Thermocouple Tests

Thermocouples are required in the system to record system performance and to control the hot oil pump.


In the Temperature Measuring page all the information can be found on the thermocouples and where they are used in the car. The program used to measure the temperatures with the Arduino can also be found there.

The first test was done using a small op amp chip. I tried to connect to it using small alligator clips. Thermocouples produce very small voltage differences based on temperature. The added resistance of these alligator clips created an error of over 20 degrees at times.

A calibration test was done using a digital oven thermometer and thermocouple in a pot that was heated up to 200c. A calibration equation was going to be used in the Arduino to correct the temperature data. In the end a more accurate op amp was purchased.

On a visit back to Canada 3 Adafruit breakout boards using the MAX31855 chip were purchased (see Temperature Measuring). All three were very accurate and could be used by the Arduino at the same time. The picture below shows a simply test were one thermocouple at a time is heated in my hand. The data was recorded by the Arduino and was easily cut and pasted into excel to be graphed.

3 thermocouple heated by body heat

1/8 inch copper pipes where used around the thermocouples so they could be used to measure fluid temperatures.


A test was done where a thermocouple was alternately dipped in ice water and boiling water. The test evaluated the accuracy of the thermocouples to measure the 100c boiling water and almost 0c ice water. This test was also used to see the temperature response of the thermocouple with the copper pipe around it. I wanted to see how long it took for the sensor to warm up or cool down and show the correct temperature. You can see the graphs below.

Thermocouple boiling water ice

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