Commonly used sensors for vibration measurement

Sensors are widely used in various applications. In different environments, in order to reduce the measurement error, specific sensors need to be used, which can effectively improve efficiency. Then I will tell you what sensors are commonly used in vibration measurement?

       1. Electric speed sensor: The electric speed sensor is a moving coil (magnetoelectric) sensor. When the sensor vibrates with the structure or the top rod on the moving coil of the sensor is connected to the structure, the moving coil of the sensor moves in the magnetic field due to the vibration of the structure, cutting the magnetic lines of force to generate an induced electromotive force. The magnitude of the induced electromotive force is proportional to the moving coil movement speed.

        Therefore, the vibration speed of the structure can be determined by measuring the induced electromotive force. Electric speed sensor inertial type, the pendulum mill sensor is fixed on the vibrating body, and the measured result is the absolute speed of the vibrating body; relative type, the sensor housing is fixed on one object, the top rod supports another object, and the measurement result is the relative speed of the two objects.

        The secondary instrument that matches the electric velocity sensor is the electric vibration meter, which is mainly composed of a calculus amplifier, a filter and a detection indicator part. It is used to amplify the signal output by the sensor and can directly measure the speed; and the displacement can be measured through the integral circuit ; and the acceleration can be measured through the differential circuit.

        2. Electric acceleration sensor: The piezoelectric acceleration sensor is referred to as a piezoelectric accelerometer. When it vibrates with the structure, the mass block in the sensor will generate an inertial force under the action of acceleration and pressurize the crystal plate. Due to the piezoelectric effect of the crystal plate, an electric charge is generated. Within a certain pressure range, the output charge is proportional to the acceleration. Therefore, the magnitude of the acceleration can be determined by measuring the output charge of the piezoelectric accelerometer. Figure 5-2 shows a schematic diagram of the structure of a piezoelectric accelerometer.

The secondary instrument of the piezoelectric accelerometer often uses a charge amplifier, which is a high-gain operational amplifier with capacitive negative feedback and extremely high input impedance. Its output voltage is proportional to the charge emitted by the piezoelectric accelerometer and inversely proportional to the feedback capacitance. It is little affected by the cable capacitance, which is a major advantage of the charge amplifier. The input end of the charge amplifier must be well shielded.

       3. Eddy current displacement sensor

The eddy current displacement sensor is a non-contact sensor with a coil on its head connected in parallel with the resonant capacitor to form a parallel resonant circuit. When the sensor coil with alternating current is close to the surface of the conductor (vibrating body) to be measured, an induced current - eddy current - is generated on the surface of the conductor. The smaller the gap between the conductor and the sensor, the greater the eddy current generated by the conductor, and the smaller the inductance of the sensor coil.

        Its output voltage is a function of the inductance, so when the gap between the conductor and the sensor changes, the gap value can be obtained by measuring the output voltage value. The main feature of the eddy current displacement sensor is that it has no contact with the measured point, so it is particularly suitable for vibration measurement of rotating shafts. It has high sensitivity, small structural size, and is insensitive to environmental influences. For example, two mutually perpendicular eddy current sensors can be used in the same vertical plane to measure the axis trajectory and axis position of the shaft.

4. Strain gauge: A strain gauge is a resistive sensor that can measure both static and dynamic structural strain. In addition to being used as a sensor to measure vibration strain, the strain gauge can also be glued to an elastic element to form a corresponding displacement, velocity, acceleration, and force sensor.

        5. Force sensor

Force sensors are probes used to measure excitation force, pressure, reaction force, etc. Force is measured by measuring the effect of force (such as strain, displacement, acceleration, etc.). Therefore, force sensors are designed to convert changes in strain, displacement or acceleration into changes in electrical quantity.

The above 5 types are the types of sensors commonly used in vibration measurement that I would like to introduce to you. Different sensors are used in different environments. When choosing and using them, you should consider many factors such as the sensor's frequency response characteristics, sensitivity, signal-to-noise ratio, and the matching between the subsequent amplification and measuring instruments according to the specific object.