Which statement correctly contrasts thermocouple fire warning systems with thermal switch systems?

• A. Thermocouples respond to rate of temperature change; thermal switches respond to a specific temperature value.
• B. Thermocouples respond to specific temperature; thermal switches to rate of change.
• C. Both respond to rate of temperature change; thermal switch also triggers a warning.
• D. Both respond to specific temperature value.

Answer: (A)

Sensors used in fire warning systems differ in what they monitor in the heat environment. A thermocouple-based warning looks at how fast the temperature is rising—the rate of temperature change. The thermocouple generates a signal that the system interprets as a rapid rise, allowing an early warning even if the absolute temperature isn’t extremely high yet. A thermal switch, by contrast, uses a bimetal element that changes state only when a specific temperature value is reached, so it triggers at a set threshold rather than based on how quickly the temperature is changing. That’s why the statement that thermocouples respond to the rate of temperature change while thermal switches respond to a specific temperature value is the correct contrast. The other ideas don’t fit because thermocouples aren’t defined by a fixed temperature threshold in the same way, and thermal switches don’t track the rate of change.