Inductor thickness measuring circuit

Circuit composition The inductive thickness measurement circuit consists of a bridge type phase-sensitive
detection measurement circuit, as shown in Figure 6-23. In the figure, the inductors Li
and Lz are the two coils of the inductive sensor, which are composed of L+ and L2. There are
two adjacent bridge arms of the bridge. The other two bridge arms are C2 and G. The diagonal output terminal of the bridge
circuit consists of VD1-VD4 and additional resistors Ri-R4
to form a phase-sensitive rectifier, and the current is indicated by the ammeter PA. RP1 is
the zero adjustment potentiometer, and RPZ is used to adjust the full scale value of the ammeter. The bridge
power supply is supplied by transformer T. T uses a magnetic saturation regulator,
and C- and C4 play a filtering role.
    (2) Circuit working principle When the armature in the inductive sensor is in the middle position. Li-L2, the bridge is balanced, Uo-Ud,
no current flows in the ammeter PA.
    When the thickness of the tested piece changes, L. ≠k, there are two situations at this time:
    1) If Li>Lz, no matter what the polarity of the power supply is at the moment, the potential at point d is always higher than the potential at point c, and the pointer of the ammeter PA
deflects in one direction.
    2) If Li<Lz. The potential at point c is always higher than the potential at point d, and the pointer of PA deflects in the other direction.
According to the deflection direction and scale of the pointer of the ammeter , the displacement direction of the armature can be seen, and the thickness change of the measured part can be calculated at the same time.