BS 6524:1984 pdf free download.Determination of the surface resistivity of a textile fabric.
1 Scope
BS 6524 describes a method for the determination of the surface resistivity of a textile fabric. It is intended for fabrics of moderate or low surface resistivity (less than 101 fl) and is not generally applicable to unhomogeneous fabrics. In certain cases however it may also be applied to coated fabrics and to fabrics containing small quantities of highly conducting fibre: such special cases are covered in Appendix A.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
2 Definitions
For the purposes of BS 6524, the definitions given in BS 57755 apply, together with the following.
2.1
unhomogeneous fabrics
fabrics that contain small quantities (less than 10%) of conducting fibres, for example epitropic or metallic fibres; or fabrics that are coated or laminated with polymeric materials where the electrical properties of the components differ substantially from each other
2.2 surface resistivity
the specific resistance along the surface of a textile fabric, expressed in ohms
NOTE The units for surface resistivity were formerly ohms per square, and refer to the resistance between opposite edges of a square in the surface of the material. Present usage requires the units to be ohms. This is correct dimensionally, it. being implicit by definition that the surface resistivity refers to the resistance between opposite edges of a square.
3 Principle
The specimen of fabric to be tested is conditioned in an atmosphere of temperature and relative humidity appropriate to the conditions in which the fabric is to be used. The specimen is then placed on a base plate and an electrode assembly placed on top. A d.c. potential is applied to the electrode assembly and the resistance of the fabric is measured.
4 Apparatus and reagents
4.1 Electrodes, consisting of a cylindrical and an annular electrode concentrically arranged within each other. Suitable electrodes, which are available commercially’, are shown in Figure 1. They are made of solid brass and are joined by annular pieces of insulating material of resistivity not less than 1014  determined in accordance with this method (see 6.2). A brass guard ring is set in the middle of the insulating ring and both rings are recessed so that they do not contact the fabric surface.
Concentric electrodes of dimensions other than those given in Figure 1 may be used and the appropriate factor (see clause 6) applied in calculating the surface resistivity, providing that the diameter of the cylindrical electrode and the gap between the electrodes are both not less than 20 mm.
4.2 A flat base plate, of insulating material of resistivity not less than 1014 Q (see 6.2) and dimensions not less
than 250 mm X 250 mm X 10 mm, used as a support for the fabric during the measurement, and in turn rested on an earthed surface, e.g. a metal plate.
4.3 An ohmmeter, with a full scale deflection of not less than 10H and accuracy ± 5 % under an applied voltage of 500 V. or an electrometer of input impedance not less than 1014 Q and a separate d.c. source with an inbuilt safety resistor.
4.4 Paper tissues.
4.5 Propan-2-ol, 1,1,2 trichioroethane or trichioroethylene, for use as a cleaning agent.
CAUTION. 1,1,2 trichioroethane and trichioroethylene are toxic, irritant and narcotic in high concentrations. Avoid breathing the vapour. Avoid contact with skin, eyes and clothing. Propan.2.ol is highly flammable and toxic. Avoid breathing the vapour. Avoid contact with eyes and skin.
5 Specimens and conditioning
A sample of fabric of sufficient size to obtain three representative measurements of resistivity shall be used.
Three test specimens shall be cut, each of size not less than 250 mm x 250 mm nor greater than the area of the base plate (4.2). No specimen shall be taken within a distance of 50 mm from any selvedge.
If a complete garment is to be tested, the base plate (4.2) shall be of sufficient size to accommodate the garment and three separate tests shall be carried out.
NOTE 1 For lined garments, each layer should be tested separately.
The specimens or garment shall be conditioned and tested at a temperature and relative humidity appropriate to the conditions in which they are to he used. For monitoring purposes an atmosphere of 20 ± 2 °C and 65 ± 2 % r.h. is widely used in the textile industry (see BS 1051) but, in practice, 20 ± 2 °C and 40± 2 % r.h. are more relevant to apparel use where antistatic behaviour is important. The conditioning time prior to carrying out the test shall be not less than 16 h.
NOTE 2 New fabrics and garments may have finishes on them which reduce the resistivity of the untreated material and which are usually removed during washing or dry cleaning. In some cases it may therefore be desirable to wash or dry clean the material before carrying out the test. An appropriate procedure should be chosen from BS 4923 or 88 4961, depending on the type of fibre and intended end.use of the material.
6 Procedure
6.1 Clean the lower surfaces of the electrodes (4.1) and the upper surface of the base plate (4.2) by wiping with a paper tissue (4.4) which has been moistened with one of the reagents (4.5).
6.2 Carry out a blank test using the procedure given in 6.3 and 6.4 but with no specimen in position, and calculate the resistivity of the insulating material.
6.3 Place the test specimen on the base plate (4.2) with the side that is being tested uppermost and place the electrode assembly on top. Connect the electrodes as shown in Figure 1.
6.4 Apply a potential of 500 V and after 15 ± I s determine the resistance using the ohmmeter or electrometer (4.3).
6.5 Repeat the procedure given in 6.3 and 6.4 on the two other test specimens or on two different parts of the garment.
7 Calculation and expression of results
7.1 Calculate the surface resistivity, p (in ohms) for each of the three values of resistance using the equation:
2irR
1°g (r2/r1)
where
R is the measured resistance (in 0):
r1 is the radius of the inner electrode (in mm);
r2 is the inner radius of the outer electrode (in mm).
7.2 Determine the mean of these three values.
8 Test report
The test report shall include the following information:
a) a statement that the test was performed in accordance with this British Standard,
i.e. BS 6524:
b) the individual surface resistivities (in ohms) for the three readings taken and the mean of these values;
c) the dimensions of the electrodes used;
d) whether or not the fabric had been washed or dry cleaned before testing, and, if so, details of the procedure used and reference to the appropriate British Standard;
e) the temperature and relative humidity at which the test was carried out;
f) details of any deviation from the specified procedure.