A Portable Precision Enclosure With High Temperature Homogeneity For The Standard Resistor

The development of QHR and CCC technique gives the possibility to establish a resistance standard with uncertainty of 10-9or less. To keep the environment temperature of the resistor to be compared in high stability becomes an essential requirement. The practical measurement activity shows that the portable air enclosure of high precision is an adequate apparatus for this purpose, which especially have a considerable effect on the case in which the inter-comparison between different laboratories.The high stability enclosure was firstly developed to maintain standard cells. The size of the standard cell is small, so the inner space size of the enclosure used to keep it is not very large too, while the size of standard resistors is much larger. Some resistors of high quality consist of several pieces with slightly different temperature coefficient and these pieces compensate each other to get very low temperature coefficient totally. Obviously the inhomogeneity of temperature will deteriorate the temperature characteristic of the resistor.In the face of the shortcoming of large capacity enclosure, which the temperature difference between bottom and top of inner space of the enclosure is large, an enclosure including multi-sensor and multi-heater is designed according to modern control theory. In theory, orthogonalization of the matrix to decouple the three parts make the control system simple and easy to run; In construction, heating wire is wound on the surface of the aluminum chamber evenly. Foam is placed between outer and aluminum chamber as thermal insulation. The outer dimension is 50?0?6cm and the inner space is 35?5?1cm, which fits one SR 102 type resistor or two Tinsley 5685 type resistors. The total weight of the enclosure is about 15 kg, which is still a portable one. Its outstanding feature is the temperature difference between top and bottom is regulatedautomatically and decreased within 1 mK. At the same time, the regulating operation determining the temperature of inner space of the enclosure and the regulating operation of the temperature difference between bottom and top is independent from each other. This enclosure is useful for the maintenance of resistance standard and for the comparison between different laboratories.