1 / 19

ME 322: Instrumentation Lecture 6 Lab 3 Calculations

ME 322: Instrumentation Lecture 6 Lab 3 Calculations. January 31, 2014 Professor Miles Greiner. Announcements/Reminders. HW 2 due Monday L3PP – Lab 3 preparation problem

gada
Download Presentation

ME 322: Instrumentation Lecture 6 Lab 3 Calculations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ME 322: Instrumentation Lecture 6Lab 3 Calculations January 31, 2014 Professor Miles Greiner

  2. Announcements/Reminders • HW 2 due Monday • L3PP – Lab 3 preparation problem • Create an Excel Spreadsheet to complete the tables, plots and question in the Lab 3 instructions, using the sample data on the Lab 3 website. • Bring that spreadsheet to lab next week and use it for your data. • HW 1 Comments • Units, significant digits • Plot using Excel (not by hand)

  3. Instrument Calibration (review) • Measure instrument output (R) for a range of known measurands (M, as measured by a reliable standard) • Perform measurements for at least one cycle of ascending and descending measurands • Fit an algebraic equation to the R vs M data to get instrument transfer function: • Linear: R = aM + b • Other: i.e. R = aM2 + bM + c • Find standard error of the estimate of R given M, sR,M • This assumes the deviations are the same for all values of M

  4. How to Use the Calibration • Invert transfer function • If linear: M = (R-b)/a • Find standard error of the estimate of M given R • sM,R = sR,M/a • For a given reading • The best estimate of the measurand is • The best statements of the confidence intervalare • M = + sM,Runits (68%), or • M = + 2sM,Runits(95%), or …

  5. What does Calibration do? • Removes systematic bias (calibration) error • Quantifies random (imprecision, non-repeatability) errors • But does not remove them • Quantifies user’s level of confidence in the instrument

  6. Manufacturer-Stated Accuracy • May include both imprecision and calibration drift • Not always clearly defined • This is one of the objectives of Lab 3 • Show how to process sample data • Format plot labels, borders, fonts,.. • Calculate standard error of estimate, confidence level • Write abstract last: Objective, methods, results

  7. Table 1 Equipment Specifications and Calibration • The absolute accuracy of the pressure standard and transmitter are nearly the same. • The confidence levels for the transmitter accuracy is not given by the manufacturer and will be determined in this experiment.

  8. Table 2 Calibration Data • This table shows two cycles of ascending and descending pressure calibration data. • The transmitter current did not return to 4.00 mA at the end of the descending cycles. • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2003%20PressureCalibration/Lab%20Index.htm

  9. Fig. 1 Measured Transfer Function • For the sample data • The measured transmitter current is consistently higher than that predicted by the manufacturer-specified transfer function. • Standard errors of the estimates for the transmitter current for a given pressure heat is SI,h = 0.034 mA, and Sh,I = 0.0064 in-WC. • The manufacturer-stated accuracy (0.0075 in-WC) for the transmitter is 1.15 times larger than Sh,I, corresponding to a 75% confidence level. • Your data may be different!

  10. Confidence Level of Manufacture-Stated Uncertainty • Find the probability a measurement is within 1.15 standard deviations of the mean • Identify: Symmetric problem • z1 = -1.15, z2= 1.15 • Your confidence level may be different

  11. Interpretation of Measurement Question

  12. Fig. 2 Error in Manufacturer’s Transfer Function • Error in the manufacturer-specified transfer function increases with pressure • Maximum error magnitude is 0.35 mA.

  13. Fig. 3 Deviation from Linear Fit • SI,h characterizes the deviations over the full range of hS • Neither the ascending nor the deviations are generally positive or negative, which suggests that hysteresis does not play a strong role in these measurements. • There are no systematic deviations form the fit correlation, indicating the instrument response is essentially linear.

  14. Abstract • In this lab, a 3-inch-WC pressure transmitter was calibrated using a pressure standard. • The transmitter current IT was measured for a range of pressure heads h, as measured by a pressure standard. • The measured inverted-transfer-function was • h = (0.1838 in-WC/mA)IT – (0.7335 in-WC), • The 68%-confidence-level confidence-interval for this function is ± 0.0064 in-WC • The manufacturer’s stated uncertainty is 0.0075 in-WC • This is 1.15 time larger than the 68%-confidence-level interval, which corresponds to a 75%-confidence-level

  15. Lab 3 Static Calibration of Electronic Pressure Transmitters February 3, 2014 Group 0 Miles Greiner Lab Instructors: Josh McGuire, Şevki Çeşmeci, and Roberto Bejarano

  16. Sxy= Standard error in X given Y Syx Sxy

  17. Example of Hysteresis

More Related