Why Doesn't the Temperature From My Monitoring System Match My Thermometer?

CHESTERLAND, Ohio - Sept. 14, 2020 - PRLog -- Problem

One of the most common questions our tech support staff gets is, "Why does the temperature measured by your data logger not match the temperature displayed on the thermometer on my refrigerator?" There is no "one" temperature in your refrigerator or freezer, but rather a range of temperatures from top to bottom and front to back. The value that you measure depends on where the probe is located.

Experimental Setup

Prior to running the test in the refrigerator, a calibration run was done to verify that the temperatures measured by the individual probes were the same.

Test Results

The temperature data collected in this test contain some very interesting information about what is going on inside of the refrigerator:

• As expected, we observed the normal cyclical fluctuations as the refrigeration compressor turned on and off. The cycles lasted a bit less than one hour.
• The coldest spot is in the lower back corner of the refrigerator. While the thermostat was set for a nominal temperature of around 1°C, in this location the temperature was consistently below 0°C. It is believed this is because the cold air flowing over the evaporator falls down the back wall of the refrigerator and settles in this location.
• Within the main cabinet of the refrigerator, there is a variation of almost 6°C between the warmest and coldest spots. The warmest spot is the top shelf in the door and the coldest spot is in the bottom drawer.

Conclusion

What does all of this mean? The temperature that you read inside of your refrigerator depends strongly on where the temperature probe is located! In many cases, we find that customers are looking at the built-in temperature display located in the door of the refrigerator and comparing it to the temperature recorded by the data logger, which is using a probe that is located on one of the shelves.

Second, even if the probes for both monitoring systems are placed within the main cabinet of the refrigerator, it is important to be very careful not to get one of the probes closer to the evaporator or the air stream that is flowing off it.

Finally, the temperature of the refrigerator will vary considerably over time as the compressor cycles on and off. If the temperature that is being compared to the data logger is being measured by a mercury thermometer or an electronic display, the response times of these can make a difference in the observed value.

For further information on refrigerator temperature monitoring, or to find the ideal solution for your application-specific needs, contact a CAS Data Logger Application Specialist at (800) 956-4437 or visit us at https://www.dataloggerinc.com.