The ZonicBook/618E data acquisition system from IOtech

A ZonicBook data acquisition system from IOtech, Cleveland, helps engineers designing and testing turbines and gas generators verify design calculations and fine-tune finite-element models. Part of the testing includes rapping components such as turbine blades with a hammer and recording the vibrations. “Subsequent analyses determine how natural frequencies, modal shapes, and other signal components affect part design and possible failure modes,” says Dan Faby, a mechanical test designer with Siemens-Westinghouse, Casselberry, Fla.

Faby primarily uses the ZonicBook to fine-tune FE analytical models, while lab tests show how close parts agree with predicted behavior. Lab tests include swept-sine analysis using force input from shakers, exciters, or large speakers that inject white noise into components such as combustion turbine transitions. In the field, however, time is a greater factor so an impact hammer typically serves as an exciter. “Impact tests are a lot faster than swept sine,” explains Faby.

Typical Modal Analysis Hardware Setup

Most newly designed turbine components undergo modal analysis. Although test engineers occasionally use an exciter or a white-noise generator to perform a swept-sine test, impact tests are quicker and can be done in the field, even on an operational turbine.

Before going with the ZonicBook, Siemens-Westinghouse used separate data acquisition systems. But, they had only two input channels and were too heavy and large to be lugged to various sites. “The ZonicBook system, in contrast, weighs less than 5 lb. And has eight channels,” says Faby. The availability of eight data channels lets two triaxial accelerometers run simultaneously with another channel used for a separate input. This setup halves data acquisition time.