Advances in High Current and Resistance Measurements to 11,000 Amps and Higher Guildline Instruments Limited

Introduction Presenter, Co-author Richard Timmons President Author Mark Evans, Guildline Engineering R&D Product Manager, DC Resistance Instruments

Presentation Outline Direct Current Comparator Measurement DCC Bridge Current Range Extenders Modular 150A DC Current Module Current Sharing Semi-Conductor Switching Performance Results Applications and Conclusions Range Extender Implementation to 3000A Current Source Operation to 11,000A Presentation Overview

The Direct Current Comparator Guildline Instruments Limited

Direct Current Comparator Bridge Ratio is Determined By Driving current/voltage through both Std. and D.U.T. resistors Toriod Turns are switched to achieve ampere-turn balance Nanovoltmeter interpolation of the residual imbalance Older bridges also use resister divider networks (i.e. partial windings) Current Reversal The current is reversed to remove thermal EMF’s P Ref.P Test Direct Current Comparator Bridge 0 – 150 mA 0 – 150 mA 0 – 150 mA Micro Controller

Existing solutions were difficult to set up and operate, requiring several devices in a system to work together to achieve a measurement These devices all have to be configured independantly Single Stage and 100A Supply

Used for very large currents where transformation ratios must exceed 2000:1 to operate with a DCC bridge (typically >100A) Multiple power supplies Multiple cascaded range extenders High current systems require pneumatic switch to reverse polarity using inert gas (typically argon) Difficult and expensive to operate Majority of the complexity is in the current generation and reversal Multi-Stage for Higher Currents

Modular 150A DC Current Module Guildline Instruments Limited

150A Modular Current Source Guildline Goals Modular 150A DC Current Source 150A on a Single PCB, Switching Power Supply Parallel Array for Larger Currents >10,000A Designed for DCC Metrology Accurate to 0.1% Excellent Stability at 0.1 ppm Low Noise, Drift, and Temperature Coefficient Built in Polarity Reversal

150A Modular Current Source Over $1Million R&D Investment These design goals have been met Patent Pending

Performance Results Guildline Instruments Limited

Noise Characteristics Smooth quiet current source, even at high power output - following trace taken with a differential probe across the 0.05 Ohm shunt at 75 Amps The ripple at the top is Johnson noise (it is there even when the 150A board is powered off) > 500nA noise at 75A

Noise Characteristics Current is ramped up and down on polarity reversal minimizing any transients or inductive spikes on polarity reversal

Other Characteristics The accuracy and reproducibility of the current source was determined over an operating temperature range of 30 – 100 degrees Celsius to ensure desired specification over expected worst case conditions Current stability was measured to be much less than 0.1ppm over 24 hours and maintained a reproducibility of better than 0.1% The output current of 0 to 150A is proportional to the input program current of 0 to 150mA at a ratio of 1000:1 Polarity switching is done at the 150A level through semi-conductor switching on the PCB The current ramps to zero at all polarity reversals reducing inductive load transients

Other Characteristics The voltage compliance reaches 9V, however the circuit is power clamped at 300W The current supply has an efficiency of 72% at 300W of power and a power factor of 99% at 300W Engineering testing at 150% rated power These specifications prove very favorable for larger current arrays greater than 1000A.

Applications and Conclusions Guildline Instruments Limited

Single Stage Range Extender High Current (up to 300 Ampere) Source Built up in 150 Ampere modules paralleled with built in polarity switching High Current Comparator 1:2000, divides current to 150 milli- Amperes Servo Tracking amplifier drives 150 milli-Amperes into DCC Resistor under test up to 300 Amperes 300A can be run on a single 120V AC circuit Test Resistor P Test x2000 Current Range Extender to 300 Amperes 0 – 150 mA 0 – 300 Amperes Micro Controller P Ref. Direct Current Comparator Bridge 0 – 150 mA 0 – 150 mA 0 – 150 mA x2000

Using a programmable integrated solution greatly simplifies the setup to make the measurement Configuration and control of the whole system is accomplished directly through the bridge or connected PC No need for mechanical relay or switch Single Stage 300A Setup

300A Measurement Data Measurement at 300A with a 100 micro-ohm shunt was repeated 12 times with a reproducibility of +/- 1.37ppm

Multi-Stage Range Extender High Current (3000 Ampere and higher) source built up in 150 Ampere Modules paralleled with built in semiconductor polarity switching High Current Comparator 1:1000, divides the current to 3 Amps that is fed into the Intermediate Current Comparator Servo Tracking Amplifier drives 3 Ampere Current Source

Multi-Stage 3000A Setup Semiconductor switching eliminates the need for compressed gas to mechanically switch the high current The range extender and integral current supplies are all completely controlled by the bridge or PC As simple to use as Single Stage Requires only a single phase 208V to 240V AC at 3000A

1000A Measurement Data Measurement at 1000A with a 10 micro-ohm shunt was repeated 12 times with a reproducibility of +/- 5.67ppm

3000A Measurement Data Measurement at 3000A with 0.1 micro-ohm shunt was repeated 12 times with a reproducibility of +/- 9.24ppm Better uncertainties with higher ohm shunts

Guildline 6623A Series For use as a range extender Guildline ONLY Specifies System Uncertainties because Range extenders must be used with a Bridge Range extenders always use a power supply

Range Extenders Calibrated via Transfer The best practice in calibrating a range Extender is to leverage a calibrated Bridge This method allows a complete and direct calibration that includes System Uncertainties, not just a Ratio Uncertainty A ratio uncertainty only includes the ratio transformation of the extender comparator windings A system uncertainty includes the contribution of the power supply, reversing switch, ratio-metric build-up of each fixed current comparator winding, as well as other components Range Extender Calibration

Basic Process Measure 0.1 ohm w.r.t. 1 ohm on a calibrated Bridge at full Bridge current output (150mA) Repeat the same measurement on the first range of the range extender (x10 typical) using the same resistors and current. The ratio should match Select a resistor 1 decade down (0.01 ohm) and measure it at a current that can be used by both the x10 and x100 range and compare the two ratios to see that they match Continue this step process for all ranges of the range extender System uncertainty includes this ratiometric build-up of uncertainties at each range to provide traceability Range Extender Calibration

3000A Current Source Clamp Meter Calibration Stand alone controller has been developed Current source has accuracy of 0.1% and stability in ppm range Use a calibrated shunt in series to increase accuracy if required Stand- Alone Controller DVM Clamp Meter Clamp Meter Clamp Meter

11,000A Current Source Controller

Conclusion Current Range Extenders / Sources up to 3150A have been delivered to customers Current Source Design up to 11,000A and Current Range Extender Design up to 6,000A completed Maximum current seems to be effectively limitless given adequate buss-bars Proven Applications are Current range extender for low resistance measurement Measurement of high current shunts Reference current source for current clamp on meters Potential Applications Test High Current safety switches DC Power Supply for super conducing magnets

Thank You Thank You Congratulations NCSL 50 th Anniversary Invitation to Visit Guildline’s Website See the new 6623A Range Extender Technology Resistance Standards DC Shunts

Providing Precision Measurement Solutions Guildline Instruments Limited