IG a1n Other Sensors Fiber Optic strain sensors bragg gratings) input optical fiber transmitted reflection Broad spectrum input light s reflected only at a specific wavelength determined by the grating spacing which varies with strain Ring laser Gyroscopes Sagnac Effect) · PVDF or pzt sensors 16.810(16682) assachusetts Institute of Technology
2WKHU6HQVRUV )LEHU2SWLFVWUDLQVHQVRUV %UDJJ*UDWLQJV LQJ VSDFLQJZK , λ UHIOHFWLRQ L O L L L LQSXW WUDQVPLWWHG RSWLFDOI EHU %URDGVSHFWUXPLQSXWOLJKWVUHI HFWHGRQO\DWD VSHFLI FZDYHOHQJWKGHWHUPLQHGE\WKHJUDW FKYDULHVZ WKVWUDLQ 5LQJ/DVHU*\URVFRSHV 6DJQDF(IIHFW 39')RU3=7VHQVRUV
IGAn II. Sensor Characteristics Dynamics Goal: Explain performance characteristics(attributes of real sensors) When choosing a sensor for a S saturation limit particular application we must non-inear S(X specify the following requirements Sensor Performance Requirements: linear dynamic range Dynamic Range and span Accuracy and resolution Absolute or relative measurement · Sensor Time constant Calibration is the process of · Bandwidth obtaining the s入X) relationshⅰp Linearity for an actual sensor. In the physical Impedance world s depends on things other than X Reliability(MTBF) Consider modifying input Y( e.g. Temp) Constraints E.g. Load cell calibration data: Power: 28VDC, 400 Hz AC, 60 Hz AC X= mass(0.1, 0.5 1.0 kg Cost, Weight, Volume, EMI, Heat S=oage(1113,5632,1043.2mV) 16.810(16682) Massachusetts Institute of Technology
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« 6 YROWDJH P9
IGAl0 Sensor Frequency Response Function X(S es+k sfX(sms+CS+k X6(t) Ideal accelerometer frf from base motion bandwidth Example: Accelerometer mE m=4.5 k=7.1e+05N/m c=400 Ns/m 11d1010316105 Typically specify bandwidth as follows Frequency [Hz] Example: Kistler 8630B Accelerometer Note: Bandwidth of sensor should Frequency Response +/-5%: 0.5-2000 Hz be at least 10 times higher than highest frequency of signal s(t) 16.810(16682) Massachusetts Institute of Technology 13
P N F [ W [E W ([DPSO P D E V ; V FV N * V V ; V PV F+ = = ++ 6HQVRU)UHTXHQF\5HVSRQVH)XQFWLRQ H $FFHOHURPHWHU P J N H1 F 1VP V N 0DJQLWXGH>G%O ,GHDO$FFHOHURPHWHU)5)IURP%DVH0RWLRQ EDQGZLGWK 7\SLFDOO\VSHFLI\EDQGZLGWKDVIROORZV )UHTXHQF\>+]@ ([DPSOH .LVWOHU%$FFHOHURPHWHU 1RWH %DQGZLGWKRIVHQVRUVKRXOG )UHTXHQF\5HVSRQVH +] EHDWOHDVWWLPHVKLJKHUWKDQ KLJKHVWIUHTXHQF\RIVLJQDOV W
1G. 10 Sensor Time Constant How quickly does the sensor respond to input changes First-Order Instruments Second-Order Instruments a-itaoy +a-+aoy Dividing by ao gives Essential parameters are +y=u K static natural In s-domain sensitivity frequency damping ratio K In s-domain K U(s)IS+1 U(s)s2+25n0,s+m τ: time constant Time constant here is T=1/5a K: static sensitivity Time for a l/e output change 16.810(16682) Massachusetts Institute of Technology Ui
6HQVRU7LPH&RQVWDQW +RZTXLFNO\GRHVWKHVHQVRUUHVSRQGWRLQSXWFKDQJHV" )LUVW2UGHU,QVWUXPHQWV )LUVW2UGHU,QVWUXPHQWV 6HFRQG2UGHU,QVWUXPHQWV 6HFRQG2UGHU,QVWUXPHQWV D G\ G \ + DG\ + D \ = E X D + D \ EX = R R R R GW GW GW 'LYLGLQJE\D RJLYHV (VVHQWLDOSDUDPHWHUVDUH D G\ E \ R += X R D GW D . ER ω D ζ D Q N NR D R Q D D DR τ . VWDWLF QDWXUDO VHQVLWLYLW\ IUHTXHQF\ GDPSLQJUDWLR ,QVGRPDLQ < V . < V . = ,QVGRPDLQ = 8 V τ V + 8 V V + ζ QQ Q ω ω V + τ WLPHFRQVWDQW 7LPHFRQVWDQWKHUHLV τ = ζωQ . VWDWLFVHQVLWLYLW\ 7LPHIRUDHRXWSXWFKDQJH