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).
Directions for testing the electrical and surface resistivity of various materials such as tubes, sheets, rods, and moulded materials.
| Identifier | ExFiles\Box 24\2\ Scan210 | |
| Date | 21th February 1922 guessed | |
| 568 DIRECTIONS FOR THE STUDY OF If the specimen is made accurately to the dimensions shown in Fig. 3, then ρ = 1.07RL. (d) Tubes. For testing the resistivity of a tube, one end shall be plugged with a good insulator, so as to prevent leakage of mercury. The specimen shall be set up and the test carried out in a manner similar to that specified in (c). (e) Conditions of test. The resistance shall be measured, at the end of each minute, over a period of ten minutes' electrification, at a potential difference of 500 volts. The resistivity shall be expressed in megohms for a centimetre cube after one, two, and ten minutes' electrification respectively. The materials shall be tested in accordance with [Image of a testing apparatus] Mercury electrode Mercury guard ring Specimen as in Fig. 3. NOTE.--The specimen must be held down in the mercury by a weight of about 50 gm. FIG. 4.—Arrangement of Specimen in Fig. 3 set up for Resistivity and Surface Resistivity Tests. conditions (a), (d), (e), (f), (g), and (h) given in Clause 2 of this Specification. 4. Surface Resistivity (Surface Leakage). (a) Moulded materials. The surface 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. The electrodes shall be connected to the battery and galvanometer as shown in Fig. 5, so as to measure the surface resistance between the mercury in the groove in the top edge of the specimen and the lower electrode. 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. (b) Sheet materials. The surface 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, the connections to the battery and galvanometer being as shown in Fig. 5. All the surfaces of the specimen shall be machined smooth, but not polished. The specimen shall be tested with the surfaces as left by the tool, unless special circumstances render it necessary for them to be finished in a particular manner in service. (c) Rods. The surface resistivity of a rod shall be tested by boring out the rod so as to form a deep cup, and turning [Image of electrical connections to a specimen] G + - FIG. 5.—Electrical Connections to Specimen in Fig. 1 set up for Surface Resistivity Test. 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. The outside surface of the specimen shall be machined smooth, but not polished. The specimen shall be tested with the surface as left by the tool, unless special circumstances render it necessary for the surface to be finished in a particular manner in service. (d) Tubes. For testing the surface resistivity of a tube, one end shall be plugged with a good insulator, so as to prevent leakage of mercury. The specimen shall be set up and the test carried out in a manner similar to that specified in (c). (e) Conditions of test. The surface resistance shall be measured, after one minute's electrification, at a potential difference of | ||