Lord MicroStrain G-Link-LXRS, User Manual

Page: 41 / 71

G-Link
®
-LXRS
®
Wireless Accelerometer Node
User Manual
Sensor Settings and Operation
41
6.4 Operational Considerations
6.4.1 Measurement Range
The accelerometer bandwidth limits the range of frequencies that can be measured. As the
measured vibration frequency approaches the upper bandwidth limitation of the
accelerometer, the accelerometer sensitivity decreases. The result is a predictable
reduction in the measured vibration amplitude when measuring beyond the bandwidth limit.
The bandwidth limitation is indicated in the node specifications ( see Specifications on page
58 ).
The low pass filter cutoff frequency setting ( see Channel Configuration on page 16 ) limits
the measured readings that will be reported based on the frequency of the signal.
Frequency readings above the selected setting will decrease in amplitude, just as with the
accelerometer bandwidth limit. For best performance select a cutoff frequency that is no
more than half of the sample rate. For example, if the target measurement is 100 Hz, and
the sample rate is set to 500 Hz, set the cutoff frequency between 100 Hz and 250 Hz.
6.4.2 Node Sampling Rates
The G-Link
®
-LXRS
®
is capable of sampling up to 4096 Hz . For measuring vibration it is
recommended to use a sample rate at least twice the value of the target frequency. This is
the minimum sample rate required to produce an accurate digital representation of the
measured signal. For example, if the target measurement is 100 Hz, the sample rate should
be set to 200 Hz or higher.
While the G-Link
®
-LXRS
®
is capable of high sample rates and high resolution conversions,
the integrated accelerometer may limit performance in certain circumstances. For example,
even though the G-Link
®
-LXRS
®
can sample up to 4096 Hz , the integrated accelerometer
(in the standard configuration) only has a bandwidth of500 Hz. Setting the node to sample at
4096 Hz would result in oversampling by a factor of about 8 , which is well over typical
practices. Oversampling by a factor of 4 times is enough for most applications.
6.4.3 Gravity Offset
During data acquisition it is normal to see up to -1 g offset due to the effects of gravity on the
sensor axis ( Figure 32 - Gravity Offset ). For more information on the sensor reference frame
see Sensor Frame on page 30 .