Improvements in Accelerometer Calibration at NIST Using Digital Vibrometry

Improvements in shaker design and laser vibrometer development has provided more precise calibration of accelerometers. Calibrations are performed at frequencies from 1Hz to 20 kHz with improved uncertainty and improved efficiency. The vibrometer mounting hardware is designed for easier optical alignment at multiple, repeatable, and unique reference positions on the shaker’s mounting table. Calibrations using this system, which is now used in the NIST routine calibration service, show excellent agreement with traditional NIST calibrations obtained using the laser interferometer methods that were developed at NIST. The legacy NIST laser interferometer system uses a shaker with a beryllium mounting table insert while the vibrometer-based system uses two shakers to cover the desired frequency range. For high frequencies (10 Hz – 20 kHz), a shaker with a ceramic mounting table which reflects the laser beam without the requiring a mirror is used. For low frequencies (< 10 Hz), a shaker with an aluminum mounting table is used. This system is described and compared with the previous calibration system. Comparison results for accelerometers are presented using the two measurement systems.