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Temperature Logger – Sample rate and memory

This part continues exploring the jargon involved with temperature loggers and focuses on the sample rate and memory size. These are critical because they determine how long a logger can be used for before information is lost.

Sample rate

This is how often the logger will record the temperature. Most loggers offer a programmable sample rate meaning you can set how often it will make a recording.

If the sample rate is set too slow then it could possibly miss an event. For example, if it is set to 30 minutes then it could miss a 15-minute rise in temperature. If it is too fast then it will consume more memory and the results will take longer to check.

For transport and storage applications a sample rate of between 1 and 30 minutes is typically required. A good recommendation is 10 to 20 minutes because this doesn’t consume a large amount of memory but is fast enough to see significant changes in temperature.

When processing items (e.g. cooking or cleaning) sample rates down to 1 per second could be required.

NOTE: Some people change from a min/max thermometer to a temperature logger and think that one reading every 12 hours gives them the information they need (i.e. two readings). This is not the case. You must sample often enough to actually record an event.

Memory

The total number of samples the logger can record is critical. It determines the fastest sample rate that is possible for an application. Once the memory is full the logger will either stop or write over the oldest readings. Either way information is being lost. The larger the memory, the better the device.

NOTE: Transferring the information to the PC means that you can re-use the memory again. You are not losing information because it is permanently stored on the PC.

The maximum time the logger will record is the sample period times the memory size. The following graph shows the duration of a logger with the sample rate set between once a minute to once every 30 minutes. Four different memory sizes are displayed.

For example, an item is to be transported for 30 days. A unit with 2048 readings memory could sample with a period of 22 minutes. It is decided that a sample period of 15 minutes is required. A unit with at least 4096 readings is required.

Help!

Don’t panic if this is confusing (or if you just hate maths). Just contact OnSolution on 02 9614 6417 and let us know what your application is. We can recommend the best unit for your needs.

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