How to measure temperature in freezers, fridges and cold storage

Fridges, freezers, and cold storage rooms or cabinets typically hold goods of significant value that will deteriorate and likely need to be disposed of if the temperature is out of the required range. Both too-high and too-low temperatures can be problematic. As unexpected scenarios like a mechanical breakdown or power failure can happen, a good system to monitor the temperature is critical to assure the quality of the goods.  

The DT Smart cold storage solution

Disruptive Technologies Sensor platform has a wireless temperature solution tailored for monitoring fridges and freezers used for food. The system is certified for EN12830, which regulates requirements for food safety; see Wireless Temperature Sensor EN12830/330s. In addition, unlike many other wireless temperature sensors, our sensors are fully integrated, without the need for connection to a wired probe outside the fridge. The fully integrated sensor makes the installation much more robust, as wired probes can easily be broken and displaced under regular usage of the refrigerator.

Selecting the right sensor type

If you plan to install the sensor where the temperature is regularly below - 25°C, we recommend using the Industrial Temperature Sensor. For more help selecting the right sensor for Cold storage applications, please check this blog entry.

The Ambient Range Extender

The goal of temperature monitoring is to measure the ambient temperature inside the cold storage unit. When measuring the air or ambient temperature, the sensor should be insulated towards the material on which it is mounted. To get a good ambient temperature reading and increase range, use the Ambient Range Extender

This sensor accessory keeps the sensor sufficiently away from metal in all directions and is a great fit for measuring temperature in fridges, freezers, or cooling cabinets. Placing the sensor directly on metal will significantly reduce the wireless range, as shown in the illustration below. 



Understanding the battery life

The expected battery life of the sensor depends on the measurement interval and the expected temperature range.

At room temperature, the expected battery life of the Standard Temperature Sensor and the Industrial Temperature Sensor is the same, because the maximum operating lifetime of our battery technology is 15 years. However, at -25°C the Industrial Temperature Sensor can last up to 2 years longer than the Standard Temperature Sensor with the same measurement interval. That's because it uses different battery chemistry.

The chart below helps you evaluate the expected lifetime of the different sensor models and select the right temperature sensor for your application.

Please note: The battery lifetimes listed here are estimates and can vary from sensor to sensor depending on usage patterns, wireless coverage, and environment.

Understanding the cold storage sensor data

Setting suitable thresholds for temperature anomaly alarms requires some knowledge of the refrigerator's behavior and usage.  Below we have presented some typical cold storage sensor data patterns and what causes them. 

Sawtooth patterns

A fridge/freezer typically uses a compressor that cools the air down to a threshold and then turns off. Thus, the temperature will gradually rise until a new threshold is reached. At this point, the compressor starts, and then the cycle repeats. This process will give the temperature data a sawtooth-type pattern; see illustrations below.

The two examples below show this sawtooth pattern. The upper shows a high-quality fridge that will keep the temperature within a narrow range. The lower example shows a simpler fridge, that will have a higher variance:



Defrost cycles

Fridges typically also have automatic defrost cycles, where the temperature is increased to make sure ice is not building up on the cooling elements inside the fridge. This will show up as regular spikes in temperature and typically looks like this:


These spikes in temperature can be high compared to the target temperature of the fridge, so it is essential to take this into account when setting alerts on temperature anomalies in fridges. 

Fridges in active use

A fridge in active use will also have a relatively high variance in temperature, as the door is opened/closed every time you insert or remove food:


Cold Storage and DT Studio

If you do not use your platform, you can use the integrated features of DT Studio for cold storage monitoring. For instance, by setting alarms using notifications, viewing live data in the project dashboard, and making reports by exporting sensor data.