Lots of information such as sensor, integrator, phase error, comparators, and sensors are explained inside this paper. The paper presents information related to current comparators, error, currents, transformers, and magnetic sensors.
Inside the paper you can get information about contactless current sensors, magnetic, sensitivity, amplitude, and instrument. Below are some excerpt from the paper:
The current measurement using shunt resistor is in some cases impractical or impossible: for large currents the shunts are heavy and they cause voltage drop and dissipate heat. They are not insulated and the conductor should be disconnected for mounting. Contactless current sensors may be used for remote conductors at high potentials, underground cables etc., but they are usually more expensive. This paper is based on overview of magnetic sensors given in . A wide range of AC and DC contactless current sensors is produced by LEM, F.W. Bell, VAC, Honeywell, Telcon and other manufacturers.
Giving more content, this paper contains information about frequency, device, errors, and current sensors.