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The problem of zero error of inductive sensor


When an inductive sensor is located in the middle position, the output of the bridge should be theoretically zero, but in fact, there is always a zero -position unbalanced voltage output (zero -position voltage), resulting in zero errors, as shown in Figure 3.13 (a). Excessive zero -position voltage will make the amplifier saturated in advance. If the sensor output is used as a control signal for the servo system, the zero voltage will also cause the servo motor to heat up and even generate zero misunderstandings. The composition of zero voltage is very complicated, as shown in Figure 3.13 (b). It contains Kishe and high -second harmonic.

The problem of zero error of inductive sensor

The main reason for generating the base wave component is that the electrical parameters of the two coils of the inductance sensor and the asymmetry of the geometric size, and the electrical parameters of the two arms of the bridge are inconsistent. Because the perioli component of the base wave can be eliminated by adjusting the location of the street iron (deviating from the mechanical zero), it usually pays attention to the orthogonal weight of the Kobo.

The main reason for the high harmonic component is the non -linearity of the magnetized curve of the magnetic material. At the same time, due to the stagnation loss and the asymmetry of the two -coil magnetic circuit, some high -number harmonic components in the two coils are different. So there was a high -number harmonic wave with zero voltage. In addition, the high -order harmonic waves contained in the incentive signal and the interference of the external electromagnetic field will also produce high -dimensional harmonics.

We should reasonably choose magnetic materials and incentives to make the inductive sensor work in a linear area of ​​a magnetized curve. Reducing the harmonic components of the incentive current and the use of the shell for electromagnetic shielding can also effectively sincerity.

One commonly used method is to use compensation circuits, and the principle is:

(1) Candid resistance to eliminate the zero -position voltage of the base wave;

(2) Parallel resistance to eliminate high harmonic zero voltage;

(3) Plum and connect capacitors to eliminate the orthogonal or high harmonic components.

The problem of zero error of inductive sensor

Figure 3.14 (a) shows the typical connection of the above principles. In the figure, R is used to reduce the orthogonal measurement of the base wave. The role is to make the effective resistance value of the coil equal to the same size. The size is about 0.1 ~ 0.50. RB is used to reduce two or three harmonics. Its role is to divert the working point of a coil (connected to A, B or B, C) to change the working point of the magnetized curve. KQ. Capacitor C is used to compensate the asymmetry of the secondary coil of the transformer, and its value is usually 100 ~ 500pf. Sometimes in order to manufacture and adjust the convenience, you can add-the C and D-potentiometer R, and use the difference between R and RA to compensate the Kiba orthogonal measurement. Figure (b) shows the actual compensation circuit of a sensor.

Another effective method is to use an external measurement circuit to reduce the zero voltage. As the aforementioned phase -sensitive detection circuit, it can effectively eliminate the orthogonal component of the base wave and the occasional harmonic component, reduce the bi -number harmonic component, and reduce the zero voltage of the inductive sensor to very small.

In addition, the magnetic circuit adjustment mechanism (such as the adjustable end cap) can be used to ensure the symmetry of the magnetic circuit to reduce the zero voltage.