1. Calibrating DC Current Shunts: Techniques and Uncertainties Jay Klevens, Ohm-Labs, Inc. © 2011

2. Measurement results normalized to NIST opening & closing values. Scale in ppm. Labs without data points are off the chart. Lab ‘X’ points are pivot laboratory checks.

3. SI Units of Measure 1820 – Ampere: electromagnetic force between two wires determined by a Watt Balance (electromagnet) 2015 – (proposed) by counting electrons over time André-Marie Ampère

4. Intrinsic Standards Volt – Josephson Junction Ohm – Quantum Hall Resistor Ampere – Derived from measuring Ohm & Volt

5. Practical Measurement Volt – Calibrated Voltmeter Ohm – Calibrated Resistor (shunt) Ampere = Measure voltage drop across resistor and use Ohm’s Law: I = E/R

6. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time

7. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving the POTENTIAL points changes the resistance.

8. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving the CURRENT points changes the resistance.

9. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving CURRENT points on multiple hole shunts

10. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Changing TORQUE on the current bolts changes resistance

11. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time ALL metals change resistance with temperature

12. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Shunts can take ONE HOUR or more to stabilize

13. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Different current = different temperature

14. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Current effect = temperature effect

15. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Inductive & capacitive components and coupling

16. Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time ‘Organic’ drift + heat + transport

17. Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard

18. Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard

19. Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard Metering shunts vs. Metrology shunts

20. Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard

21. Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard Current comparator bridge

22. Larger error bar uncertainties use the ‘comparison against a calibrated standard shunt’ method. Smaller error bar uncertainties use the ‘current comparator bridge’ method.

23. 100 Ampere ILC What went wrong and why: Four-wire resistors – connection errors Temperature dependent – not factored <0.2 ppm + <0.2 ppm + <0.2 ppm + UUT (type A)

24. 100 Ampere ILC Artifacts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time

25. 100 Ampere ILC – 2 nd Round 1)Four-wire connection errors 2)Temperature dependence 3)Frequency dependence (n/a: dc only) 4)Drift over time Goal of second round of 100 Ampere ILC: Address and correct type B measurement errors Final results to be presented in Measure Magazine

26. Thanks to NCSLI and its Utilities and Measurement Comparison Committees NIST for measurement services and technical assistance And especially, All the participants for your efforts and contributions