Two types of sensors need to be installed during the vibration test. One is a sensor installed at the “monitoring point” for detecting (or monitoring) the product’s response status parameters during the vibration test, which is called a monitoring sensor. The other is installed at a certain (or several) specific control point (or reference point), and the sensor used to detect the closed-loop feedback control signal is called a control sensor.
In the vibration test specifications, it is clearly defined that the “detection point” of the test sample is the installation point of the measurement sensor used to monitor the vibration response characteristics on the table, fixture, and product. The “detection point” can be any one of the following three points, or multiple or multiple location points can be selected according to the needs of the test:
1) The point that best reflects the vibration response characteristics of the product
This point refers to a detection point on the product that can represent the statistical average characteristics of the product’s vibration response. Theoretically, any product will exhibit a certain “mode” when it is excited, and the mode of any product has peak points (lines) and valley points (lines), and the vibration amounts of these peak and valley points (lines) The values can only represent the actual vibration state of the point. Therefore, a point with greater stiffness on the product should be selected. This point is less affected by peak and valley fluctuations, and its response characteristics can basically reflect the dynamic characteristics of the product as a whole.
2) The most sensitive point to vibration on the product
The product is composed of multiple components, components, and parts, some of which are particularly sensitive to vibration. The product may suffer functional failure or structural damage when subjected to lower-level vibration acceleration. Since the actual installation status of the product in the laboratory is different from that in use, monitoring the acceleration values of these vibration-sensitive points in real time during the test to ensure that they do not exceed the predetermined acceleration limit value not only protects the product from serious overload It is an effective measure and is also an auxiliary means to detect whether the fixture design and installation meet the test requirements.
3) The point on the product where the vibration response acceleration is the largest
The point on the product where the vibration response acceleration is maximum is not necessarily the origin of the product failure, so the point on the product where the vibration response acceleration is maximum and the point on the product that is most sensitive to vibration are usually not necessarily the same point. When the acceleration at the maximum response acceleration point on the product exceeds the estimated maximum value, the product may not necessarily experience functional “failure” or structural damage, but the given estimated maximum value is generally the maximum allowable value of the structural design ( There is a safety factor) or the actual measured value of similar products in the past. Therefore, when the response value at this point exceeds the estimated maximum value, it must indicate that some “variation” has occurred in the transmission characteristics of the assembly of the fixture and the test piece. , it is necessary to stop the test and carefully consider and analyze whether there are problems in the fixture design, installation, control procedures and sensor installation and use.
In the vibration test specifications, it is clearly defined that “control points” are detection points used to realize closed-loop control of vibration tests. Whether it is an analog or digital vibration control system, it is used to detect the vibration status of the product and feed back information to the control system. Sensors (displacement or acceleration) are installed at “control points”. Depending on the structural complexity and importance of the product being tested, one control point can be selected to implement single-point control, or multiple control points can be selected to implement multi-point leveling.
Uniform control or weighted control.