Relative type
The electric sensor is based on the principle of electromagnetic induction. That is, when a moving conductor cuts magnetic lines of force in a fixed magnetic field, an electromotive force is induced at both ends of the conductor. Therefore, this Sensors produced based on this principle are called electrodynamic sensors.
The relative electric sensor is a displacement sensor based on the mechanical receiving principle. Since the electromagnetic induction law is applied in the electromechanical conversion principle, the electromotive force generated is proportional to the measured vibration speed, so it It's actually a speed sensor.
Eddy current type
The eddy current sensor is a relative non-contact sensor that measures the vibration of an object through the change in distance between the end of the sensor and the object being measured. of displacement or amplitude. Eddy current sensors have the advantages of wide frequency range (0 ~ 10 kHz), large linear working range, high sensitivity and non-contact measurement. They are mainly used for static displacement measurement, vibration displacement measurement, and vibration measurement of rotating shafts in rotating machinery.
Inductive type
Based on the relative mechanical receiving principle of the sensor, the inductive sensor can convert changes in the measured mechanical vibration parameters into changes in electrical parameter signals. Therefore, there are two forms of inductive sensors, one is variable gap, and the other is variable magnetic permeability area.
Capacitive
Capacitive sensors are generally divided into two types. That is, variable gap type and variable common area type. The variable gap type can measure the displacement of linear vibration. The variable area type can measure the angular displacement of torsional vibration.
Inertial type
The inertial electric sensor is composed of a fixed part, a movable part and a supporting spring part. In order for the sensor to work in the displacement sensor state, the mass of its movable part should be large enough, and the stiffness of the supporting spring should be small enough, that is, the sensor should have a low enough natural frequency.
According to the law of electromagnetic induction, the induced electromotive force is: u=Blx&r
Where B is the magnetic flux density, l is the effective length of the coil in the magnetic field, r x& is the coil in the magnetic field relative speed in.
In terms of sensor structure, the inertial electric sensor is a displacement sensor. However, since the electrical signal it outputs is generated by electromagnetic induction, according to the electrical law of electromagnetic induction, when the coil makes relative motion in the magnetic field, the electromotive force induced is proportional to the speed at which the coil cuts the magnetic lines of force. Therefore, as far as the output signal of the sensor is concerned, the induced electromotive force is proportional to the measured vibration speed, so it is actually a speed sensor.
Piezoelectric
The mechanical receiving part of the piezoelectric acceleration sensor is based on the inertial acceleration mechanical receiving principle, and the electromechanical part utilizes the positive piezoelectric effect of the piezoelectric crystal. The principle is that certain crystals (such as artificially polarized ceramics, piezoelectric quartz crystals, etc., different piezoelectric materials have different piezoelectric coefficients, which can generally be found in the piezoelectric material performance table) exert an external force in a certain direction. When it is acted upon or deformed, charges will be generated on its crystal surface or polarization surface. This transformation from mechanical energy (force, deformation) to electrical energy (charge, electric field) is called the positive piezoelectric effect. The conversion from electrical energy (electric field, voltage) to mechanical energy (deformation, force) is called the inverse piezoelectric effect.
Therefore, the piezoelectric effect of the crystal can be used to make a load cell. In vibration measurement, since the force on the piezoelectric crystal is the inertial force involved in the inertial mass block, the number of charges generated is equal to The magnitude of acceleration is proportional, so the piezoelectric sensor is an acceleration sensor.
Piezoelectric force
In vibration tests, in addition to measuring vibration, it is often necessary to measure the dynamic excitation force exerted on the specimen. Piezoelectric force sensors have the advantages of wide frequency range, large dynamic range, small size and light weight, so they are widely used. The working principle of the piezoelectric force sensor is to utilize the piezoelectric effect of the piezoelectric crystal, that is, the output charge signal of the piezoelectric force sensor is proportional to the external force.
Impedance head
The impedance head is a comprehensive sensor. It integrates a piezoelectric force sensor and a piezoelectric acceleration sensor. Its function is to measure the excitation force at the force transmission point while measuring the motion response of the point. Therefore, the impedance head consists of two parts, one part is the force sensor and the other part is the acceleration sensor. Its advantage is that it ensures that the response of the measurement point is the response of the excitation point. When in use, connect the small head (force-measuring end) to the structure, and the big head (measuring acceleration) to the force-applying rod of the exciter.
Measure the excitation force signal from the "force signal output terminal" and measure the acceleration response signal from the "acceleration signal output terminal".
Note that the impedance head can generally only bear light loads and can therefore only be used to measure light structures, mechanical components and material samples. Whether it is a force sensor or an impedance head, its signal conversion element is a piezoelectric crystal, so its measurement circuit should be a voltage amplifier or charge amplifier.
Resistance strain gauge
Resistive strain gauge sensor converts the measured mechanical vibration into the change in resistance of the sensing element. There are many forms of sensing elements that realize this electromechanical conversion, the most common of which is the resistance strain sensor.
The working principle of the resistance strain gauge is: when the strain gauge is pasted on a certain specimen, the specimen is deformed by force, and the original length of the strain gauge changes, thus the resistance value of the strain gauge changes. Experiments have proved that when the specimen is Within the elastic range of the strain gauge, the relative change in resistance of the strain gauge is proportional to the relative change in its length.
Laser
Laser sensor is a sensor that uses laser technology to measure. It consists of laser, laser detector and measurement circuit. Laser sensor is a new type of measuring instrument. Its advantages are that it can achieve non-contact long-distance measurement, fast speed, high precision, large measuring range, strong resistance to light and electrical interference, etc. It is very suitable for non-contact measurement applications in industry and laboratories.