Magnet Investments

Measurement Of Resistance

RESISTANCE MEASUREMENT 1. Preambuloentendemos by electrical resistance of objects, materials or instruments opposition to the passage of electric current in DC and stationary regime conditions, i.e., when there is not more electric field that needed to maintain the constant flow of current in the inside of the element. The physical phenomena of electrical conduction are well known and the value of the electrical resistance has been quantitatively defined as the ratio of the difference of potential applied between the ends of the electric element in question and the intensity of the current passing through it. The value of resistance, as it is well known, depends on the Constitution of the conductive element, i.e. its resistivity, and the physical dimensions of the one.

For its part, the resistivity is not strictly invariable but that depends on fundamental, although not exclusively, the temperature, and sometimes in a not inconsiderable amount.Depending on the nature of the driving Electric, the value of the resistance of a particular physical item will present more or less perseverance or stability in general depending on both the test levels and external conditions such as humidity, temperature already cited, and on occasions, of the different electromagnetic radiation intensities, so that is usual and necessary to specify together with ohmic value differential measurement conditions. The experimental determinations of their value should be inexcusably DC if it is to make such determination with a medium to high accuracy. A certain degree of ripple of low frequency voltage and/or test current is permissible measurements involving exclusively mean value instruments. Sometimes, such is the case of electrolytic elements, admits that the measurement is carried out in low frequency alternating current to eliminate undesirable parameters that would introduce uncertainties of greater amount than those caused by electromagnetic effects of variable fields.Of the different procedures for measuring this electrical parameter we will consider three broad groups: those that use voltage values intensity of compensation those who directly provide their value 2.