US Pat. No. 6,798,214
Description
A ‘Resistance Lab in a Box‘
The Smart Resistor combines, into one transportable device, all the items needed to maintain resistance: a set of standard resistors, a controlled temperature bath, a low thermal emf scanner, and measurement data.
Advantages of the Smart Resistor
Eight resistance Standards – To maintain and disseminate the ohm, a laboratory must have a set of resistance standards, usually at decade values (1 W, 10 W, 100 W, etc.). The Smart Resistor contains eight resistors. A typical model has eight decade values covering the range from 1 W to 10 MW. However, any eight resistance values may be specified at the time of order. Due to power and leakage limitations, the values should be between 0.1 W and 10 MW.
Constant temperature bath – Traditional resistance standards are usually held in a constant temperature oil bath; these baths are bulky, noisy, and can not be transported. The Smart Resistor contains a constant temperature enclosure, allowing portability. The control circuitry has sufficient power to overcome variations in ambient temperature. The nominal setting is 25.00 °C. In normal room environments, this constant temperature housing has a stability better than 10 mK.
Environmental immunity – The standards are hermetically sealed for immunity from changing barometric pressure and relative humidity.
Characterization of standards – A resistance standard has no value without its characterization. This data includes a reference value in ohms, coefficients of temperature, power coefficient, frequency response and its drift over time. The Smart Resistor’s internal computer maintains all this data and displays it to the user. The data is available for integration into automated systems.
Corrected for drift – As time passes, the Smart Resistor’s calendar applies drift corrections to the displayed value. The Smart Resistor’s software generates and maintains control charts for each of its eight standards.
Low thermal emf scanner – The Smart Resistor’s 8-channel low-thermal emf scanner cards are by DataProof, a world leader in scanner technology. This integrated scanner allows automated buildups. Any of the eight resistance standards may be selected as R1 or R2 on the front panel.
Internal data logger – The Smart Resistor contains a battery powered temperature logger, to monitor and warn of exposure to potentially damaging temperature extremes during storage or transit.
Cost Savings of the Smart Resistor
A single Smart Resistor is designed to replace eight resistance standards, a constant temperature bath, a low thermal emf scanner, a precision thermometer, a temperature data logger and resistance maintenance software. The cost is significantly lower than these separate components.
Automating the Resistance Lab
The Smart Resistor is designed with simple, intuitive operator controls. All functions and controls can be integrated into an automated system via the Smart Resistor’s interfaces. The standard interfaces supplied include ethernet and IEEE ports.
Protecting Resistance Standards
Traditional resistance standards can be permanently damaged by exposure to temperature extremes. The Smart Resistor contains a battery-powered temperature data logger, constantly monitoring its internal temperature. Even in storage, the logger will sample and store temperatures hourly for a period of approximately two years.
A rugged transit container is available for the Smart Resistor.
Future Developments
The Smart Resistor Model SR covers the range from 0.1 W to 10 MW. A SmartShunt, Model SS, is planned for use as a low resistance standard, containing five decade values from from 1 W to 0.000 01 W. It may be used for high accuracy current measurement, up to 300 amps. A high resistance standard, Model SH, is planned for resistance between 1 MW to 1 TW. Extended models are planned, including a high current shunt.
Longevity
The Smart Resistor is designed for extended use. Care has been exercised to select reliable and rugged components.
The Smart Resistor carries a two year parts and labor warrantee.
Technical Support
Ohm-Labs provides lifetime technical support for all products – upgrades are generally available at no cost.
