A very common question is “why does my temperature logger have different values to the fridge display?” For example a fridge may have a digital display and a temperature logger but they never show the same temperature. They may show a different range (e.g. one may only fluctuate by 1° while the other by 3°), or have a different average (e.g. one may show 2 to 3° while the other 2.4 to 3.4°) or both.
Is the discrepancy showing the logger or fridge is wrong because surely it must be impossible for them to both be right?
The short answer
It is possible for the readings to be significantly different. If they are both within the required range then don’t worry about it.
If, however, they are outside the required range you will need to assume they are both correct, and determine why one of them is too hot or cold and fix the problem.
Sources of differences in temperature readings
There are a number of reasons why the readings could vary significantly.
- The inaccuracy of the units may cancel each other out or add to each other. That is, if you are using two devices with a 0.5° accuracy (which are both HACCP compliant) it is possible for them to differ by up to 1° to each other and still be compliant because one is half a degree low and the other half a degree high.
- 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. For vaccine fridges, even though they have a fan circulating the air, they will still have locations that are significantly cooler (where the cool air enters the fridge) to others (where there is poor air circulation or where it returns out off the fridge). Over stocking a fridge makes this significantly worse.
- Some devices respond to the temperature faster than other devices. These devices will appear to have a much larger temperature variation then a device with a slow response time.
- 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 one is wrong. There are reasons for the variations. If you have results that you can’t explain please contact OnSolution on 02 9614 6417 and we will gladly discuss them with you.