Which device produces an electric voltage proportional to temperature?

The correct choice, the thermoelectric pyrometer, operates on the principle of thermoelectricity, typically involving two dissimilar metals joined at one end. When there is a temperature difference between the junction (where the metals meet) and the other ends, a voltage is generated. This voltage is directly proportional to the temperature difference, allowing for an accurate measurement of temperature.

This device is particularly favored in industrial applications, as it can measure high temperatures without direct contact with the material being measured. The relationship between voltage and temperature makes it a reliable choice for monitoring temperatures in various processes.

Other options, while capable of measuring temperature, do not produce an electric voltage in the same direct manner as the thermoelectric pyrometer. The optical pyrometer measures temperature by interpreting the color of light emitted by a hot object, instead of generating a voltage based on temperature differences. The infrared thermometer detects infrared radiation emitted by an object to estimate its temperature but also does not work on the principle of generating voltage in proportion to temperature. The latent heat sensor, focused on phase changes in materials, measures energy changes rather than providing a direct voltage proportional to temperature.