In the world of testing laboratories, ISO 17025 is the gold standard for quality management. However, a critical question arises: Can a laboratory satisfy all ISO 17025 requirements without meeting some basic criteria regarding test data fidelity, resolution, and accuracy? The answer, surprisingly, is a huge ‘Yes’ – and the implications are significant.
1.0 The ISO 17025 Paradox
ISO 17025 sets out the general requirements for the competence of laboratories. While it emphasizes the importance of reliable results, it doesn’t explicitly define minimum standards for data resolution or accuracy.
1.1 A Tale of Two Resolutions: 14-bit vs. 24-bit Data
We’ll compare the results obtained using two different data acquisition systems: one with 14-bit resolution and another with 24-bit resolution. Machine manufacturers show these as counts.
>> 14-bit Resolution System
– Number of discrete levels: 2^14 = 16,384
– Load resolution: 100 kN / 16,384 ˜ 6.1 N
>> 24-bit Resolution System
– Number of discrete levels: 2^24 = 16,777,216
– Load resolution: 100 kN / 16,777,216 ˜ 0.00596 N
2.0 Data Comparison:
Let’s look at our test data:
Example: Say the machine outputs the first data point with value of 9993.9N The 14-bit DAQ will show it as 10000.0N and the immediate next point acquired during the test will be shown as 10006.1N and next data point as 10012.2N. There are no data points available between 10000.0N, 10006.1N and 10012.2N, as the best resolution the machine and the DAQ can offer is only 6.1N.
As you can see with these kinds of losses, you will invariably miss or get wrong values of peaks in the test curve.
For soft matter and rubber materials, these low-resolution data points may put you on the wrong path of material compound development and failure analysis. For use in FEA-CAE, the test data needs to be flawless.
In comparison the data from a 24-bit system will have a resolution to a value of 0.00596 N and you are well covered to get the right peaks break & modulus for any kind of material.
3.0 The ISO 17025 Compliance Conundrum
Here’s the catch: The 14-bit systems fully satisfy ISO 17025 requirements but don’t directly address the fundamental issue of test data fidelity, or accuracy
4.0 Conclusion: Beyond Compliance
Compliance with ISO 17025 while important, is not always sufficient to ensure that test data meets the needs of all end-users and provides them the quality that is required.
Scientists & engineers must look beyond mere compliance and consider the specific requirements of their applications.
When selecting a laboratory, one should consider asking:
1. Resolution of the data acquisition system?
2. Is the equipment appropriate for the level of precision required?
3. What is the data rate of the equipment?
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