Korea University M1000 P7 vibration survey — 2014-07-25

To verify whether the vibration environment meets the user’s requirements after installation of the M-1000 P7 vibration isolation platform.

Measurement date and time: 2014-07-25 (Fri) 17:30, measurer: Choi, Sungwon

Measurement site: 2nd floor, Industry–University Building, College of Engineering, Korea University

With the FEI SEM installed, tuning and vibration measurements were carried out while some equipment functions were operating.

Measurement locations were the front-center of the isolator top plate and the front floor (base) of the isolator.

Isolator intrinsic performance is favorable.

With Active on, the vibration environment on the isolator top is E Class or better.

The FEI side indicated that because the vibration environment during setup was much more favorable than typical day-to-day conditions, pass/fail could not be determined. Low-frequency motion from foot traffic was the main concern; it was agreed to measure during daytime hours when student traffic is higher and to report on the following Monday (2014-07-28). Accordingly, for the Z axis, measurement was performed under forced excitation rather than capturing the ambient site condition as-is.

Judgment: condition favorable.

During tuning, low-frequency phase margin was generally ample and high-frequency phase margin was tight. With low payload mass or changes in passive characteristics, the Z axis was tuned with minimal stability margin and the work was completed.

In Passive state an abnormal peak appeared on the Z axis at 45 Hz; it was also seen in open-loop and made tuning difficult. After the FEI engineer adjusted SEM cabling slack, the anomaly no longer appeared in open-loop and performance could be achieved, but the final performance measurement still showed weaker performance near that frequency.

The apparent limitation in high-frequency horizontal-axis performance is considered to be because high-frequency excitation was not applied.