BS EN ISO 8031:2020 pdf download – Rubber and plastics hoses and hose assemblies — Determination of electrical resistance and conductivity For tests requiring the measurement of the electrical continuity between end fittings or through continuous internal or external bonded wires, the instrument used shall be an ohmmeter sufficiently accurate to determine the resistance to within ±10 %. For tests where, according to the product standard, determination of the electrical continuity between the end fittings of a hose assembly is required, without measurement of the actual electrical resistance, a 4,5 V battery in combination with a 4 V (0,3 A) test lamp can be used. For determination of the electrical resistance through the hose wall (required by some hose product standards for hoses used in explosive atmospheres), the instrument used shall be an ohmmeter with a capacity of 10 12 Ω and the measurement shall be made at 500 V d.c. The instrument shall be sufficiently accurate to determine the resistance between the lining and the cover as measured through the hose wall to within ±5 %.
4.2.2 Electrodes and contacts General For tests conducted in a laboratory, the equipment described below shall be used. For field tests, and for routine tests and product acceptance tests in a manufacturer’s plant, this equipment is not practical, and alternatives may be used as described in 4.6.1, and Electrodes shall be formed on the surface as bands 25 1 2 − + ( ) mm wide around the circumference by means of a conductive silver lacquer, colloidal graphite or a conductive liquid. When a conductive liquid is used, the electrode contact area shall be completely wetted and shall remain so until the end of the test. Unless otherwise specified, the conductive liquid shall consist of
— 800 parts by mass of anhydrous poly(ethylene glycol) of relative molecular mass 600;
— 200 parts by mass of water;
— 1 part by mass of wetting agent;
— 10 parts by mass of potassium chloride. When a conductive silver lacquer or colloidal graphite is used, the surface resistance between any two points on a sample of the dried film shall not exceed 100 Ω. Clean metal contacts shall be applied to the electrodes so that the contact area is approximately the same size as, but no greater than, the electrodes, except where otherwise stated. In the case of hoses of less than 50 mm bore, it is difficult to apply the conducting liquid accurately to the hose bore, and it is preferable to use a brass plug of external diameter equal to or greater than the hose internal diameter (ID), coated with conducting liquid and then pushed 25 mm into the hose. Special electrodes and contacts
The following special electrodes and contacts shall be used for the determination of the electrical resistance through the hose wall, and other test methods:
a) Outer electrode: a copper sheet-metal band, of standard width 25 mm, clamped around the outer hose wall (see Figure 1).
b) Inner electrode: 1) for hoses of less than 50 mm bore size, it is recommended that a tight-fitting brass plug (solid for small bore sizes and hollow for larger sizes), of minimum length 2 × the pitch of the helical wire(s) (for hoses incorporating helical wires) or 0,5 × ID (for hoses without helical wires), be used; 2) for hoses of more than 50 mm bore size, it is recommended that an adjustable copper sheet- metal band, tightly fitting the bore of the hose (expanded against the lining by spring action), of minimum width 25 mm, be used;
c) Contacts for connecting the electrodes to the ohmmeter should preferably be soldered or brazed to the electrodes to minimize resistance between ohmmeter and electrode (see Figure 1).
d) Alternative to b): a 25-mm-wide conducting foam plug completely wetted with a suitable conductive liquid (see of outside diameter slightly larger than the inside diameter of the hose to ensure a snug fit with good electric contact with the hose lining and connected to a suitable insulated conductor (see Figure 3, items 1 and 3). This electrode is recommended for use with hoses with corrugated linings or linings which are less flexible than rubber (i.e. PTFE).
e) In order to establish good electrical contact with the cover of a corrugated hose, it is recommended that a conducting foam strip 25 mm wide, completely wetted in suitable conductive liquid (see, be placed round the full outside circumference of the hose, underneath the electrode described in item a) above.