Measurement of shadow mask vibration and Q value using two position-sensitive detectors

A noncontact optical system that can measure both the vibration characteristics of the shadow mask and the relative distance (Q value) between the shadow mask and the phosphor surface of the glass panel of a cathode ray tube (CRT) is developed. Two position-sensitive detectors (PSDs) were employed to detect the positions of two beams that were reflected by the shadow mask surface and the inner surface of the glass panel. The relative distance between them is critical for the performance of the CRT. The vibration signals obtained from the PSDs were displayed in both temporal domain and spectral domain by using LabView software. The resonance frequencies of 20, 75, 400, and 490 Hz were identified and the low 20 Hz component was responsible for generating discomfort to the human eye.