BS EN ISO 15091:2020 pdf download – Paints and varnishes — Determination of electrical conductivity and resistance
This document specifies a method for determining the electrical conductivity and the electrical resistance of coating materials. The conductivity is usually measured for water-borne paints and varnishes, including electrodeposition coating materials, and the resistance is usually measured for solvent-borne paints and varnishes. If required, the resistivity of the coating material is calculated from either of these measurements. The method is applicable to products having a conductivity less than 5 µS/cm, corresponding to a resistivity greater than 200 kΩ⋅cm. The conductivity of coating materials influences their processibility in the presence of an electric field. This is particularly important for electrodeposition paints and coating materials which are processed electrostatically.
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.
ISO 1513, Paints and varnishes — Examination and preparation of test samples
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4618, Paints and varnishes — Terms and definitions
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
3? Terms? and? definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1 electrical resistance
R ratio of the potential difference along a conductor and the current through the conductor
Note 1 to entry: Resistance is given by Ohm’s law shown in Formula (1):
quotient of the length and the cross-sectional area of a conductor
Note 1 to entry: It is given by Formula (5):
From Formula (2), it can be seen that it corresponds to the ratio of the resistance to the resistivity of the conductor material.
For the determination of the resistivity by resistance measurement, this geometrical factor, i.e. the cell constant of the measurement assembly, will need to be known.
Cell constants are given in reciprocal centimetres (cm –1 ).
4.1 Measurement of the resistance
The resistance may be determined by;
a) the measurement of the current through a sample and the voltage acting on the sample, or;
b) comparison of the measured resistance with a reference resistance.
For the current/voltage measurement, usually a constant pre-determined voltage is applied to the sample, and the current is measured with a suitable measuring instrument (e.g. a moving-coil instrument or a digital instrument). The resistance is then calculated from Formula (1). See Figures 1 to 3.
To compare the resistance of the sample with a reference resistance, a bridge circuit is used in which the resistances are balanced so that the bridge current becomes zero. The resistance of the sample is calculated from the ratio of the resistances of the bridge circuit. Because the bridge current is zero, errors which can result from the existence of a load on the voltage source when the voltage/current measurement method is used are avoided. The only contributions to the overall measurement error are any uncertainty in the reference resistance and any uncertainty in the adjustable resistance. See Figure 4.
4.2 Avoidance of electrolysis and polarization effects In order to avoid electrolysis or polarization effects which would falsify the measurement, measurements of the resistance are usually carried out using alternating current. The frequency of the voltage applied to the measuring cell should, however, be as low as possible in order to minimize the contribution made by the reactance of the measuring cell, which acts as a capacitor.