ME 322: Instrumentation Lecture 4 January 26, 2015 Professor Miles Greiner Had extra time, could add a few more slides next year Lab Guidelines and grading, pressure gages, Manometers, Instrument sensitivity

Announcements Turn in HW 1 now – use ME 322 student number, not name HW 2 due Monday 2/3/2014 – assignment and reading on Web Go to PE 113 for lab this week – Lab 2 - Statistical Analysis of UNR Quad Measurements – Download and read instructions Lab 2 Instructions and Lab Guidelines Download Extra-Credit Opportunity, Help at Science Olympiad – See Letter with instructions here See Letter with instructions here – Saturday, February 7, 2015, 9:00am to 3:00pm – ~1% course grade extra credit, equal to ~One homework or lab assignment ~4 points on a test – Sign up by Wednesday, January 28, 2015

Lab Grading Participation (assigned by lab assistants) – Work in 2-person lab groups (assigned in lab) – Be on time (responsibility to lab partner) – Be prepared (read lab instructions, in future labs bring prepared Excel and LabVIEW files) – Participate and interact with your partner in setting up experiment, acquiring data, checking consistency, retaking data if necessary, writing report, and cleaning up. – Be professional and patient (treat the TA’s well) Report (assigned by grader) – Following directions and answering questions – Calculations results (based on your measurements), and – Clear tables and plots (formatting)

Plots Clear Engineering Communication Use units, symbols and variable names Make plot, labels and symbols big enough to see clearly Avoid frames that make the plot smaller These features are graded

Tables Font size, variable name, symbols, units Grids, centered Clarity, simplicity Average Standard Deviation Long Side Length, L [ft] Short Side Lenth, S [ft] Area, A [ft 2 ] Cost, C [$] Average Standard Deviation L46481 S13523 A C

Pressure Generally can’t see it Need gages (gauges) to – Qualitatively know when it changes – Quantitatively measure it Units: Force per area – [Pa] = [N/m 2 ]; [kPa] = [1000 Pa]; [MPa] = [10 6 Pa] – [psi] = [lbf/in 2 ] Gage Pressure – Amount a vessel’s pressure is above its surrounding’s – P GAGE = P – P ATM P P ATM

Some Gages Bourdon Tube Diaphragm Manometers – Vertical – Inclined – Water Head, h

Instrument Transfer Function Relationship between the instrument reading R and its measurand M (quantity being measured) – May not be linear

U-Tube Manometer Measurand Reading Fluid Air (1 ATM, 27°C) Water (30°C) Hg (27°C) ,565  P = 0 Reading Sensed Fluid Density Manometer Fluid Density

Transfer Function Low  m (alcohol) High  m (mercury)

Inclined-Well Manometer h1h1 h2h2  P = 0 ATAT AWAW R  P1P1 P2P2 Use a scale on the measuring tube to measure R directly

Transfer Function

Inclined Manometer Transfer Function Large  Small 

General “Linear” Instrument Characteristics R MAX  R MIN M MAX  M MIN

Sensitivity affects both Resolution and Range In general, it is not hard to change sensitivity – Increasing S improves resolution – but decreases range Resolution as a fraction of Range

Instrument Repeatability Will an instrument give the same reading every time it is exposed to the same Measurand? Why not? – Transfer function may drift with time. So at a later time the readings may shift to consistently higher (or lower) values than before. Referred to as Systematic or Calibration Error – Random variations of uncontrolled inputs (such as RF (radio frequency) noise, orientation of instrument, humidity, hysteresis), may lead to Random variations of the Reading. Referred to as Random Errors or Imprecision

General Instrument Desired Input (Measurand M) i.e. length, pressure temperature Output Reading R (deflection, number of steps, needle angle) Instrument Undesired Inputs Controlled (i.e. temperature, orientation) Uncontrolled (i.e. RF frequency, walking stride length x 1, x 2, x 3, x 4, x 5,…

General Transfer Function Reading R = fn(M, x 1, x 2,…, x n ) How to find the Transfer Function? – Theory: good for simple device (manometer) Done in other classes Only includes the effects you model (at best)! – Calibration: Controlled measurement process Measure reading (R) while exposing instrument to a range of measurands (M) that are being measured by a reliable standard (used to determine M).

Calibration Correlation Correlate Reading R with Measurand M (least squares fit) – May not be linear Uncontrolled inputs can cause R to have undesired variations of the same M! The size of the variation is a measure of the instrument impression – random, inconsistent output Systematic errors can be removed using calibration, but random errors cannot! Standard Instrument Under Test

How to reduce Measurement Imprecision? Improve the control of undesired inputs, and/or Use a different instrument that is less sensitive to uncontrolled inputs

Calibration Transfer Function DataCorrelate Scatter – Uncontrolled inputs instrument

Transfer Function Plot Actual Outputs Best fit line