Answer to Question #234403 in Mechanical Engineering for Saint

Question

When the cold junction of a thermocouple thermometer is at 5 C and the hot junction at 110 C, the millivoltmeter shows a deflection of 3.5 mV towards the left. The hot junction is now put in an unknown temperature while maintaining the cold junction at 5 C. The millivoltmeter now shows a deflection of 4.7 mV towards the left. Calculate the unknown temperature.

Answer 1

$E = A * \Delta T$ Eq. 1

Where A is a constant of the thermocouple material, E is the emf produced due to temp. difference between hot and cold junction.

Given T0 = 5

T1 = 110 and EMF = 3.5 mV

Therefore, 3.5 = A * (110-5)

Or $A = \frac{3.5}{105} = 0.033$

Now Given, E = 4.7 mV

T0 = 5

T1=?

Using eq. 1, we get,

4.7 = A * (T1 - 5)

4.7 = 0.033 T1 - 0.167

Or T1 =

$T1 = \frac{4.7 + 0.167}{0.033} = 146.15 deg . C$

Therefore, the hot junction temp. = 146 deg C