NEW! A Direct Helium Recovery System eliminates nearly all helium loss and its associated costs!
Transportable & Affordable QHR Standard
System Accuracy to <0.02 PPMThe 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 6800B QHR Standard System to meet the needs of national laboratories and primary industrial laboratories worldwide.
The MI 6800B 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. Systems using 12 T magnets have also been built.
Liquid helium shortages, erratic deliveries, and steady price increases have become commonplace. This shortage, along with continuous price increases causes many labs to have difficulty efficiently reaching their measurement goals. With the 6800B’s integrated helium re-liquification system, you essentially have your own helium store.
With the 6800B, we have integrated a superconducting magnet system into a small, laboratory helium liquefier allowing for near zero-loss of helium. The minimal costs associated with operating the liquefier far outweigh the high cost of liquid helium. Depending upon liquid helium usage, a system will typically pay for itself within 2 years of continuous operation.
System operation time can be defined as follows:
- System cool down: 2–3 days
- Sample checks: half-day
- QHR measurements versus 1 kΩ: half-day
- Scaling down to 0.1 Ω or up to 100 kΩ: 1 day
All system operations can be completed within 1 week.
We developed the 6800B using our many years’ experience in quantized Hall system design, resistance measurements, and cryogenics. It is the world’s first portable QHR standard. It is modular in design and consists of three parts: sample, cryogenics system, and bridge measurement system. These components may be purchased separately.
Several options are available including extra QHR samples, 6800B software, and a stainless steel liquid helium transfer line for customers using liquid helium.
Sample:
The 6800B Resistance Standard sample provides the absolute value of resistance related to the Von Klitzing constant of 25812.807 Ω. Operating on step I = 2 plateau and i = 4 plateau, the 6800B compares the QHR value of 12906.4035 Ω to either a 10 kΩ or 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 40-L helium-filled dewar with fields to 8 T or 9 T supplied by the integral magnet. Due to its integrated helium recovery system, 6800B is designed to operate continuously. Special precautions have been taken to avoid contaminating or damaging the sample.
CryogenicsThe 6800B cryogenics system (see the diagram) consists of a 40-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 6800B 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. You can then remove the sample.
The 6800B addresses your need for a more economical system by helping relieve the requirement to purchase liquid helium every time you wish to operate the system. Previous systems required the purchase of more than 100 L of liquid helium. In addition, the cost of liquid helium continues to increase. With the 6800B, you can cool down the system using helium gas cylinders (9 to 10 cylinders are required). We also offer an optional direct helium recovery system where the boil-off gas is captured and stored in a separate portable storage tank, making it the ideal solution for the long-term shutdown. With the system’s closed-loop operation, no external plumbing or gas bag is required. The 6800B provides an average re-liquefaction rate of 18 L/day.
Measurement SystemThe 6800B measurement system includes the Accubridge® 6020Q DCC bridge operating in room temperature air, enabling two resistors to be compared with accuracies to better < 0.02 ppm.
The Accubridge® bridge compares the QHR device directly to either a 10 kΩ or 1 kΩ standard 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 1 kΩ 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 can be used on its own or with MI’s 6800B software for automated measurements.
The 6800B system is modular in design and the three parts, the 6800B sample, the 6800B Cryogenics and the 6800B Bridge may be purchased separately. Several options are available to the user including extra QHR samples, 6800B software and for those that have liquid helium a stainless steel liquid helium transfer line.
