Current Sensor

A current sensor is an essential electronic component designed to detect and measure the flow of electric current in a circuit, whether AC, DC, or both. It converts the current into a proportional electrical signal—typically voltage, current, or a digital output—that can be read, recorded, or used for control and protection purposes. Current sensors play a critical role in power systems, industrial automation, electric vehicles, renewable energy, and smart electronics.

Working Principle

Current sensors operate based on a range of physical principles that enable accurate measurement of current flow without directly interfering with the circuit. The choice of principle affects the sensor’s accuracy, isolation, bandwidth, and application suitability. Below are the most common working principles used in current sensing technologies. Please see SUCH for detailed information.

• Hall Effect Principle: The Hall effect principle relies on the behavior of a magnetic field when a current flows through a conductor. As electric current passes through the conductor, it generates a perpendicular magnetic field. A Hall element positioned near this conductor detects the magnetic field and produces a Hall voltage that is directly proportional to the current. This voltage is then amplified and converted into a usable output signal. Hall effect current sensors provide excellent electrical isolation between the primary circuit and the output signal, which enhances safety in high-voltage environments. They are available in both open-loop and closed-loop configurations, offering flexibility based on accuracy and cost requirements.
• Shunt Resistor (Current Sensing Resistor): This method involves placing a low-resistance precision resistor in series with the current path. As current flows through the resistor, it causes a small voltage drop, which can be measured using an instrumentation amplifier. The current is then calculated using Ohm’s law (I = V/R). While this technique is highly accurate and cost-effective, it lacks electrical isolation, making it more suitable for low-voltage applications. Additionally, shunt resistors can generate heat and power loss at high current levels, so thermal design considerations are essential.
• Current Transformer (CT): A current transformer operates on the principle of electromagnetic induction. It consists of a toroidal magnetic core with a secondary winding. When alternating current flows through a conductor (acting as the primary winding), it induces a current in the secondary winding proportional to the primary current. CTs are commonly used for measuring high AC currents in power distribution systems. They offer inherent electrical isolation and are capable of handling large current loads with minimal signal distortion. However, they are unsuitable for DC measurement since induction only occurs with changing currents.
• Rogowski Coil: The Rogowski coil is a flexible, non-magnetic loop that encircles the conductor carrying AC current. It detects the changing magnetic field and produces a voltage that is proportional to the derivative of the current. By integrating this voltage, the actual current waveform is reconstructed. This type of sensor is highly accurate over a wide frequency range, making it ideal for measuring large, fast-changing AC currents in systems like welding machines and inverters. Its non-intrusive nature and flexible form factor make it easy to install around existing conductors.
• Magnetoresistive and Fluxgate Sensors: Magnetoresistive sensors detect variations in magnetic field strength based on changes in material resistance. These sensors are highly sensitive and suitable for applications that require precise low-current detection. Fluxgate sensors, on the other hand, utilize a magnetic core that is excited with an AC signal. When exposed to an external magnetic field generated by current, the core’s saturation behavior changes, which is then detected through secondary windings. These sensors are known for their exceptional accuracy, stability, and low offset, making them well-suited for aerospace, laboratory, and medical applications.

Types of Current Sensors

1. Open-Loop Hall Effect Current Sensor: An open-loop Hall effect current sensor uses a Hall element to detect the magnetic field produced by the primary current. It processes this signal through an amplifier to produce an analog output such as 0–5V or 4–20mA. The design is simple, cost-effective, and capable of measuring both AC and DC currents. While it offers fast response and good linearity, it has lower accuracy compared to closed-loop models. Open-loop sensors are widely used in general-purpose applications such as solar inverters, battery monitoring, and motor speed controllers.
2. Closed-Loop Hall Effect Current Sensor: Closed-loop (or compensated) Hall effect sensors incorporate a secondary coil wound around a magnetic core, along with a feedback circuit. When the Hall element detects a magnetic field, the feedback coil generates a current that cancels the field, maintaining magnetic balance. The compensation current is directly proportional to the primary current and can be measured accurately. These sensors offer high linearity, fast response, low temperature drift, and excellent accuracy, making them suitable for high-performance systems such as industrial motor drives, precision power analyzers, and electric vehicle controllers.
3. Shunt-Based Current Sensor: A shunt-based sensor uses a precision resistor to measure current by monitoring the voltage drop across the resistor. This method is often integrated into compact ICs with built-in amplifiers and protection features. It is ideal for low-power applications such as power supply monitoring, battery management systems, and microcontroller-based systems. Though lacking galvanic isolation, shunt sensors are extremely compact, efficient, and provide high precision in controlled environments.
4. AC Current Transducer / Transformer: This type of sensor is specifically designed to measure alternating current. It converts the input AC current into a standardized output signal such as 4–20mA, 0–5V, or RS485, which can be easily interfaced with PLCs and data acquisition systems. Some models include built-in signal conditioning and isolation features. AC transducers are commonly used in electrical panels, building automation systems, HVAC equipment, and power monitoring applications.
5. Rogowski Coil Current Sensor: Rogowski coils are flexible, air-core sensors used for high-speed AC current measurement. Their non-saturating core and wide dynamic range allow them to accurately detect transients and harmonics in electrical systems. They are lightweight and can be easily wrapped around busbars or cables without cutting or disconnecting the circuit. Their signal requires integration to reconstruct the actual current waveform, typically handled by an external integrator circuit or digital processor.
6. Split-Core Current Sensor: Split-core sensors feature a hinged or detachable core that enables easy clamping around existing wires or busbars. This design allows for quick installation without interrupting service, making it ideal for retrofit applications or temporary measurements. These sensors are available in both Hall effect and CT versions, and they typically output analog or digital signals for energy management systems, building automation, and load analysis.
7. Digital/Smart Current Sensor: Smart current sensors are equipped with onboard microcontrollers or digital signal processors (DSPs) that allow advanced features such as digital output (I²C, SPI, RS485), self-calibration, signal filtering, and fault diagnostics. These sensors offer high integration and programmability, which simplifies system design and improves reliability. They are widely used in IoT devices, automotive electronics, and smart energy meters, where data communication and precision control are critical.
8. Multi-Channel Current Sensors: These current sensors are designed to monitor multiple current paths simultaneously, either through multiple shunt resistors, multiple Hall elements, or transformer channels. Multi-channel sensors save space, reduce wiring complexity, and improve measurement efficiency in systems with several current sources or loads. They are often used in power distribution units, server power monitoring, and integrated control panels.