Laboratory Samples: Traceable and Non-Traceable Measured Values¶
ConCertainty distinguishes between two types of laboratory samples – depending on whether the measured values obtained with them are traceable or not. This distinction determines which statements you can make about your measurements and which calculation steps are possible when determining measurement uncertainty.
Non-Traceable Measurements¶
Repeated measurements of the same sample over time can be used to determine whether the results are consistent: if the values show little scatter, the measurement is precise. Whether the measured value is correct – i.e., whether it accurately reflects the actual composition – cannot be derived from this.
This aspect feeds into the contribution to the reproducibility of the measurement uncertainty.
In ConCertainty, you create such samples as laboratory samples without certificate data.
Traceable Measurements¶
If a certificate with documented reference values is available for a sample – e. g. for a certified reference material (CRM) or a standard – your own measured values are traceable to these values. This allows you to check whether your own measured values agree with the certified values: if they deviate systematically, a bias is present.
This aspect can feed into the determination of measurement uncertainty via the contribution to comparability (trueness).
In ConCertainty, you create such samples as laboratory samples with certificate data. The certificate contains the following for each parameter:
- the certified value with unit
- the associated uncertainty
- the coverage factor k, if it deviates from the certificate-wide value for a specific parameter
Info
Laboratory samples with stored certificate data are marked in the overview list with a quality-mark symbol.
Effect on Measurement Uncertainty Determination¶
The type of laboratory sample determines which calculation steps its measured values can feed into:
| Without certificate data | With certificate data | |
|---|---|---|
| Contribution to reproducibility | ✓ | ✓ |
| Contribution to comparability | – | ✓ |
If no measurement data is available for a parameter on a sample with certificate data, the comparability component for this parameter cannot be calculated – in this case, the calculation is automatically omitted.
Info
Make sure that the parameters stored in the certificate match the parameters of the test profile being used – and that the respective stored unit is identical to the unit of the test profile. Only if the parameter matches and the unit is identical can the sample be used as a comparability sample for this parameter.