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Calibrating DC Current Shunts: Techniques and Uncertainties Jay Klevens, Ohm-Labs, Inc. © 2011
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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.
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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
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Intrinsic Standards Volt – Josephson Junction Ohm – Quantum Hall Resistor Ampere – Derived from measuring Ohm & Volt
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Practical Measurement Volt – Calibrated Voltmeter Ohm – Calibrated Resistor (shunt) Ampere = Measure voltage drop across resistor and use Ohm’s Law: I = E/R
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving the POTENTIAL points changes the resistance.
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving the CURRENT points changes the resistance.
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Moving CURRENT points on multiple hole shunts
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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
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time ALL metals change resistance with temperature
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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
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Different current = different temperature
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Current effect = temperature effect
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time Inductive & capacitive components and coupling
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Characterizing Current Shunts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time ‘Organic’ drift + heat + transport
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Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard
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Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard
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Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard Metering shunts vs. Metrology shunts
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Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard
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Calibrating Current Shunts 1)Comparison against calibrated shunt 2)Comparison against resistance standard Current comparator bridge
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Larger error bar uncertainties use the ‘comparison against a calibrated standard shunt’ method. Smaller error bar uncertainties use the ‘current comparator bridge’ method.
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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)
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100 Ampere ILC Artifacts 1)Four-wire resistors 2)Temperature dependent 3)Frequency dependent 4)Drift over time
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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
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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
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