HBM CMD Serie Bedienungsanleitung Seite 69

Tips for piezoelectric measurement technology
The pre‐stressing of the force washer is necessary to
ensure the linearity and structural durability of the sensor.
We recommend that the force washer is pre‐stressed to
at least 10% of its nominal (rated) force. The force
washer itself can be used to determine the pre‐stressing
force.
The sensitivity of the measuring chain changes, depend­
ing on the design used to generate the pre‐stressing
force. If HBM CPS pre‐stressing sets are used, the sen­
sitivity of the CFW piezoelectric force washer is reduced
by 7 to 12%. So for reliable determination of sensitivity,
the force washers must be calibrated after mounting.
Calibrating by means of calibrated force transducers
One way to calibrate the sensors is to use calibrated
force transducers. An amplifier is required, as well as a
force transducer. Reference force transducers based on
strain gages, such as the C18 or Z30a series, are ideal
for this. Force transducers for industrial applications,
such as the S9M from HBM, can also be used. If a rele­
vant amplifier for sensors based on strain gages is not
available, you can also use CFT‐series sensors.
When choosing a reference transducer, make sure that
the accuracy that can later be achieved is no better than
the precision of the calibration process determined by the
accuracy of the reference measuring chain.
Calibrating the measuring chain in three steps
As already mentioned above, a measuring chain that is
to include the (CFW) piezoelectric force washer as sen­
sors must always be calibrated when the sensor is
mounted. This means that once calibration has taken
place, the mechanical mounting conditions must not be
changed in any way. This particularly applies to
pre‐stressing.
CMD 67
A2781-3.1 HBM: public