Analysis of a national comparison in the field of electrical low dc resistance

• A comparison on low resistance among INRIM and 19 Laboratories gave positive results.
• Three standard resistors were characterized before their circulation.
• The measurements were corrected at 23 °C to enhance the comparison significance.
• The traceability transfer from INRIM to Secondary Laboratories is correct.
• The verification of the procedures by the Accreditation Body is satisfactory.

In this paper a measurements comparison between the National Institute of Metrological Research (INRIM), acting as pilot Laboratory, and nineteen Italian Secondary Calibration Laboratories in the field of low dc Electrical Resistance is presented and discussed. This comparison was carried out on commission by the Italian Accreditation Body of Calibration Laboratories ACCREDIA-DT. As traveling standards three Tinsley mod 3504C four terminal standard resistors to be calibrated in oil respectively at 5 A and 20 A (1 mΩ), 1 A and 5 A (10 mΩ), 0.1 A and 1 A (100 mΩ) were involved. The temperatures at the measurements thermal regimen allowed a correction at 23 °C of the results. The comparison results, shown graphically and as distribution of the normalized errors, were satisfactory, except in the case of a Laboratory whose measurements were outside its accreditation field.