Sample interview questions: Can you explain your knowledge of different types of temperature sensors used in hydronic systems and their calibration requirements?
Sample answer:
1. Thermocouple:
- Utilizes the principle of Seebeck effect where a voltage is created when dissimilar metals are subjected to a temperature difference.
- Common types include Type J (iron-constantan) and Type K (chromel-alumel).
- Requires calibration over multiple points along its measurement range for accurate readings.
- Offers quick response time and relatively low cost.
2. Resistance Temperature Detector (RTD):
- Measures temperature changes based on the varying electrical resistance of a metal conductor (Platinum is commonly used).
- Resistance increases with rising temperature.
- Requires 2, 3, or 4 wire configurations for accurate measurement and compensation of lead resistance.
- Provides high accuracy, stability, and linearity but can be more expensive than thermocouples.
3. Thermistors:
- Semiconductor devices exhibiting large resistance changes with temperature variations.
- Negative Temperature Coefficient (NTC) thermistors exhibit decreasing resistance with increasing temperature, while Positive Temperature Coefficient (PTC) thermistors do the opposite.
- Offer high sensitivity and can be used over a wide temperature range.
- Calibration is generally not required as they are often used in control systems where changes are more important than absolute values.
4. Infrared (IR) Temperature Sensors:
- Measure temperature by detecting infrared radiation emitted by objects.
- Non-contact type, allowing measurement without direct physical contact.
- Useful for measuring temperatures of moving objects, inaccessible areas, or hazardous environments.
- Calibration is essential to ensure accurate readings and compensate for fac… Read full answer
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