井径仪是探矿工程中必不可少的仪器之一,目前采用的井径仪种类很多,直径(井径仪的外径)有75、50、40、37毫米等。就测量臂来分,有棱形臂、三臂、四臂等。开臂的方法除棱形臂之外又分;冲击式、拖壁式、电磁铁式等等。棱形臂的井径仪虽然不用开壁装置,但由于测量臂的支撑力大,若井径仪自身重量轻,又不另加接重物,下井是很困难的,特别 Caliper is one of the indispensable instruments in prospecting project. There are many types of caliper currently used, and the diameters (diameter of caliper) are 75, 50, 40, 37 mm and so on. On the measuring arm to points, there are prismatic arms, three arms, four arms and so on. Open arm method in addition to the prism arm is divided; impact, drag-wall, electromagnetism and so on. Although the caliper of the prismatic arm does not need to have a wall opening device, it is very difficult to go down if the caliper itself is light in weight and without additional heavy loads due to the large supporting force of the measuring arm.