Description:
Measurement of high resistance standards (10 MΩ to 100 TΩ) and high voltage resistive dividers (100 MΩ to 225 MΩ) are made using modified Wheatstone bridge techniques. The most accurate technique used for high resistance uses programmable dc voltage sources in the main ratio arms of a modified Wheatstone bridge. Programmable bipolar dc voltage sources with ranges from 220 mV to 1100 V having expanded uncertainties (k=2) on the order of 6 μV/V provide the best accuracies for high resistance measurement. Similar Wheatstone bridges are used to calibrate high voltage dividers at voltages ranging from 10 kV to 220 kV. The best high voltage sources available in this range have an expanded uncertainty of 100 μV/V. The only commercially-available precision sources have uncertainties on order of 500 μV/V in the 1 kV to 10 kV range, more than an order of magnitude greater than commercial sources covering the other voltage ranges (i.e. 1 kV and below). Test laboratories would benefit from development of a commercial bipolar programmable dc voltage source with expanded uncertainties on the order of 6 μV/V to 10 μV/V to bridge this gap in measurement capability. Such a programmable dc voltage source would allow extension of the voltage range for calibration of high resistance standards and allow comparison of high voltage resistive dividers to high resistance standards in the 1 kV to 10 kV range with traceability to quantum resistance standards.
Commercial multifunction calibrators are used as the bipolar dc sources the high resistance bridges as they have state-of-the-art uncertainty for dc voltage for the 220 mV to 1100 V ranges. Unfortunately, as the name suggests, they have other functions such as ac voltage, ac current, and resistance that are not utilized for dc voltage applications and only add cost if they are not used. Commercial dc only calibrators exceed the 1-year specification of multifunction calibrators by 1.4 to 2.8 times on the corresponding ranges of 220 mV to 1100 V. To make high resistance bridges more cost effective and therefore more widely used in standards laboratories, an alternative dc voltage-only source with the same performance as that of state-of-the-art multifunction calibrators is needed.
The development of an alternative 1 kV dc bipolar voltage source technology that could be scaled to 10 kV would (1) improve performance in the 1 kV to 10 kV range and (2) provide a cost effective alternative to calibrators in the 220 mV to 1100 V range. This technology would be of interest to NIST as well as other standards and commercial laboratories.
Technologies that would scale from the existing voltage range of 1 kV up to 10 kV are desired. A programmable bipolar dc voltage source that has linearity error of less than 1 μV/V over the range 1 kV to 10 kV would be complementary to the state of the art sources at 1 kV. State-of-the-art voltage sources have expanded uncertainties of 6 μV/V over a one-year interval at 1 kV. To be useful in automated bridges, the bipolar programmable dc voltage source would need to be controllable by IEEE-488.2 interface or USB interface from a computer just as other instrumentation in an automated bridge would be. Front panel display of the output state (i.e. energized or standby) and voltage would be necessary for safe operation in a laboratory environment.
Phase I expected results: Design a bipolar programmable dc voltage source that extends the range from 1 kV to 10 kV and meets the project goals described above.
Phase II expected results: Construct a prototype 1 kV to 10 kV bipolar programmable dc voltage source based on the design of Phase I and demonstrate that the specifications and performance described above are met.
NIST may be available to work collaboratively on design concepts, discuss goals, and to aid in prototype evaluation.
