Toroidal Coil

It is a sensor to measure welding current. A copper wire is multi-lapped around belt-shaped core. Also, it is called Rogowskii coil, whose theory has been known since early times.

    

When a current i flows through a conductor, magnetic field is generated by Ampere's right-screw law. Magnetic flux intercrosses the coil, generating electro-motive force v in the coil (Figure 1).

Output voltage v in the coil is proportional to coil cross section and the number of turns of winding; therefore, accurate measurement is conducted by means of toroidal windings as shown in Figure 2.

Toroidal coil features an air-cored coil which measures a large current without saturation. As the electro-motive force, however, is differential, it needs to be integrated through electronic circuit to restore waveform and to be an effective value.
Toroidal coil is applied to a current path (secondary conductor) extending from welding transformer to electrode. The coil is coupled with Miyachi Weld Checker for weld quality control, and it is also coupled with welding power supply for feedback control.

    

Toroidal coil line-up
Selectable by magnitude of current to be measured and application

Model No.	Coil length	Major application
MB-400L	400mm	< Fixed > For feedback control by constant-current timer
MB-800L	800mm	< Fixed > For feedback control by constant-current timer
MB-400K	400mm	Detachable For portable Weld Checker
MB-800K	800mm	Detachable For portable Weld Checker
MB-35E	35mm inner dia.	< Fixed > For feedback control by fine power supply For mount-on Weld Checker
MB-60E	60mm inner dia.	< Fixed > For feedback control by fine power supply For mount-on Weld Checker
MB-29F	29mm inner dia.	< Fixed, 10 times sensitivity > For small current feedback control by fine power supply For mount-on Weld Checker
MB-45F	45mm inner dia.	< Fixed, 10 times sensitivity > For small current feedback control by fine power supply For mount-on Weld Checker