Hall Current Sensor
A closed-loop Hall current sensor uses a Hall element as a magnetic sensor. The Hall element is placed in the air gap of the magnetic core. It senses the magnetic field strength and outputs a signal. An amplifier circuit receives the Hall element's output and amplifies it into a current signal, which is then provided to the secondary compensation winding. The magnetic field generated by the secondary compensation winding in the magnetic core is equal in magnitude but opposite in direction to the magnetic field generated by the primary current at the air gap, thus canceling out the primary magnetic field and forming a negative feedback closed-loop control circuit. If the secondary current is too small, the generated magnetic field is insufficient to cancel out the primary magnetic field, and the amplifier circuit will output a larger current. Conversely, the amplifier circuit will reduce its output current, thereby maintaining the magnetic field balance at the air gap. If the primary current changes, the magnetic field balance at the air gap is disrupted, and the negative feedback closed-loop control circuit will also adjust the secondary output circuit to restore magnetic field balance.
Fluxgate current sensor
A fluxgate current sensor measures weak magnetic fields by utilizing the nonlinear relationship between the magnetic flux density and the magnetic field strength of a high-permeability magnetic core under saturation excitation with a square wave voltage. This physical phenomenon acts like a "gate" to the measured environment's magnetic field; passing through this "gate" modulates the corresponding magnetic flux and generates an induced electromotive force. This phenomenon is used to measure the magnetic field generated by a current, thus indirectly measuring the current.
The magnetic sensor, composed of an excitation core and an excitation coil, detects the magnetic field and uses a feedback circuit to compensate the secondary compensation coil with current, ensuring the sensor always maintains a zero-flux state. The product of the compensation current and the number of turns of the compensation coil is proportional to the measured primary current.