DIN EN 60051-5-1991 直接显示的模拟电器测量仪及附件.第5部分:相位表/功率因数表和同步指示器的特殊要求
Direct acting indicating analogue electrical measuring instruments and their accessories; part 5: special requirements for phase meters, power factor meters and synchroscopes (IEC 60051-5:1985, edition 4); german version EN 60051-5:1989