This calibrator provides a single-frequency (100 Hz), single-level (1 g) check on the GR Vibration Pickups or any pickup whose total mass is 300 grams or less. It can provide on-the-spot calibration of vibration-measurements and can also be used to compare transducers or to calibrate working transducers against a standard transducer.

Operation of the calibrator is simple. A pickup of known mass is attached to the shaker, either in place of one of the removable 50-gram disks or to one of the disks by double-faced pressure-sensitive tape. The user adjusts the Level control until the panel meter, calibrated in grams, indicates the mass of the pickup. The pickup will then be automatically subjected to an acceleration of 1 g at 100 Hz.

The 1557-A is a small, battery-operated unit consisting of a transistorized electromechanical oscillator and a cylindrical shaker. The acceleration output of the calibrator appears at two pillbox-shaped 50-gram disks mounted on an internal cylinder that projects through the sides of the instrument.