| 摘要 |
PURPOSE:To make it possible to highly accurately measure the resistivity change of even large- sized parts having change in configuration and plate thickness by a method wherein the measuring terminal interval is more than 0.8 times as much as the power supply terminal interval, and the power supply terminal interval is less than 0.4 times as much as the plate thickness. CONSTITUTION:The interval between the power supply terminals 1 and 2 of an electric resistance measuring circuit according to the four-terminal potential difference method is represented by L, and the interval between the detecting terminals 3 and 4 by l. The relationship between the potential difference output ratio and l/L is as shown in the figure: when l/L is more than 0.8, the potential difference output is substantially saturated, and a high output can be obtained, so that the resistance change can be measured with high sensitivity. On the other hand, if the plate thickness to be measured is represented by (t), the relationship between the output potential difference and L/t is as shown in the figure: when L/t>0.5, only a minute change in plate thickness causes the potential difference value to vary, so that the degree of accuracy largely lowers. Therefore, L/t is should be at least less than 0.4. Thereby, for even large-sized parts, the degree of deterioration due to change with time can be highly accurately measured by using a resistivity change. |
