Application notes - Resonance Dwell Testing (bo0250) Dwell Testing — ^^^""\ L L. L L L .L L. £ £...
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I 1 £ £ L-| 1 I 1 ■ ■ ■ l i ■ , „ — ■ ■ , ■ £ £ L-L-L - ! - ! L L '^b T T ^ '^^^* W ^ * * ^^^^^ * *f ' ff f f r t W ^ ^ ^ ' V W f f f f f j ' L^ L^ L" L" L 'L 'L 'L 'L » — £ £ £ f f L* ^ ^ ^ ¥ / f * 7 « - f Y n ^ ^ ^ ^ Y ^ ^ ^ ^ £ £ L"L L-L"L L^^^^T^ 'f f f f f ^ ^ * \^^^^^^ ^ ^f f f f f £ £~ £~ £~ L 'L ' r l i £ ' ■ ' ■ £■£■-£■---- -L | | | — | , | ■ m *fl*fff ^-W^-VnWVl^^' ^ T ^ * ^ r r r ^ f V ^ ^ ^ ^ ^ T ^ ^ T ^ r 'f<r*~~ L f f W r t \ \ \ W f f f f W f t A \ ^ V f ^ £ £ £ £ L-L"L L ^— — — L- L- L- L - L-L-L L —L ' £ £ £ £ £ £ L~ —LTL-L~L L L t^T^* * * * J-WWHIIII-^ ^ their resonance frequencies, in f/«///f//f■l¥|^^Y\^^^^^^Ylv/« *fff^^+^\^^^***ffffff^*^+^^^^^T*ffffff* i^\^\^wW/rf/r'Pn tl\^w////fn\^ *^^\,Li'* rffff* L"L LL-L L.—_*..*.££ £ L £ L ^^m...'~ L L LL !—"—...!■ L . L L -V-—'-— L —V—-— L L - L ^ L , \ , V-TL - . £ L . 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W . » ' L L L V-T— — . £ £ A L L L L —L " — ^—. L L L - L L - L L L L ' ' I V / ' " ' £ £ £ £ £ £ L-L-L J L L £ £ £ ^ £ £ £ £~ £ L T ^ t L — L — ■ ' ^ ^ ^ L"L L — » " ' £ ^ £-£ " i ' » ^ ^ ^ T ^ ^ ^ f c t L ' " * £ * £ £ £"£ £ L^L L L ■ " - — ' £ £ £ £ £ i ' L V — ^ L. L"/ - - » . * . !.!,!■ L L"L ' i T K ' ^ L L. £ £ £ L ' ' 1 — [ " *\£ L_L_L L LLL L L - - . L^» £ test object. During such tests, ■ ■ L - L . L . L . L . L . £ ■ W W l ' / Z / f f r t — m W ■£ I £ £ £ L-L-L L . ^ ^ T ^ ^ ^ F r r r * ^ ^ ^ ^ ^ . — . * ( 1 * * ^ " £ £ £ £ L - L - L T L | L . ■ £ £ £ £ £ LTL-L"LTL L^ ^ ' ^ I ^ L ' ^ r* the resonance frequency will '.'L'.'L'.'.'L'.'.V' £ £ L £ £ L L. '_ / L^ £ £ £ £ .'L , J J J J £ L. L_L L L L L 'L - . ' L , . L ' L L L L .L J L L L L 'J - * . '■ — . ' L ^(* L L'L LJU. J J . \ ft * * * * * * * I r . ' L 4 l A j j J ■. JJL \~££^£££££££££ L"L-L L . —» L^- £ £ £ £ £ £~ £~ £~ L \ .^***f* f f f f ^+*\^^^^* '+*fff+\^^^^^^i V £ £ £ £ £ £-£-£-,,,, ^ . L /f/f* *^^\Wkf f c . J £ ^ £ ^"L L T ~ V -.- L. L L. ^ L L . — ^ L L^ L^ L L L L L 1 .... V t L^— L"L L"L L L L .-.- L » . . . ' < l < f l L"L-| L-L-L^ L-L-L I ' LLLLL' . f i ^ i f ! L-L-LLLLL.L' £^ £ £ £ £ L T L " L L L L L L . £~ £ £ £ L-L-L"! LL LLL' L.— L^ L ' ^ * " * ^ - * ^ ^ ^ ' ^ ^ ^ ^ L^ L1 f f n A « \ \ \ W / / f f f / i « \ V . V . ' L^ L - !■!■!■ L_ L 'L^L L L 'L '— £ £ £ £ £ L ' L 'L L . *.. ^ £ £ £ L L 'L 'L^^^^ ' ^ ^ ^ ^ ^ . . . . . T T Tr — ^ ' ^' T L—rf I" LL-L ^ ^ ^ ■ ■ ■ ■ -L-L-L-L. ' ' I L^ I . ■ ■ L_ L 'L 'L 'L 'L ' — _ ^ — L ' L" L" L" L 'L" L 'L ' ' „ £ £ £ £ £ L" L" L" L 'L 'L 'L 'L . -' ^ H ( / / W l ^ « « « ¥ / / f L L" L" L" L 'L 'L . L '— £ £^ £ £ £ L 'L"»^^^ T '* ^ ^^f f # < f tT T *^ * *T * W^^^^f + T * \ ^^^^' ^ ^ ^^^ * 1 change, in order to ensure that i ^ ^ ™ ^ ^ " L L L L L . the object is tested at the cor- £■£ £ L-L-L-L - L - L - L L L . L L L ' £ £ £ £ £-£-L A * V V fffff L L V L — ' L L " L " " . " L ' L^ L . L" ■ I I L-| I . . L"L- - L _ L . ■ \ £ £ £ L-L-L-L' * ^ * * * * * t J J £ £ L-L-L"! LLL L L . — £ £ £ L_ L" L^L" L 'L 'L - . - . . ' £ £ £ £ £ L." L_ L 'L 'L 'L . . . . - L^ L^ | L" ■ ■ ■ ■ b"b"b"b *»»'»»»» ' f t b b"b *V ' " ^ \ ^ \ ^ ' f (' ~rt^^^^^^ T ■ ■ £ £ £ :£-£-£-£-^W '**** x..' £ £~£ L-L-L-L L I ...... ^ ^ I L-L-L-L L L L L L . L .