Hospital Vibration Environments for Medical Devices

 

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An engineer recently asked me to recommended a vibration test level for his device, which would typically be mounted on a hospital table, including surgical tables.

Well…  shock would almost certainly be worse than vibration, particularly if the device were somehow accidentally dropped on the floor.  Then there are transportation and shipping shock and vibration environments.

A logical approach would be to take some accelerometer measurements on hospital tables, but this is rather impractical for a number of reasons.  One is that there could be wide variation from one hospital to the next, depending on HVAC systems, vibration-inducing surgical devices, etc.

But my acquaintance insisted that he needed a vibration test level for hospital environments.  Well there are no ISO-type standards that specify hospital vibration that I am aware of.  So I made an innovation as shown in the following edited response.

* * *

I am enclosing a paper, which has levels in terms of one-third octave velocity spectra. These are intended as “not to exceed” levels for floor vibration, for both equipment and people.

So here is what I propose for hospitals… Start with the Workshop level in Figure 1 of the paper. This is the highest curve in the family of curves shown.

Assume that the Hospital level would be the same Workshop level, which is conservative for our approach. Now the device may be mounted on a table which amplifies the floor vibration at least at certain frequencies. So add a conservative 12 dB margin as a goal.

The coordinates are shown in the following table.

Freq (Hz) Nominal
Accel (G^2/Hz)
Nominal +12 dB
Accel (G^2/Hz)
4 2e-05 3.2e-04
8 1e-05 1.6e-04
80 1e-04 1.6e-03

The nominal PSD is 0.0634 GRMS overall.

The nominal plus 12 dB is 0.25 GRMS overall.

Power and monitor the device during the following test steps.

Start the test at the nominal level (after the shaker equalization) for some TBD length of time.

Then increase the level in 3 dB increments will the same dwell time as the nominal level.

The goal is the plus 12 dB level.

If the component passes the plus 12 dB, then you are successfully done. If the component fails at a lower level, then we might need to “sharpen the pencil” on the input level, or make design modifications.

The innovation is that we are using a widely-accepted, “not to exceed,” floor vibration level as a basis for deriving a component test level.

* * *

Tom Irvine

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