一、引言 在生产现场工作的自动化仪表,其周围环境温度的变化是很激烈的,例如冬天会降到零下几十度,而夏天又会上升到零上几十度。因此按照国家规定的部颁标准,要求在 I. INTRODUCTION The automation of the work in the production site, the temperature changes in the surrounding environment is very intense, such as the winter will drop to minus a few dozen degrees, but in summer will rise to zero on the dozens of degrees. Therefore, in accordance with the provisions of the ministries and regulations of the state requirements