measurement of current in 220v ac line.

[ghsreshma]

hai.
i'm working on a project, speed control of motor by hysteresis current control method.my question is, i want reference current for my hysteresis band. so i'm measuring load current where my load is single phase induction motor of current rating 0.4A. how i have to measure my load current? which sensor i have to use? is their any need to reduce the 220v ac to DC voltage? i have to compare this current with my line current, how can i compare these two quantities?please help me

 

[klystron]

Use a current transformer and a ballast resistor

 

[Darktrax]

Additional to the classic current transformer method, there are now available devices which look like current transformers in that they generally have a toroid form that you pass the current wire through, (optionally with more than 1 turn), but are Hall-effect sensors. Some simply amplify the sample, other more accurate types use a null coil and a feedback method in the internal electronics.

Small ferrite current transformers can also do an excellent job. They just have to have a core big enough not to saturate. Ferrites have such a high permeability, they could more easily saturate unless provided with an intentional air gap.

Hall-effect devices can work down to DC. Either sort can measure complex phase components that may be present . Choose those with bandwidths high enough to to faithfully sample the pulse-width modulated pseudo-AC used to drive AC motors from inverters and servo drives.