Stages of measurement systems Sensor: senses physical variable being measured Transducer: converts sensor signal into useful/detectable signal Signal conditioning: modifies transducer signal (amplifier, filter,etc.) Output: provides indication of measurement Control (feedback): often feeds information to a process to change input Experimental Test Plan 1- Parameters: What question am I answering, what needs to be measured, what parameters or variables are involved? 2- System and tolerance: What ways can I measure this, how good do the results need to be? 3- Analysis: How will I interpret the results, how good is my answer, does it make sense? Variables Independent: changes in others = no affect Dependent: changes in others = affect Discrete: can only take on finite number of values (A/D 10 bit => 1024 values) Continuous: any value in a range Extraneous: not controlled during measurement but affect output Noise vs. Interference

Noise: a random variable (requires statistical description) stochastic: randomly determined. Interference: produces undesirable deterministic trends. Calibration Apply a known input (standard) to observe the system output Fitting a line, curve, spline, etc. to calibration data to determine functional relationship between input and output signals.

Static: variables remain constant through measurement Dynamic: variables change during measurement (determine useful frequency range) Static Sensitivity: slope (K) of a static calibration curve. ! = !"(!!)!" . Must evaluate the slope of the curve. Range: minimum to maximum measureable (input and/or output). Resolution: smallest increment in the measured value that can be discerned.

Interference Noise

Chapter 1

Accuracy: measure of absolute error = true value indicated value. % relative accuracy => = 1 !!"#$ !"#$% 100 [this requires knowledge of true value i.e., calibration] Precision: measure of repeatability (does not require calibration) Bias error: difference between average and true value (aka systematic error)

Uncertainty Combined estimate of range of error in a measurement due to instruments, random, systematic, calibration etc. Examples of Instrument Error:

Precise Accurate and Precise Neither