Figure 2-8.
Simplified balance network
m. When a DC voltage from the thermocouple and the reference supply is
applied to the galvanometer circuit (fig 2-9), the magnetic modulator (T2) produces
a 5 kHz output containing magnitude and polarity information relative to the input
DC.
This 5 kHz signal is then applied to a tuned carrier amplifier where the
signal is amplified and undesirable frequencies are attenuated. The tuned carrier
amplifier output is then fed to the synchronous demodulator. The demodulator is a
balanced demodulator that has no output when no signal is applied. The push-pull
oscillator and frequency doubler generates a 2.5 kHz signal that is fed to the
magnetic modulator and a 5 kHz signal that is fed to the synchronous demodulator.
With DC applied to the input of the magnetic modulator, a DC current flows through
the meter which is proportional in magnitude and like in polarity to the input DC.
Figure 2-9.
Galvanometer block diagram
28
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