■ £ £ £ £ £ L-L-L-L L . . £ £ £ ££ L-L-L" ^>\w: „■:■-;- ;;I;>;V;#A « * > ■ ' : ' : : : • '^J<>>:■.:■ '/L■■■'--":y>:\>:\r. _ ■:-:v.^-:-v^;;L-:-"-ii-:-:^:'^"j"i-^^;'X , ^'^---^^^'-. , ''----L-: ^i\**A* .L , -..L-L-L i L i L-L i LLLLL.Jfc . — £ 7 L^ L^ ^ ^ ^ L . 'L "L 'Z'Z'Z'Z' £ £ £ £ L J T L" L 'L 'P ^ 7 J- 7 J £ . L .\'.'. ^ L "L 'P J Zg2 J £ J L . ^ ' L 'JL 'Z'J 7 7 J J J ' £ A " ' ' ' ' ' ' ~ ~ ^ V ' ' ' ' " . . v O K W mtect frequency, the excitation has to be tracked, and locked tol '.WWX^ t t*tt 'L'.'.'.'L'.'.'J.' L. L 1 L. L'L "-\ *^ L.L I.I.I. L^ L \ T ^^i^ T - - - ^*fl I h ■£■£ LL ,,^r£^ £ £ £ £ L L"L-L L - i ■ L ..»..» L. . . . . . T , 'f\7^f<ff T ("^^ T ' ' ^ ^ T ' 'J^*VWS T ^^^ T " " " ' f f i m m ^ ' ■/«* " . . . V L , 'J £ £ £ £ £■£ L-LLILL...' £ £ £ £ L... L L . L . . £ £ , £ , \ .L .... ' ^ | L-L"L T L L . —»» £ £ I £ L"L"L L L"L L-L-L-L L " L — !■!■!■ the critical resonance trequen- •"• : - : -^ ;: -' r ' ^i F111 * 1 * J * 1 T cyi I n i s application note de- ^ ^ I ~...,,££££ ^*^£f£ff...?~J^££.-.m'L^~~£m^'-- ^ ^ ^ ^ ^ ^ ■ J 1L^T ^ ^ ' ^ 'f/ff'r — L-L-L L-LL.L.— L^ £ L_ L_ L_ L ^ * L . . . £ ■ ' ^ L_ L" L L" L 'L 'L . . . £ £ £ £ L_ L" L 'L 'L . - . . . ' £ L_ L" L" L" L 'L 'L * * ^ L ' ' ' ' ' ' ' . ' ■ £ ^ ^ | 'L-L- ■ ■ £ I " " - . ! . . ! . " L-LLLL.V £ £•: £■£ L - L " T ^ ^ ^ L . . . - ^ T T V L"LTL I . — I . ; L-L-L-'L L \ . L . . ■ L^— L^ L_ L L 'L 'L 'L . . ' ' L 'L 'L 'L . . . . ' £ £ T ■ . I ■ ■ I^ T >>^^ T i^ T » T T T Yril'^ ' ■'■ "^ ■b"b' LL U L ' £ ' £ ' b L "b b~— L — L ' L_L "b T ' L "b L L — L ' ' L ' 1 ■ ..... !».. £ £ £ £ £ L"L-L-L , ...'. "L L. 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' L. £ £~ L ' L 'L — L^» L^ L^ ' " L_ L_ L" J g ^ T ^ ^ 7'!'!■''jjj'■), / " ^<'^i i i i >' ' - ' • ' ; / ' ; 1 ^ 1 '-' ''' ' y' ^ "'^Jp' T ' v'- ■ ■ ■ '■' ^ ^ - ^ ^ ^ t 4 / An instrumentation set-up for resonance dwell testing, using an accelerome- ter as the response transducer. * * * Introduction Many types of structures, mechani- overcome by modern instruments such the 1050, adjusting the generator fre- cal components, and material speci- as the Brtiel&Kjaer Vibration Exciter quency until the phase shift is again mens are required by industrial and Control Type 1050. The 1050 incorpo- ±90°. military standards to undergo fatigue rates high-resolution drift-free fre- testing. One common fatigue test is quency control, as well as extremely The resonance dwell system is called resonance dwell testing. This is stable vibration and force control. shown in the opening figure. In this used to test an object continuously at system, the force and acceleration sig- a particular resonance. In principle, In particular, in lightly damped test nals are supplied by a Force Trans- this