A growler test, utilizing magnetic viewing film, can help a technician visualize the bars of a rotor. This test utilizes a portable growler for exciting the rotor and magnetic field viewing film for recording results. This test method is widely used for diagnosing an open rotor, but is not effective for minor defect detection.
A skilled technician is required for effective diagnosis. Results are low fidelity and minor defects will go undetected, even by trained personnel.