🔍 Key Concepts

• Radio Frequency Interference (RFI) and how it couples into control circuits • How small capacitors can be used as bypass or filter components for high-frequency noise • Difference between components that block DC/low frequency vs. those that block high-frequency signals

💭 Think About

• Think about what kind of interference a nearby radio system produces: is it low-frequency or high-frequency? Which components are most effective at shunting that kind of noise away from sensitive circuits? • Compare what a very small capacitor does versus a very large capacitor when placed across motor/tachometer leads. Which one mainly affects high-frequency noise without disturbing normal operation? • Would adding a resistor in series help with high-frequency radio noise on a feedback line, or could it affect the elevator’s control signal instead?

✅ Before You Answer

• Check which option involves a small-value capacitor that would primarily bypass or filter high‑frequency interference rather than change the DC or low‑frequency operation of the tachometer circuit. • Verify which component choice is least likely to disturb the normal tachometer feedback signal but can still drain off radio‑frequency noise to ground or across the leads. • Eliminate options that would significantly change the normal operating characteristics (speed, feedback, or torque) of the elevator motor/tachometer circuit.