would seem to be a simple task: objects, the problem of a varying reso- ducer Type 8200 and an Accelerome- the frequency and level controls of a nance frequency can be particularly ter Type 4384, respectively. These sig- vibration exciter system should be ad- troublesome. It can be solved only if nals are compared in the 5885. The justed to excite the test object at the the resonance conditions are accurate- output of the 5885 is supplied to the required stress level, at the desired ly monitored, and the excitation fre- 1050, forming a feedback loop which is resonance. However, in practice, reso- quency is adjusted accordingly. used to lock the generator frequency nance dwell testing puts a number of to the varying resonance frequency. demands on the instrumentation. The The Resonance Dwell Unit Type resonance frequency of the test object 5885 has been designed to solve the Occasionally, the engineer may changes due to progressive fatigue, problem associated with a varying res- want to maintain a phase shift other and for example, temperature effects onance frequency of the test object. At than 90°, for example, if either one of on the internal damping. resonance, the phase angle between the transducers introduces a phase the input force and the response accel- shift. The addition of a selectable , eration is ±90°. A small change in phase-shift stage (option WH2122) oOlvmg t l l G p r o b i G m S frequency results in a large change in * ensures operation under such condi- the phase angle. When the phase shift tions. Problems associated with frequency between these signals changes, the ' and output-level instability have been 5885 activates the frequency sweep of *• *. * BO 0250-11 /
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Transcript of Application notes - Resonance Dwell Testing (bo0250) Dwell Testing — ^^^""\ L L. L L L .L L. £ £...
Resonance Dwell Testing —
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'. I 1 £ £ L - | 1 I 1 ■ ■ ■ l i ■ , „ — ■ ■ , ■ £ £ L - L - L - ! - ! L L ' ̂ b T T ^ ' ̂ ̂ ̂ * W ^ * * ^ ̂ ̂ ̂ ̂ * * f ' f f f f r t W ^ ^ ^ ' V W f f f f f j ' L̂ L̂ L" L" L ' L ' L ' L ' L » — £ £ £ f f L * ^ ^ ^ ¥ / f * 7 « - f Y n ^ ^ ^ ^ Y ^ ^ ^ ^ £ £ L " L L - L " L L ^ ^ ^ ^ T ^ ' f f f f f ^ ^ * \ ̂ ̂ ̂ ̂ ̂ ̂ ^ ^ f f f f f £ £~ £~ £~ L ' L ' r l i £ ' ■ ' ■ £ ■ £ ■ - £ ■ - - - - -L | | | — | , | ■ m * f l * f f f ^ - W ^ - V n W V l ^ ^ ' ^ T ^ * ^ r r r ^ f V ^ ^ ^ ^ ^ T ^ ^ T ^ r ' f < r * ~ ~ L f f W r t \ \ \ W f f f f W f t A \ ^ V f ^ £ £ £ £ L - L " L L ^ — — — L- L- L- L - L - L - L L — L ' £ £ £ £ £ £ L~ — L T L - L ~ L L L t ^ T ^ * * * * J - W W H I I I I - ^ ^
