – Change in output (characteristic lines) when same pressure is applied consecutively, same conditions, same direction Repeatable not necessarily accurate But if very accurate, are some what repeatable
- Not understandable from name, Disease cured in the 1950s Hysteresis- difference in output (characteristic lines) increasing pressure vs decreasing pressure from full span pressure cycle. 5/9 point calibration Again, zero point errors, full scale errors, linearity, repeatability, and hysteresis all are used to compose reference accuracy. Value for each, % of span Errors cannot be added, some errors will affect others, visa versa, errors are compounded, root sum square common, IEC does not define
- So, manufactures who claim 3 sigma specification conformance, means 99.7 % of devices are manufactured to meet specifications.
- The reference accuracy guaranteed on specification sheets is just an accuracy based on laboratory conditions. Temp ambient and process – zero and span SP- changing process conditions – zero and span
- This calculation OMITS Static Pressure Zero Effects and is therefore not correct. Zero trim at line pressure cannot eliminate SP-Zero effect, since the line pressure is changing constantly in the process Root sum squared for compounding of errors
- Root sum squared for compounding of errors
- Overpressure another measurement error, mainly for DP transmitters Surge pressure can be generated by water hammer action (start up, shut down), caused by wrong sequencing of three-valve manifold, opening the vent/drain plug of D/P Tx, process upsets. Not always noticeable
- Stability – drift, degradation of components and sensor over time,
- All operating conditions