1. Is an initial stress required?
HBM has two different piezoelectric force transducer designs available:
The CFW force washers and the CFT force transducers.
The CFT force transducers are calibrated and are delivered with test certificates. As these force transducers are already pre-stressed internally, they are suitable for immediate application. Renewed calibration of the measurement chain is not necessary.
The CFW force washers are significantly flatter in design and are not pre-stressed. Pre-stressing is required when mounting.
These transducers must be calibrated when in a mounting condition.
The pre-stressing of the force washer is necessary to ensure the linearity and structural durability of the transducer.
This pre-stressing means that another mechanical element is mounted parallel to the force transducer.
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 initial stress.
A part of the measuring force is now shunted through the pre-stressing element. Pre-stress and force shunt are determined by the installation situation. It is therefore necessary to calibrate the force washers after mounting is complete, i.e. to compare the output signal of the transducer with a known force. The accuracy of the measurement results depends here mainly on the accuracy of the calibration.