Magnetic Field Distribution of Shadow Mask having a Magnetic Circuit around a Frame Periphery and its Affection to the Electron Beam Trajectory

The shadow mask in a color CRT is a soft thin iron plate which regulates the electron beam path. The mask may be magnetized by ambient magnetic fields, and the magnetization may change the beam path. As a result of the mask magnetization, the CRT screen may show color changes. We introduced magnetic circuits on the periphery of a shadow mask frame in order to decrease the mask and frame magnetization. The magnetic field distribution around the shadow mask was measured, and the effect of the circuits was evaluated through calculations of the change in electron trajectory. The addition of a magnetic circuit may be effective for decreasing the color change in CRT screens.