In order for the vibration sensor to obtain accurate and effective data, it must be installed on the structure under test by an appropriate method without any distortion caused by the installation. If the motion of the test object is not accurately transmitted to the sensor, the sensor cannot accurately measure the motion of the object. This requires that the installation of the sensor is fixed throughout the test frequency range. However, in different applications, according to the actual needs of the test system, the installation method is also different. The amplitude frequency response curves obtained by different installation methods are also different. The following is a brief introduction to several main vibration sensor installation methods.
Magnetic Base Installation
In industrial vibration monitoring applications, since the sensor requires periodic point-to-point rapid measurement, it is very suitable to install with a magnetic base. When using a magnetic base to install, the magnetic force will make the adapter and the sensor move towards the mounting surface, but when they are in contact, the magnetic force will have a larger impact on the acceleration, which will damage the sensor chip or its internal electronic components. Most magnetic mounts are heavy, so they are mostly used in low frequency tests with vibration frequencies less than a few hundred hertz. When the magnetic base is installed for intermediate frequency testing, the test surface needs to be effectively treated to increase its resonance frequency.
Adhesive Installation
In many cases, it is required to install the sensor without damaging the mounting surface, such as when the mounting surface cannot be installed with threaded holes (due to composite surface material, insufficient structural thickness, small mounting surface or multiple mounting points, the sensor may move randomly ), you need to install with adhesive at this time, so that the sensor can become a part of the test object. The hardness of the adhesive after hardening plays a very critical role in the test performance of the entire system. The more the adhesive between the sensor and the surface of the structure being measured, the worse its transmission performance. When using adhesives to install sensors, operating temperature is an important factor to consider. Adhesives include hot-melt adhesives, super-adhesives, paraffin wax, and double-sided adhesives.
Bolt Installation
The best way to install the sensor is to use bolts. The power conductivity of bolts is better than any other installation method. Bolt or screw installation can make the sensor and the surface of the object to be measured completely close contact. Also, ensure that the length of the bolt is correct to prevent the bottom of the bolt from contacting the sensor. If the bottom of the bolt touches the sensor, it will stress the sensor and cause output errors. At the same time, in order to ensure the repeatability of the vibration sensor installation, too much torque will cause damage to the sensor, so a torque wrench must be used to install the sensor.
The following pictures are the above installation methods
Amplitude Sensitivity and Frequency Response Error
Set | 20 | 80 | 160 | 400 | 500 | 1000 | 1200 | 1500 | 2000 |
Acquisition | 18.75 | 81.25 | 159.375 | 400 | 500.15 | 999.87 | 1200 | 1502.1 | 1999.9 |
Set | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
Acquisition |
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Magnetic | 0.987 | 0.996 | 1.085 | 1.219 | 1.300 | 5.075 | 3.125 | 1.012 | 0.498 |
Adhesive | 0.991 | 0.996 | 1.066 | 1.132 | 1.178 | 1.989 | 3.739 | 1.479 | 1.199 |
Bolt | 0.990 | 0.990 | 0.991 | 0.993 | 0.994 | 0.998 | 1.012 | 1.024 | 1.035 |
The following tables show the frequency-amplitude curve under different installation methods
Frequency Response Analysis of Vibration Test by Installation Method
The frequency response of the system consists of amplitude-frequency characteristics and phase-frequency characteristics. The amplitude-frequency characteristic represents the relationship between the increase or decrease of the gain and the signal frequency; the phase-frequency characteristic represents the phase distortion relationship under different signal frequencies. According to the frequency response, the ability of the system to reproduce signals and the characteristics of filtering noise can be more intuitively evaluated. Install the above-mentioned installation methods for testing, and get the amplitude sensitivity and sensitivity frequency response error. Take our company's model YD285 vibration sensor as an example for testing. Install the accelerometer on the vibrating table using a magnetic base, glue and bolts. Then when the acceleration value is 1g, the amplitude under different installation modes is affected by frequency. It can be seen from the above experimental data and the graph of the table that the amplitude of the magnetic base installation method reaches as much as five times the set value at about 1000 Hz, and then the amplitude value decreases rapidly, which shows that the sensor and the magnetic base have reached the value at 1000 Hz. Resonance phenomenon; in the same way, the amplitude of the adhesive installation method reaches its maximum at about 1200 Hz, and resonance phenomenon also occurs at this time. The amplitude of the bolt installation method is basically consistent with the set value within the experimental frequency range, which shows that the bolt installation method is least affected by the vibration frequency.
Conclusion
At lower operating frequencies, all three installation methods are possible, but at higher frequencies, when the installation environment allows, we choose bolt installation as much as possible. This installation method will greatly reduce the amplitude distortion caused by resonance.
