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Understanding Your Calibration Certificate

Interpreting you Calibration Certificate
 
When you a faced with a Calibration Certificate for your equipment - it can be confusing to know what is important and how to interpret the information provided.cert image crop
 
Below is 5 very easy steps to understanding a Calibration or Test Certificate
 
The report will be divided up into 5 main areas
  1. The details about the IUT– instrument under test (your instrument)
  2. The testing laboratory’s reference equipment details
  3. The test method used
  4. The results including the corrections
  5. The uncertainty
 
Instrument under test
The IUT must be uniquely identified in such a way that it will not be confused with another item
 
Reference
The testing laboratory equipment and test method is required to be on the Certificate by the regulatory bodies
 
Results
The results should contain your instrument readings and a correction. Always add any correction given on the Report. This will improve the accuracy of your IUT.
 
Example
A reference thermometer reads 100 °C.  Your thermometer reads 102 °C. The correction is -2 °C.
 
Therefore if your thermometer is reading 98 °C when you measure your process then add -2 °C.
Your process actually measures 96 °C.
 
By applying corrections you get the very best out of your equipment – you improve its accuracy.
 
                                                                Uncertainty
conf1Any IANZ endorsed report will have an uncertainty statement on it. This is where we see people’s eyes gloss over & people struggle to understand what it means.
 
An uncertainty statement allows you to have a certain level of confidence in your results. In the example above we have determined your process is 96 °C but how certain are you of that?
Check the report…
For example the uncertainty may be stated as ± 0.2°C. That’s great as I now know my process is measuring between 95.8 °C and 96.2 °C.
 
Your report will also give a k factor. E.g. k=2.
The k factor is a statistical calculation that lets you know how often my uncertainty will be ± 0.2 °C.  When k = 2 you would be safe to assume that 95 % of the time my instrument reading will have an uncertainty of  ± 0.2 °C.
 
It’s good to have a low uncertainty value as this usually means your instrument is precise, has good resolution and the testing laboratory has good reference equipment.
 
If your instrument does not read precisely in a stable environment (gives repeatable readings) then buy a new one.
You will never have confidence in your equipment and you will never be able to trust the results.
 
It is better to have a repeatable, inaccurate instrument than an imprecise one because you can always apply the corrections to achieve an accurate reading.
 
Need help. Contact Teltherm.
 

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