Hall effect sensors are widely used for precise, contactless current measurement in applications ranging from industrial automation to renewable energy systems. LEM, a leading manufacturer of current and voltage sensors, offers both open-loop and closed-loop Hall effect sensors, each with distinct advantages. Open-loop Hall effect sensors offer simpler, cost-effective solutions with wider ranges but lower accuracy, while closed-loop sensors provide higher accuracy and faster response through compensation, at the cost of complexity and size.
In this blog, we’ll explore how Hall effect sensors work, compare open-loop and closed-loop types, and highlight specific LEM models along with their applications.
How Hall Effect Sensors Work
As we highlighted in the previous blog, Hall effect sensors operate on the Hall effect principle – discovered by Edwin Hall in 1879. When an electric current flows through a conductor or semiconductor placed in a perpendicular magnetic field, it experiences a force that pushes charge carriers (electrons or holes) to one side. This results in a voltage difference across the conductor, known as the Hall voltage.
Types of Hall Effect Sensors
Hall effect sensors are available in two primary types:
1. Open-Loop Hall Effect Sensors
These measure the magnetic field directly and output a proportional voltage. These are simpler, cost-effective, and energy-efficient but less accurate.
2. Closed-Loop Hall Effect Sensors
These use a compensation coil to counteract the magnetic field and maintain accuracy. They are more precise, stable, and fast-responding but require more power.
Now, let’s dive deeper into each type.
Open-Loop Hall Effect Sensors
Design: These sensors have a Hall effect sensor placed in the air gap of a magnetic core. The current-carrying conductor passes through this core, generating a magnetic field that is measured by the Hall sensor.
Measurement: The Hall sensor’s output voltage is directly proportional to the magnetic field, which in turn is related to the current. This output is then amplified to provide a usable signal.
Advantages
✔ Lower cost
✔ Compact and lightweight
✔ Low power consumption
✔ Suitable for DC, AC, and pulsed current measurements
Limitations
✖ Lower accuracy compared to closed-loop models
✖ Limited frequency bandwidth
✖ More affected by temperature variations and external magnetic fields
Common LEM Open-Loop Models are HAS series, HAT Series, HAX series
Closed-Loop Hall Effect Sensors
How They Work
Design: These sensors also use a Hall effect sensor and a magnetic core, but they include a compensation circuit – ie, a feedback coil to generate a counteracting magnetic field.. This stabilizes the Hall voltage, improving accuracy and response time while minimizing external influences.
Measurement: The Hall sensor in a closed-loop sensor operates in a “zero-flux” condition. The compensation current is adjusted to maintain this condition, and the value of this current is proportional to the primary current.
Advantages
✔ High accuracy and linearity
✔ Fast response time
✔ Less affected by external magnetic fields and temperature variations
✔ Ideal for precision applications
Limitations
✖ Higher cost
✖ Requires more power compared to open-loop sensors
Common LEM Closed-Loop Models are LA 25-NP, LA 100-P, LA 305-S etc
In summary:
| Feature | Open-Loop Hall Effect Sensor | Closed-Loop Hall Effect Sensor |
| Design | Simpler | More complex |
| Accuracy | Lower | Higher |
| Linearity | Lower | Higher |
| Temperature Drift | More susceptible | Less susceptible |
| Response Time | Slower | Faster |
| Cost | Lower | Higher |
| Size | Smaller | Larger |
| Power Consumption | Lower | Higher |
| Dynamic Range | Wider | Narrower |
Choosing the Right Sensor for Your Application
If cost and power efficiency are your main priorities, open-loop sensors (e.g., HX 03-P, HAS 50-S) are ideal.
Applications of LEM Hall Effect Sensors
LEM’s Hall effect sensors are widely used in:
● Industrial automation – Motor control, power monitoring, and factory automation.
● Renewable energy – Solar inverters, battery management systems, and wind turbines.
● Automotive applications – Electric vehicle battery management, regenerative braking, and ABS systems.
● Consumer electronics – Power supplies and home automation.
Conclusion
Hall effect sensors provide a non-contact, efficient, and accurate way to measure current. LEM’s open-loop sensors offer affordability and simplicity, while closed-loop sensors provide high precision and stability for demanding applications.
For detailed specifications, explore LEM’s official product catalog or contact Globetek – we are LEM’s oldest distributors in India – and would be happy to assist you in end-to-end procurement of these products.
