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1.5.2 Function of Piezo Measuring Transducer
The measuring transducers (MP25 / MP200 / MS25 / MS10) have piezo-quartz measuring
cells integrated. Because of the preloading of the cell during manufacturing, the emitting
electrical load (Coulomb) is determined. Since different cell sizes are available, the emit-
ting electrical loads of the transducers are different.
The engraved calibration values on the transducer define the emitted load (Coulomb) per
Newton - Meter (Nm).
i.e. if a force of 1 Nm is put to the measuring cell, a load is emitted, which is defined by the
calibration value.
Example for the calibration value: 172 pC / Nm
1 pico Coulomb = 0.000 000 000 001 C
The measuring electronic has a charge amplifier integrated, which transforms the emitted
electrical load from the transducer into an electronic voltage. The voltage depends on the
integrated capacitor, which is on the measuring input. i.e. at a range capacitor of 1000 pC,
a load of 2000 pC is converted into 2 V. Each measuring range is rated to +/- 5V.
1.5.3 Drift (Piezo Measuring Transducers)
A characteristic of the charge amplifier is the drift. This drift is caused by the input-
resistance of the input-transistor. Through this input-voltage, the charge amplifier drifts into
a positive or negative direction. Therefore, it is important, to start the measurement imme-
diately prior to the screw driving.
1.5.4 DMS-Bridge
The electrical resistance of each strain changes when deformed. The cause of this defor-
mation may be power, pressure, torque, deflection, angle, etc. The resistance of the de-
formed DMS (strain gauge) consists of its basic resistance R (no load) and the consequen-
tial occurring resistance-change R.
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