19.1 Introduction

Traceability is defined as an unbroken chain of comparisons (calibrations), each having a stated uncertainty, which relates the result of a measurement or the value of a standard to stated references. Wherever practical the maintained electrical standards are taken as such references.

A chain of measurements can be extended from any convenient reference point in such a chain, providing the route to a primary standard of measurement can be traced. An accredited calibration laboratory provides a widely accepted point of reference in the chain of traceability. [3]

Although in many countries traceability through accredited calibration laboratories for a range of measurements (mass, temperature, low voltage) is readily available, a similar service for high voltage measurements is not so common. The concept of the approved measuring system introduced in IEC Publication 60060-2: 1994 [1] helps to redress that deficiency.

The concept regards the complete measuring system as an entity in the traceability chain, and it includes the voltage divider (or other converting device), lead from the test object, lead damping resistor, low voltage transmission system, attenuator, recording instrument and earthing cables.

The designation of Approved Measuring System is applied by the user to a measuring system which is shown to comply with requirements of an Initial Performance Test (I). The designation cannot be presumed to apply indefinitely, and the user is required to perform regular performance checks, and to repeat the performance test at less frequent intervals. The results of all of these calibrations and checks are...