# Installed the wrong thermocouple but still worked

#### Abraham

Can anyone provide some insights on the below-mentioned problem
Scenario:-
The pasteurization machine requires a temperature of 150 degree C which is being reached but tests show that the bacteria count is too high, which means the liquid is not getting hot enough. The machine uses a K type thermocouple and recently it was replaced incorrectly by a type J thermocouple.

Why did installing the wrong thermocouple resulted in what seemed to be the right temperature according to the digital readout but that actually was too low to properly pasteurize?

#### udshred

First
Can anyone provide some insights on the below-mentioned problem
Scenario:-
The pasteurization machine requires a temperature of 150 degree C which is being reached but tests show that the bacteria count is too high, which means the liquid is not getting hot enough. The machine uses a K type thermocouple and recently it was replaced incorrectly by a type J thermocouple.

Why did installing the wrong thermocouple resulted in what seemed to be the right temperature according to the digital readout but that actually was too low to properly pasteurize?
It is because each type of thermocouple generates different millivolts according to its hot junction(sensing point)temperature and the cold junction(reference point) temperature. Or in other words the sensitivity of each thermocouple type is different from other type. The mV/degree centigrade generated is different for type 'k' and type 'j'.

#### David_2

The analog input circuit always 'tests' the input for an open circuit, because thermocouples typically fail "open". But the presence of any Type thermocouple will pass the burn-out test.

Most modern analog inputs can be configured for any of a number of different types of thermocouples. It's the analog input (or its CPU) that 'interprets' the mV output of the thermocouple to convert to a temperature value. An expected input of X mVs for a certain temperature from a Type K is achieved at a much lower temperature for a Type J as you can see from graph below.

I hope no unpasturized product made it out of the plant.

#### Abraham

The analog input circuit always 'tests' the input for an open circuit, because thermocouples typically fail "open". But the presence of any Type thermocouple will pass the burn-out test.

Most modern analog inputs can be configured for any of a number of different types of thermocouples. It's the analog input (or its CPU) that 'interprets' the mV output of the thermocouple to convert to a temperature value. An expected input of X mVs for a certain temperature from a Type K is achieved at a much lower temperature for a Type J as you can see from graph below.

View attachment 607

I hope no unpasturized product made it out of the plant.
Nope it did not