BS EN IEC 62812:2019 pdf free.Low resistance measurements -Methods and guidance.
Resistance measurements are typically compromised by a variety of phenomena, for exampleserial resistance in the measurement path, self-heating or non-ohmic properties. Whether theeffect of such phenomena on a resistance measurement is acceptable or not depends on themagnitude 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 witha tightening of the permissible tolerance.
This document specifies methods of measurement and associated test conditions thateliminate or reduce the influence of adverse phenomena in order to improve the attainableaccuracy of low-resistance measurements.
The methods described in this document are applicable for the individual measurements ofthe resistance of individual resistors, and also for resistance measurements as part of a testsequence.They are applied if prescribed by a relevant component specification, or if agreedbetween a customer and a manufacturer.
2Normative references
The following documents are referred to in the text in such a way that some or all of theircontent constitutes requirements of this document. For dated references,only the editioncited applies. For undated references, the latest edition of the referenced document (includingany amendments) applies.
IEC 60068-1，Environmental testing – Part 1 : General and guidance
IEC 60115-1:2008,Fixed resistors for use in electronic equipment – Part 1: Genericspecification
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 lIEC 60115-1 and thefollowing apply.
A list of used letter symbols and abbreviated terms is provided in Annex A.
lSO and lEC maintain terminological databases for use in standardization at the followingaddresses:
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. ET potential difference occurring at the junctions of dissimilar conductors when a temperature difference exists between the junctions.
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 offsetvoltages,radio frequency interference,electromagnetic interference,electrical noise, or non-ohmic contacts. However，these phenomena are not discussed here as they are notspecifically related to the measurement of resistance.
The voltage to be measured increases with an increase of the measuring current,which mayalso result in effects which are adverse to the measurement.Such phenomena are discussedin Clause 4.
4.2 Lead and contact resistance
A conventional method for measuring a resistance is to use a constant current source with aknown (or measured) output current and a voltmeter for measuring the voltage across theunknown resistor，while the connection is built with a single pair of test leads, as shown in Figure 1.BS EN IEC 62812 pdf download.