Lecture 2 Basics of Sensing: Sensor Characteristics. ECE 5900/6900 Fundamentals of Sensor Design

Transcription

1 ECE 5900/6900: Fundamental of enor Deign 1 Lecture Baic of ening: enor Characteritic

2 enor ytem Example Glucometer: Glucoe Meter (monitor blood ugar level for diabetic patient) Tiny blood drop Tet trip Thermitor Meter Control, Working and Reference Electrode Amperometry Circuit Tet trip f c = 100 Hz Glucoe -> Glucoe Oxidae -> Electron -> Change in Current ( μa)

3 enor Characteritic -Output Format -Tranfer Function -Calibration -Accuracy -Reolution - Hyterei -Nonlinearity -aturation -Output Impedance -Dynamic Characteritic -Environmental Factor

4 enor Characteritic: Output Format Example: Accelerometer Output of a ingle phere Wheel Robot 4 enor ytem may produce a et of output electrical characteritic uch a voltage, current, charge, frequency, amplitude, phae, polarity, pecific hape, time delay, and/or digital number or code.

5 enor Characteritic: Output Format Example: Tactile enor Array 5

6 enor Characteritic: Output Format Example: Gyrocope Output 6

7 enor Characteritic: Output Format Example: Analog Output to PWM Output 7 Goal: Take enor input and control the ervo (direction of motion on a Robotic Arm) More Example of enor Output Electrical Characteritic

8 enor Characteritic: Tranfer Function Tranfer function decribe the input (timulu, ) and output (repone, ) of a enor ytem 8 Tranfer function can be repreented a table of value, a graph, formula or a olution of equation Example: Preure enor Example: CO enor

9 enor Characteritic: Tranfer Function More Example 9 Tranfer Function Invere Tranfer Function (to determine the coefficient)

10 enor Characteritic: Tranfer Function Model and Function Approximation 10 Common Function: Linear A B Input (timulu) Y intercept lope=enitivity Output (Repone) Common Function: Log A e A B B ln Invere Tranfer Function A B A Bln

11 11 enor Characteritic: Tranfer Function k k B A B A Model and Function Approximation D C B A d c b a C B A c b a Common Function: Power Common Function: Polynomial d c b a

12 enor Characteritic: enitivity Nonlinear Tranfer Function ha different enitivity at different interval Ue Linear Piecewie Approximation and pline Interpolation to etimate enitivity 1 Linear Piecewie Approximation enitivity=firt derivative of the tranfer function b i i i where, i = mall increment of input i = mall increment in output

13 enor Characteritic: enitivity pline Interpolation: Example and Matlab' Curve Fitting tool 1

14 enor Characteritic: Calibration If the enor' pecified over a broader range than what i required, we need to calibrate the enor ytem 14 Either the model of the tranfer function or a good approximation ha to be known before calibration ection..1,.... Fig..4: Calibration of thermitor: (a) grinding, (b) trimming of reference reitor, (c) calculation of tranfer function

15 enor Characteritic: Accuracy Accuracy i very important a it repreent highet deviation from the ideal value at the input Error tolerance (the output can change regardle of manufacturer' pecification!) 15

16 enor Characteritic: Accuracy Example: Laer Diplacement enor: pec: 1mV/1mm, Obervation: 10.5 mv for 10 mm, 5% error 16 Accuracy can be repreented a 1) Directly in term of the meaured value (e.g. tolerance of 0.15 deg C of a temperature enor) ) A % of the input pan (e.g. flow rate: 000 foot per minute with % accuracy ) A % of the meaured ignal 4) In term of the output ignal (e.g. digital LB)

17 enor Characteritic: Output Impedance In order to connect the enor to the interface circuit, it i important to know the output impedance, Z out 17 enor with current output hould have very high Z out enor with voltage output hould have very low Z out enor with voltage output enor with current output