An instrument engineer/ technician wants to create a temperature reference for a

Question

An instrument engineer/ technician wants to create a temperature reference for a thermocouple transmitter by freezing some water, knowing that the freezing point of water at sea level is 32 degrees F (or 0 degrees C). He inserts the thermocouple into a cup of water, then sets the cup and thermocouple inside a freezer until the water is frozen solid. He then takes the cup out of the freezer and connects the thermocouple to the temperature transmitter for calibration.

What is wrong with the technician’s procedure? What must be done differently to ensure a reference
temperature of 32 degrees F (0 degrees C) at the thermocouple tip?

Explanation / Answer

The wrong with technician process is that he inserted the thermocouple into a cup of water and then set the cup and thermocouple inside a freezer until the water is frozen solid but the fact is that water freezes at 0oC but frozen solid (ice ) can go to temperature below 0oC also.

He should take the fozen solid and wait for it to melt and when it has just melted (liquid form) connect the thermocouple to the temperature transmitter for calibration to ensure a reference temperature of 0oC. As when ice has melted into liquid will be at 0oC.

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