#Standard resistance values license#
#Standard resistance values series#

It is recommended that all the national metrology institutes use the same value for the Von Klitzing constant, which is R k-90вЂ‰=вЂ‰25.812807вЂ‰kО©. The definition of the ohm has been related to the QHE by means of the Von Klitzing constant. Those reference standards are calibrated against the Quantum Hall Resistance (QHR), which is the most accurate resistance standard therefore, it is used as a primary standard of resistance. NIS standard resistors are periodically calibrated at the BIPM by comparison with their reference standards. For the standard resistors from 1вЂ‰kО© to 10вЂ‰MО©, the traceability chain is done by NIS 10вЂ‰kО© model SR104 standard resistor and three Hamon transfer standards. The traceability chain at the National Institute of Standards (NIS), Egypt, for the standard resistors from 100вЂ‰mО© to 100вЂ‰О© is started by using NIS 1вЂ‰О© Thomas-type standard resistor. Traceable and standard resistors are used in this study. This is done to study their effects on the accuracy and on the precision of the resistance standards measurements in the ranges from 100вЂ‰mО© to 10вЂ‰MО© to select the best applied source for each range. So, in this paper, a practical comparison is done with applied voltage source and applied current source. In the potentiometric bridge method, an applied dc voltage source is usually used to pass a constant current through the standard and the uut resistors. A constant current through the two resistors should be achieved to avoid errors and improve the accuracy. Then, the voltage drop ratio across the two resistors is measured.

#Standard resistance values series#

A known current could be passed through the standard resistor in series with the unit under test (uut) resistor. This method can be considered a direct application of Ohm's law. One of these methods is the potentiometric bridge method. When the used instruments are stable, a high accuracy and low uncertainty in the measurement can be obtained. So, resistance measurements can be accurately made by comparing the unknown standard resistor with another standard resistor that has a known and traceable value. The most precise methods for resistance measurements are made by bridges where standard resistors are compared with each other. For the high-resistance standards measurements, different methods are used such as current comparator bridge, DMM-based method, substitution method, and modified Wheatstone bridge. These methods suffer from some drawbacks such as the current source, and the DMM in the voltвЂ“ampere method should be calibrated the ratio technique depends on the linearity of the DMM. There are also voltвЂ“ampereвЂ“metric and ratio technique methods. There are different methods for measuring low-ohmic resistance standards such as direct current comparator with range extender, direct reading with a digital multimeter (DMM), and substitution method. Because of increasing demand for high accuracy for industry and for the scientific metrology, more accurate measurement methods are being developed. For high-ohmic standard resistors, it is important to make more accurate measurements because secondary laboratories used them in the calibrations of small dc currents and commercial teraohmmeters. Measurements of low-standard resistors are important for the power industry because of their use in high dc currents calibrations. Low- and high-resistance measurements are important fields in electrical metrology.

#Standard resistance values license#

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.