their resonance frequencies, in f /« / / / f / / f■ l¥ |^^Y\^^^^^^Ylv /« *fff^^+^\^^^***ffffff^*^+^^^^^T*ffffff* i ^ \ ^ \ ^ w W / r f / r ' P n t l \ ^ w / / / / f n \ ^ *^^\,Li'* rffff* L"L LL-L L.—_*..*.££ £ L £ L ^^m...'~ L L LL !—"—...!■ L . L L - V - — ' - — L — V — - — L L - L ^ L , \ , V - T L - . £ L . L ^ L ' . £ £ £ £ £ £££■££■ * £ - £ - £ - L , \ \ W £ £ £ £ £ £ £ £ £ £ £ - , , , , , , ^ ■ £ £ £ £ £ £-£-£-^ \ \ — £ £ £ £ £ L " L - L L L _ . — L - r r * T * V ^ ^ \ ^ ^ T * r f r r r r ^ ^ ^ ^ ^ ^ ^ ^ T * * T * W ^ r r r r r * l ^ ^ ^ ^ V — » ^ ^ L L L L L — £ £ £ £ £ £ L " L L ^ L L V L V L L L . L^ L L " L L V ^ . i . £ £ £ £ £ L " L L - L V — £ £ £ £ £ £ L " L L L V — f f f f f i l W V 1 ■ — ■ I ■■ ' L " ! L L L " L " L V L ' ■ ' ' ^ ' ^ ' ^ « ' « * - * ^ \ ^ ^ ^ V ^ ^ ' * *
i order to provoke fat igul in the ^ \ \ \ - . \ \ \ ■.■-'■.■ — /£££ £££ £££. ,„£■„„.'JSt~£ £ £ £ £ £ £-. L . „,J~-J-^ £ ££ £ . £i.X,X<C'-J-'j L ' ' . . - . O . > K- ", , £ -L ' " ^ V J . . ' ^ . „ ' : - ' V ' l . - J J j ! " ' L £ 'f.XV^.Jj't ',',£*£ . ^ X^J^^',',',~'^'^.^^£...~X..,l^^
- L L L L L L L L — L — L — ' L V £ £ £ f / J r t \ \ \ \ « A M » V f f W / / l ^ ^ \ \ \ V J ^ J f f f . f \ \ \ \ \ M J W W W f f f f f L \ \ A \ \ Y — / ^ ^ L ^ ^ ^ ^ L L L ! ! - — ! ■ . L . L L_ L" L L L t ' l W t V ! . ! ■ ! ! ! ! ■ - - - V L L L L L L L L L V - T - T " \ L \ L L L L L . W . » ' L L L V - T — — . £ £ A L L L L — L " — ^ — . L L L - L L - L L L L ' ' I V / ' " ' £ £ £ £ £ £ L - L - L J L L £ £ £ ^ £ £ £ £~ £ L T ^ t L — L — ■ ' ^ ^ ^ L " L L — » " ' £ ^ £-£ " i ' » ^ ^ ^ T ^ ^ ^ f c t L ' " * £ * £ £ £"£ £ L^L L L ■ " - — ' £ £ £ £ £ i ' L V — ^ L . L " / - - » . * . ! . ! , ! ■ L L " L ' i T K ' ^ L L . £ £ £ L ' ' 1 — [ " * \ £ L _ L _ L L L L L L L - - . L^» £ test object. During such tests,
■ ■ L - L . L . L . L . L . £ ■ W W l ' / Z / f f r t — m W ■£ I £ £ £ L - L - L L . ^ ^ T ^ ^ ^ F r r r * ^ ^ ^ ^ ^ . — . * ( 1 * * ^ " £ £ £ £ L - L - L T L | L . ■ £ £ £ £ £ L T L - L " L T L L^ ^ ' ^ I ^ L ' ^ r *
the resonance frequency will ' . ' L ' . ' L ' . ' . ' L ' . ' . V ' £ £ L £ £ L L . ' _ / L̂ £ £ £ £ . ' L , J J J J £ L . L _ L L L L L ' L - . ' L , . L ' L L L L . L J L L L L ' J - * . ' ■ — . ' L ^ ( * L L'L L J U . J J . \ ft * * * * * * * I r . ' L 4 l A j j J ■. JJL
\~££^£££££££££ L"L-L L . —» L^- £ £ £ £ £ £~ £~ £~ L \ . ^ * * * f* f f f f ^ + * \ ^ ^ ^ ^ * ' + * f f f + \ ^ ^ ^ ^ ^ ^ i V £ £ £ £ £ £-£-£-,,,, ^ . L / f / f * * ^ ^ \ W k f f c . J £ ^ £ ^ " L L T ~ V - . - L. L L . ^ L L . — ^ L L̂ L̂ L L L L L 1 . . . . V t L̂— L"L L"L L L L . - . - L » . . . ' < l < f l L " L - | L - L - L ^ L - L - L I ' L L L L L ' . f i ^ i f ! L - L - L L L L L . L ' £^ £ £ £ £ L T L " L L L L L L . £~ £ £ £ L - L - L " ! L L L L L ' L . — L̂ L ' ^ * " * ^ - * ^ ^ ^ ' ^ ^ ^ ^ L̂ L1 f f n A « \ \ \ W / / f f f / i « \ V . V . ' L̂ L - ! ■ ! ■ ! ■ L_ L ' L^L L L ' L ' — £ £ £ £ £ L ' L ' L L . * . . ^ £ £ £ L L ' L ' L ̂ ̂ ̂ ̂ ' ^ ^ ^ ^ ^
. . . . . T T T r — ^ ' ^ ' T L — r f I " L L - L ^ ^ ^ ■ ■ ■ ■ - L - L - L - L . ' ' I L̂ I . ■ ■ L_ L ' L ' L ' L ' L ' — _ ^ — L ' L" L" L" L ' L" L ' L ' ' „ £ £ £ £ £ L" L" L" L ' L ' L ' L ' L . - ' ^ H ( / / W l ^ « « « ¥ / / f L L" L" L" L ' L ' L . L ' — £ £^ £ £ £ L ' L " » ̂ ̂ ̂ T ' * ^ ^ ̂ f f # < f t T T * ̂ * * T * W ̂ ̂ ̂ ̂ f + T * \ ^ ̂ ̂ ̂ ' ^ ^ ^ ̂ ̂ * 1
change, i n order to ensure t ha t i ^ ^ ™ ^ ^ " L L L L L .
