From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specification for testing the resistivity of hard composite dielectrics and insulating materials.
| Identifier | ExFiles\Box 24\2\ Scan209 | |
| Date | 21th February 1922 guessed | |
| HARD COMPOSITE DIELECTRICS (INSULATING MATERIALS). 3. Resistivity (Specific Insulation Resistance). (a) Moulded materials. The resistivity of moulded material shall be tested on a specimen of the shape and dimensions shown in Fig. 1, and set up generally in the manner indicated in Fig. 2. The specimen shall rest on three pins fixed into the lower steel electrode, the top of the pins being 2 mm below the upper edge of the steel electrode. The internal diameter of the steel electrode shall be 98 mm, and the specimen shall be so placed that it does not touch the internal surface. The depth of the electrode in the inner cup shall be approximately 2 mm; and the groove in the top edge of the specimen shall be filled with mercury. For temperatures not exceeding 100° C. mercury electrodes shall be used. For higher temperatures suitable fusible metal electrodes shall be used, if necessary, according to the temperature. When the resistivity is calculated on the area of the upper electrode the result will be low owing principally to the increased area in contact with the lower electrode. The error will be approximately 15 per cent, and if this degree of accuracy is desired the result should be corrected accordingly. (b) Sheet materials. The resistivity of sheet material shall be tested when possible on a specimen of the shape and dimensions shown in Fig. 1. When it is impracticable to obtain a specimen 20 mm thick the overall thickness may be reduced to a minimum of 12 mm, the thickness of the base being 5 mm in every case. The other dimensions shall be in accordance with Fig. 1. The specimen shall be set up, with suitable electrodes as in (a), generally in the manner indicated in Fig. 2. All the surfaces of the specimen shall be machined smooth, but not polished. (c) Rods. The resistivity of a rod shall be tested by boring out the rod so as to form a deep cup, and turning the outside surface. The dimensions shall be as shown in Fig. 3. The specimen shall be set up for testing, with suitable electrodes as in (a), generally in the manner indicated in Fig. 4. If L = length in millimetres, r1 = inner radius in millimetres, r2 = outer radius in millimetres, R = measured resistance, ρ = resistivity, then ρ = 2πRL / loge(r2/r1) Fig. 1.—Specimen for Resistivity and Surface Resistivity Tests. Fig. 2.—Arrangement of Specimen in Fig. 1 set up for Resistivity and Surface Resistivity Tests. Fig. 3.—Specimen (machined from Rod) for Resistivity and Surface Resistivity Tests. | ||