How to measure temperature in freezers, fridges and cold storage

Fridges, freezers, and cold storage rooms/cabinets typically holds goods of significant value, that will deteriorate and likely needs to be disposed of if the temperature is not within the required range. Both too high and too low temperatures can be problematic. As unexpected scenarios can happen, like a mechanical breakdown or power failure, a good system to monitor the temperature is critical to assure the quality of the goods.  

Disruptive Technologies Sensor platform has a wireless temperature solution tailored for monitoring fridges and freezers used for e.g. food. The system is certified for EN12830, which regulates requirements for food safety, see Wireless Temperature Sensor EN12830/330s. Unlike many other wireless temperature sensors, it is fully integrated, without a wired probe that needs to connect to a device outside the fridge. This makes the installation much more robust, as probes can easily be broken and displaced under normal usage of the fridge. 

The goal of temperature monitoring is to measure the ambient temperature inside the fridge/freezer. To measure the air or ambient temperature, the sensor should be insulated towards the material it is mounted on. 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 greatly reduce the wireless range, as you can see from the illustration below:

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A fridge/freezer typically works by using a compressor that cools down the air down to a threshold, then turns off. The temperature will then gradually rise until a new threshold is reached. At this point, the compressor starts, and the cycle repeats. This will give a sawtooth type pattern on the temperature, see illustrations below.

A high-quality fridge will keep the temperature within a narrow range:

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Simpler fridges will have higher variance:

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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:

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

A fridge in active use will also have a relatively high variance in temperature, as the door is opened/closed, food is taken in/out etc.:

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To set good thresholds for temperature anomaly alarms, therefore, requires some knowledge of how the fridge behaves, and also how it is used. 

Buy a kit today to try out monitoring of fridges, freezers or other cold storage solutions, please visit https://store.disruptive-technologies.com/ to get started.