In electrical engineering, current sensing is any one of several techniques used to measure electric current. The measurement of current ranges from picoamps to tens of thousands of amperes. The selection of a current sensing method depends on requirements such as magnitude, accuracy, bandwidth, robustness, cost, isolation or size. The current value may be directly displayed by an instrument, or converted to digital form for use by a monitoring or control system.
Current sensing techniques include shunt resistor, current transformers and Rogowski coils, magnetic-field based transducers and others.
Current sensor
A current sensor is a device that detects electric current in a wire and generates a signal proportional to that current. The generated signal could be analog voltage or current or a digital output. The generated signal can be then used to display the measured current in an ammeter, or can be stored for further analysis in a data acquisition system, or can be used for the purpose of control.
The sensed current and the output signal can be: Alternating current input, analog output, which duplicates the wave shape of the sensed current. bipolar output, which duplicates the wave shape of the sensed current. unipolar output, which is proportional to the average or RMS value of the sensed current. Direct current input, unipolar, with a unipolar output, which duplicates the wave shape of the sensed current digital output, which switches when the sensed current exceeds a certain threshold
Requirements in current measurement
Current sensing technologies must fulfill various requirements, for various applications. Generally, the common requirements are: High sensitivity High accuracy and linearity Wide bandwidth DC and AC measurement Low temperature drift Interference rejection IC packaging Low power consumption Low price
Techniques
The measurement of the electric current can be classified depending upon the underlying fundamental physical principles such as,
Faraday's Law of Induction
Magnetic field sensors
Faraday Effect
Hall effect sensor. Transformer or current clamp meter, (suitable for AC current only). Fluxgate sensor, (suitable for AC or DC current). Shunt resistor, whose voltage is directly proportional to the current through it. Fiber optic current sensor, using an interferometer to measure the phase change in the light produced by a magnetic field. Rogowski coil, electrical device for measuring alternating current (AC) or high speed current pulses. Giant Magnetoresistance(GMR): Magnetic field sensor suitable for AC & DC Current with higher accuracy than Hall Effect. Placed parallel to the magnetic field.
The Hall Effect current sensor is a type of current sensor which is based on the Hall Effect phenomenon discovered by Edwin Hall in 1879. Hall Effect current sensors can measure AC, DC, or pulsating current.
Shunt resistors
Ohm's Law is the observation that the voltage drop across a resistor is proportional to the current going through it.
This relationship can be used to sense currents. Sensors based on this simple relationship are well known for their lower costs, and reliability due to this simple principle.