User's Manual

HVM200 Manual Transducer Selection 1-3
The HVM200 could also be utilized
through an alternative direct input.
This would require, however, the use
of some kind of external signal
conditioning unit such as an external
source of ICP power, or an external
charge amplifier.
• Charge mode sensors output a high impedance, electrical
charge signal that is generated by the piezoelectric
sensing element. This signal is extremely sensitive to
corruption from environmental influences. To conduct
accurate measurements, it is necessary to condition this
signal to a low impedance voltage before it can be input
to a readout or recording device. A charge amplifier or
in-line charge converter is generally used for this
purpose.
Transducer Sensitivity
With accelerometers, the proper sensitivity depends on the
application being performed. If the application is a high
vibration level application, a low sensitivity should be
selected. For low vibration level applications, a high
sensitivity accelerometer should be used.
Transverse sensitivity may also affect measurements. It is
defined as the unwanted output signal of a motion sensor
when subjected to motion perpendicular to the sensitive
axis. This is usually expressed as a percent of the normal
axis sensitivity. For example if you are using a tri-axial
accelerometer and place an input signal on the Z axis, your
X axis could also be reading a level even though there is
really no x-axis signal present.
Resonant Frequency
The resonant frequency is defined as the frequency at which
the structure will readily vibrate. For accelerometers, there is
one frequency at which the accelerometer vibrates much
easier than at other frequencies. At this point, the reading
will be very high, and could overload the input of the
HVM200. However, for most of the recommended
accelerometers, the resonant frequency is well above the
upper limit of the HVM200, and will subsequently be
masked out by the low pass filter on the HVM200. If the
resonant frequency becomes an issue, it is recommended
that an external mechanical filter be used.
Frequency Range
Most recommended accelerometers will have a frequency
range sufficient for use with the HVM200. Refer to the