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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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