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02/05/2024

High temperature. The thermocouple on the engine has failed. Kongsberg Troubleshooting

The No. 1 auxiliary engine has activated a high exhaust temperature alarm. In this article we will analyze the actions of electrical engineer to find and fix these problems.

High temperature. The thermocouple on the engine has failed

In the exhaust system on the engine there are two thermocouples that measure the temperature at two points (A and B), these points correspond to their group of cylinders. The values at both points should be approximately equal (at 500°C), but the thermocouple at point B showed a temperature of 620°C and it continued to rise on the AMS monitor.

Normal operation of thermocouples
Normal operation of thermocouples

The first thing to do in such situation is to transfer the load to another generator, stop the first engine, let it cool down and remove the thermocouple from the "glass" (the flask where the sensor is installed).

ThermocoupleThermocouple
Thermocouple

Using a temperature calibrator, we check the thermocouple, gradually heat it up and compare the value on the Kongsberg K-Chief alarm monitoring system monitor.

Temperature calibrator (instructions)
Temperature calibrator (instructions)
Temperature values on display
Temperature values on display
Heating the thermocouple to 200°C
Heating the thermocouple to 200°C
Comparison on AMS monitor 200°C
Comparison on AMS monitor 200°C
Heating the thermocouple to 400°C
Heating the thermocouple to 400°C
Comparison on AMS monitor 400°C
Comparison on AMS monitor 400°C
Heating the thermocouple up to 500°C
Heating the thermocouple up to 500°C
Comparison on AMS monitor 500°C
Comparison on AMS monitor 500°C

As a result of the test, it turned out that at a heating temperature of up to 500°C, the thermocouple shows the correct value with a small error, but when increased to 550°C, it begins to increase sharply (first to 580°C, then to 600°C).

Starting and terminal box
Starting and terminal box
Junction box
Junction box
Amplifiers
Amplifiers
Checking the signal cable contacts to monitoring system
Checking the signal cable contacts to monitoring system

Checking the amplifier and tightening the thermocouple contacts did not give positive results, so it should be replaced with a new one.

Another similar situation was described in a previous article with a pressure sensor. But in that case, simple calibration helped; in this case, the thermocouple will have to be changed.

Thermocouple (instruction)
Thermocouple (instruction)
New thermocouple (ready for installation)
New thermocouple (ready for installation)
Heating the new thermocouple to 550°C
Heating the new thermocouple to 550°C
Comparison on AMS monitor 550°C
Comparison on AMS monitor 550°C

The new thermocouple was tested using a calibrator up to 550°C and showed stable operation. The temperature was calibrated using the Span potentiometer on the amplifier because... there was a small error.

Thermocouple installation
Thermocouple installation

After installing the new thermocouple, it was tested on a working engine and showed normal, stable operation.

In this article I would like to focus on the fact that the old thermocouple worked correctly up to a certain temperature (up to 500 degrees Celsius). After this temperature, the thermocouple began to give false readings. Apparently, after 500°C, the sensor broke through to the housing. 

The same problem often occurs with heating elements (heaters in different systems), when at a certain temperature the heater spirals begin to penetrate the housing and low insulation comes out. This will be written about in other articles.

System model: Alarm monitoring & control system Kongsberg K-Chief 500

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