Hale et al. (1986) report on the change in resistance of a Cathode Ray Tube (CRT) bleed resistor. The resistor has the function of regulating the power supply to the CRT by providing a constant impedance across it. If the bleed resistance increases, the effect will be severe front-of-screen distortion, where the outside edges of a video image are curved. If the resistance decreases significantly, the circuit will be overloaded and the display will power down. The main criterion for the performance of the resistor is the change in its resistance with time. The following degradation model describes the relationship between the change in resistance with time and the applied temperature.
A manufacturer observes the resistance of two resistors tested at two different temperatures of 80 and 120 C. The results of the test, which is conducted for 1000 hours, are shown in Table 6.21.
The normal value of the resistor is 250 MΩ. The edges of a video image become unacceptably curved when the resistor’s value changes to 340 MΩ, and failure of the display occurs when the resistance’s value reduces to 180 MΩ. Determine the time to system failure (distorted video or failed display) if the resistor is expected to operate normally at 30°C.
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