the object is tested a t t he cor-£■£ £ L - L - L - L - L - L - L L L . L L L ' £ £ £ £ £-£-L A * V V fffff L L V L — ' L L " L " " . " L ' L^ L . L"
■ I I L - | I . . L " L - - L _ L . ■ \ £ £ £ L - L - L - L ' * ^ * * * * * t J J £ £ L - L - L " ! L L L L L . — £ £ £ L_ L" L ^ L " L ' L ' L - . - . . ' £ £ £ £ £ L . " L_ L ' L ' L ' L . . . . - L̂ L̂ | L" ■ ■ ■ ■ b"b"b"b * » » ' » » » » ' f t b b"b * V ' " ^ \ ^ \ ^ ' f ( ' ~ r t ^ ^ ^ ^ ^ ^ T ■ ■ £ £ £ :£-£-£-£-^W ' * * * * x . . ' £ £~£ L -L -L-L L I . . . . . . ^ ^ I L -L-L-L L L L L L . L . ■ £ £ £ £ £ L -L -L-L L . . £ £ £ ££ L-L-L"
^>\w: „■:■-;- ; ; I ; > ; V ; # A « * > ■ ' : ' : : : • '̂ J<>>:■.:■ '/L■■■'--":y>:\>:\r. _ ■:-:v.^-:-v^;;L-:-"-ii-:-:^:'^"j"i-^^;'X,^'^---^^^'-.,''----L-: ^ i \ * * A * . L , - . . L - L - L i L i L - L i L L L L L . J f c . — £ 7 L̂ L̂ ^ ^ ^ L . ' L " L 'Z' Z' Z' Z' £ £ £ £ L J T L" L ' L ' P ^ 7 J - 7 J £ . L . \ ' . ' . ^ L " L ' P J Zg2 J £ J L . ^ ' L ' J L 'Z' J 7 7 J J J ' £ A " ' ' ' ' ' ' ~ ~ ^ V ' ' ' ' " . . v O K W
mtect frequency, the excitation has to be tracked, and locked t o l
' .WWX^ t t*tt ' L ' . ' . ' . ' L ' . ' . ' J . ' L. L1 L. L'L " - \ * ^ L.L I.I.I. L̂ L \ T ^ ^ i ^ T - - - ^*fl I h ■£■£ L L , , ^ r £ ^ £ £ £ £ L L"L-L L - i ■ L . . » . . » L . . . . . . T , ' f \ 7 ^ f < f f T ( " ^ ^ T ' ' ^ ^ T ' ' J ^ * V W S T ^ ^ ^ T " " " ' f f i m m ^ ' ■ / « * " . . . V L , 'J £ £ £ £ £■£ L - L L I L L . . . ' £ £ £ £ L . . . L L . L . . £ £ , £ , \ . L . . . . ' ^ | L-L"LTL L . — » » £ £ I £ L"L"L L L"L L -L-L-L L " L — !■!■!■
the critical resonance trequen-•"•:-:-̂ ;:-'r ' ^ i
F 1 1 1 * 1 * J * 1 T cyi I n i s application note de-^ ^ I ~ . . . , , £ £ £ £ ^ * ^ £ f £ f f . . . ? ~ J ^ £ £ . - . m ' L ^ ~ ~ £ m ^ ' - - ^ ^ ^ ^ ^ ^
■ J 1L^T ^ ^ ' ^ ' f / f f ' r — L - L - L L - L L . L . — L̂ £ L_ L_ L_ L ^ * L . . . £ ■ ' ^ L_ L" L L" L ' L ' L . . . £ £ £ £ L_ L" L ' L ' L . - . . . ' £ L_ L" L" L" L ' L ' L * * ^ L ' ' ' ' ' ' ' . ' ■ £ ^ ^ | ' L - L - ■ ■ £ I " " - . ! . . ! . " L - L L L L . V £ £•: £■£ L - L " T ^ ^ ^ L . . . - ^ T T V L " L T L I . — I . ; L - L - L - ' L L \ . L . . ■ L̂ — L̂ L_ L L ' L ' L ' L . . ' ' L ' L ' L ' L . . . . ' £ £
T ■ . I ■ ■ I ̂ T > > ^ ^ T i ^ T » T T T Y r i l ' ^ ' ■'■ "^ ■ b " b ' L L U L ' £ ' £ ' b L"b b ~ — L — L ' L _ L " b T ' L " b L L— L ' ' L ' 1 ■ . . . . . ! » . . £ £ £ £ £ L "L-L-L , . . . ' . " L L . L . . . . « L . p scribes llllifc ins t rumenta t ion r|-t- ■ | r*ffff**+^i\^^£^££t- i V f f / W
T ^ t ' _ ■£ £ I L " | L -L-L-L L ' L . — £ £ £ £ f _ . ' £ff*/
■ _ ■ ■ • • • • . <<.... sss-.: .CC'Z'i:0.'\>.''.r ■ . s . ,
Ifknd procedures used for sulk,.; ^ ^ " L - L - L - L - L L . . . . ■ £ I ! ! . — — ! ■ £ £ £ £ L . . . V L L . . ' L" L ' L ' L ' L . . .
cessful vibration testing at cnt - i I - * V ^ ^ ^ L L L — ££££££ ^ " L . L\ L V " V ^ " V ' L V .
