In this final part on temperature loggers we investigate the other specifications and features that differentiate temperature loggers and thermometers.

Software The great benefit of loggers is the ability to view the results and save them for later use. Each logger will typically have its own software. They vary in what the software can do and how easy it is to use.

If customised software is required contact OnSolution on 02 9614 6417 and they can work with suppliers to provide a product that meets your requirements.

Construction Like most items, temperature loggers break. Consideration should be given to the robustness of the logger if it is to be transported or regularly moved. Stainless steel loggers are available. Most loggers are plastic Water resistance is another feature that should be considered if the logger is to be used in a wet or dirty environment. Water damage is a common occurrence. Within the food industry it is strongly recommended that water-resistant loggers be considered.

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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.

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A very common question is “why don’t two monitoring devices show the same temperature?” For example a fridge may have a digital display and a temperature logger but they never show the same temperature. Is the logger discrepancy showing the logger is wrong, because surely it must be impossible for them to both be right?

There are a number of reasons for this:

The inaccuracy of the units may cancel each other out or add to each other. They are monitoring different locations. There is a large temperature variation in fridges, containers, rooms etc as you move from the centre to the outside, top to bottom and even left to right. Unless the two sensors are in identical locations, they are measuring different temperatures. Some devices respond to the temperature faster than other devices. This is discussed in a previous blog. Some devices provide a calculated value. This is particularly true for vaccine fridges where they simulate a vial of a particular size. Do not assume that one is right and...

Sources of errors It should be noted that the accuracy is dependent upon a number of factors. They are:

The instrument: The device itself will cause errors because of limitations in digital processing and physical issues (eg "cold junction compensation" with thermocouples). Sensor: The sensor is often the greatest source of error in the reading. It is also difficult to compensate for sensor errors. It requires that only sensor ever be used with the instrument and that it be used at a certain temperature. Thermistors and PT100s are interchangeable within 0.4°. Thermocouples, however, have much larger errors. Type K can have errors up to 2.2° and 1° for type T. Special tolerances can reduce the Type T's errors by half and make them acceptable for use with food. Type K should never be used with food. They are outside the 1° accuracy required. Note that the accuracy required is the total of the instrument and sensor error. For example, if an instrument has a 0.4° error and a sensor has...

Resolution The resolution is an indication of how specific the answer is. It is measured in degrees. The smaller the value, the better the device. For example, a resolution of 0.5° means that a reading of 3.5° could be between 3.25° and 3.75°. A resolution of 0.1° means that a reading of 3.5° could be between 3.45° and 3.55°.

The maximum permissible resolution depends upon the application. For example, when monitoring body temperature it is critical to have at least 0.1° resolution. For food this degree of resolution is often not necessary. The change in temperature that has to be recorded is a couple of degrees and a resolution of 0.5° is often acceptable.

Accuracy The accuracy indicates how close to the actual temperature a reading is. The smaller the number, the better the device. The current HACCP requirement in the food industry for accuracy is typically 1°C.

Accuracy versus resolution The difference between accuracy and resolution can be seen in this simple analogy.

Two people...

Temperature loggers have been used to monitor refrigerators and freezers for many years now. They can also be used for display and serving areas. This provides critical information on how your equipment is operating.

There is also a rapidly growing demand to monitor individual pallets or boxes. This then allows the user to detect if the product has been left out of the refrigerator or freezer, when and for how long. It provides critical information on how your operating procedures are being followed.

If you are involved with the transport of food then temperature loggers can now stay with your products from start to finish. On one side, temperature loggers are now being used to monitor everything from beef, pork, chicken and sea food to fruit, vegetables, nuts and berries to milk and dairy products to frozen products. On the delivery side temperature loggers are monitoring caterers, deliveries and mobile food stalls.

Over the next couple of months I plan to write more about specific applications.

Find the cause Since the time and date are recorded it is possible to tell when temperatures occurred. From this it may be possible to determine who was in possession of the item, or who was working at the time. This information can then be used to help place the responsibility on the correct party or fix the problem. Ultimately it can help stop the problem occurring again.

An exporter discovered that his goods had been left on a tarmac for a number of hours in a tropical country. The temperature logger clearly indicated when it occurred and for how long. In this case it was possible to place the liability but it also meant that the problem could be addressed to stop it happening again.

Not all cases are this easy. With no supporting proof, however, it is nearly impossible to force a company to accept responsibility for spoilt items and fix the problem.

Save money The shelf life of many items is temperature dependent. Maximise shelf life by ensuring items are always at the right temperature....

Thermometers simply display the current temperature. Many people will already be using thermometers within their business but they have some significant limitations. Just because the temperature is right now (as shown on the thermometer) does not mean that it was always right. A min/max thermometer partially fixes this issue by telling you if it has been outside the temperature limits.

So a thermometer can tell you if things are good or bad now, and a min/max thermometer can tell you if things have always been good or bad, but that’s it. You don’t know when things started to go bad, how often, or for how long. Thermometers are an essential part of ensuring that your staff are aware of the temperature and are keeping an eye on it.

Temperature loggers This is where a temperature logger becomes an invaluable tool. A temperature logger records the date, time and temperature at regular intervals. The results can then be displayed at a later time. It is like having someone constantly writing down the...

For the transport and storage of vaccines 2° to 8° are the critical temperatures. In fact, vaccines are still viable below 2° but once some vaccines freeze they are no longer viable. So 0° is actually the super critical vaccine temperature and 2° provides a buffer zone to take into account inaccuracies and other sources of variations.

Higher temperatures will shorten the shelf life of a vaccine. It is similar to storing milk – the warmer it is, the shorter the time it will last. The “Strive for 5” campaign is focused on providing an optimum temperature to aim for. It moves the focus away from the negative and to an ideal.

There are a number of temperatures that play a key role within the food industry. The obvious ones are 0° and 100°. After all, the drinks need ice and the tea has to be hot. 22 to 24° is the ideal room temperature.

5° and 60° have been specified within the Australian New Zealand Food Standards Code as being the range in which microbiological growth can occur. This is the danger zone. If food is left too long within this temperature range then potentially deadly micro-organisms can grow.

Heating food above 60° will kill the micro-organisms. It will not, however, remove the toxins that may have been introduced. Cooling food to below 5° will almost slow the growth of micro-organisms.

The Foods Standards Code states that if you are receiving, storing, processing (including defrosting and preparing), cooling, reheating, displaying and transporting potentially hazardous foods then you must be able to prove that you have not exposed the food to this critical temperature range for too long.

If...