Protection during vibration tests
Vibration environment tests, especially life tests, durability vibrations, structural strength vibrations and other tests have a long cycle. The test objects are sometimes high-value products. During the test process, test personnel often have to patrol or patrol around the site. Testing work requires that the vibration table and testing equipment used in the vibration test process must have the characteristics of safe operation, easy operation, reliable use, and long working life. It also has various protection and warning measures, complete and reliable safety interlocking devices, and even a multi-margin safety design to prevent damage to test equipment, test devices, test pieces, and test personnel. On the other hand, the test operator must also have a sufficient understanding of the potential safety hazards that may arise during the vibration test, and take preventive and emergency measures in advance to ensure that the vibration test is carried out safely, reliably and normally.
The safety and reliability of vibration tests are divided into three levels. The first is to ensure the safety of test operators, including the ability to protect the operators’ personal safety during normal operations or even misoperations. The second is the protection of the product under test. Once the control system fails and the response of the product under test is out of control, the multi-margin protection system will participate in the protection of the product under test and automatically shut down. The third is the safety of the test equipment itself. When the test system of the equipment fails and the out-of-control environmental conditions exceed the extreme range, the multi-margin safety protection system that is independent of the test equipment control system can automatically cut off the energy supply and shut down. check.
1) Protection of personnel safety
Vibration tables are equipment with large electrical power consumption, large currents, and strong electromagnetic induction on site. Personnel participating in vibration tests must have basic safety knowledge in using electrical appliances:
a) The vibration control test room must have a good ground wire. The ground resistance value of the ground wire should be lower than 40. If it can be as low as 1~20, it is very good.
b) The power amplifier of the electric vibration table is a high-current electrical equipment. There is a strong electromagnetic field around it, and electrostatic induction is easy to occur. An insulating rubber sheet should be laid on the ground around the power amplifier. During the vibration test and for a period of time afterwards, never touch the power amplifier at will, especially the capacitor components in it, to prevent injuries from high voltage or electrostatic discharge.
c) If it is necessary to observe the test conditions at close range during the vibration test, the observer must not stand in the direction of the vibration axis to prevent the test piece from falling along the vibration axis due to breakage of the mounting bolts, causing personal injury.
2) Protection of test pieces
Most of the objects of vibration testing are finished products, and some test pieces are expensive, and it is more necessary to prevent non-experimental damage.
a) For large or expensive test pieces, hanging protection should be provided during the test to prevent the test piece from tipping or overturning during the test.
b) No matter what vibration control scheme is adopted, for some large or expensive test pieces, it is recommended to install protective monitoring sensors at the vibration-sensitive points of the test piece to monitor the vibration response of the test piece in real time to prevent the test piece from suffering Damage due to severe overload. If the monitoring sensor can be connected to the overload protection device, once the test piece is overloaded, the protection device will immediately send an alarm signal and shut down immediately.
c) Operate the vibration table strictly in accordance with the vibration table operating procedures. Before turning off the power amplifier, the vibration controller must be kept in a closed-loop working state. To prevent the controller from malfunctioning while the power amplifier is in working condition, causing the vibration table to lose control and seriously damaging the test piece, the vibration controller must have an open circuit protection system.
3) Protection of test equipment
Vibration testing equipment is a closed-loop control system. Failure in any link in the system will cause the vibration testing system to lose control. Therefore, vibration testing equipment has many self-protection devices:
a) Control system: The control system should usually be equipped with an open circuit (break circuit) protection device. The parameters set by the control system should have a hierarchical management mode. Operators who have not been granted this level of rights cannot enter or change the control system at will.
parameter. b) Power amplifier: The power amplifier itself must have over-voltage and over-current protection for electrical parameters, and the power amplifier device must have over-temperature (degree) protection. There should be chain protection between various parameters of the power amplifier.
c) Vibration table: The vibration table itself should have over-travel alarm and protection. The moving coil of the vibrating table has over-temperature (degree) protection. For air-cooled vibrating tables, the air inlet temperature should always be kept below 30°C. For water-cooled vibrating tables, there should be cooling water pressure and temperature protection, etc. .
Among these three levels, the protection and alarms at the first and third levels must be ensured. At the second level, corresponding auxiliary means can be selected to implement different levels of security protection based on the importance and value of the product being tested. They do not have to treat everyone equally.