The Quantized Hall Resistance Standard is internationally recognized as the representation of the ohm and is the most stable resistance standard known. Many national laboratories and industries are finding a need to provide highly accurate, traceable reference standards in support of their “hi-tech” environments. The 6800B system has been developed to meet the needs of national laboratories and primary industrial laboratories around the world.
The MI 6800B (Quantized Hall Resistance Standard) is a fully automated primary standard developed as an economic means to provide a highly reproducible resistance standard. This system is a completely “turn-key” system and requires little to no manual intervention. A wide neck storage dewar and instrumentation rack are mounted on castors for portability. A variable temperature pumped 4He refrigerator with integral 8 Tesla, or optional 9 Tesla magnet can be installed.
With the integrated helium re-liquefaction system you have your own helium store. Liquid helium shortages, erratic deliveries and steady price increases have become commonplace. This shortage with continuous price increases causes many labs to have difficulty efficiently completing their measurement goals. Measurements International solves this problem with their re-liquefaction helium liquefier; which is like having your own liquid helium store.
MI has integrated a super-conducting magnet system into a small, laboratory helium liquefier allowing for near zero-loss of this system. There are minimal fees associated with the operation of the liquefier that is far outweighed by the high cost of liquid helium. Traditionally, depending upon liquid helium usage, a system will pay for itself within two years of continuous operation.
System operation time can be defined as follows:
Within one week, all system operations can be completed.
The system is a development of many years of experience in Quantized Hall System design, Resistance Measurements, and Cryogenics.
The 6800B system is the first portable Quantized Hall Resistance Standard in the world and consists of three parts, all of which are supplied and described on the following page.
Sample: The 6800B Resistance Standard sample provides the absolute value of resistance related to the von Klitzing constant of 25 812.807 459 3045 Ω. Operating on step i = 2 and i = 4 plateau, the 6800B compares the QHR value of 12 906.403 73 Ω and 6453.201 865 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.
Cryogenics: The 6800B consists of a 40-litre dewar with a pumped 4He refrigerator, an 8 Telsa or 9 Telsa superconducting magnet with a support assembly, temperature sensor, heater and a 19″ instrument rack with superconducting magnet power supply, temperature controller, helium level sensor and an oil-free mechanical vacuum pump.
The dewar is mounted on heavy-duty castors for transportability from one room to another. The system can also be shipped cold from one facility to another as a primary reference transfer standard.
Recent design improvements to the system have been implemented to allow for the addition of an easier method for sample interchange. By including this into the design, users of the 6800B can now easily interchange samples at their convenience without exposing the sample to the atmosphere until it has reached room temperature.
The model 6800B has been designed to address customers’ need for a more economical system helping relieve the dependence on having to purchase liquid helium every time you wish to operate the system.
Previous systems required the purchase of 100 litres of liquid helium. The cost of liquid helium is still increasing and will increase going forward. With the 6800B system, customers can now cool down the system using helium gas cylinders (9 – 10 required) at an estimated cost of approximately $100/cylinder.
MI is the ONLY commercial supplier of the QHR system.
Further to this, MI can also offer the optional direct helium recovery system where the boil-off gas is captured and stored in a separate space-aged portable gas storage tank, making it the ideal solution for long term shutdown. With system closed-loop operation, no external plumbing or gas bag is required. The 6800B provides a system which has an average liquefaction rate of 18 litres per day.
Measurement System: An improved Direct Current Comparator Bridge (model AccuBridge® 6020Q) operating in room temperature air which allows two resistors to be compared with accuracies to 2 parts in 10-8. The AccuBridge® 6020Q Bridge is used to compare 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: in short, to carry out all the 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 down from the 1 kΩ resistor to establish values for 1, 10, 100, 1 k, 10 k and 100 kΩ primary resistors to a very high level of accuracy. The 6020Q Bridge can be used stand-alone or with Measurements International’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 6020Q Bridge may be purchased separately. Several options are available to the user including extra QHR samples, a stainless steel liquid helium transfer line to allow continuous operation.
|Accuracy QHR to 1 k||< 2 × 10-8|
|Stability||< 1 × 10-8|
|Insulation Resistance||> 1013 Ohms|
|Magnet Strength||8 Tesla or 9 Tesla|
|Plateaus||i = 2, i = 4|
|Temperature||4He, 1.2 Kelvin|
|Dewar Size||40 Litres|
|Operating Environment||18 to 34 °C, 10 to 80 % RH|
|Warranty||1 Year Parts & Labour|
Either Rs or Rx can be selected as the standard. Uncertainties specified at 2 sigma level (95 %) includes
all secondary specifications such as linearity and noise
with a ± 2 °C
|0.1 Ω to 100 kΩ|
|Rs or Rx||Ratio & Uncertainty (ppm)|
|1 Ω||< 0.05||< 0.015||< 0.015||< 0.02|
|10 Ω||< 0.02||< 0.015||< 0.015||< 0.02|
|100 Ω||< 0.02||< 0.015||< 0.015||< 0.02|
|1 kΩ||< 0.02||< 0.015||< 0.02||< 0.02|
|10 kΩ||< 0.02||< 0.02||< 0.05|
|Linearity||< 0.005 ppm of Full-scale|
|Operating Conditions||10 °C to 35 °C, 10 % to 90 % RH Non-condensing|
|Test Current Range||10 μA to 150 mA|
|Test Current Resolution||18-bit|
|Display||Touch Screen Display (No external keyboard), Resolution 0.001 ppm|
Option A: Direct Helium Gas Recovery System for Long Term Storage
Standard Resistor Oil Bath
Temperature-Controlled Standard Resistor Air Bath with GPIB
1 Ω Resistor with Carrying Case
Series of Four-Terminal Air Resistors from 1 Ω to 100 kΩ
Series of Four-Terminal Air Resistors from 1 mΩ to 100 mΩ