The working principle of the clamp ammeter is to use the principle of electromagnetic induction to clamp the wire to be measured into the core of the silicon steel sheet of the clamp ammeter. At this time, the clamped wire is equivalent to one turn of the current transformer. , Belongs to the primary coil. When there is current passing, it will induce a secondary current in the secondary coil in the clamp-type ammeter, and the measured wire current can be read out on the dial of the clamp-type ammeter.