# Aircraft Temperature Sensing: Scale Conversion and CSD Monitoring

> Learn aviation temperature sensing fundamentals, including Celsius/Fahrenheit/Kelvin conversion and operational monitoring of CSD oil temperature limits.

- **Subject:** 022 — Instrumentation
- **Section:** 022-01 — Sensors and Instruments
- **Topic code:** 022-01-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/instrumentation/sensors-and-instruments/temperature-sensing/

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Temperature measurement in aviation is essential for monitoring systems like engines and generators, as well as for atmospheric data.

## Temperature Conversion
Pilots and engineers must be able to convert between different temperature scales: Celsius (°C), Fahrenheit (°F), and Kelvin (K).

The relevant formulas are:
*   **Fahrenheit to Celsius:** $^\circ F = 1.8 \times (^\circ C) + 32$
*   **Kelvin to Celsius:** $K = ^\circ C + 273$ (or $^\circ C = K - 273$)

For example, a temperature of 20°C converts to 68°F ($1.8 \times 20 + 32$) and 293 K ($20 + 273$). Note that 0°C corresponds to 273 K.

## Application: Constant Speed Drive (CSD)
Temperature sensing is critical for the **Constant Speed Drive (CSD)** unit. The CSD is a hydraulic-mechanical device that regulates the generator's speed to ensure a constant output frequency, regardless of engine speed changes. It connects to the engine via a dog clutch.
*   **Monitoring:** The cockpit provides warnings if the **CSD oil temperature is too high** (often accompanied by low oil pressure/level).
*   **Action:** In such cases, pilots can disconnect the CSD in flight to prevent damage. Once disconnected, it cannot be re-engaged in the air and requires maintenance on the ground.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.