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.L..L-L-L-L-L-L^-L,LLL.L...OL-L-L-L-LK LLL ' . - <"R i ' V ^ ^ , . ; - - . ; 1 : . ? . ^ ' / ' ^ \ C ; ^ ^ ^ ̂ ' - , ' ^ ^ ^ U ̂ V ■ ■ -V V \ ^ ^ i ( v v V X W K
. ■ ££££££££■£-..£-.......~~ £ £ £ £ . 9 , , , , ' . . ^ > ^rf*X \ \ * ^ L * > " L- £ £ £ £~. , , , . ' - 0 - L- L- tfS v,,„\,Z,Z,JjZ\Z,££. £t.,,.,"Z?jZ^£yh>.£\-,..V2j2-ir h.-1-l-h.h. ̂ ' . " ' ' ' ' < — -^5.-' '<<<£ £ b ^ B ^ ■ " ' k J ' ^ B L ■ ^ B f - " ^ B _ A ^ ~ * ^ ^ " ^ J * J — * F ^ V *■*£ - * ^ ~ ^ k ^ ^ * \ J ^ ^ J 1 1 1 L'"L-L-L L » ■ » . . . L' £ £ L ' L L J L L L L L L . [ » . . . l V - . L L L. L L_ ' L ' L L" L . L V . . * * * ^ l l l W W ■ — l l ■ ' IF C ■ J i l l ■ 1 W T ■ * V C ■ * - ■LL....L.L-L-L-L-L-LL.L- .>0?L-J L'L L-L, L L L . . 0 . L'L-, L-L-L-L" L L L L V - ? ? ,
I f /"i I i f |—* f i l l r^ I 11 [ r^ *̂s 1 *fc i m t 1 ■■■ ■ I X ' rf** J t J l ^ l E \ ^ l \ > w & K.̂ .v . ■ . I L I . |
1 O ^ } \ . L jL'L' ,-0rjrj^?j:L, ,LLL ,r ,L0jjj-0>L?L ^ V - ^ ^ ^ ^ ^ ' ' T L L I I I _ , — ^ ^ — . — I ' l - L - L L L - | | - ■ | | 1 f [ l L L L . T ^ B ^ ^ » " L L L ' L ' L £ - . . | ■ L_ L" L ' L ' L ' L . ' L . - . £ L L" £ | L_ L ' L . ' L ' L . . . . . | £ L_ L" L" L^L ' L ' L L ' L . . . | £ £ L_ L, L" L" L ' L_ L L . ' L ' L ' p . . i' i' . " L . . _ . _ . ' - 1 . . » . . * i' i' i' . " . _ . _ i' . " | - . " . . . . . . . * i' i' i' . " | _ . " | _
A J:"L-»>V / / / *O^:O . — £ £ £ , £ L" ► . . . " " L L | L L . . L ' £ £ £ £ £ L " L L - L L " L L V L̂ — I . ; L - L - L - L - ! L L . . . ■ ! ■ ! ■ ! ■ L_ L" L J ' L L L ' £ £ £ £ L_ L" L ' f L . L . £ £ £ £ L^L_ , ^ ^ M. £ £ £ L L_ L̂ L" L" L . L . _ . L . L̂ L . £ L L ' L L L . . - L L. L L ' L , L L L L L V » . V L . L̂ L" ££ L L L L L . . " T " ^ - 1 L L L ' " L J , V - . - . - . - V L. L L . " L^L_ L ' L L V - . - . - . - L. L. L V ■ " . L L ' L L V » - . " " ^ T * < ^ f " b b"b b b ' ' 1 L ' ' ' ' ' C ' ' ' f T T * T ^ T * ' y l f l f Y f * ^ ' ^ T r T ( r C * T ^ , ' 1 ' i * ^ T , ' l r l r l r ^ ' r , * 1 t * * * T " " l r ' n * ■ . — ^ ^ | L - L - L - L - L . - L L . . ' ~ £ £ £ L - L - L " ! L L L . . . ' £ £ £ £ L_ L L ^ L " L ' L . . - . L . ! ■ ! ■ ! ■ L" L L L" L L L L . * . . — £ £ L L^L_ L" L ' L ' L L L . _ . . . . L L_ L" L . . L L . L̂ _ L L L" L L" L" L ' L . _ . . ' » •
