After common temperature logger mistake 1 of not being turned on, mistake number 2 is reported to us less, but more common. There are many users who set their sample rate to one sample every couple of hours. This is typically 4 hours for the Thermocron and even slower for Logtags.
The likely cause
This is likely a hangover from min/max thermometers, where staff would check them once or twice a day and write down the readings. Users believe that the sample rate is repeating this process. The reality was that a min/max thermometer was responding reasonably quickly to changes in temperature and would “remember” the highest and lowest temperature. In one sense, they were sampling every second of the day and only remembering two readings – the highest and lowest.
The Consequences
For a temperature logger to adequately capture temperature variations, it should sample at a reasonably fast rate, defined as fast enough to obtain a couple of readings during an event of interest. For instance, if you’re concerned about whether the temperature exceeded the limit for half an hour, a sampling rate faster than 30 minutes is essential. We would recommend a sample rate of 10 to 15 minutes to ensure meaningful coverage.
Sampling only once an hour runs the risk of entirely missing the event. Furthermore, if a sample is captured, estimating the duration of the event becomes challenging. With a one-hour sampling rate, you only know that the reading was good an hour before and an hour later, leaving the event duration uncertain, ranging from minutes to nearly two hours. With a sample rate of 4 hours, this scenario worsens, as the event could potentially last from minutes up to almost 8 hours. The difference between stock being too warm for 8 hours and for just 30 minutes is significant.
The Solution
The solution is very simple. Sample more frequently.
Reality
The reality is that stock in fridges and freezers take time to heat up and cool down so an incident in a fridge or freezer will actually need to last a reasonably long time to have an impact on the stock. So slowing the sample rate down to 20 to 30 minutes is justifiable. My recommendation is to keep it at or below 20 minutes.
The other extreme
In the next blog, we’ll cover the other extreme.