教学演示电表（万用表），灵敏电流计等磁电式电表是中小学实验室中常用的教学仪器。在使用中常因表头线圈受到大电流冲击，或因碰撞摩擦而断裂。线圈断头多数发生在线圈的表层（脱胎线圈包括内表层），或引线接头处。因为表层接触空气容易受潮氧化变细。若断头发生在引线接头 Teaching demonstration meters (multimeters), sensitive ammeters and other magnetoelectric meters are commonly used teaching instruments in primary and secondary school laboratories. In use, the head coil is often subjected to a large current or fractured due to impact friction. The majority of coil breaks occur at the surface of the coil (without the tire coil including the inner skin), or at the lead joint. Because the surface contact with air is easy to moisture oxidation and thinning. If the break occurs in the lead connector