■: ■: . : . - - . : ■ : - . ■ ■:►:■:.:■:.? :■ > : ; - - > : - - ■ : - - : - - / • L L L L L L L L L . ' " - £ £ £ £ £ £ £ £ L" L" . . - - . - L- £ £ £ £ . . . . - - - J £ £ £ L . . . „ ' Z ' ~ £ £ £ £ L L L L 0 . . J J ^ L"^ L L 'L 'L O j ? - . ' 'L 'L 'L 0 1 0 J J , J " L - > L 'L ' J J ? l . , J J J ? ' L - ' L L 'L 0 J ^ - ^ ^ " L ^ L L . 'L . ^ ^ ^ ^ ^ L 'L . 'L 'L V ^ ^ L L ^ / L L ' . ' ' O j J ^ J ^ ^ V ' ' ' — ^ ^ ^ ^ " ■ l V L , L » ^ Y # / / f / l , / « / l V N ^ M ^ ^ , * , / f ( l V r t \ L V ^ £ £ £ £ L . . . \ , \ . . ' £ £ £ £ £ L " L L . . . ' ! ■ ! ■ ! ■ L - L - L ^ L " L L — IL ^ L . - . - T L L . L. L ^ L L L L . V i . £ £ • . £ £ £ £ L L L L V ^ ^ ^ ^ L . L .L L L L L L L L V ^ ^ - ^ L . L .L . L L L L L L . - . - T - - . - . - . L L. ' L L L L - . L L V - . - . - . - . - . L. . L ■ L L L L L L V « J - T - T - T L. L. L. L ^ L ' L M
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^ L l ■ | L - L - L - L " b ^ ^ T ^ ^ ^ ^ ^ T A T * ^ r r r * " r t ^ ^ ^ ^ T A T ^ * £ L - L - ! - ! ££££"£ L" L ' L ' L ' L ' — £ £ £ £ L" L ' L ' L ' L . — £ £ L_ £ L_ L ' L ' L ' L . L L . £ £ L_ L_ L L ' L ' L . L . . . ' £ £ £ L_ L" L" L" L L ' L . . - . L . L̂ L L ' L_ L L ' L ' L - . . — - . L I ^ L" L L ' L ' L . . — - . - . - . - . L L L L" L L L L . L V » . . L . - . L̂ L̂ . L. L . ' L ' L L L ' L . V - L L L. L. L, L_ L ^ L " L ' L ' L ' L V » V _ ^ i t L ' L " L" L L L L ' g ^ ^ f c ^ | ^ L - L - L - L ' L L L L L̂ L̂ L" L" L" L" T L ' L ' L ' £ £ £ £ £ f £~ ^ \ W ' ' £ £~ £ £~ L W ' L . » » L̂ £ £ £~ £~ £■ L ■ L ' L . L . £ £ £ £ f f L ■ L" L ■ L ■ » » . ■ i - £ £ f f f L" L" L ■ L ■ L . . I £ L" £ f f L ^ L " L ■ L . L . » » L̂ L̂ L" L" L" L" L L ' L ' L . » » / L̂ L̂ ' ^ L" L ' L ' L L ' L . - . - . — L . L̂ L^L_ L^L_ L . ' L . . . » L L . L̂ L L L — L ' L ' L . - . - . . L̂ - L L . " L_ L_ L ' L ' L ' L L . - . . - . L̂ L . L_ L_ L ^ L ^ ^ ^
^ f c J ^ ^ l - - L - L L L ' ' ' ' ' £ £ £ I " ' ' | _ ' ' ' £ £ £ | - L - L L - L L L ' ' ' ' | | ^ L" L" L ' L ' L ' L ' L ' £ £ £ £ £~ £ L ' £ £ L | £ L - L - ' L - L L . . ' £ £ £ £ £ L - L - ' L L L L ' £ £ £ £ £ L - L - L - L L L . . . . . £ £■£ L - L L L - L L L . £ £ £ £ " £ L - L - L - L - L L L . L . — V ) L" £ L" L ' L" L" L" — L . — £ £ L . L_ L" L L L p f L . . . . ' L . £ £~ L ' L ' L — L^» L̂ L̂ ' " L_ L_ L" J g ^ T
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t
4 /
An instrumentation set-up for resonance dwell testing, using an accelerome-ter as the response transducer.
