Page 327 - Introduction to Marine Engineering
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Instrumentation and control 301
Alternating current positioning motors can be used as transmitters
when arranged as shown in Figure 15.27. Both rotors are supplied from
the same supply source. The stators are star wound and when the two
rotor positions coincide there is no current flow since the e.m.f .s of both
are equal and opposite. When the measured variable causes a change in
Transmitter
Figure 15.27 A.C, positioning motors
Measured variable
pressure signal
Beam
Feedback
force
L
Pfrf J U- Variable inductor / \ Pivot ~pinS^ {
t
Electromagnet
Oscillator L__ Output
amplifier
a.c. supply
Figure 15.28 Force balance electronic transmitter
