How to measure temperature in freezers, fridges and cold storage rooms

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 ensure the quality of the goods. 

Disruptive Technologies offers a wireless temperature solution for accurately monitoring cold storage in various environments. It uses Temperature Sensors and Probes combined with APIs and dashboards.

• Grocery and convenience stores can use the solution to maintain food shelf-life and minimize waste.
• Food service environments can use the solution to ensure food safety and quality.
• Healthcare can use the solution to provide the safety and compliance of stored medical products and biomedical samples.

In addition, consistent temperature monitoring can help to identify poorly performing units that need maintenance to avoid downtime and reduce energy waste.

The DT Smart cold storage solution

Wireless Temperature Sensor

The Wireless Temperature Sensor accurately measures the temperature of the surrounding environment.

The Ambient Range Extender

The temperature sensors should measure the air temperature inside the cold storage unit. To reduce the influence of surface temperatures when measuring temperature, the sensor should be insulated towards the material on which it is mounted.

Use the Ambient Range Extender (2nd Gen) to ensure good ambient temperature reading, increased radio range, and robust mechanical mounting using industrial adhesive or cable ties.

Note! Placing the sensor directly on metal without the Ambient Range Extender significantly reduces the wireless range, as shown in the illustration below. 

Wireless Temperature Probe

The Temperature Probe connects with any PT100/PT1000 probes, providing accurate temperature measurements (±0.2°C / ±0.36°F). It is ideal for consistent and precise temperature monitoring in various applications when the regular Temperature Sensor is unsuitable.

DT Studio & API

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

Installation advice

To ensure accurate temperature readings, follow the installation manuals and these simple guidelines:

✅ Choose the right spot
Install the sensor away from direct airflows (like doors or vents) that could affect readings. Place the sensor close to the discharge vent for the best understanding of unit performance.

✅ Secure the sensor
Make sure the sensor is in a stable location to prevent it from being knocked off or disturbed. If the sensor is fastened using adhesives, ensure the surface is dry, clean, and warm.

✅ Keep it consistent
If you’re installing sensors in multiple units, place them in the same spot for consistent results.

✅ Document everything
Note the exact location and how each sensor is mounted for easy maintenance. You can also take photos of each installation to keep a visual record for future reference.

Analyzing the temperature measurements

1. Initial setup and verification
2. Use notifications
3. Data analysis in DT Studio
4. Long-term trend analysis

Initial setup and verification

After installation, it is essential to verify that all equipment functions correctly and maintains the prescribed temperature ranges. Both examining data in Studio and setting up notifications can be leveraged to identify potentially faulty equipment.

Use notifications

Focus on units that generate frequent alerts, as a high alert frequency often signals the need for maintenance or a detailed inspection.

Data analysis in DT Studio

Setting suitable thresholds for temperature anomaly alarms requires 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 gradually rises until a new threshold is reached. At this point, the compressor starts, and then the cycle repeats. This process gives the temperature data a sawtooth-type pattern; see illustrations below.

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

Defrost cycles

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

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

Fridges in active use

An actively used fridge experiences significant temperature variations as the door is opened and closed. The temperature fluctuates throughout the fridge - door compartments are typically warmer due to exposure to warm air, and colder areas are usually found on the bottom shelf since cold air sinks.

Additionally, temperature varies based on how full the fridge is; a fully stocked fridge retains cold better and maintains more stable temperatures, while a half-empty fridge allows for increased air circulation, leading to more significant fluctuations.

Long-term trend analysis

Monitor individual sensor data over extended time frames, paying attention to gradual changes in average temperatures. A consistent rise or drop could signal the need for maintenance or suggest a potential future failure.