Annex
9323A_002-476e-11.24 Page 73
In their dynamic behavior, piezoelectric sensors are superior
to all other measuring methods. Their high rigidity results
in the highest possible natural frequencies. Piezoelectric
sensors are thus ideal for measuring measurands which
change rapidly over time. Their dynamic behavior is
thereby largely determined by the surrounding structure.
Therefore the frequency response of the entire measuring
arrangement must be investigated for the largest possible,
useful measuring range.
There are two possibilities here:
Frequency analysis
The measuring arrangement is stimulated e.g. with an
impulse hammer and the sensor output signals then
subjected to a frequency analysis. The results is presented
in terms of an amplitude and phase response curve
FEM
Finite Element Method: Finite Element Method (FEM) is a
numerical procedure for the approximate solution of
differential equations having boundary conditions. Using
the FE-Method, various problems from physical areas can
be calculated. A computing field obtains an arbitrary
number of elements, however, being finite in size and
number.
Note: In the finite element method, a homogeneous body
is substituted for the sensor closely approximating to the
dimensions and average density of the sensor. The average
modulus of elasticity of this equivalent body is then
continuously varied until its natural frequency coincides
with that of the actual sensor (technical data). An
equivalent body defined in this way is usually a good
approximation of the sensor. The equivalent substitute
body is inserted into the structure to be simulated, and by
this means the natural frequency of the structure is
calculated. Using this procedure, the FEM can be used to
determine the frequency behavior of a measuring
arrangement with good approximation
10.5 Influence of temperature
Temperature changes during a measurement result in an
error signal in the form of a zero drift. In critical
applications, we recommend that protection be provided
for the sensor as far as possible against changes in
temperature.
Temperature error of the zero point (static error)
Temperature error [unit of the measurand/°C] is the
greatest change to the output signal in a specified
measuring range after a specific sensor temperature
change, following which the sensor is again in thermal
To Next Page
Loading...
