ISO 21178:2020 pdf download – Light conveyor belts — Determination of electrical resistances.
5.1 Method A: Measurement of surface resistance, R OA , omni-directionally 5.1.1 Applicability This method is applicable to belts which are electrically two-dimensionally isotropic in the plane of the belt. 5.1.2 Principle An electric current of specified voltage is passed via electrodes through a suitably prepared test piece taken from the belt. 5.1.3 Apparatus (see Figure 1) 5.1.3.1 Sheet of insulating material, a little larger than the test piece. 5.1.3.2 Two cylindrical and coaxial electrodes (see Figure 1), with contact surfaces machined flat and polished, as follows. 5.1.3.2.1 Electrode 1, circular. 5.1.3.2.2 Electrode 2, annular. 5.1.3.2.3 Material of electrodes, either brass or stainless steel. 5.1.3.3 Ohmmeter, having a measuring range up to 10 10 Ω and accurate to within ±5 %.
5.1.4.7 Contact medium The electrical surface resistivity of the contact medium shall not be higher than 10 4 Ω. For checking this value, use the same electrode arrangement as described in Clause 6. Examples for suitable contact media are silver lacquer or a jelly. NOTE A jelly having the following composition is suitable: — Anhydrous polyethylene glycol of molecular mass 600: 800 parts by mass; — Water: 200 parts by mass; — Potassium chloride: 10 parts by mass; — Soft soap (pharmaceutical quality): 1 part by mass. 5.1.5 Procedure The temperature and relative humidity in the test room shall be in accordance with ISO 18573, Atmosphere B. Measure the temperature and relative humidity in the test room. Place the test piece on the sheet of insulating material, with the test surface upwards.
5.1.6 Expression of results For each surface of the belt subjected to test, record the electrical resistance, in ohms, measured for each test piece, and calculate the mean of the values recorded for that surface for the three test pieces. Record the electrical resistance for the two surfaces of the belt separately. 5.1.7 Test report The test report shall include the following information: a) complete designation of the tested light conveyor belt material and the manufacturing date; b) reference to this document, i.e. ISO 21178; c) test room temperature and relative humidity; d) conditioning period; e) contact medium, if applied; f) voltage applied to the electrodes; g) results of the tests; h) date of test; i) any deviations from the standard test. 5.2 Method B: Measurement of surface resistance R OB in longitudinal and transverse directions 5.2.1 Applicability This method is applicable to belts which have electrically varying properties in the plane of the belt, especially those where fabrics have conducting threads in the longitudinal direction which can be exposed on the belt surface. 5.2.2 Principle An electric current is passed via electrodes clamped in a suitable arrangement to the surface of a test piece of the belt material. 5.2.3 Apparatus (see Figure 4) 5.2.3.1 Earthed screen plate 5.2.3.2 Bottom plate, made of insulating material, such as polymethylmethacrylate, polytetrafluoroethylene or similar, having dimensions 600 mm × 200 mm × 20 mm.