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Temperature monitoring of freezers

1 November 2019 Tags: temperature freezer strains storage

When I started my own lab we simply did not have any mechanisms in place in the Division to measure temperatures in critical freezers and to raise an alert. For our day to day work we use a –20°C freezer for stocks. Strains do not last as long, but it does make day to day strain work significantly easier. Early on I tried to find a suitable system for temperature monitoring that could raise an alarm when temperatures reach a critical point. At that particular time VWR was the only company that offered equipping a large –20°C freezer with an alarm and alert system for a reasonable price of about £950, much cheaper than a lot of other companies. However, the problem was that, conveniently, they asked for the entire freezer being shipped to their installation site.

When I discussed the issue a couple of years later with Philip Dunning from SLS he pointed me towards Testo and within less than a week I had a very friendly sales representative in my office. For what I want and need their products are fantastic. They offer a range of measuring devices and solutions to keep users informed of all sorts of environmental conditions, including temperature measurements. I opted to try their Saveris 2 T2 temperature logger in combination with a flat cable temperature probe. The small logging device sits outside of the freezer and is connected with the temperature probe inside the freezer via a reasonably flat cable. There is a mild distortion of the door seal by the cable, but as far as I can tell temperature loss is minimal. Testo is also offering a device completely situated in the freezer, but connectivity is a greater issue here, and since I was running into connectivity issues anyway I did not want to try this particular solution.

I had an initial problem in setting up the device, but this was fixed within a short period of time by absolutely fantastic and very competent phone support. By now we have 5 of these devices in the lab and setting them up has never been a problem again. The data logger need to be configured to access a local WiFi network. Once a connection is established the loggers access a dedicated cloud service provided by Testo where temperature readings are recorded. This can be extensively customised to define upper and lower temperature limits that trigger user alerts, but as data points are stored over long periods fluctuations can be monitored, which will help in detecting the decline of a certain freezer. When I set up the devices our IT department was utterly unhelpful in allowing network access, but it was very easy to set-up a small local personal Wifi network, which has not given me any grief in years. Three was the only company at the time to offer a SIM with network data that wil not expire and the data volume generated by even 5 loggers is absolutely tiny. Occasionally the loggers will download firmware upgrades if necessary, but even these are very small. Up to 10 data loggers can connect to a single Wifi network.

For our needs the system simply works and has been working for years. For our specific configuration we do encounter relatively regularly that the logger fails to connect to the Wifi network. They normally successfully pick up the connection next time they try to connect, but the connection failure triggers an alert, which is indeed necessary, because if the connection failure persists then obviously critical limits will obviously not trigger the necessary alarms. However, as these are triggered every now and then I never have used the SMS alert option, but rely on email alerts. So far I never felt that this was a problem. There were only a few instances where critical temperature limits were reached, all of which generated by user manipulation rather than failure. The system picked all of these up without any issue and the alarm was correctly raised, allowing us to respond and double-check.

A single data logger comes with two ports. Thus, if freezers are physically close two separate probes can be read by a single logger. Alternatively Testo also offers door monitors, which we are currently not using. Thus, it is possible to monitor temperature and whether the door is tightly closed or not, which we will start to use in the near future. The combination of one data logger and a single ribbon probe a couple of years back came to under £250. This includes free basic cloud support, with a premium upgrade being available for purchse. However, at least for our needs the basic option is more than sufficient.

Overall I am extremely happy with this system and happily recommend it to anybody with similar needs.

The Saveris 2 temperature logger is produced by Testo AG and was purchased via SLS.