在重型机械制造业中,用小型量具测量大外径的方法,早在40年代已有介绍,我国对这种方法的应用也有了不少的经验。弓高测径仪、鞍形指示计和测量带就是利用间接测得弓高、弦长和圆周长,进而计算出外径的“以小测大”的机械式量具。前两者示值范围小,后者测量精度很低,并均有不能直接读数之缺陷。针对上述不足,近年来有人提出可直接读 In the field of heavy machinery manufacturing, the method of measuring large outer diameter with small measuring tools was introduced as early as the 1940s. Our country has a lot of experience in the application of this method. Bow height gauge, saddle type indicator and measuring belt is the use of indirect measurement of bow height, chord length and circumference, and then calculate the outer diameter of the “small measure” of the mechanical measuring tools. The first two show a small range, the latter measurement accuracy is very low, and both can not be directly read the defect. In response to the above shortcomings, it has been proposed in recent years that it can be read directly