Transportable & Affordable QHR StandardAccuracy to < 0.02 PPM
The Quantized Hall Resistance (QHR) Standard is internationally recognized as the representation of the ohm and is the most stable resistance standard. Many National laboratories and industries need to provide highly accurate, traceable reference standards to support their hi-tech environments. Measurements International (MI) developed the 6800A QHR Standard System to meet the needs of National Measurement Institutes and primary laboratories worldwide.
In the International System of Units, the ohm is derived from the volt and the ampere. In practice, quantized Hall resistors have been used in national laboratories to represent resistance since 1990. These resistors are semiconductor devices which, when cooled to 1.2 K or less in a magnetic field of several tesla, yield values of resistance which are essentially invariant and are believed to be multiples of fundamental constants. By international agreement, the first multiple is taken to be equivalent to 25812.807 Ω.
The MI 6800A QHR System is a fully automated primary standard developed as an economic means to provide a highly reproducible resistance standard. This turnkey system requires little to no manual intervention. For portability, a wide neck storage dewar and instrumentation rack are mounted on castors.
A variable-temperature pumped 4He refrigerator with integral 8 T or optional 9 T magnet can be installed. Alternatively, the system can be operated continuously if a supply of helium exists in the facility. The cryostat is designed to operate over a 4–7-day period on one fill. Typically, all measurements can be performed in 2–3 days. You can prepare the system in a half-day and cool down the second half of the day. Within 2 or 3 days you can have the system cold and the complete measurement of QHR versus 1 kΩ as well as scaling down to 0.1 Ω or up to 100 kΩ.
The 6800A provides an economical means to accurately and precisely establish and measure resistance values from 0.01 Ω to 100 kΩ. We developed this system using our many years’ experience in quantized Hall system design, resistance measurements, and cryogenics.
The 6800A is the world’s first portable QHR standard. It modular in design and consists of three parts: sample, cryogenics system, and bridge measurement system. These components may be purchased separately.
Sample:
The 6800A Resistance Standard sample provides the absolute value of resistance related to the Von Klitzing constant of 25812.807 Ω. Operating on step I = 2 (»8 tesla and 1.2k), the 6800A compares the QHR value of 12906.4035 Ω to a 1 kΩ resistor. The reference or sample, developed at the National Research Council of Canada (NRCC) is maintained at 1.2 K in a mobile 55-L helium-filled dewar with fields to 8 T or 9 T supplied by the integral magnet. The system is designed to operate over 3–7 days. Special precautions have been taken to avoid contaminating or damaging the sample.
Cryogenics:
The 6800A cryogenics system consists of a 55-L dewar with a pumped 4He refrigerator, an 8 T or 9 T superconducting magnet with support assembly, temperature sensor, heater, and a 19” instrument rack. The rack holds a superconducting magnet power supply, temperature controller, helium level sensor, and an oil-free mechanical vacuum pump.
To enhance mobility, the dewar is mounted on heavy-duty castors. The system can also be shipped cold from one facility to another for use as a primary reference transfer standard.
The 6800A is has been redesigned to allow an easier method for sample interchange. You can more easily interchange samples at your convenience without exposing the sample to atmosphere until it has reached room temperature.
Measurement System:
The 6800A measurement system includes the Accubridge® 6020Q DCC bridge operating in room temperature air, enabling two resistors to be compared with accuracies to < 0.02 ppm. The Accubridge® bridge compares the QHR device directly to a 1000 Ω transfer resistor. The bridge can also be used to measure the field dependence of Rxx and Rxy, to make precision measurements of Rxx, and to measure the contact resistance of the QHR device. It can carry out all measurements necessary to ensure the accuracy of the QHR resistor. The bridge and low thermal matrix scanner can then be used to build up or build down from the 1000 Ω resistor to establish values for 1 Ω, 10 Ω, 100 Ω, 1 KΩ, 10 kΩ, and 100 kΩ primary resistors to a very high level of accuracy. The 6020Q Bridge can be used on its own or with MI’s 6800A software for automated measurements.
The 6800A system is modular in design and the three parts:
- 6800A sample
- 6800A Cryogenics
- 6800A Bridge
May be purchased separately.
