BRUEL & KJAER 2694A, Руководство пользователя

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CHAPTER 4
The Use of Control Software BZ 5291
17
The Amplifier Setup menu has a main parameter line where you can choose High-
pass Filter , Optional Filter , and Output Sensitivity .
Use the cursor to select the desired channel after you have selected the parameter
option.
High-pass Filters
: For choosing the high-pass filter option, i.e., the lower limiting frequency for
the input channel in question, the cut-off frequencies are –1 dB down for DeltaTron/
voltage inputs. Alternative, high-pass filters are available upon request with a maxi-
mum of 6 high-pass poles or 8 low-pass poles, with a maximum of 8 poles in all.
The high-pass filter cut-off frequencies and attenuation slopes for the DeltaTron/
voltage inputs are 0.1 Hz (40 dB/dec.) and 1.0 Hz (40 dB/dec.).
In general it is best to set the lower limiting frequency as high as possible (without
affecting the desired measuring range) in order to reduce environmentally induced
low-frequency noise and to reduce the settling time of the filters.
Optional Filters
: If fitted, you can select the optional filters shown in Table 4.1, depending on the
type of input module.
Single Integration : The acceleration signal is integrated once to provide a velocity
output signal. This is the instantaneous vibration velocity magnitude.
Double Integration : The acceleration signal is integrated twice to provide a displace-
ment output signal.
In order to increase the signal-to-noise ratio of the measuring instruments in the
vibration measurement chain, you can use the parameter which yields the flattest
frequency spectrum. For broadband (wide frequency content) measurements on ro-
tating machines, the velocity parameter is found to be the best in 70% of all cases;
acceleration in 30%. Displacement parameters are sometimes used for measure-
ments of low frequency and large displacement vibrations often encountered on
structures such as ships, buildings, bridges and heavy machinery.
Note: When complex signals such as shocks and impulses are measured, velocity
and displacement parameters should not be used as they introduce phase errors,
resulting in serious amplitude measurement errors.
Table 4.1
Typical uses of optional
filter types. All optional
filters can be used with
any type of input if
required. Other filters
are available upon
request
DeltaTron/Voltage Input Part Number
A-, B-, C- and D-weighting ZE 0847
Single and double integration ZE 0848
Hz
BE164411.book Page 17 Friday, May 18, 2001 11:51 AM