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Implementation and Verification of Building-up AC-DC Current Transfer up to 10 AMamdouh. M. HalawaAC-DC Difference @ 10 mA (100 % of rated current)AC-DC Difference @ 5 mA (50 % of rated current)Current level-dependence of the 10 mA TCC at 55 Hz6.0 µA/A3.1 µA/A-2.9 µA/ATable 1. Current level-dependence of the 10 mA TCC, for example, at 55 Hz.Figure 3. AC-DC difference of 10 mA TCC at 50% and 100% of the rated current.Current level-dependence corrections (μA/A)Range 10 Hz 55 Hz 500 Hz 1 kHz10 mA 6.9 2.8 - 7.7 - 4.725 mA 3.5 - 17.9 - 12.5 - 1450 mA - 4.1 - 11.9 - 0.8 -12.7100 mA 0.2 - 7.6 - 6.4 - 6.8250 mA - 8.5 - 8.2 - 0.2 6.20.5 A - 1.4 - 2.8 - 0.8 - 14.81 A -7.8 - 3 - 3.6 - 22.62.5 A - 0.2 5.2 - 9.3 - 0.15 A 0.7 0.5 0.5 3.610 A 0.2 12.3 18.2 6.2Table 2. Current level-dependence corrections of the building-up process.Figure 4. Variation of the level-dependence correction, for example, of 50 mA, 0.5A, 1Aand 10 A.3. Measurement of Level-Dependence of TCCsSelf-heating is assumed to be thecause of current level dependence ofthe AC-DC difference in shunts. Thisleads to the approach to measurecurrent level dependence usinga shunt with negligibly low selfheatingas a standard [13]. This leveldependence is, of course, taken intoaccount when determining the AC-DC differences of the CTTs set at thedifferent frequencies.In the present work, two TCCs(PMJTC and Holt) were loaded atboth full and half of their nominalinput current (10 mA) to evaluatetheir current level-dependences. TheHolt TCC (UUT) was first connectedin series with the reference converter(PMJTC) and its AC-DC differenceswere measured at the full signal (10mA). Then the UUT was connected inparallel with a similar one (2nd UUT)(or a precise resistor) having the samerated current and then connected inseries with the reference converter(PMJTC). The AC-DC differenceof the UUT was measured anothertime against the reference converter(PMJTC). With this configuration,the injected current of 10 mA fromthe system fully flows throughthe reference converter (PMJTC),hence the conditions at the referenceconverter (PMJTC) remain unchanged,while only half current (~ 5 mA) flowsthrough the UUT. The results fromthe two tests were compared and thecurrent level-dependence of the UUTwas then determined at 55 Hz, forexample, as listed in Table 1. Fig. 3shows the results of the 10 mA TCC. Itcan be seen that the AC-DC differenceof the 10 mA TCC decreases withhalved injected current.As illustrated in Fig. 3, the changein the AC-DC differences are 6.9, 2.8,7.7 and 4.7 μA/A at 20, 55, 500 and1000 Hz respectively. Comparedwith the usual low uncertainties (afew μA/A) of the AC-DC differencesfor this type of calibrations, thesechanges are significant and correctionsCal Lab: The International Journal of Metrology30 Oct • Nov • Dec 2012