Description Of Operation - HBM MC2A Manuel D'emploi

9
MC2A
2

Description of Operation

The measuring amplifier type MC2A completes inductive HBM transducers to
a simple measuring arrangement. It has two main purposes.
The measuring amplifier provides a supply voltage for the inductive half
bridge. The signal from the connected transducer is converted into a propor-
tional D.C. signal.
A pair of precision resistors connected to the wheatstone bridge completes
the inductive half bridge arrangement. The generator G provides a symmetri-
cal bridge excitation voltage of 1.8 V (effective value) with a carrier frequency
of 5 kHz.
The mechanical quantity results in a transducer output signal being propor-
tional to the measured value, which passes to the carrier frequency amplifier
TF via the input amplifier EV.
The screw driver potentiometer P 21 serves to balance the zero output signal
of the transducer. Depending on the selected measuring range (switch S 21)
the measurement signal will be amplified more or less. The screw driver po-
tentiometer P 22 serves to adjust the gain continuously in a given range
(range fine adjustment).
The signal is lead from the carrier frequency amplifier to the phase controlled
demodulator D. The demodulator being switched with the generator frequency
demodulates the measurement signal with correct phase. Thus an unambigu-
ous reference of the sign (polarity) between measurement signal and output
signal is obtained. A measuring frequency range of 0−100 Hz is produced
when a Butterworth Low Pass Filter is used. The demodulator is phase de-
pendent and consequently the reference phase must be matched to the trans-
ducer signal. This can be achieved by adjusting potentiometer P 25. The recti-
fied signal is amplified in the differential amplifier DV by a factor of 2.5 to an
output signal of " 5 V (in relation to negative).
With the addition of an optional final stage the mode of operation can be
changed so that the final signal is either a voltage or a current output. The op-
erator can then choose between a voltage of max. 5 V or a current from 4 to
20 mA using switch S 22.
The output signal from the differential amplifier DV does not only depend on
the option described above but also on the limit switch GR. The latter can be
adjusted with potentiometer P 23 between 0 and 5 V. If the signal exceeds the
set voltage a transistor is activated via the Open Collector output providing a
max. voltage of + 28 V and a max. current of 50 mA.
A1974−2.2 en/de/fr
HBM