STANDARDISATION OF STEEL SURVEYING TAPES |
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| Abstract: | AbstractSurveying tapes of steel are much more satisfactory mechanically than those of invar, and are less subject to secular changes of length, but the magnitude of their coefficient of thermal expansion demands a closer knowledge of their temperature than can be obtained with ordinary thermometers suspended near the tapes. The measurement of steel tapes in terms of their electrical resistance has therefore been investigated. The history of this work is traced. The use of resistance methods has proved satisfactory in the field, and under Laboratory conditions at the N.P.L. the accuracy of 1 part in 2 millions in the measurement of the lengths of 24-metre and 100-foot tapes of steel is attained. Such steel tapes appear to have remained stable on the average within about 2 parts in a million in 25 years. |
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