**6. Conclusions**

In this paper, we presented the measurement setup for the calibration of measurement bridges for non-conventional instrument transformers. We have discussed the main implementation challenges and characterized the most significant uncertainty contributions. Based on technical specifications and statistical analysis, we have performed a comprehensive uncertainty budget of the calibration setup that has been further validated by an experimental measurement campaign carried out at METAS laboratories.

The proposed analysis allows for identifying the main challenges of a calibration process that requires a synchronous generation of both analog and digital quantities. The research project will now focus on the minimization of the uncertainty contributions (with specific attention to the analog measurement chain) and on the extension of the proposed infrastructure to non-stationary signals, as the ones that a plausible instrument transformer might deal with in field applications.

**Author Contributions:** Conceptualization, G.F.; Formal analysis, G.F.; Investigation, G.F.; Methodology, G.F.; Supervision, M.A.; Writing—original draft, G.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project (17IND06 FutureGrid II) has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
