Measurement Computing eZ-Record rev.2.1 - Manual (Page 40)

40
eZ-Record Manual January 2001
Note: Transfer function displays assume the reference channel is a force
channel. You MUST define the response channels to be the correct type of data
(acceleration, velocity, or displacement) that you are acquiring. Define these in
the data type column of the Calibration window. This allows the data to be
integrated or differentiated correctly to derive the desired transfer function.
O
CTAVE
T
YPE
Many sounds, including audible noise for a transmission line, are broad band,
having components that are continuously distributed over a range of frequencies.
The spectrum of such a sound can be approximated in terms of a series of octave
band or one-third octave band pressure levels. A band is designated by its
center frequency, f
0
, which is the geometric mean of the upper and lower
frequencies of the band. (See ANSI/ASC S1.6-1984.)
Open Octave Menu: Press “D” + “O”.
Use the down arrow key to highlight your selection and press “Enter”.
Full: An octave band extends from a lower frequency, f
0
2 to twice the lower
frequency ( 2f
0
).
Third: A one-third octave band extends from a lower frequency ( f
0
/ 2) to
3 2 times the lower frequency ( 6 2 f
0
). The Octave (one-third octave)
band sound-pressure level is the integrated sound-pressure level of all
spectral components in the specified octave or one-third octave band.
I
NTEGRATION
/D
IFFERENTIATION
Open Int/Diff Menu: Press “D” + “I”.
Use the down arrow key to highlight your selection and press “Enter”.
This is for display purpose only and does not modify the data.
Differentiation/Integration is only active when frequency domain data is
displayed. Select single or double integration, single or double differentiation
or none. Make your selection on the popup menu.
Differentiation and Integration are calculated by dividing each element of the
function by (jw)^n, where j is the square root of -1; w is the product of 2 pi
times the frequency of the block element; and n is an integer from +2 to -2.
n = 2 is double integration
n = 1 is single integration
n = 0 has not effect
n = -1 is single differentiation
n = -2 is double differentiation.