HBM PACEline CMD600 Manuel D'emploi page 38

38
CMD600
The two piezoelectric quartz rings are surrounded by an enclosure of two
metal half shells. The coaxial plug on the left has external contact with the
enclosure and internal contact with the charge discharge between the two
washers.
Cross-section through a force washer
The charge present on the outer surface of the crystal is picked up by
electrodes and processed by a charge amplifier into a voltage or current
signal.
The sensitivity of piezoelectric force sensors is given in pC/N. The output
signal can be calculated by
Q = d * F
Where F [N] is the applied force, d [pC/N] the sensitivity of the sensor used
and Q [pC] the electric charge that represents the useful signal of the sensor
caused by the applied force.
NOTE
Piezoelectric sensors always need to work with an initial stress.
The sensitivity of the force sensor is determined by the piezo material used
and independent of the measuring range. Sensors in the same series (e.g.
CFT/50kN ... CFT/120kN) output approximately the same amount of charge
for a specific force. Differences are explained by the type and construction of
the initial stress which represents a force shunt. This is necessary to achieve
good linearity and hysteresis properties.
A2781−2.1 en/de/fr