IEC 62812:2019 pdf download

IEC 62812:2019 pdf download.Low resistance measurements – Methods and guidance
1 Scope
Resistance measurements are typically compromised by a variety of phenomena, for example serial resistance in the measurement path, self-heating or non-ohmic properties. Whether the effect of such phenomena on a resistance measurement is acceptable or not depends on the magnitude of each effect in comparison to the resistance and to the required accuracy. Hence, the risk of erroneous resistance measurements increases with decreasing resistance and with a tightening of the permissible tolerance. This document specifies methods of measurement and associated test conditions that eliminate or reduce the influence of adverse phenomena in order to improve the attainable accuracy of low-resistance measurements. The methods described in this document are applicable for the individual measurements of the resistance of individual resistors, and also for resistance measurements as part of a test sequence. They are applied if prescribed by a relevant component specification, or if agreed between a customer and a manufacturer.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60068-1 , Environmental testing – Part 1: General and guidance IEC 601 1 5-1 :2008, Fixed resistors for use in electronic equipment – Part 1: Generic specification IEC 60294, Measurement of the dimensions of a cylindrical component with axial terminations
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 601 1 5-1 and the following apply. A list of used letter symbols and abbreviated terms is provided in Annex A. ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp 3.1 electromotive force e.m.f. difference in potential that gives rise to an electric current 3.2 thermoelectric e.m.f. E T potential difference occurring at the junctions of dissimilar conductors when a temperature difference exists between the junctions 3.3 low resistance resistance for which the predictable error when measured with a conventional two-wire sensing method is significant in comparison to the required precision or to the stated tolerance 3.4 four-wire sensing Kelvin sensing four-terminal sensing four-point sensing electrical impedance measuring technique using separate pairs of wires for carrying the measuring current and for sensing the potential difference in order to eliminate the impedance contribution of wiring and contact resistances 3.5 two-wire sensing conventional electrical impedance measuring technique using one pair of wires for carrying the measuring current and for sensing the potential difference on the same wires
4 Resistance measurement phenomena
4.1 General The measurement of a low resistance usually relies on the measurement of a low voltage, which requires a number of precautions against typical detrimental phenomena such as offset voltages, radio frequency interference, electromagnetic interference, electrical noise, or non- ohmic contacts. However, these phenomena are not discussed here as they are not specifically related to the measurement of resistance. The voltage to be measured increases with an increase of the measuring current, which may also result in effects which are adverse to the measurement. Such phenomena are discussed in Clause 4. 4.2 Lead and contact resistance A conventional method for measuring a resistance is to use a constant current source with a known (or measured) output current and a voltmeter for measuring the voltage across the unknown resistor, while the connection is built with a single pair of test leads, as shown in Figure 1 .