Measurement circuit and measuring method of LVDT (Linear Variable Differential Transformer)

Abstract

The invention discloses a measurement circuit of an LVDT (Linear Variable Differential Transformer). The measurement circuit comprises a sinusoidal pulse width modulator, a signal conditioning circuit, a linear variable differential transformer, a first sampling circuit, a second sampling circuit and a controller; the sinusoidal pulse width modulator is used for outputting pulse width and frequency-adjustable rectangular wave signals; the input end of the signal conditioning circuit is connected with the sinusoidal pulse width modulator; the signal conditioning circuit outputs amplitude and frequency adjustable sinusoidal wave signals; the primary coil of the linear differential transformer is connected with the output end of the signal conditioning circuit to receive the sinusoidal wave signals as LVDT excitation signals; the secondary coil of the linear differential transformer outputs LVDT differential signals; the input end of the first sampling circuit is connected with the primary coil; the input end of the second sampling circuit is connected with the secondary coil; and the controller is connected with the output end of the first sampling circuit and the output end of the second sampling circuit and is used for performing amplitude normalization processing to output an LVDT linear position. With the measurement circuit of the LVDT, relatively complicated analog circuit parameter adjustment is avoided, zero-point residual voltage, phase drift and sensor nonlinearity can be effectively compensated. The measurement circuit has the advantages of high stability and can reduce measurement errors.

Description

Technical field [0001] The present invention relates to the technical field of LVDT measurement. More specifically, the present invention relates to an LVDT measurement circuit and a measurement method thereof. Background technique [0002] A linear variable differential transformer (LVDT) is a linear displacement sensor, which is constructed as a differential transformer and includes a barrel-shaped primary coil, two sets of secondary coils, and a nickel-iron alloy iron core. The iron core is a moving part, and its position affects the magnetic field coupling between the primary and secondary windings. The ends of the secondary coils with the same name are connected together, and the output signal is the difference between the signals of the two coils. When the primary coil has an AC excitation signal, the amplitude and phase of the output AC differential signal from the secondary coil reflect the linear position of the iron core. The principle of RVDT (Rotary Variable Differe...

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Problems solved by technology

However, this type of analog measurement circuit usually has the following disadvantages: 1. The circuit is composed of analog devices, and the parameters of the analog devices are cumbersome to adjust, and it is easy to introduce errors and drifts; 2. When the iron core is at zero, theoretically, the coupling to the secondary The magnetic flux of the primary coil is the same, so the differential signal of the secondary output is zero; in fact, due to the imbalance of the coil, parasitic capacitance, leakage resistance and other reasons, there will be a zero residual voltage; a compensation circuit can be introduced to eliminate the zero residual voltage, At the same time, nonlinear errors will be introduced near the zero point; 3. The demodulation circuit needs the output of the reference oscillation circuit as a reference signal. When the sensor output is in phase with the reference signal, the demodulation circuit can work well, but each link in the signal chain There may be a phase shift, and an analog phase adjustment circuit needs to be introduced to compensate for the phase shift in the signal chain. At the same time, there are also problems of poor compensation accuracy and drift, and the adjustment is cumbersome; 4. The LVDT sensor depends on its structure, and there will be certain nonlinearity. Especially when it is close to the full scale, the output signal has a roll-off, which will affect its effective measurement range; a nonlinear correction circuit needs to be introduced, and in an analog system, there are also problems such as poor correction accuracy, drift, and cumbersome adjustment.

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