Measurement Techniques for Evaluating Current Range Extenders from 1 Amp to 3000 Amps
Marlin E. Kraft
When measuring standard resistors at different ratios with a Direct Current Comparator (DCC) incorporating Current Range Extenders (CREs) how do you know the value measured is correct and how can you evaluate the measurement uncertainty? This paper will discuss a process developed at the National Institute of Standards and Technology (NIST) that measures a set of low value resistors at the same current using different ratios. The design of modern automated DCCs allows measurement currents up to about 150 mA, and DCCs can operate at 1:10 ratios with uncertainties well below one part in 10-6. Higher currents require CREs with ratios from 1:10 to 1:100,000 or more. I will explain how low uncertainties can be obtained by measuring high quality medium current resistors at different power levels so that they can be used as standards when measuring the high current resistors. By using this measurement technique, you will be able to determine if your range extender is functioning properly.