* * *
Introduction Many types of structures, mechani- overcome by modern instruments such the 1050, adjusting the generator fre-
cal components, and material speci- as the Brtiel&Kjaer Vibration Exciter quency until the phase shift is again mens are required by industrial and Control Type 1050. The 1050 incorpo- ±90°. military standards to undergo fatigue rates high-resolution drift-free fre-testing. One common fatigue test is quency control, as well as extremely The resonance dwell system is called resonance dwell testing. This is stable vibration and force control. shown in the opening figure. In this used to test an object continuously at system, the force and acceleration sig-a particular resonance. In principle, In particular, in lightly damped test nals are supplied by a Force Trans-this would seem to be a simple task: objects, the problem of a varying reso- ducer Type 8200 and an Accelerome-the frequency and level controls of a nance frequency can be particularly ter Type 4384, respectively. These sig-vibration exciter system should be ad- troublesome. It can be solved only if nals are compared in the 5885. The justed to excite the test object at the the resonance conditions are accurate- output of the 5885 is supplied to the required stress level, at the desired ly monitored, and the excitation fre- 1050, forming a feedback loop which is resonance. However, in practice, reso- quency is adjusted accordingly. used to lock the generator frequency nance dwell testing puts a number of to the varying resonance frequency. demands on the instrumentation. The The Resonance Dwell Unit Type resonance frequency of the test object 5885 has been designed to solve the Occasionally, the engineer may changes due to progressive fatigue, problem associated with a varying res- want to maintain a phase shift other and for example, temperature effects onance frequency of the test object. At than 90°, for example, if either one of on the internal damping. resonance, the phase angle between the transducers introduces a phase
the input force and the response accel- shift. The addition of a selectable , eration is ±90°. A small change in phase-shift stage (option WH2122)
o O l v m g t l l G p r o b i G m S frequency results in a large change in * ensures operation under such condi-the phase angle. When the phase shift tions.
Problems associated with frequency between these signals changes, the ' and output-level instability have been 5885 activates the frequency sweep of
*• *. *
BO 0250-11 /
*
Alternative response transducers
For lightweight test objects, the addition of any mass, even that of a very small accelerometer, cannot be tolerated. A non-contact means of measuring the response is essential to prevent detuning the test object.
A Capacitive Transducer MM 0004 measures vibratory displacement without making physical contact. It is well suited to many types of beams, diaphragms and panels. It is used with a microphone preamplifier to provide a signal to the Type 5885. Figure 1 illustrates such an instrumentation set-up.
Since acceleration and displacement are 180° out-of-phase, they will both exhibit a 90° phase shift at resonance. Consequently, they are equally suitable for use with the the Type 5885.
Velocity signals can be used in some applications, but since the phase shift at resonance is not 90°, option WH2122 must be used.
The Laser Velocity Transducer Type 3544 is another example of a non-contact transducer which can be used to detect the resonance. It incorporates an integrator to produce a displacement signal, which can be used directly with the Type 5885.
Alternative force signals The level of input force to the test
object is measured and kept constant by the 1050. The force signal is also used as an input to the 5885. In the systems shown, the force signal is generated by a Force Transducer Type 8200. The force transducer is connected directly to the test object, and via a push-rod to the vibration exciter. For measurement of large forces, Force Transducer Type 8201 is available.
In some applications, it may be advantageous to obtain a force signal by other means. Since the force generated by a vibration exciter is proportional to the current through the driver coil, a driver-coil current signal may be used to measure and control the
Fig. 1. An instrumentation set-up for resonance dwell testing, using an optical response transducer, and a Slave Filter Type 5888.
V
force. Briiel&Kjaer power amplifiers, O o n t r o l HCCWVRCV such as the Types 2707 and 2708, pro- y
vide output signals proportional to the T h e r e s o n a n c e d w e l l u n i t t m c k s t h e driver coil current. p h a g e ftt r e s o n a n c e t o w i t h i n ± 5o
Consequently, there can be a small C* 1 -P'lf ' " difference between the detected reso-Olglldl lllieilllg nance frequency and the true reso
nance frequency of the test object. The system in Figure 1 includes the However, this is of little importance
Slave Filter Type 5888. The 5888 is a g i n c e t h e 5o p h a s e d e v i a t i o n c o r r e „ two-channel filter used to remove s p o n d s t o a n a m p i i t u d e deviation of noise and distortion from the force o n ] v Q 0007 and response signals. Although the inclusion of the slave filter is not essen- T h e d e v i a t i o n f r o m t h e r e s o n a n c e tial to the operation of the resonance f r e q u ency is dependent on the damp-dwell unit, its use eliminates signal i n g a s w e l l a s t h e r e S 0nance frequency, harmonics, and improves resonance a n d c a n i n m o g t c a g e b e i g n o r e d > F o r detection and tracking accuracy. example, for a test item with a Q of
100 and a resonance frequency of A , , • j • o 100 Hz, the maximum error would be Automatic stopping or 4omHz. the test
Often it is necessary to stop the test . Conclusions after a pre-set change in the resonance frequency, for example, before a crack The Vibration Exciter Control Type has occurred. By appropriate selection 1050 plus the Resonance Dwell Unit of the sweep limits, the test can be set Type 5885 constitute a fatigue-test-to automatically stop at a pre-defined ing-at-resonance system, by adjusting frequency. The Vibration Exciter the excitation frequency, according to Control Type 1050 can set safety lim- changes in the resonance frequency of its around the excitation level, which the test structure. in combination with the sweep limit, provides a complete safety window for the test.
