What is a thermopile?

Question

Examoogle · Accepted Answer

Option D: Series of thermocouples

Explanation & Concepts:
A thermopile is an electronic device that converts thermal energy into electrical energy, consisting of several thermocouples connected in series. By connecting multiple thermocouples in series, the thermopile increases the total output voltage, making it significantly more sensitive to small temperature changes than a single thermocouple.

Working Principle: The thermopile operates on the Seebeck effect, where a temperature difference between two dissimilar electrical conductors creates a voltage difference. By arranging thermocouples in series, the Seebeck voltages add up, allowing for the detection of very low levels of incident infrared radiation or heat flux. The junction exposed to the heat source is called the 'hot junction,' while the other is maintained at a reference temperature, known as the 'cold junction.'

Key Formulas: $V_{out} = n 	imes \alpha 	imes (T_h - T_c)$ — where $n$ is the number of thermocouples, $\alpha$ is the Seebeck coefficient, and $(T_h - T_c)$ is the temperature difference.

Key Points: Increases sensitivity compared to a single thermocouple.; Operates primarily on the Seebeck Effect.; Used extensively in infrared radiation sensors and heat flow meters.; Series connection ensures the additive nature of the Seebeck voltages.

Advantages: High sensitivity for low-intensity radiation detection.; Self-powered (no external excitation required).; Compact and rugged construction.

Disadvantages: Slower response time due to thermal mass.; Requires stable reference temperatures for absolute measurement.

Applications: Non-contact infrared thermometers.; Gas sensors and fire detectors.; Heat flux measurement in industrial processes.

Additional Info: The total output voltage of a thermopile is $V_{total} = \sum_{i=1}^{n} \alpha_i \Delta T_i$.. Option A is incorrect because a single thermocouple is just a simple junction, not a 'pile'.

Answer: D is correct — A thermopile is an array of thermocouples connected in series to amplify the output voltage generated by a temperature gradient.

Exam Tip: Always remember that in series, voltages add up, while in parallel, current capability increases but the total voltage remains equal to a single unit (assuming matched characteristics).

Examoogle · Answer

Option A: Single thermocouple

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Option B: Series-parallel connection of thermocouples

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Option C: Parallel connection of thermocouples

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