High Pressure Manganin Gauge with Multiple Integral Calibrants

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Abstract
A high pressure Manganin gauge with multiple integral calibrants has been developed. It allows accurate and continuous pressure measurement in the 100‐kbar range at both room and elevated temperatures. The gauge is designed for use in piston‐cylinder, multianvil, and other relatively large volume pressure apparatus. One modification of the gauge consists of a Manganin coil wound on a threaded insulating sleeve which encloses a core of primary calibrants. Bismuth, thallium, and barium have been used for calibrants because they provide four widely separated fixed points in the 100‐kbar range. The principle of the gauge's operation is based on (a) the nearly linear dependence of the resistance of Manganin on pressure, (b) the volume discontinuities accompanying pressure‐induced first‐order phase transitions in the calibrants, and (c) the appreciable strength and rigidity at high pressure of commonly used solid pressure‐transmitting media. The over‐all response of the gauge consists of nearly linear segments of increasing resistance vs pressure between well‐established fixed points. The extension of the range of the gauge to higher pressures and its use for semiquantitative estimates of unknown volume changes accompanying polymorphic transitions are described.