BRUEL & KJAER 2305 - Automatic Recording of Frequency Characteristics

Strain Gage Apparatus Type 1516 in strain gage measurements a special
output terminal facility on the apparatus can be utilized for this purpose.
The dynamic signal may be directly analysed, or it may first be recorded
on a tape recorder and afterwards analysed. A measuring arrangement for
analysing dynamic signals from the strain gage bridge by the la tter method
is shown in Fig. 6. 11.
Fig. 6.11. 111 easuring equipment employed to frequency analyse the dynamic
strain signal recorded on a tape.
The frequency spectrum obtained from measurements made on the dynamic
stress of a connecting rod in a one cylinder four-stroke combustion engine
is shown in Fig. 6.12. To keep all the frequency components within the
range of the analysing equipment, the tape was played back with a 10 times
higher speed than when originally recorded. The different magnitudes are
given in dB relative to 15 .uStrain.
o [J COD 0 00 a 0 0 0 0 0 0 0 0 0 0 0 0 000 [] 0000 0 0 0 0 0 0 0 0 0 0 aDD 0 0 0 0 0 0 CJ [J 01
::::d:ll llliilll"1~:1
9S0rpm illS .OJ
ynlaq:led
z..L .. J~S-s,.: ...1... 10 JO
L u.. ,.,-=- .... ""' --=-
....... ~o-J.2:kti)o' "
w..s..l.O.O...-"",, __
1.oct.:B.M.S-.r-s.. . ~a 0 100 1000 I000O :aoooo cI> _" ! ,~ u..
QP 0123 10 100 1000 10000 tll ~/:nn1 A ......
Fig. 6.12. Spectrogram of dynamic strain in the connecting rod of
a combustion engine.
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