In a thermocouple the cold junction is at 20 °C and the neutral temperature is at 250 °C. The inversion temperature is:

Explanation:

Thermocouple Neutral and Inversion Temperature

Definition: A thermocouple is a device used to measure temperature, consisting of two different types of metals joined together at one end. The junction of the two metals produces a voltage that is related to the temperature difference between the "hot" and "cold" junctions. Two important temperatures associated with thermocouples are:

• Neutral Temperature: The temperature at which the thermoelectric voltage reaches its maximum value for a given cold junction temperature.
• Inversion Temperature: The temperature beyond the neutral temperature at which the thermoelectric voltage begins to decrease and eventually becomes zero.

Given Data:

• Cold junction temperature = 20°C
• Neutral temperature = 250°C

Formula: The relationship between the neutral temperature (T_n), inversion temperature (T_i), and cold junction temperature (T_c) is given by:

T_i = 2 × T_n - T_c

Here:

• T_n is the neutral temperature (250°C).
• T_c is the cold junction temperature (20°C).
• T_i is the inversion temperature.

Calculation:

Substitute the given values into the formula:

T_i = 2 × T_n - T_c

T_i = 2 × 250 - 20

T_i = 500 - 20

T_i = 480°C

Correct Option: Option 1 (480°C)

This is the correct answer because the inversion temperature is calculated accurately using the formula and the given data.

Additional Information

Important Information:

To understand the analysis further, let’s evaluate the other options:

Option 2: 500°C

This option assumes that the inversion temperature is simply double the neutral temperature, without considering the cold junction temperature. However, the formula explicitly accounts for the cold junction temperature, and neglecting it leads to an incorrect result.

Option 3: 520°C

This option is incorrect because it exceeds the calculated inversion temperature. There is no basis for this value within the context of the formula provided.

Option 4: 460°C

This option underestimates the inversion temperature. It might result from an incorrect application of the formula or a misunderstanding of the relationship between the neutral and inversion temperatures.

Conclusion:

The inversion temperature is a critical parameter in understanding the behavior of thermocouples. It is calculated using the relationship between the neutral temperature and the cold junction temperature. In this case, the correct inversion temperature is 480°C, as determined by the formula T_i = 2 × T_n - T_c. This temperature represents the point at which the thermoelectric voltage begins to decrease after reaching its maximum value at the neutral temperature.