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Can you self check your thermometer with only ice and water?



  In this month's experiment we are going to go through a way to check if your thermometer or temperature data logger is accurate and check whether it may need replacement or recalibration.

For many industries measuring temperature accurately is very important. For example food safety standards in Australia require all thermometers to be accurate within +/-1C. Below we will go through an easy way to confirm accuracy on your probe thermometers and dataloggers using an ice slurry. Ice slurries are used because they will always have a temperature of 0C (with pure water at standard atmospheric pressure)

Equipment
Large bowl or container
Enough ice to half fill container
Distilled water (or tap water, however this will decrease accuracy)
Thermometer 0560-1113
Datalogger to be tested EL-USB-1
 

Method
Fill container ½ full with ice
Pour in cold water until the ice is almost covered
Leave for 2 minutes and stir for 10 seconds - this is an ice slurry
Place probe of thermometer to be tested into the ice slurry and slowly stir and leave it for around 5-10 minutes. If you are calibrating a datalogger, protect the logger in a waterproof bag and immerse the whole logger in the slurry and leave for 15 minutes or longer.
For the datalogger, download the data and the temperature readings should stabilise around 0°C (± 1°C ) taking into account the written manufacturers specification for the unit. For the probe thermometer, the readings should also stabilise to within 1 degree of 0C.


Figure 1: Ice bath ready to be used for self checking of thermometer and data logger


Figure 2: EL-USB-1 submerged in ice bath taking measurements for review

Results
Both the 0560-1113 and EL-USB-1 returned readings of 0.0C when placed in the ice slurry. As both units returned temperature readings within the ± 1°C of 0°C they meet the requirements of the food standard and hypothetically could be returned to service. 

Figure 3: 0560-1113 displaying exactly 0.0°C in the ice slurry


Figure 4: Graph of the EL-USB-1 over time when it was submerged in the ice slurry

Discussion
Ice Slurry calibration checks are a great way of testing whether a thermometer or datalogger is still measuring accurately as they are easy to make, low in cost, and use readily available items. The units we tested passed calibration perfectly, but it could happen that a thermometer may read high or low by less than 1 degree and still pass calibration. In an instance like this, the difference should be recorded and then this value should be used as a correction factor for future readings. For example if a thermometer read 0.5C in the ice slurry, then 0.5C would need to be taken off the readings whenever this thermometer is used.

If you would like to discuss this experiment further please contact one of our friendly Scientists via email or phone on 1300 737 871.
  

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