General Mechanical

General Mechanical

Random Vibration of PCB

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    • abhi.mrt22
      Subscriber

      Recently, I have performed a random vibration analysis on my PCB. I have applied 6.06 Grms from 20Hz to 2000Hz at the PCB mounting positions. The maximum response occurs at one of my relays which is about 30 Grms. Is this Grms value is in the safe range or not? According to its datasheet, this component passed both random vibration and shock test and the details are given below:

      Random Vibration: 10 Grms is applied from 20 Hz to 2000 Hz  

      Shock: 100 G is applied for 10ms duration

      Now, I am unable to conclude whether my relay fail or pass during actual vibration testing. Is there any thumb rule or criteria from which we conclude this condition?

      Can we go with this reason: As the maximum response is 30 Grms, then the maximum peak response in G would be 3 times of 30 Grms which is something 90 G. Since the component was undergo a shock load which is about 100 G, so our component will safe under 30 Grms random vibration response.

      How can we use the random vibration and shock related data given in the datasheet to predict our system performance?

    • Ashish Khemka
      Ansys Employee

      Hi,

       

      Please see if the following link helps:

       

      Random Vibration Analysis - ANSYS Innovation Courses

       

      Regards,

      Ashish Khemka

    • peteroznewman
      Subscriber

       

      A manufacturer of relays will test hundreds of samples at higher and higher levels of random vibration. They will count the percentage of samples that failed at each level. They do statistics on the whole data set to estimate, with 95% confidence, the Grms where no relays will fail, and that value turned out to be 10 Grms. 

      Let’s make up some data and imagine that at 30 Grms, 20% of relays failed and 80% of relays passed.  Now you have an analysis that predicts 30 Grms. Will you be satisfied with a 20% failure rate? I don’t think so. Perhaps the manufacturer only found 2% failed at 30 Grms. We don’t know, they don’t publish that level of detail.

      All we know is that the datasheet says, don’t use these relays where the random vibration level exceeds 10 Grms. I suggest a redesign. Either change the PCB support or layout of where those relays are on the board (move them closer to the supports that see only 6 Grms) or choose a different relay that can survive 30 Grms.

       

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