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Is there any reason one might want to measure both the primary and secondary coils on an LVDT? I assume the primary coil excitation voltage would be constant, but I see circuits around that measure both for some reason.

Thanks in advanced

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Is there any reason one might want to measure both the primary and secondary coils on an LVDT?

To get better accuracy is the usual reason. The amplitude is somewhat subject to noise perturbations so, if you also measure the phase angle between primary and secondaries you get a more reliable result. To do that you need to know what the primary wave form is. This is normally done by gating each secondary signal with the primary signal (converted to a square wave) and this produces a superior signal to noise ratio than just measuring amplitude directly. In effect the receiver uses synchronous demodulation to obtain the two amplitudes.

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  • \$\begingroup\$ As an 'unusual reason', I have had the misfortune of interfacing a multichannel LVDT conditioning system where the common excitation circuit was affected by lvdt loading, producing load/signal dependent output(s). The situation the OP describes could mitigate that issue. \$\endgroup\$ Feb 3 '20 at 16:03
  • \$\begingroup\$ @Jaywalk have we finished with this now or do you wish to ask further questions? \$\endgroup\$
    – Andy aka
    Feb 20 '20 at 18:56

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