SACA Motor Control Practice Exam

The measurement of resistance is a key method for determining if an indicator lamp has failed. When a lamp is functioning properly, the filament inside the bulb (or the LED in modern lamps) presents a specific resistance value. If the lamp is burned out or failed, the circuit path is disrupted, leading to an infinite resistance (open circuit) or a significantly altered resistance value, indicating a problem.

By testing the resistance with a multimeter, you can assess whether there is continuity through the lamp. A reading of zero or very low resistance suggests the lamp is intact, while a high or infinite resistance indicates a failure. This method is particularly effective because it requires that the electrical supply is off for safety and accurate readings.

Other measurements like voltage and current are relevant for assessing the operation of the lamp while it is powered, but they do not directly indicate a failure. If there is no voltage present at the lamp circuit, it does not confirm the failure of the lamp itself, as there could be other issues upstream in the circuit. Measuring frequency is typically not relevant for indicator lamps, as these devices are primarily concerned with DC or standard AC voltage scenarios rather than frequency-related issues.