位移传感器

Constant current source two-way charging

Measuring inductor inductance value can be completed in a few seconds, but to make it inductive sensor, the inductance long-term work in a direction of excitation, will appear remnant magnetization and affect the performance of the sensor, more over positive journey and reverse journey are variation considerably.
Measure inductance value of the test circuit
Measuring the displacement of the test design

The test design by measured the displacement as shown in figure below. Homemade coil and skeleton, the coil single around is 160 turn, the long is 20mm. Magnetic bar diameter 8mm ,long 30mm, with strong adhesive in the micrometer mobile stem.
Constant curre inductive displacement sensor
Foreword

Inductive displacement sensor is a kind of the metal induced linear device, switch on the power, in the switch of the induction surface will not generate an alternating magnetic field, when the metal objects close to the induction surface, the metal is generated eddy current and absorb the oscillator energy, make the oscillator output amplitude linear attenuation, and then based on the attenuation changes to complete without contact with the purpose of testing object.

Put this formula in SCM (Single Chip Micyoco )in the final test data, such as shown. In order to calculate the convenient, unit is s (microsecond), test of micrometer accuracy is 10 s , we can see that the errors caused by nonlinear is not uniform. Positive and negative error distribution is more appropriate.
Conclusion

Through the test shows this method can be used to design inductive displacement sensor. Because this method has no need of high frequency sine excitation, and can measure the smaller inductance value, so design the sensor can reduce coil and consideration of different structure.
Inductive Displacement Sensor
Principle of Measurement

To be used the switch circuit with constant current source circuit to charge the electrical inductance. Only after diode discharge measurement inductance value principle as shown in figure shows.
sensor coil inductance value and displacement relationship curve
Test data analysis

The inductance coil received diagram measured inductance LX , the electric constant current source charge is 100mA(milliampere) , the time of two-way charging and discharging four state each is 500 s (microsecond), to measure displacement x and reading N data is shown in table below.
displacement x and reading N data

The table data according to the N as the independent variable to find N and displacement x second order fitting curve formula is as follows.
inductance coil and the displacement of the schematic diagram

Coordinate starting point has no special requirement, only consider displacement and timing gauge numerical N (namely inductance value). Measurement of displacement x is used micrometer drive displacement rod movement and then moving magnet. Every 1mm with bridge measured displacement point of inductance value as standard inductance value, and so to get inductance value and displacement relationship curve as shown in figure